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Aug 09, 2013, 05:59 PM
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Build Log

Build log Windrider B737 Jetair

After reading and seeing some posts about finished Boeing 737 models from Windrider, I decided even if it didn’t fit exactly in my collection (I never was an airline buff), I had to have that model and finish it in some Belgian colors. I kind of liked the winglets and being a -700 I opted for a model of the well documented OO-JAR of the Belgian tour operator Jetair in its delivery configuration. Here you see a picture of the aircraft landing back at the Seattle Boeing factory after its maiden flight. Being christened with the Enjoy name on its nose seemed appropriate for an RC airliner.

I purchased the model “all in” during a sale of the Austrian dealer Lindinger, it was cheaper as the glider version! but from the start I discarded the engines, ECS’s, fans and retract system because I wanted more robust units. The RC group pages about that model contained valuable information which I thoroughly analyzed during months before deciding the configuration and modifications to my model. Getting all the necessary parts and trims also took months because most had to be imported from China, USA and various European suppliers. My choice felt on 5S fed HK2855-2100 engines powering CS10 fans with aluminum nosecone through 80A ESC’s. Gears had to be metal trunion 4mm hardened shaft with scale wheels on dampened springs, geardoors on all 3 legs and single slotted Fowler flaps. Realistic sequenced lightning set all around the vinyl covered airframe with Caligraphics detailing. Separate power source for electronics and engines. Metal gear servo’s all around, digital for flight controls, analogue for accessories. Double slotted flaps, spoilers and leading edge flaps have been envisioned but finally discarded because of weight and complexity versus efficiency gain.

Mid June 2013 I after completion of other projects I gathered all my parts and took the foam pieces out of the box. Although a carbon fiber 8mm rod was provided for wing spar, I bought a more rigid one at my LHS. Carbon quality varies as much as the price even within a single brand, between 7 and 25 euro for a meter, I choose not to compromise on quality for anything on this airplane but I hadn’t expected that hefty price tag. I also discovered a nasty transport damage on the starboard wing aileron tip. The last inch was almost separated and stood at an angle. To correct it I had no choice as to glue a piece of carbon scrap to align the outer and inner portions again. I then sanded the wings, getting rid of any mold and finish residue. Vinyl adheres better with the oily top removed, and is so thin the tiny many dotted circles of the mold are much too visible if not flattened out in advance. I now will bring you my build log, in the chronological order I used (thus mixing sub-assembly preparations with actual buildup). Following picture shows the way I straightened out the transport damaged aileron, repair was made on the top part which will be vinyl covered anyway. Also visible are the obvious flap and spoiler panel lines discussed later.

1) Wing reinforcement and flap modifications
Whist the aileron repair dried I glued the 3 and 2mm wooden engine pod supports together with (Bison) PU wood glue. That glue is slow setting and expands quite a bit, filling all voids and becoming rock solid overnight. I used it extensively on various foam airplanes and it forms very strong connections between plastics, wood, metals and other synthetic materials such as foam and carbon. Excesses have to be Dremeled off because it becomes so hard it is hardly possible to cut it off or sand it down. The new 8mm CF wingspar was cut an inch longer (57cm) as the original and Dremeled off circular at both ends to facilitate insertion in the wing and through the wooden engine pod support. At this point I cutoff the small useless foam bits in the wing recesses nacelle assembly, that prevented the dry fitting for trial purposes.

I then proceeded with the delicate task of cutting out the flaps. Think more than twice before making those cuts, there are many ways to do it, but they are all irrevocable. If you look at the wing from behind you will see that the outlines for the outer flaps don’t line up between top and bottom. Furthermore the very thin foam piece between flap and aileron would lack sturdiness, and the fixed part between the inner and outer spoilers behind the engine again doesn’t match with top and bottom outlines either. Without functional spoilers this cutout even became irrelevant. Further analysis of the inboard flap possibilities revealed it would substantially weaken the non-scale foam main gear reinforcement, and after cutout the ensuing thick flap block could hardly be made aerodynamically shaped at the front to be effective. Furthermore the fan would blow a lot against that flap (straining the actuator servo) in case of a full flap go around. All these factors made me decide to eliminate inboard flaps altogether, and concentrate the efforts on outboard fowler flaps with a concealed actuator mechanism.

After many thoughts I finally came up with the following cutting method. Forget about the tiny fixed part between ailerons and flaps and keep it as part of the flap. I first made a vertical cut top to bottom all the way through, following the upper flap panel line between inboard and outboard flap. Then I put the wing upside down on supports and made a cut bottom to top, all along the front of the flap line (watch out for the fake line). I used a brand-new knife extended well open and at a shallow angle which will keep more rigidity in the wing, reduce the amount of flap leading edge sanding, and create a smoother Fowler airstream as with straight vertical cuts. With a bit of dexterity it was possible to make one single cut joining the lower forward edge of the flap with the back (upper) end of the spoilers. Imperfections primarily occur at the canoe opening positions and can be corrected later. The resulting flaps end up like a flimsy foam flat pyramidal constructions, but these had to be reinforced anyway you cut them out.

Being unable to mentally figure out the results of moving the Hobby King product 9213 hinges fore or aft, I resorted in making life size drawings of the wing/hinge/aileron combinations at various angles and positioning. I wanted to find a position in which it grabbed sufficiently on the flap reinforcements, was not in the way of those horizontal and vertical CF reinforcement bars, hugged the wing intrados without visible gap in full up and takeoff flap position, but formed a visible venturi effect gap in the full down position. These drawings also gave me an idea of the travel a z-link had to push, to reach desired flap angles. This would help me figure out the possibilities to completely hide the flap servos and actuator linkages within the hollowed out canoes. My idea to further aerodynamically shape the top of the flaps by sanding and then covering their top with 0,8mm balsa could not be tackled before basic reinforcements were into place. I therefore first glued a 3,5 x 1 mm CF strip flat over the leading edge top of the flaps, thereby straightening the damaged line resulting from the cutting along the canoe recesses. Continuously monitoring the difficult to maintain position and angle of this strip over the canted surface allowed me a few hours later to cut the excess glue with a knife just before it became too hard. The balsa cap will be glued later on along the back of that strip. Only when that assembly was dry was I able to make the indentation to accept the vertical CF strip. This was positioned at the existing flap bottom panel line were the secondary flap deploys. The distance between the CF strips is also sufficient to allow mounting of the HK flap hinges without weakening structures, even bonding with them for additional strength during flap deployments.

To get better depth accuracy cutting the trenches for CF reinforcements or servo and light wires, I applied red tape to my Japanese type saw, about 5mm above the saw teeth. I prolonged the false flap panel lines to the end and pushed the 3,5 x 1 mm CF strip into the glue I previously forced into the cut. This makes a strong bond which is necessary because the cut went hallway down the very flimsy flap foam. Each half hour during the curing I swiped away the excess swelling glue so the secondary flap outline of about 1mm deep will be kept, and further down, the outside the cuts will be filled and sanded before covering. Note all reinforcements run wider as the flap, because the flap can only be reduced to its final width after the hinges have been installed and lateral clearances during its crooked operating range have been checked.

As you see this methods needs lots of trial and error plus dry fittings, and the same applies to our next cut for the insertion of the vital 4,5 x 1mm CF strip in the existing but deepened out bottom wing panel line, running from a point just in front the halfway aileron position, straight through the engine mount plywood towards the ESC spaces. The latter assembly can only be glued in altogether and will be performed at a later stage.

With the flap top covered with balsa, the torsional resistance improved dramatically and made it possible to use only one servo per side, but to find that out the flap hinges had to hold the assembly into place rigidly. Further experimentation with hinge positions was not simple because the canoe recesses leave only minimal foam depth. This would have been no problem had I not been overeager to hollow out my canoes earlier. Making the canoe cut between the wing-flap separation and hinge pivot point first would have been wiser. The solid canoe part (remaining fixed on the flap) could have been cut with a small slit over the hinge, and minimal recess around the pivot point, resulting in a stronger anchor point for the hinge. The front canoe part remaining fixed over the wing then could be hollowed out as necessary to accommodate the other side of the hinge and servo pushrod. Correcting this early mistake now will take time to reconstruct.

A picture of the progress after two weeks (more time spent thinking, drying, cutting, Dremeling, sanding and dry fitting, as actual building, but experimenting is half the fun on a project like this). Both wings are upside down, one with the flap and hinges in place, and the wing reinforcement CF through the engine mount, the other showing the roll sanded flap recess under the original spoiler top. Balsa capped flap top shown below will pivot within that recess. Also visible are the hollowed out canoes, Japanese saw with red depth mark tape, PU wood glue, HK flap hinge and paper drawings to evaluate hinge positions versus flap leading edge within carved out shaped flap recess in wing, uninstalled CF wing reinforcement with hole through the assembled engine mount plates, stronger 8mm CF wing spar with rounded tips, and possible servo flap actuator position for invisible mechanism through the canoe(s).

The canoes having been molded in pairs, separating them resulted in excess quality foam pieces I used for fabricating hinge supports for the wing and flaps. I first glued small CF cross-members between both CF spars on the flaps. These were separated by just the width required for the HK hinges to get stronger lateral support. Next I carved as long as necessary on the excess foam parts so they could be glued on the constructed CF frame and would fill the hollowed canoes completely, thus providing full lateral support around the flap hinge part, with minimal play. This is where the HK hinges are vastly superior to the Dubro hinges most of the previous builders used. Another advantage is that one the predrilled holes (for glue to grab) can also be used as a pushrod attachment point. My hinges therefore have to be anchored strongly to the flaps because they will form the basis for the actuation and will have to absorb the substantial (torsional and aerodynamic) forces. The grab on the wing part of the hinge is spread over a larger area so CF reinforcement was not necessary, and only the outside part of the hinges were “foamed”. To strengthen bonds like that I make perforations in both sides of the glued area to allow the glue more grab area in depth. The inside part of the hinge remaining free to allow the pushrod to move along the hinge. In fact I think my initial mistake of hollowing the canoes resulted in a bonus, the hinges are now strongly bond to the wing and aileron, and the canoes less structural for their support. This allows me to vinyl the flat part of the wings and flaps first (much easier), and vinyl the complicated canoes separately. The canoes will later be glued solid for the flap part, but hot-glued on the wing part to facilitate servo (arm) replacements or adjusting if ever necessary.

During the previous months when reading the B737 RC group forum I had copied all the interesting paragraphs from previous builders onto a personal file containing about 100 pages. After I had made my decisions about my desired options I could eliminate more than half, and highlighting the very important bits it became a very handy document I consult continuously during the build process. Furthermore I had saved interesting pictures of other’s build processes, and together with pictures from all angles of the Jetair real aircraft in a separate album, allowed me quick reference to get things right. On one of the pictures I saw somebody also had reinforced the top of the wing around the engine support with CF strips. Holding the wing against a light source definitely showed a thinner weak structure but I discarded the frontal reinforcement because Ming’s carry through leading edge CF rods take care of that. At the back it’s a different story and I used the panel line close to the spoilers to insert a 7-inch long CF strip extending either side of the engine support. This coincides with the later to be applied “no step” outline you find on most airline liveries. I initially thought those lines were straight but as seen on the picture of my aileron repair, they are slightly curved, and a bit more difficult to cut, completely neglecting the kind of W-bend in Ming’s molding. I glued the strips in just deep enough to keep the original groove depth. Following picture depicts one separate flap with CF hinge support frame, the other flap and wing with hinge reinforcements glued into place. Hinge/actuator linkage not depicted for clarity behind trial positioned servo, canoes loose next to their end position. On the other wing (top view) you can see the glued CF reinforcement strip above the engine mount position.

I then cut out the flap actuator servo recess so it would be completely encased within the wing, and firmly glued to a top custom cut plastic piece bolted onto hardwood blocks in the wing (to neutralize the high torsional forces). The deep recess had little effect on the wing structure thanks to the additional CF reinforcement into that area on top of the wing. For the small connection between the servo arm and the hinge pushpoint I opted for z-bent 1,5mm rods. The little space within the canoes didn’t allow for quick links or other adjustment methods so the length of the rods between both z-bends had to be carefully looked upon. Only 4,5cm long, there was little risk the thin rod would bend and I mounted the servo arm at about 90° up angle so retracted the flaps would lie flat against the hollowed out wing and no force was exerted on the servo, and extended the arm ended up in line with the pushed out rod, so once deployed fully, aerodynamic forces would push against the servo itself instead of trying to rotate the arm back. Using the inner arm hole at 7mm from center those 2,6kg/cm metal gear analog servo’s could push more than 3kg for the extension. On the aft hinge part I used the holes at 12mm from the pivot point which should be suitable for the rotation to about 40° for full flaps. Needless to say, it took me a few hours of trial and error using a servo tester to get everything right. Mechanical adjustments being impossible when everything will be glued in place, it will be mandatory to use two separate mixed in channels to command the port and starboard flap servo’s, with the servo reverse function on the transmitter for the inevitable mirror movement and end point electronic adjustments.

I elected to route the flap servo wire by deepening the nearby panel line, then along the back of the engine mount foam towards the innermost canoe cutout, which I carved out just sufficiently to accept the JR connection for the extension wire, then forward into the long CF trench which at that place runs much deeper, so the wires will only be inserted after the complete engine support/CF long reinforcement strip has been glued in the wing. Further routing via the ESC space to the mid wing opening where the receiver will be mounted. I preferred the latter because with the position lights, strobes, landing lights, ailerons, flaps, main retracts and throttles (all duplicated for each wing) there will be more cables in the wing as connections to the fuselage (only elevators, rudder, nose gear sequencer plus steering, and rotating beacons, plus of course the engine batteries). For ease of possible replacement of the (digital) aileron servo’s I decided to route the leads via the outboard canoe space, where the connection to the extension wire will occur. With all wing canoes later affixed with easy to remove hot glue, replacement of failed wing servo’s will be possible with minimum damage to the finish.

Having purchased a complete airliner lightning set with double strobe lights, red green and white navigation lights, twin flashing red beacon lights, and strong landing lights, all controllable in pairs through a single dedicated radio channel, it became obvious this would involve lots of additional wires. The control box will be fixed on the middle of the wing, in the same large factory cutout the receiver will be housed in. Looking at the wiring diagram I saw I could use a single common negative wire for all the lights, and individual colored wires for the individual positive wires. In order to minimize volume and weight I ordered thin flat 14-pole colored computer cable, which can be custom stripped according the required number of wires needed. The wings already have so many grooves for factory and custom CF reinforcements, plus servo wire channels, I didn’t dare to weaken it further by enlarging existent channels or cutting additional ones. The required 3 thin wires to the wingtip lights fit next to the aileron servo wire, then via the much too deep recessed oval fake inspection holes (who will be partly filled up before vinyling). The individual correct valued resistors can then be soldered to the positive wires at the connector to the light control box (again facilitating future replacements). Following picture shows the starboard wing flap with its canoes firmly glued to the hinges and already vinyled. On the wing, the flap recess also has been vinyled (including the fake spoilers on top), servo positioning and wiring routing, but finished canoes and flap servo cover plate not in position for clarity. Wing vinyling will be much easier without these protuberances glued in place. Port wing eventually got the same treatment a while later.

The question: what next? became rather difficult to answer. Try to follow my reasoning. Wingtip navigation lights and strobes are mounted in the curved part of the winglets, which are rather large but delicate on this model. Ming gave us the choice between straight tips or winglets (both in the box), with only an option to glue either one solid. While this might be practical for the straight tips, the winglets would be extremely vulnerable to transport damage, and repair works on the gear, flaps or ailerons at the bottom of the wing next to impossible. Making winglets removable at that thin wing end had to be seriously thought after, because the colored and white navigation light plus one strobe also needed to be connected each time. Those 3 wires running from the wingtip via a flat channel into the fake ovals to the aileron servo, then had to be routed together with the aileron servo wire in the existing front channel towards the ESC space. With wires had to be inserted vertically together to fit in the channel (designed to only accept one) and worse, they had to be routed somewhere through or around the wooden engine bearers at the place of their largest load and vibration. Cutting through seemed less indicated, and there was a way through minimal foam removal in the foam part around the wooden bearer, then along the place where the front CF spar is visible, and direct into the ESC space towards the center of the wing box.

To find that out I had to dry position the engine bearer wooden and foam box and noted once they will be glued it will be very difficult to vinyl the minimal clearance areas. Looking at the two piece engine nacelle, I noted mold help pieces and star patterns better be removed first. Some mold traces were so deep these had to be filled to create a smooth air inlet and exhaust. Engine cowls were in two halves, if you want to work on or exchange an engine or fan later on, better not glue them together but build in a custom system to keep them strongly together with the engine in place, but relatively easy removable for maintenance purposes. From the present stage, everything else on the wing (except the landing gear) has to be prefabricated because they all have to go in together and get glues at the same time for solidity. This is especially true for the already prefabricated large CF strip true the wooden engine support, together with the foam engine pylon and upper cowling half, but including the servo and lightning wires. With the half nacelles hanging down, it will be more difficult to work on the winglets, so I think preparing and dry fitting that sub-assembly is the first step to tackle. All those progressive steps will be covered in next chapter as they are completed in turn.

2) Wing sub-assemblies and mating.

Winglets: I looked into my scrap box for CF tubes that could glide into each other but ended up with 1,8mm wire that fitted relatively tightly into 2mm CF tube. 4 pieces of 2 inch long wires were cut and after predrilling parallel holes glued into the winglet as deep as possible (due to the upward curve). They stick out just over the flat joining foam and are glued to that for added rigidity. When dry, I predrilled holes in the wing to first accept the wires, then further drilled out for the 1-1/4 inch long CF tubes that were glued in the wing. These are a bit longer for rigidity and to cater for excess glue clogging up the length of the tube were the wire has to penetrate. The little imperfections in alignments already form a first part of the friction to hold the winglets in place when fitted.

Next job was to install the lights in those winglets. The red or green navigation light is positioned close to the strobe light, and a white navigation light at the back end. The light system I ordered in Germany has double stobe effects and can be sequentially and individually commanded through a single button from my transmitter, idem for the rotating beacons and landing lights.

Looking at the wiring diagram I noted all lights use the same negative lead. It thus became feasible to use only 3 wires in each wing, one common negative, one positive for the navigation lights, and one positive for the strobes. With the necessity of each LED having a resistor I experimented replacing both resistors of the navigation lights with a single one of different value (mounted close to the control box in the wing center section) but the results were disappointing, one of both lights dimming too much. Apparently each LED needed its specific resistor in series in its own circuit. If I wanted to keep a 3-wire layout for those lights I thus was forced to install those resistors after the split, which meant in the winglet. The resistor for the strobe still can be mounted in the wing center section (easier to replace if needed later). The solution for that problem was found by preassembling and soldering all wires, resistors, LED lights and connector into a single custom assembly, and delicately carving out recesses in the foam to glue them in place in one go.

After the electrical subassembly was completed, I liberally applied liquid isolating rubber around everything but the LED’s, to avoid nude wires to touch each other, and the metal pieces keeping the winglet in the wing. Although this is a 2 meter span model, the nature of an airline wing makes it very thin in a scale model, and requires well thought out engineering for installing nonstandard subsystems without losing too much structural strength.

When solidified I used hotglue to press the assembly into the wing so it could later be removed for maintenance without ruining the winglet. At the same time I also created a channel along the lines of the fake oval access panels on the bottom of the wing. This method allowed me to glue a thin 3 wire (part of a 15 wire computer flat cable) wing long cable, kept horizontally at the tip part to keep wing strength, then from the aileron servo vertically along the aileron servo wire in the precut channel towards wing center. After testing proper functioning of all lights, both wires were glued in, except for the small portion between the aileron servo and its connector under the closest flap forward canoe fairing. That way eventual later digital aileron servo replacement can be done with minimal damage to a finished wing. Hot glue (FMS or Hobby King) not really hardening over time, also ensures the survivability of foam models through flexing in case of mishaps.

The connector I used for the winglet is standard JR for servo’s, but I opted not to install the cap cover because it made the link so tight and critical in alignment, this would cause problems inserting the winglet assembly, and would require forces too great to apply on the winglets when pulling them apart. Next I used lightweight (Perfax Super) filler to cover the electric assembly at the bottom of the winglet, and the wires in the wing, till everything was as smooth as the original foam. This required multiple layers and much sanding, but I like working with that substance because even when hardened, it still remains relatively elastic and is ideally suited for highly flexible foam wings.

To finish the removable winglet subassembly, I vinyled it but this was much more difficult as expected due to the complex compound curves of this single piece of foam. Both sides had to be applied separately but luckily the back square end is just large enough for a small but strong invisible overlap. The leading edge of the original is highly polished aluminum so I opted for chrome adhesive. Unfortunately this is thicker as standard vinyl and doesn’t bend very well. The complex leading edge curve necessitates tackling the job in separate sections, and the first attempt in overlapping both sides around the thin leading edge failed overnight because of the stiffness of the material. I resolved the problem next morning by cutting away the extreme front part 1mm behind the leading edge on both sides, upper and lower flat parts remaining in place. I then made short cap strips that were kept bend around a small tube for some hours, the adhesive back paper then being removed and the parts pushed around the leading edge with a slight overlap to each other, the flat back parts solidly bonding to the already in place flat chrome strips. From a short distance, it is visible, from a distance only an avert critical eye will see this puzzle.

I then applied the Caliegraphics made Jetair logos to the winglet. Especially for the fuselage I had requested the red and white logos and letters to be sufficiently opaque not to be discolored by the blue background. Callie obliged but I was surprised how thick these stickers were compared to the thin material she used for my base white colored T28 Trojan. The end result is very pleasing and was trial mated to the still unfinished wing.

Please note I only make one wing at a time so I can avoid repeating early mistakes on the other wing, using these pages as an assembly manual. Next chapter will cover the landing lights and engine nacelle installation.
Last edited by BAF23; Oct 17, 2015 at 05:02 PM.
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Dec 22, 2014, 11:27 AM
The sky is the limit
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Progress during the year 2014

Landing lights

To have a better funneling of the landing lights I ordered lenses from I choose for 45° lenses, too wide for a narrow scale beam, but making it sufficiently visible for the audience during the turn to final and passes in gear down configuration. The lights have to shine down for that, but also have to be visible by the people who are above the model centerline during taxi. These strong strobe type LED’s have to be positioned within the lenses assemblies but had no way of keeping them in position. I resolved that problem by shaping small plastic scrap parts after drilling a 5mm hole in them. I then glued those plastic supports to the back of the lenses, keeping sufficient space open for the evacuation of excess heat.

While drying I soldered wires to the shortened LED legs and Dremeled out the 2cm diameter deep hole in the leading edge close to the fuselage. I then drilled from the middle of the wing into the back of the opening, and pulled the prefabricated assembly in after having painted the sides silver. Everything sits just tight without glue, making it possible to replace a light without cutting foam apart, and the assembly can be oriented slightly in their tunnel by pushing it around with a long thin screwdriver through the wire channel. I then took scrap clear plastic from food containers to find out the shape to cover the leading edge up to the nearest panel lines.

When satisfied I then cut and hot shaped 0,5mm clear polyester clear plastic leading edge covers which were then hot glued (with their protective paper still on the outside) over the slightly thinned leading edge within the nearest panel lines. This left sufficient area for the plastic to bond with the foam, keeping the wing leading edge shape intact, and will be covered together with the rest of the wing, hiding its plastic nature (looking like just another complete panel). Next picture shows the assembly with and without the cover paper before applying filler to smoothen out the transition with the adjacent curves.

With those big round lenses the shape of the aperture is not yet as per real B737-700 but this will be created later when covering the wing with vinyl and aluminum tape, with only the correct shape of the clear part then cut free. After filling the gaps around the transparent portion, I then made the cuts into the adjacent so-called NACA cooling intakes. I wanted them to be functional because I’m planning on making the main and nose gear door fairings, and those will close the only gaps allowing air into the fuselage. With two heavy batteries inside I thought it wise to foresee some ram air cooling of the inside fuselage. The APU exhaust in the tail will be made functional to allow sufficient airstream. After the cut they don’t look like NACA intakes anymore, that is because the foam is very thick at that place. The adjacent forward wing attachment screw dictated me not to cut too much material away but substitute steeper angles for the shallow ones, which would have weekened that important stress area too much.

Engine nacelles

Next item to cater for were the engine nacelles. It is better to completely prefabricate a nacelle with everything in it, and cover or paint at least on the top, because once glued in place together with the wing reinforced carbon rod, working on the nacelles becomes much more cumbersome and some areas just become inaccessible. My desire was having nacelles that were strong enough to transmit the thrust from the fans to the wing, be able to execute an engine or fan change without tearing everything apart, and having smooth airflows into and out of the nacelles.

After having analyzed various solutions adopted by previous builders, I absolutely wanted to avoid weakening the already flimsy plywood nacelle backbone that dampens reverberations and gains stiffness through the surrounding foam. I saw others further carve out the foam behind the engine to accommodate the ESC in the slipstream for better cooling. While that was tempting, I rejected the idea of taking away a major portion of the rigidity of the top of the foam nacelle, and it disturbed the outflow too much with all the wire connections. The Change Sun 10 blade fan and Castle 70mm casing is supplied with an optional nose lip, and has two stubby side “ears” to somehow attach it to a frame. Attaching it on one side by bolting it to the plywood was one possibility, but again required making holes in the plywood, and once in position and permanently surrounded by foam, impossible to detach anymore. Noting that the front of the fan body was a snug fit into a ring in the back of the lip, made me decide to strongly glue the surfaces of the foam to the plywood, then slightly carve out the foam and make an indentation into the plywood as to accept the lip (as seen on one of the pictures showing the winglet wiring).

This picture shows the lip positioned in the carved out upper nacelle half, and the fan body that can be pushed snugly into it, still with its two handles. The bottom part of the nacelle was then cut just behind the lip, and the front solidly glued to the top part and again around the lip. The horn shape of the lip makes an excellent stop against the foam all around the fan assembly, not a luxury considering that (hopefully more than)one kilogram of push will be applied to that unreinforced foam structure. Following picture shows the lip solidly encased within the glued front bottom and top halves. The inside of the nacelle already had a slightly wider diameter to accept standard 70mm fan casings, so this could easily be used to squeeze the fan in position laterally and backwards, the thrust keeping it in position against the lip. The only unchecked force was the torque, but that could be countered by inserting one of the ears into the slit in the bottom nacelle cover. The top handle was completely eliminated in order not to interfere with the plywood/foam bonding.

In order to solidify the lip and minimize turbulence just in front of the fan, I then used lightweight filler to blend the horn with the intake wall. When sanding was completed, you even couldn’t see the lip anymore. It became part of the forward structure and spread the loads produces by the engine and fan all around the nacelle. In the meantime a friend of mine had mated the Turnigy L2855-2100kv engines with aluminum nose spinners and affixed them in the Castle cyclone fan casing with TC Castle CS10 fan before dynamically balancing them with a purpose purchased Australian piece of equipment I don’t understand well. I used (hidden) double hinges to allow the lower aft part of the nacelle to swing out of the way so when I got the completed assemblies back, I was able to just slide them against the back of the lip, and after closing the nacelle by means of two nylon bolts (into embedded nylon nuts in the other foam part), everything was snug without using any means of fastening the propulsion assembly. This will much facilitate fan/engine removal for possible replacement or balancing. Following picture shows how the system works, and which hinge type I used as pivots. The actual intake front being of a different aluminum color (anti-ice system), I opted to paint that and the interior of the intake, instead of using vinyl that would be difficult to shape, and if becoming loose, would get placarded against the fan and destroy the engine. That is about as far as I got before I quit for winter sports in March. Shortly thereafter I got entangled in a variety of large glider projects (as can be read in my other blog pages), and flying plus the inevitable weekly maintenance took precedence over any form of building.

After about 7 months of standstill, winter 2014 was a good time to pick up the Boeing project with the intention to finish it before undertaking any other of the many other kits awaiting assembly. Using the almost completed starboard nacelle as a pattern, the port one could be easily prefabricated. On the picture below you can see the individual parts after having been dry fitted. At the back of the nacelle, you can see where I made a slit to position the white nylon nuts in the center of the holes that I drilled for the long nylon screws that keep the back of the aft nacelles together. Just after the picture was taken, the slit with the nut got filled with Tec7 filler/glue to prevent the screws from rotating within, and obtaining smooth inner exhaust surfaces again. The middle of the nacelle is being kept together by the two strong black hinges, glued with Tec7 in angled slits. To facilitate vinyling, the other sides of the hinges were only be glued after the separate elements had been covered. Note the minimal plywood backbone that has to absorb and counter the serious thrust and weight loads of the overhanging engine assembly during G maneuvers or hard landings, no wonder I saw so many of them broken after mishaps. That 5mm thick plywood engine bearer is created by gluing one 3mm and one 2mm identical shape together, done well in advance with epoxy over their complete common surface, and allowed to dry overnight. I suppose the different thickness has been chosen to eliminate resonance at certain engine frequencies. 5mm still is thin, it is therefore imperative to stiffen the assembly by applying strong glue on every bit of surface on both sides of the plywood, and pressing the foam around it together to ensure uniform contact capable of better absorbing side loads. The lip receiving the frontal fan casing was then also epoxied into place, as well as the joint between both forward halves. It took quite a bit of epoxy to do that, but other glues were either not strong enough, or expanded during the drying phase, which could later prevent the tight tolerance between the lip and engine case to fully engage.

Vinyling the nacelles was no fun because the shape continuously varies at any point, and it was more a question of compressing the vinyl instead of stretching it. To facilitate the job I first made paper templates, 4 in total. One was for the lower front half of the intake, one for the upper half front to back, one for the support beam on top of the nacelle till the exhaust, one for the visible sides of the support that joins it with the wing, and one that covers the lower horizontal flat area of the support. The paper side-templates were then refined as to also be usable in mirror, and the patterns were then transferred on the back of the vinyl to produce the 14 pieces necessary for the covering of both nacelles with minimum visible overlap. Initially it took me about 1-1/2 hours of delicate application (millimeter by millimeter of flattening out of the flat vinyl on the compound curved nacelle panels, but in the end I could do one panel per hour. It was not perfect, but with only about 3 intentional cuts where there just was too much vinyl to compress, the result was acceptable. After the leftover internal parts were painted natural metal, the engines got inserted (not fastened by any means), the lower pod was closed and secured by the 4mm nylon screws, and the Caligraphics and fan disintegration red stripes applied. This completed the nacelle sub assembly, but I still didn’t mount them on the wings at that time because they would be in the way for turning the wing around for further sub assembly work and adjustments.

Main landing gear

After having read and seen on videos so many gear mishaps with the Windrider B737, even planning on operating mainly from a smooth hardened runways, I decided to swap most of the Windrider provided retract system by stronger and more scale looking sub items. On following picture you can see on the left side: the kit provided landing gears with the weak 3mm pins, plastic trunions, common R/C wheels, and small plywood plaque to glue it to the wing bottom. On the right side you see the replacement PW-RC landing gears with metal trunions made for 4mm pins, these pins are hardened steel 4mm engine shafts ordered from Heads-up RC. The original spring loaded gear legs can be reused after being bored out to 4mm. Main scale wheels are Robart 2-1/4 low bounce tires with correct hubs for inside and outside, nose wheels are 38mm Hobby King wheels with correct hubs and much better proportions and dimensions.

Pic gear 737

A first positioning of the original gear in the wing revealed serious shortcomings. Although Ming installed the gear on a kind of elevated pedestal that would have caused so much interference with inboard flaps that I omitted installing the latter, when retracted, the wheels still sit much too deep into grossly oversized wheel wells, while the legs are partly up in the airstream and prevent gear doors from being installed flush. This is a contradiction because curing one fault only augments the other. With diabolo type gear it is impossible to mount the assembly at an angle, and the gear mechanism I intended for the Boeing are 90° pivoting systems. I also don’t understand why such a small and thin plywood support was fabricated to only be glued to a fraction of the larger available surface of the artificial foam platform. At least my new gear mechanism sits deeper, but some engineering was required to correct this complex case, because I want a reliable strong landing gear that looks as scale as possible.

Most of the time when the model is on the ground, people even don’t see the gear except for the outer wheels, but once a B737 is in the air, those wheels become the bottom of the aircraft and are part of what people see. I know some people buy this Windrider model to quickly build it as an airliner, then tear holes in the sky flying aerobatics fully happy with retracted nosegear sticking half out, and maingear creating a lot of drag while being flimsy and the weakest part of the kit. So Ming, if you read this, please pay a bit more attention to the engineering aspect before putting molds of future projects in production, producing the foam won’t cost an extra dime, and the larger thicker plywood just a tad more. I have no idea how many B737 kits ended up to people modifying it to more solid (carbon stiffeners), more scale (flaps and nose gear doors), versus people who just fly it out of the box with just a few decals applied. It is my believe that if you ever produce kits of a B747, Concorde, or DC4/6/7 ;-) that you at least engineer the kit in a way that we can more easily modify it according to our scale desires (flaps etc). The fact I bought the B737 kit from a German well known retailer, including engines and landing gear for a discount price that was less than the basic foam (glider) airframe, illustrates that R/C flyers are not interested in cheap substandard accessories. I was able to sell my engines, fans, and ESC’s to a fellow club modeler, and still don’t know what I will do with the surplus gear items, but this was the cheapest way of getting me shock absorbing diablo gears. I’m sure with the dedicated followers you have, and the number of people who appreciate your productions, it could be possible for you to produce kits with provisions for making flaps, and including landing gears that are capable of handling hard and soft surfaces, whilst looking more scale than what you provided on the 737. The few dollars you spare the present way, cause a lot of people to discard your so called premium kits from their dream list. Keep the basic kit available, but also include a quality product accessory kit in your offerings. I’m sure that getting everything from one source will get you lots of new customers who are now afraid of tackling such a project because the parts needed to make it a reliable and scale looking aircraft have to be purchased in three continents with expensive shipping prices for the many small items we need. I’m convinced a lot of modelers would prefer to let you cash in on part of the extra money, instead of the many postal systems (which are not always reliable). And Ming, please don’t feel offended, I just tried to give you some pointers for an even more thriving business. You already gave us a basic kit which we could only dream of, and at a reasonable price, but more is within reach… I wandered away from the technical analysis again, but here is the picture of the sub-standard product as delivered in the Windrider kit, dry fitted in the wing.

Compare that to the tight flush fit of the real aircraft, and you’ll understand that more modifications were needed, including the fabrication of main gear leg doors and full nose gear doors. Here is a picture of the underside of OO-JAS, a sister ship of my OO-JAR, taken during a low pass at a Sanicole airshow. Note the exposed main outer wheels but aerodynamic doors over the legs, the NACA intakes and APU exhaust. The rear of the engine nacelles cannot be faithfully reproduced without losing much engine thrust. The real nacelles have an inner longer exhaust for the hot engine core exhaust, and an outer portion for the cold fan exhaust. Our EDF’s are in fact only the fan portion of such high-bypass engines, and nothing can be put in the way to restrict our exhaust airflow.

I started the gear upgrade by dismantling the legs from the original retract servos, the latter going into the crap box for eventual use in models lighter than 3kg. Having read on RC groups that the springs in the legs were too stiff, even for relatively heavy 737 models, just taking away one screw allowed the “oleos” to come apart so the spring could be extracted to be shortened. People before me did the math’s, so I just cut one full revolution for each main leg (which apparently reduced compression force from 5 to 4kg), but for the nose strut I went even further and cut off 1-1/2 turns (with the Dremel). Cutting more would have provided that real spongy look during taxi, but in case of runway excursions or nose first crash-landing, I didn’t want the strut to bottom too soon because the full forces then get transmitted to the long foam nose.

To further diminish the friction of the system, I got out my elbow grease and 600 grit sanding paper to get rid of the rough horizontal indentations created when machining the aluminum on a lathe. That caused undesirable friction, but after sanding, polishing, and lubricating, each oleo operated much softer than when delivered. With everything still apart, I used my column drilling machine to carefully enlarge the 3mm to a 4mm hole on the top. It is imperative that it is well aligned and without any play to accept the 4mm gear pins. Because the springs had been greased ! the interior was sticky, and ear sticks (cotton swabs) had to be used to get the drill remains out of the interior. Failure to clean that out thoroughly probably would result in particles eventually falling in between the sliding surfaces, causing serious friction or even jamming of the oleos.

Inserting the former engine-shafts through the created hole felt tight, but also allowed to measure how long those shafts had to be. The ones I got were 5cm long, and had an indentation for an E-clip at 1,5cm. That short bit was perfect for insertion in the metal trunion, but the other bit was much too long and would prevent the oleo from fully compressing. That bit could be maximum 2cm long, but anything over 1,3cm just hung in the air around the spring, and was of no use. I therefore decided to shorten those former engine shafts to 3cm, 1-1/2 cm on each side of the E-clip. Only one side had to be shortened that way, and that was done with a normal (not hobby) angled grinder with metal abrasive disc. Remember this shaft is 4mm hardened steel and very tough. The 2mm thick disc was also used to create the flat spots where grub screw would keep everything from rotating or falling off. Although not strictly necessary, I mounted the E-clips on the axle to ensure it would under no circumstances be pushed deeper into the trunion. If it starts sticking out through the back, the gear will not be able to move to the fully up nor down position anymore. Testing that proved the retract system shut itself off instead of burning the engine with the risk of electrical shorts.

A dry fit of the oleo over the 4mm pin was essential for discovering that using the servo tester, those bulky oleo cylinders pushed against the electric motor casing close to the trunion with the gear in up position, an undesirable situation that was easily corrected by using the Dremel sander to hollow out a millimeter of the plastic casing (and even a tad of the metal), and slightly flatten the outside of the oleo where it could cause a pressure (and auto cutoff of the linear servo). With all those original parts corrected (every single one of them!), reassembly of the actuators and oleos could begin. The 3mm (grub) screws that didn’t need to be touched anymore got the thread lock treatment, the ones that still had to get out for better fittings into the wing, were just slightly tightened dry.

The awful looking original wheels and tires had been removed at the start of the operation, and replaced by low bounce scale straight thread 2-1/4 inch Robart main wheels. These come with two different hub cabs, and for our B737 the plain ones are used on the outside of the outer wheel (that forms the underside of the fuselage when retracted, the spoked hubs being used in the inside of the inner wheels. Whilst the original wheels had wide rims and narrow tires, the Robarts completely enclose the wheel attachment in a narrow inner wheel, but allows the tire to balloon outside the rims in a natural way. It is possible to take the rims apart (by removing 3 screws) and insert special order foam inserts for heavier models. It is my belief that with the rims in place, these four tires are up to the task of coping for a 5kg model, if not, I could still order those inserts and easily install them later on.

Each twin wheel kit comes with a set of 3 different adapters for various diameter wheel axles. The 4mm ones are the middle size. The four small size ones went into the scrap parts bin, but I used the large ones to make spacers that I inserted closest to the gear leg. I came up with that solution to widen the distance between both wheels (the real aircraft needs that distance to accommodate the multiple disc brakes), but also to keep the original wheel axis (length). I realize this increases the arm for the forces during heavy touchdowns, but count on the very solid feel of those 4mm original wheel axis and the softened springs to cope for that. By trial and error, I found out that sanding and shaping those large plastic hub adapters to fit around the gear leg, then using the original metal spacer before sliding both rims with their 4mm adaptors over the axle, left just sufficient thread to mount the original self-locking nuts within the given constraints. For the inside wheel, the middle of the area around the nut had be Dremeled off a bit on the inside (thus invisible).

One sub assembly being completed, I couldn’t resist making a picture of before and after. In front and to the left, the old 3mm lightweight kit supplied actuator next to the toy wheels, to the right, the slightly larger stronger metal trunion gear. In between, the 4mm shortened pin and E clip plus the polished oleos and spring with a single turn having been cut off. Next row, all the bits and pieces for a diablo in chronologic order next to each other, being assembled over the axis. In the back: The nose wheel systems (new one with 4mm pin already provided). All of this surrounded by the various tools I needed to complete the tasks, except the column drill and Dremel which are mounted on my work bench. I also took the opportunity to weigh a single kit supplied maingear (95gram) versus my stronger scale unit (138grams). That is a 50% increase but still only 1% increase (per gear) regarding the predicted flyaway weight. The improved looks are just a fraction of the vast gain in strength, and are well worth the penalty.

Duplicating all this for the other main gear was simple, but with the wheels wider apart, the uncovered sides facing each other were very visible and therefore unacceptable. For each wheel Robart provides both a dish and a spoked cover. Having used one of each in the diablo, I could not find any use for the remaining plain cover, but figured I better used the remaining spoked one on the outside facing part of the inner diablo wheel. Being concave in shape and having to fit over the axle (I didn’t dare to shorten the adapters for fear of wobbling), the only solution was to make a hole in the middle that would fit tight around the axle adapter. Measuring a full centimeter across, it only left one millimeter of thin plastic between the hub and the spokes. Needless to say, drilling that out was a very delicate affair that had to be performed with the column drill by gradually increasing the drill diameter a millimeter at a time from 3 to 10mm. The result is well worth the effort and is very visible when looking at the aircraft from the sides. The fact that no cover was available to put on the on the inner side of the outside wheel will have little effect because it will mostly remain hidden from direct view.

Next came the steerable nosewheel assembly. Retract and oleo were straightforward and carbon copy of the previous assemblies, but the narrow wheels now left much of the original 3mm axle sticking out. After some measuring and brainstorming I came up with the solution of using one of the discarded 3mm main gear pins The 36mm length with a E-clip slit on one side was perfect for my needs. The wheel on the other side could hardly be slid over the axle and was left as is, the new axle was then slid through the oleo, and after the slightly enlarged wheel middle was slid over the axle, the E-clip secured everything in position. Besides looking very Boeing scale, the assembly which has to pass through the gear doors is only 33mm instead of 55mm wide in the original nose gear. Here is a picture of the latest main and nose gear modifications, but still unpainted.

The nose gear went back in the box for use when tackling the fuselage, but the main gears were presented for dry fit in the wing, one in retracted, the other in extended position. To start with, none got in: some internal mounting screws caused lateral protrusions in the plastic casing, which had to be taken care off by Dremeling on both sides. These gears also were a little deeper, but Dremeling away 2mm of the foam at the bottom had to be done carefully because not much foam remained for strength at that place. The gears could now be pushed down and finally proved my estimates to be on the ball. With a presumably 5mm extended plywood baseplate, the oleo legs are almost flush with the wing (ideal for fitting the doors to them), and the outside wheel of the widened diabolo became flush with the fuselage when fully retracted. Closing down the excessive opening was easy to replicate the real shape of the underside of the 737. The gear work so far took 10 hours, and according to what I read, the nose gear and doors final-fit is even worse. But I first wanted to tackle the weakest link because it is of no use to reinforce the gear mechanism, if it is bolted to a small plywood plate that is only glued on top of non-penetrating EPO Olifin foam material. Compare the look of following picture with the one earlier in this chapter, already an improvement.

Message broken up in two parts because of picture upload problems
Last edited by BAF23; Dec 25, 2014 at 03:16 PM.
Dec 22, 2014, 04:40 PM
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progress year 2014 part two

Part two of the 2014 update after I had to split up the entry because of picture loading problems

Next task was to integrate the pre-assembled bogies in the wing. I didn’t think that Ming’s odd shaped small 3mm plywood pre-drilled plaques would be up to the task of absorbing forces other than smooth runway perfect landing operations. I thus took a 4mm plywood piece and measured how large I could make it to still fit on the pedestal, then cut it in a rectangular shape so it also could stand more side forces. The opening in the pedestal was then widened to accept the larger plaque. After seeing so many videos of Windrider 737 dangling their landing gears, I also discarded the kit supplied minimal wood screws, and decided to use 3mm bolts with anchored claw nuts. Unfortunately the holes in the plastic retract plaque had been drilled very close to the body, and with almost no distance from their annoying protrusions that accommodate the crews holding their body to the plaque. That required each claw nut to be Dremeled off to be able to fit along the gear motor bodies. The two furthest could keep their 4 pins, but the 2 nearest even had to be tangentially shaved so much that only 3 teeth remained. Those teeth were not so much for preventing rotation, but because the nut would be unreachable after the plaque was glued in the wing, they also had to keep these nuts in position for the rest of the airframe life. Following picture shows Ming’s smaller, thinner odd shaped plaque next to the 4mm rectangular ones I made with adapted claw nuts around the retract body. The temporary mounted assembly was then presented in the wing to see where the wheels ended up in the vast cutouts, and how close the gear legs were to the wing to make geardoors fit.

That allowed me to measure how much space remained between the retracted tires and their cavernous wells. Using house grade thick scrap isolation panels, I drew some circles on them and used a figure saw to cut the odd shaped inserts. Having only measured the caverns on the outside, I was totally unprepared to discover that they were not cylindrical but conical towards the inside (just the opposite from what should have been), so my inserts had to be further shaped by sandpaper to make them fit. On following picture you see where they have been cutout from, and how ridiculous the kit supplied tire looks next to the factory cut wells. You also can see how every plaque-receiving surface has been carefully adapted to accommodate even the claw nuts and bolts after final and irreversible assembly. From that point on, pieces became so large, plus filling and sanding would be messy, all following work was performed on the clean floor of my work room, not the warmest feeling in winter, but with a foam knee cushion it was workable for hours.

By that time tolerances got so tight that various gear cycles had to be made with the servo tester because the odd angles during the intermediate phases caused the wheels to touch here and there, and that had to be eliminated. When both main gears operated freely and the angles at both endpoints seemed correct, I removed the landing gear units and replaced them with delivered plaques which I still have no clue why they came for with the retracts. Luckily they were of identical size and were now mounted with countersunk bolts on the plywood. Even with 4mm wood they sat deeper than the pedestal tops, so I filled the complete area with about 3 coats of lightweight filler before ending up with a completely flat pedestal bottom. In order not to have the spare plaques becoming part of the structure each time the filler was half dry, I delicately removed it from its seating. Sanding in between was also part of the process, and the cavern inserts got the same filler treatment by finger instead of by credit card due to their rounded nature. Following picture shows the situation immediately after the first filler application, using liberal amounts of lightweight filler and pushing/scraping it off with a credit card to minimize sanding later.

main landing gear gear doors

While that was being corrected, I got my brain in gear to figure out how to make practicable gear doors. My constraints where the following: no extra servos, lightweight but able to cope with the relatively high airloads, look scale, flush covering the gear mechanism when retracted, but being able to cope with gear leg compression without damaging the expensive Robart tires when extended. The variation between flat surface, straight angle and rounded curve on the same panel made me opt for easy to bend “blech” (tin can material 0,6mm thickness) that I had laying around from an old Stampe cowling. After figuring out a rough outline, I cut this out with old scissors, then made a 90° bend (has to be done in one go because after two times the material just separates) to fold a flap around the top of the gear leg. I then made pencil marks where to drill the 4mm hole for the gear pin, and 3mm hole where the grub screw was inserted in the leg. The pin with its E-clip was then removed and reinstalled on top of the gear-door attachment, then all was secured in one go with a panhead 3mm bolt that was cut at such a length that with 2 roundels at the outside it just could be tightened sufficiently to hold the leg firmly in position on the pin. I do not understand they only use a single instead of a double screw placed across the other side of the leg. This will probably be the weakest link of the modified landing gear. I used two roundels so I can remove one later to tighten the screw further in if necessary. Of course Locktite was used to keep that bolt from loosening, but even if it does, the leg will only rotate a bit but not fall out, because of the flat spot I made earlier on the 4mm pin. The other side of the pin then got reunited with the retract trunion, where the two grub bolts also could be Locktited within the pivots. After that final subunit assembly it could be positioned over the wing, so another 90° bend could be made at the wing/fuselage junction, and the lower fuselage curve made by judicious application of thumb pressures. Here is a picture that illustrates the first step in fabricating a gear door.

After much cutting, trial fitting and gradual filing, things started to finally operate freely and laying flush where it was supposed to, so the exterior of the gear door got vinyled, the interior remaining natural metal as per real aircraft. As you can see on the following picture, thickness of filler material and vinyl paper has been taken into account, and only very close inspection will reveal some minimal cheating to allow the tire to compress against the flat part of the inner geardoor instead of against the very sharp edges on their bottom.

Final wing component assembly

During the drying of the subsequent layers of filler, I tackled the wing to fuselage attachment system. Having read that some previous builders had experienced alignment problems I decided to allow for dry fittings before gluing anything firm. The claw nuts were pushed into the sausage shaped plywood supports that later have to be glued in the fuselage. The long bolts were not too tight in the claws, but might have to be made a bit conical to enter well when not exactly aligned, to be checked at a later stage. On the wing side, previous picture shows one of the four circular cutouts where precut large plywood roundels had to be seated to spread the loads of the bolt to the foam around. All that plywood was 3mm thick, and because I plan to fly only scale, this wood should be strong enough for the positive G forces. As you can see in the picture, due to the shape of the lower fuselage, the wood would sit too deep on one side but stick out on the other. I therefore increased the depth by two millimeter before gluing the wooden roundels. When that was dry, 3 more layers of filler were used (and sanded) to obtain smooth contours everywhere on the bottom of the wing.

On the left side of previous picture you can see a large cutout area where the ESC’s are supposed to be, one for each engine in his respective wing, covered by a preformed plastic cover with large ventilation holes for cooling. The Rohs Sky Power 80 Amps ESC’s with 6 Amp Becs are suitable for up to 6 cells and fit nicely in that place. I also used that cutout to run the electric cables to the ailerons, winglet light system and flaps. With the possible heat development of the ESC’s on the ground, I was afraid of only the bottom side being cooled and the topside to melt the wires, creating a general shortcut with ensuing loss of the model. I therefore made a center foam pedestal to keep the ESC away from the flat glued wires, and allow more air to circulate in those confines. To keep the cover panel in place, I suppose I had to glue it, but I prefer to bolt it so I can check and service that area later on. Because you cannot bolt in foam, I shaved off the bottom 3mm of the 8 pedestals and glued 9x9x3mm plywood blocks fabricated from Ming’s gear plaques. The ESC’s were then test fitted and proved to have 4mm bullet connectors while the engines had 3,5mm ones, and the length of those 3 wires also had to be shortened somewhat in order to have a smooth engine exhaust. The other side of the ESC’s had short stubs with Deans connectors, hardly suitable for 5S 80A peak power bursts. After correcting all previous problems, I was able to paint the various wells and also did the Robart hubs in a kind of soothed metal, the color of disk braked wheels, whilst the flat outside panel got vinyled.

Final wing assembly came into sight, but with the nacelles in position it would be impossible to vinyl the bottom of the wing around it, and prevent working on a wing put flat on its belly to vinyl the top part. An event driven sequence was then made up. After correcting the last blemishes on the top part of the wings, I completely vinyled them and applied the trim and panel lines. From then on turning the wing upside down could only be done over a clean and flat soft towel. I then vinyled the fuselage bottom part, and the area forward of the ESC compartments. After making paper patterns for the inboard leading edge aluminum covers (also surrounding the landing lights), those non-elastic panels were pressed in one go onto the vinyl and hold well, but some distortions were unavoidable because nothing on that wing is straight, omnipresent very subtle curves seriously hamper application of rigid cover materials. That inner leading edge had to be done at this stage, because it would be very difficult to do that with the nacelle in position.

After making a dry run with the nacelles and the additional almost wing wide reinforcement CF strip, I let PU wood glue enter the thin extra slit in the wing, and manually further applied in on most of the area where the nacelle contacts the wing. During assembly I already made sure no vinyl was between those parts, and now I had to avoid smearing glue at the aft part so the flap servo cables could be taken out if the servo had to be changed, and around the hole where the 8mm CF carbon wing rod passed through the plywood support. If you glue the nacelle in and the glue fills part of the hole or so, there is no way you can access it to clear the hole so you better take good care of that, and with some dry wing rod penetrations before the glue settles, make sure the glue hadn’t expanded in that critical space. During the drying process, excess glue was regularly wiped off on top of the CF wing reinforcement so no sanding of the hard material had to be done before filling the slight depression with lightweight filler. Whilst awaiting for everything to harden, I vinyled the aerated ESC plastic covers, the outer wheel dishes, and painted the wired wheels and wheel wells in a metallic color, using my fingers on the almost dry paint to obtain some weathering/brake pad dirt effects on the wheels. Next morning I only needed light sanding on the bottom of the wings before covering the complete lower surface with various bits and pieces around the gear pedestals and canoe openings.

With the retracted landing gear width causing the inner wheel to stick out in the fuselage, I waited to assemble those till the end. With the gearplates having conical screw holes, I used countersunk screws so everything was flat, but also to have the largest contact area. After having reinforced so much on the landing gear components, I opted to use 3mm nylon screws to mount the landing gear assembly to the wing. I deliberately created that weakest link for test flying and until my landing technique was ok for that Boeing. I read that it needs quite a bit of distance to rollout after landing, and if I cannot stop on the remaining runway, the incursions in the grass might cause forces on the gear that (due to my increased rigidity) could tear the wing apart. Something has to give at one point, so I prefer it to be the nylon countersunk bolts. Even if the head is torn off, heating up a screwdriver with a lighter allows it to be pressed into the remains of the broken bolt so it forms a new deep slit that allows the bolt to be turned out of the orifice. If those nylon bolts prove to be too weak for normal operations, I still can replace them by countersunk metal bolts, but wonder what will then break away in a heavy impact or sideways movements on our tarmac runway. Following picture illustrates the neat appearance of the finished modifications to the gear pedestal strongpoints, the wheel wells and the geardoors. At this stage the ESC and wires had been removed to allow easier vinyling.

Next is a head-on view in dirty configuration. Gear and (fowler) flaps are down for landing, landing light openings were enlarged versus the real 737’s narrow slits that hardly would allow the light to shine anywhere but very slightly down. I hope these will now be more visible from about 20° up (for ground ops) to 20° down (for overhead passes). You can also clearly see the much enlarged NACA intakes that will further be channeled up into the fuselage foam blocks for cooling of the batteries.

With the flaps up, gear down and winglets installed, the top of the wing looks smooth and slender, but from that angle the picture shows an unrealistic angle of the starboard winglet. The Robart wheels and geardoors add much to the overall scale appearance of the model from this angle, and are well worth the time and effort I spent on them.

The chrome leading edges have been very difficult to apply because besides tapering in thickness, the complete leading edge bow with subtle increase in sweepback over its entire width, there is not a single straight line on this entire wing, except for the trailing edges. Contrary to vinyl, that thin aluminum chrome foil has no elasticity to accommodate even the slightest deviation from straight (well it follows the one curve around the leading edge but that’s it). I used the crease lines that suggest 4 leading edge slat sections, but even that necessitated a unique pattern for each section to be made in paper and then transferred on the back of the foil. There is no way to cut some foil off once it has been applied (without visibly distorting or damaging it). The application was very delicate, because it is a tapering strip that covers less than half the depth of the slats, so no panel lines to guide you. On the bottom of the wing they end in the crease line of the slat. Applying it first vertically against the front of the wing dictates the first bend in the foil, but then does not allow you to bend the foil flat anymore against the top nor bottom of the wing. The only practicable solution I found was to first apply it on the flat top part, (gu)estimating how far back, then force it vertically against the extreme leading edge, and making 3 or 4 more cuts in the bottom part before forcing them flat in a slight overlap on the small bottom part. The very wide portion between the fuselage and engine pods was even worse because of the many angles and thickness changes plus the landing light cover transitions. Any wrinkle is very visible on that highly reflective foil but that is no wonder because I purchased it on a roll used for making self-adhesive mirrors on closets of camping cars.

On that picture you can hardly see that the leading edge is nowhere straight, but believe me when I tell you so. This picture also clearly shows how difficult an ineffective an inboard flap modification might be, let stand how much landing gear rigidity you would lose cutting out the necessary part of the gear pedestal. I’m glad I choose for only outboard single slotted flaps. At one time I envisaged adding a fourth fake canoe to cover up the aileron actuators, but it was too late to do it because I already had installed the servos in Ming’s cutouts, and the horns in the ailerons, and both are in line, not aligned with the airstream but at 90° to the aileron hinge line. While not scale, I think it would blend well with the other canoes (same spacing) but that modification needs catering for at a very early stage of wing build. Hereunder is another picture showing the difference in how far back the chrome leading edges run at various spans. Looking very carefully you can also see that besides the aft line of my chromed leading edge, and the trailing edge of the wing, no other line runs perfectly straight. After putting both completed wings with their beefed up landing gears, winglets, engines and ESC’s installed on the scale, it indicated 1,8 kilogram.


Since the first knife cut on the kit, I worked approximately 12 full weeks to get to this stage. Being retired, I not only work part-time on my models, but when on a project often 10 hours or more each day. Counting 5 days in a week (I sometimes have other more social activities), this would bring the total to roughly 500 hours so far, and I still have to tackle that enormous fuselage. Who said that foamies are only for kids and serious modelers should stay away from them? On RC groups I see others needing only one week to complete a Windrider B737, and then tearing up holes in the sky performing aerobatics with non-reinforced wings, but frequently encountering gear problems. It’s their money and choice, but I much prefer to make one of the few nice and affordable ARF airliner kits as realistic as possible, and reinforcing various parts and the wing even I never intend to loop or roll it. I have many other (scale) aircraft like Stampe, Trojan and F16 for (scale) aerobatics, you can see some of them on my blog After working for an estimated 800 hours on a project like this, it will be my flagship and I will treat it with the respect it truly deserves.

I also decided that although I mostly will store and transport both wings in one piece, just separated from the fuselage, I won’t permanently join the wings because that would make future maintenance much more difficult. The friction of the carbon joining rod and foam wing overlaps are sufficient to keep things together on the ground, and the four wing bolts into the fuselage when it’s in the air. For that reason all the wiring from one wing will remain permanently connected to the receiver and light control box mounted in that wing center section, the wires of the other wing connected by two multiplex plugs, one for the lights and one for its servo’s.

Ming, I thank you so much for providing us with an excellent “starting product” that we can further develop into personalized jewels, and after the 747, please consider making a basic Douglas DC7 that we can chop off to “easily” modify them into a DC4, DC6 or even Carvair, instead of us having to make fuselage extensions to portray longer versions as the popular 737-800 or 900. RC Group forums, thank you so much for providing hundreds of pages (about most available kits) of excellent builder and user information. Before I even purchase a kit, I make a quick read from the first entry on, to learn more about the kits, the flaws and good points, and how it flies. After purchase I read all entries in detail, and copy relevant data and pictures in a subject grouped personal file about that model, and keep adding data as more people provide inputs. For the 737 I extracted relevant info from the 500+ thread pages and compiled it into 54 pages of useful tips, which I continuously use as guidelines, and have proved invaluable so far (next week I’ll consult my notes about the nosewheel and their door modifications, but already have an FMS T28 nosebay part awaiting modifications). Next to that I have 63 pages of notes regarding the Change Sun 70mm fans and their combination with shrouds, engines, ESC’s and spinners, and that has driven me to the choices I made for my 737 motorization.

I often read posts in disbelief, of people joining a forum and without having read any of the previous entries just coldly request info that is already available on that forum. For our 737 kit, there is no straight answer to the best powerline or essential modifications because our models vary from a straight out of the box Boeing quickly assembled as per Ming’s three page building instructions with just a few custom decals applied to it, to highly modified and much heavier models intended to operate in a scale way from hard surfaced runways, or in typical RC aerobatic way from a grass surface. Each require specific arrangements regarding materials, number of cells in the batteries, control throws etc, and I therefore understand why some very knowledgeable contributors are reluctant to answer overly simple questions that have been asked many times before. If buyers don’t take the time (nobody “has” time) to read and collect the available information, they should refrain from buying “basic” kits, and stick to the excellent “bind and fly” fully decorated RTF kits available on the market today. Excuse me for digressing into such rants, I don’t want to offend people, but as they say in the real aviation world “let the air to the professionals” and if you just want to play, don’t harm anything but your wallet, and don’t clutter useful forums with irrelevant post, questions or videos.

This is also the reason why I don’t post on the forum each time I want to do something (that often gets changed anyway), but prefer to await publishing a comprehensive illustrated relevant story on my blog of how it all ended up at the end, giving a heads up on the forums to the link of that blog when something useful was added. Newer people on the forum then can bookmark that link and see everything in logical sequence without having to browse through hundreds of pages on the forum to find previous entries about that specific model or builder’s modifications.

I also want to apologize to the people whose entries I deleted on my blog pages. Your entries have always been useful or flattering, but because this is a build log, I remove them when a next phase of the build is posted, so people can read the build log in chronological sequence without being interrupted by comments. Your comments are still welcome and appreciated, and will stay on as long as the next build log entry is being added, and that might take months or a year, but don’t feel offended when I finally delete your comments.

If you hadn't enough by now, you can continue to read the build logs of my various other aircraft and gliders on
Next report will probably be around end February 2015 after the completion of the fuselage.
Last edited by BAF23; Dec 25, 2014 at 03:22 PM.
Feb 06, 2015, 01:19 PM
The sky is the limit
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Windrider Boeing 737 nosewheel and doors

nose wheel retract and steering

After the completion of the wing it became time to start on the fuselage. With the nosewheel apparently causing the most troubles to other builders, I started analyzing the situation. With the strengthened and visually enhanced nosewheel and retracts assembly preassembled, it seemed easy to position it in the factory hollowed-out gear compartment and there seemed to be plenty of space available to mount the directional servo. What initially seemed a piece of cake, quickly turned out to become a mental nightmare. Windrider’s twin minuscule wooden base plates looked like a joke and their position was so low that the gearleg made the aircraft too tall on the ground in an unnatural (scale) body angle. With retracts traveling a 90° angle, that long leg resulted in the wheels sticking halfway even with the gear in the retracted position, an awful sight. Furthermore the kit-provided nosewheels were so wide that an overly long and wide gear-well had been cutout, seriously degrading the looks of the aircraft in flight. Predecessors had successfully used modified FMS T28 nosebays with geardoor mechanisms to produce a mechanical and aesthetic solution, and I also had ordered one but looked puzzled at it.

My much narrower gear was only 33mm wide (if retracted fully centered), the FMS box was 60mm wide and 4cm longer than the total length of my gear plus motor, so those geardoors would have looked out of proportion when open on the ground. I looked at pictures of the real aircraft to find out how Boeing had resolved the equation. On a full-size 737, the nose gear pivots 120° up on wide arms that are hinged almost as low as the geardoors on the bottom of the bulkhead between the cockpit and cabin, coinciding roughly with the forward part of the passenger entry door. Therefore the leg length is minimal, and that reflects in the geardoor length coming only halfway the cockpit windows. Except for the expensive (and heavy) Robart gears, I know of nobody else producing landing gears traveling 120° of arc, so that was out of bounce. I had been toying with the idea of a much shorter gear installed at an angle with a 30° nick in the leg, but the Windrider provided gearlegs I had (modified with softer spring damping) couldn’t be shortened, and during tight turns those wheels would make such awkward angles as the ones from a Super Constellation, that I quickly eliminated that possibility. With the long legs, first thing to do was to find out how deep in the fuselage the pivot point had to be to have the aircraft on the ground with a realistic body angle, and to have the wheels completely inside geardoors when retracted. The only way to find that out was to assemble the fuselage parts on the wing, and find out and measure experimentally. The small wing area didn’t prepare me well for the sight of how BIG this fuselage was when assembled.

Using various supports, it didn’t take long to find out that the pivot point for the leg had to be 40mm higher than the bottom of the fuselage. After dismantling the model again, I choose to use the starboard forward shell-half as the master, and all the other parts were placed back on the shelf for some time. Positioning my gear in the fuselage at the correct pivot point height, I noticed that my smaller wheels would end up completely within the fuselage if I removed just a bit of foam from the top of their up location. I know the wheels are too much forward under the cockpit but otherwise the pivot point would show the gear down to be too far behind the first bulkhead, detracting even more from the looks of the real nose.

With the fore and aft limits delimited, it became obvious that the model gear-well extended further back from the pivot point, only to allow space for the retract trunions, but although there was no need for the geardoors to be any longer than the actual leg in down position, a possible gear change required a screwdriver to be inserted to remove all 4 screws. In the meantime I had given up the idea of gear door electrical mechanisms often requiring one or more servos plus a sequencer, and figured out a system that kept the doors open by a spring, and closed mechanically by the gear pulling them shut. This would be much more reliable to operate in the long run. I decided to invest that saved weight in a stronger plate to mount the gear on. Expecting few lateral forces, I set for a 6cm wide plywood plate. Most forces would probably be exerted backwards on the wheels if the model encounters bad stretches of pavement or uneven soil, and looking at the inside of the fuselage I could find no reason why at the most stressful area they had the least foam traverses. To cater for that I opted to lengthen the plate so the aft forces on the leg could be transmitted to an up force on the foam reinforcement aft of a void. The plate could be made much more narrow at that spot because no lateral forces would end up there. Compared to Windrider’s ridiculous 2mm wooden pieces, I choose for 3mm 5ply wood. For solidity I again used claw nuts on the back, instead of the simple wood screws. This time Dremeling off material from the side of the nut to make it fit was insufficient. These nut were made for wood of at least 4mm thickness, so the nut channels also had to be Dremeled off accordingly.

After a dry fit and a few gear cycles the plate was declared ok, but then came the steering mechanism, and with the single arm of the stronger gear, there was no way I could cut wood to accommodate the movements without substantially weakening the gear attachment points. After much thinking, the only solution I found was to use the metal symmetrical arm of the original nose retracts after an offset drilling to a 4mm center. The arms being thinner, I had to use spacers to keep it from the edge of the wood during retraction (see previous picture for intermediate installation). I made a new baseplate for this different setup, and the looks of that pleased me a lot regarding stiffness and anchor points. Gluing a little piece of flat wood on the plastic motor casing allowed the steering arms to lay flat against it, whatever deflection it had during the retraction. Now the nose wheels will always start to lower aligned with the airstream, and that also was a requirement for not ending up with wheels jammed sideways against the doors.

Next picture shows the FMS T28 nosewheel box with doors closed, to the left my new assembly ready for insertion, to the right my first attempt at a baseplate carved out for the shown steering rod, further right Ming’s original 2mm minimal twin wooden baseplates around the 3mm pin retract and wider wheel assembly, his steel cables for the steering being usable in my modification.

Ming’s position for the steering servo was ok, but had to be deepened due to my higher positioned leg with the gear up. I made plywood plaques to embed in the foam so the servo sits firmly but can be screwed in and out if replacement is needed.

With the desire for a short turning circle on the ground, I measured that about 1cm of travel was necessary at the end of the arms on the retract side. The gear in up position caused the cables to slack about 16mm, allowing full rudder movement in the air without causing any forces on the steering servo. With the high speed at which the model will travel during takeoff and landing, precise steering around a well-defined neutral position was essential, so I choose for a digital servo, with metal gear and bearing, and with 2,5kgcm sufficiently powerful to steer, even on uneven fields. Just as in my F16, I planned on programming 80% expo for a good mix between precise steering around the neutral, but ample movement towards the end of the travel. To get the cable travel correct I had to replace the original symmetrical servo arm by a larger one from another brand.

Somebody in the club who’s also into airliners made an operating R/C model of a airport tow vehicle. The nosewheels are lifted from the ground and sit on the back of the truck, causing the steering on the aircraft to be reverse operated, not very good for the servo. Furthermore, during turns of the truck, my digital servo will try to keep the diabolo steering straight, causing wear, buzz and electrical drain. If on landing I would overrun the runway, I’ll end up in grass, and the uneven forces on the diabolo again would be transmitted directly to the servo. Adjusting the length of the steel cables to be exactly stiff without undesired tension with the gear down was challenging. These three problems all got resolved by using stretches of spring between the cables and the steering arms of the nosewheel (note wooden strips to keep the gear centered in up position).

After adjusting and testing all possible positions of gear and steering servo, I had to mount the complete baseplate at a small angle (see first picture of gear assembly). That way the gear-down wheel position corresponded to the one of the real aircraft in regard to the cockpit/cabin bulkhead, and the wheels were just high enough to allow (thin) closed doors that follow the fuselage contours in the up position. Foam that had been cut off on one side to allow for that angle, was glued at the other side to keep things tight and strong. For everything to operate freely, quite a bit foam had to cut out of the compartment and that was only the start. Ming’s single strand channels for the retract and steering power cables were only good for a one time operation. Major surgery would be required if either system had to be replaced later, so I also widened those openings to allow the short stubs with their JR plugs to be extracted through the foam if necessary.

Front geardoors

Next I spent another day just figuring out possible solutions for the geardoors. I never thought those doors would take two weeks of work to look and operate in an acceptable way. Because I had that FMS T28 nosebox laying around, I decided to use the parts, but in the end modified every single bit so much that starting from scratch would probably have been faster. The plastic box measuring 185x60x50mm was monstrous and I only ended up using a little bit of the endplates as door pivot anchors. I used their full width to anchor them in slits in the foam at the front. I also used the doors because they already had some semblance of rounded to flat shape, but were 3,5cm too long and I cut them off at the back (flat part). Not only that, but I also reduced their width by 5mm. This left 2,5cm with a little of in the fuselage in open position, and corresponded well to the proportions of the nosewheel diameter and distance between the wheels and the doors when compared to pictures of the real aircraft. A 2mm carbon stub was then glued at the back to replace the cutoff hinge pin. New 2mm holes had to be drilled in the baseplates for the narrowed doors to close without a gap. With a door in position it was obvious both endplates had to be at a 90° angle to the doors, and that this now led the bottom of the aft plate to come exactly where the bulkhead with gear pivot is on the real aircraft. On the other hand, it left a triangular 6mm void between the plate and the kit’s aft gear compartment cutout. Luckily I hadn’t thrown away any of the bits of foam that I had removed to install my gear, and they came in very handy during all the following adaptations.

With the geardoors closed it was obvious their flat bottom was no match for the pronounced longitudinal curve at the bottom of the fuselage in that area. Whilst the doors were only thin plastic, their rigidity came from a solid full length spine at the pivot line, to bend that could only be done by heat. My Dremel gas solder iron had an accessory to funnel heat to the front, and although tedious and using a lot of gas, I got the doors to follow the convex fuselage instead of being straight. Furthermore the radius of the fuselage bottom is very different from the one of the T28 bottom and to obtain that, I had to glue small plastic plates to the up physical restraints to obtain radius, but that in turn created a gap between the doors, and that could only be corrected by closing the hinge holes and drilling new ones partly into the original ones. On the other hand, the longitudinal door bow remains when the doors are open 90°, so the line at the hinge is not straight anymore but a curve.

Cutting off foam in a bow to allow the door to open, created a very visible void between the closed door and fuselage. Gluing foam behind the door hinge line closed that gap, but to allow that foam to pivot inward when the door opened, required the recently added fuselage foam to be cut inwards at an angle. It just took an eternity of gluing, cutting, shaping and sanding before doors and fuselage match in open as well as close positions. It was a nightmare with more to come.

To actuate the doors I already had cut the midpoint arms from the doors and glue them at the front. The retraction of the gear and positioning of the steering servo plus wheels in the up position left no space at all for a door mechanism halfway. This being a jet, I also preferred to have the doors securely held where the airstream hits them, the rest of the door following in trail. The FMS box comes with a clever system for one servo to transmit its movement to lateral pivots into vertical links to the door arms. Not using a separate servo, I discarded the much sought-after traverse part, but the length of the vertical actuators with on one end a z-bend and on the other an adjustable nylon quick link, guided me to a trial connecting those doors via the links to a plate on top of the retracted wheels. The idea was that the very last bit of the wheel movement would pull the doors shut, and a spring to the bottom would keep the doors open even during moderate side loads.

I first tried a system with a hinge mounted on the steering servo plate because it looked compact and lightweight, but it didn’t work well because the moments of the wheel and door actuators were a complete mismatch (trial fitting can be seen 2 pictures up). The idea of using a plate that forced both diabolos to become/remain centered in fully retracted position, transmitting the movement to modified scrap servo arms glued to the side of that plate to actuate the vertical links, proved practicable. I therefore rebuilt the system with a longer lever pivoting from a hinge placed well forward in the nose, requiring additional foam cuts, but this time the moments produced by the raising wheel were superior than before with the same servo force, and allowed much finer adjustments of the door mechanism. It weighed a bit more (still less than an extra servo, sequencer, and pivot assembly) and proved to be a winner.

In retrospect I think it would have been better to replace the nosewheel strut by a much shorter one. It had been impossible to modify the original strut because I couldn’t chop off the top around the 4mm pin, or the bottom without sacrificing the suspension. A much shorter leg could have been installed much lower, and the doors would have been much shorter, thereby hardly have any longitudinal bow (like the real B737), greatly facilitating overall door fit in all positions.
Feb 06, 2015, 04:20 PM
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fuselage and final assembly

cabin ventilation

After the nosegear subassemblies had been glued into position, I decided to further open up the foam where the pilots’ legs and feet would be, and thus getting some airflow through the length of the cabin when the gear is down. I figure that with the taxi and takeoff, the battery compartment becomes hot, and that after raising the nose to high alpha, some cool air entering before gear retraction might be be beneficial to the batteries. After initially having cut some fuselage foam along the window height, I later came to the conclusion that with the thickness of the foam all around the fuselage, there was no need for that kind of floor, and I cut everything away between the circumference, except for a single reinforcement pillar just above the wing leading edge. The wing NACA intakes were then prolonged onto the fuselage so that 2x1cm channels running through the 85mm thick fuselage foam bloc came out in the front of the battery compartment, allowing for cooling even with the nosedoors closed.

Bringing air into a fuselage, with only a large magnet held battery hatch as a way out, is looking for trouble. In the tail section there already was a decent size channel in the foam to get the wires to the elevator and rudder servos. Searching the web for pictures of the B737 APU system, it became clear that the channel could be further carved out to the end of the tail, providing an air outlet for the fuselage overpressure, looking very scale as an APU outlet. An old plastic 16mm diameter tube formerly containing solder, got cut into appropriate dimensions and angles, then glued into one tail half. Above that I made a smaller diameter fake APU intake, and almost at the top of the tailcone, made another slit towards the elevator servo connection space for the white taillight. Gluing the sticking out taillight at that time would further complicate the application of the vinyl, so I prebuilt an assembly comprising the light, resistor, and soldered everything together in a long shrink tube sleeve, creating a stiff enough assembly that could be put in (slightly retracted) position when the fuselage halves were joined and vinyled, but after the vinyl has been punched at the correct spots, these assemblies can just be pushed out the last millimeters to protrude and spread light just as on the real bird. The same system then got applied to the top and bottom rotating beacons. Furthermore, those subassemblies can be pulled out from within if LED lights or their associated resistors have to be replaced.

Tail subassembly

The work at the tail end automatically brought me to the connections of the tail surfaces and their electronics to the rest of the fuselage. Having read that previous builders even went as far as not even attaching their vertical or horizontal tails because the excellent EPO molds fit so well and tight together, I toyed further around that idea. Whilst the vertical stabilizer felt solid without reinforcements, the horizontal ones felt very flimsy outboard of the built-in carbon rod reinforcements. With such large surfaces I wanted to have all 3 feathers removable for storage, and even for transport because of their delicate nature. I therefore decided to keep the servos in the surfaces so that I only had 3 small electric connections to make in the common base cutout, instead of having all servos neatly in the fuselage, but with mechanical connections at the field. Aesthetically it might not be as pleasing, but this was much more practical for field use. For the large rudder actuation I used an analog 2,6kg metal gear servo and only had to slightly deepen the tight factory cutout so that it could be completely hidden from view except for the steering arm cutout. The foam rudder hinge looked very unreliable against the sun, entire strip lengths were just air! The horizontal surfaces looked much better in that respect. Allowing the vinyl to flow through the hinges rectified that weakness.

The horizontal feathers slide into the fuselage in a realistic positive dihedral, but that automatically prevents the use of a carry through spar (to join both carbon rod stiffeners). With the factory cutouts you either have to buy a reverse servo, open up a servo and resolder wires at the pots, or use a servo reverser, but none of those choices appealed to me. When looking through the assembly it was obvious that a little surgery (by physically turning one of the digital servos around in a new cutout) could do the job, structural integrity being kept by filling the old void with the material from the new one, plus the close proximity of the carbon rod. This is not the first time I applied that trick and I never experienced problems with it. I keep servo reversers in stock, but don’t trust them for elevator controls. The less electronic gimmicks, the less chances of failures (as my choice to eliminate nose door servo and sequencer also prove). Another reason for my elevator servo choice is that I want to minimize the number of plugs to be connected on the field between the fuselage and wing, but more about that in a later paragraph.

Figuring out he electrics

On the other hand, physical space for connections and wiring choices have to calculated in at an early stage for such a complex model, and took me two days of thinking and drawing schematics, with unavoidable associated headaches as a result. A very detailed wiring diagram of the internal, plus fuselage to wing servo connections was drawn at this stage, because I intended to work with isolated power sources for flight controls, retracts, and light system. After juggling with the variables I finally came up with a possibility to use just two Multiplex plugs, one female coming out of the front fuselage part and a male one coming from the tail part, both inserted vertically through the battery hatch into their counterparts glued on top of the port side of the wing junction box.

To get all those servo’s connected though only two multiplex plugs required me to use common negative wires, and separate positives for the gear system and the flight controls. Each function got controlled separately by its own signal wire. The loom going to the tail required meticulous attention to fabricate, with multiple splits to individual JR plugs within the limited confines of the void between the horizontal stabilizers. Longer leads made it easier to make the connection, but the space was limited to accept 3 JR connections plus extra wire length. The problem of connecting 3 specific surfaces via the same type of connectors again got resolved by gluing both elevator JR connectors on top of each other, the remaining longer connector obviously being the one operating the rudder after it passes through the vertical opening for the connection to be made. To facilitate correct insertion, sequence numbers were written on the inside of the tail feathers, and the receptors were marked with a strip of white isolation tape on the side the white connector wire has to be inserted. Those are the little details that make life easier on the field, where inevitably an audience will gather during assembly that unique model (which a lot of Belgian people took for holiday trips). The opening towards my exhaust tube had been closed by foam so the connectors couldn’t fall through anymore.

It became obvious that at that stage, all three feathers had to be worked on at the same time. All 3 required the servo cutouts to be deepened for a few millimeters to allow lightweight putty to create a smooth surface to vinyl on, that also the control horn cutouts needed to be deepened at one side to allow the same. The kit provided pushrods looked sturdy, but care had to be taken not to twist too much between the metal and the plastic, because the latter quickly erodes and allows the rod to run almost freely through the plastic, completely negating your control inputs. The system of control horns being inserted on one side of the foam cutout, and plates being pushed on to retain it on the other side, seemed simple but didn’t provide sufficient stiffness around the thin remaining foam layer. If I choose digital servos to have precise elevator controls, those subtle movements had to be transmitted precisely to the elevator as well. I therefore opted to use expanding PU glue to be sure the horns took along more adjacent stiffer foam in their movements. The servos were not glued in place, the tight cutouts provided sufficient stiffness that applying lightweight filler around and on top of the servos and their wires, blocked them under the vinyl, but if they had to be replaced, it could be easily done without having to cut too heavily in the flimsy horizontal tailplanes. A few more coats of filler and sanding over the servos and tail blemishes made the surfaces ready for covering.

Next came my best invention on this aircraft so far. To allow easy removal of the three tail feathers for transport and storage, I drilled 4mm vertical holes in the foam from under the fin, through the supporting shoulders on top and below the thick foam where the horizontal stabilizers join. I then glued 4mm carbon tubes in those aligned holes so they couldn’t spread out further during use. I also glued a short plastic tube in the fuselage half in front of the vertical tail front-end. I then glued measured lengths of bendable soft plastic Sullivan Nyrods in the vertical tail so that the front one catches in the fuselage, and the vertical ones can be guided into the carbon horizontal stabilizer alignment holes. The vertical tail will be kept in its tight receptacle by airstream, but the same airstream cannot force the horizontal stabilizers out and back anymore, because their fronts are kept in place by the yellow vertical rods. All 3 tail assemblies are thus removable, and are kept tight for flight condition without any visible means once assembled, and no tools are required (elements of this construction van be seen in the exploded view picture of the tail assembly a few pages back).

Covering the tail surfaces with vinyl was not too difficult, but the lighter blue for the fin came from another supplier, was much stiffer and needed generous heat application to follow the shapes and corners. Pushing the material to the deepest part of the rudder hinge required much finesse, and the shape of the rudder balancer on top made it very challenging to decide when and where to cut in order to cover all visible surfaces with a minimum of seams. On the real 737 the rudder continues down to the fuselage, and the horizontal stabilizers pivot up and down (for trim) along a flat part of the fuselage. With Ming’s system of inserting the 3 tail feathers tightly in fuselage slots, he opted for added solidity by molding larger base areas. That means it is more difficult to vinyl because now parts of the (painted) fuselage are on his horizontal tail foam, as well as the base of the non-scale rudder. I then used the servo tester to mechanically adjust the neutral and full throw positions of the 3 servo’s by varying the length of the short pushrods and the holes they are inserted in in the arms and horns. Apparently some predecessors fly with just a centimeter of control throws, but for my maiden flight I prefer to have more throw to eventually compensate for anomalies in aerodynamics or balance. Once the neutral trim positions have been mechanically readjusted, and configuration changes and stall checks can be done with less than full control deflections, then the throws can be reduced mechanically in order to benefit from the full servo power and sensitivities. The 3 completed tail feathers together with their single easy attachment system and electrical connections can be seen in following picture taken during a later stage of vinyling.

The electrical system nightmare

Wiring looms were then routed through the front and back of the fuselage, and spot glued in position with hot glue applications between local isolation tape (to keep the different wires grouped) and the EPO. Next came the electrical connections between their controllers and the final destinations. Because most servos and lights are in the wing, I had chosen to install most of the electrics in the central wing box, but available space is not abundant because it is mostly taken by Ming’s extensive foam block reinforcements between wing and fuselage. What remains is a 17x5x4cm space to squeeze everything in, and because I wanted the wings to be separable for heavy maintenance, wiring between both wings had to pass over various plugs as well. The detailed wiring diagrams became very complicated and were often amended while on the spot changes had to be made, or new ideas popped up.

After much reasoning I decided to apply following schematic setup. Each engine gets powered by its own fuselage mounted 5s2700 25c (later more c’s?) battery. After the EC5 plugs the main wires go via the original Deans connectors through the 80Amp ESC’s into the engine, the internal 6Amp BEC being used to power the landing gear and nose wheel steering from the port ESC (green), the lights controller from the starboard ESC (blue). From the previously mentioned Deans connectors, separate wires run through two Castle Creation 10Amp BEC units into the dual power supply wires of a Spectrum AR9110 receiver. That way I am guaranteed to always have power to my flight controls, even after a single battery failure, short in the gear or light system, or single BEC failure of one of the ESC’s or external BEC’s. This way of thinking now provides me complete power assurance without requiring separate receiver batteries. All negative wires are joined at various places throughout the wiring to minimize the number of connections, and ensure ground even if some subsystem or connector fails. The simplified scheme (upper half) should make the power setip easier to understand. Black negative wires are only shown for power distribution. On the bottom half is how things are connected between eachother in the aircraft, depicted with the same color coding regarding power source, but in fact these encompass both the power and wire signals for simplification. You can imagine how the detailed scheme looks, with all the soldering pins and common power take offs and splits. I’ll spare you those images.

After having installed the power wires to their respective controllers, I mounted the receiver flat on the bottom of the port wing and started making the connections to the port wing servos, wing to fuselage connectors, and port to starboard wing connectors. Next I connected the positive wire to all 3 retracts and the nose wheel steering, and their signal wires through triple y splits via the various connectors to the receiver channels. Using commercial connectors at this point would have been crazy, so each wire was custom fabricated using a JR connector at junctions or at the servo (so the latter could be easily replaced if necessary). All other connections were soldered to each other, common JR plug splits, or on the Multiplex pins. The wires from the starboard wing systems were then routed via the wing connectors to the receiver ports, but a servo reverser was inserted between JR connectors of the flap instead of soldered. That would allow me to replace the servo reverser, or eliminate it from the system if I later would use a receiver with more channels. I then ran all the lights system cables through the connectors to end up on the lights controller box space on the starboard wing bottom.

At that time I discovered that the German lights system control box had internal wiring I was unaware of, and after consulting qualified club members they confirmed it used the positive as a common, and negative to control the lights. It was too late to change my aircraft wiring because the common negative was applied from the early start inside the winglets and embedded wing wires, and couldn’t be changed anymore without considerably breaking up things. I didn’t install that controller but had to start searching for a controller from another brand, offering a similar separate lights activation, but with common negative grounding. The lights wires were left unpowered and bunched up in that space, cut at the approximate length, labeled but still without connectors. Here is a picture of the spaghetti in the wing, before the plug contacts got engulfed in liquid rubber.

Let’s start run around clockwise starting from the lower left wheel. The blue thing is the 10A external BEC from the port battery, Next to it is the common landing gear plug powered from the port ESC BEC. Left in the compartment is one of the 3 Spectrum satellite receivers, the other 2 are in the forward and aft foam blocs flat with the fuselage junctions. Further towards the middle you can see the black AR9010 receiver. On top is the Multiplex connector nr1 joining the wing with the forward fuselage electrics. Lying next to it is a JR extension to facilitate later receiver binding processes. Both Deans plugs run through their respective ESC’s, and you can also see the blue 10A BEC from the starboard battery. Next obvious plug is the Multiplex one labeled W. This one connects both wing halves together, and the 3 other JR connections with green labels (T for throttle, L for lights and G for gear) also stay together as long as both wings are not separated from each other. I used separate plugs for those because each of those systems use separate power sources. The last Mpx connector at the bottom is the nr 2 one (reverse direction from 1 to avoid mistakes) connects the (port) wing to the aft fuselage electronics.

All this wiring soldering and sorting out took about 50 hours to complete, the most dreaded part of this model assembly (I got headaches and came close to nervous breakdown in the process). It was with more than apprehension that I first connected the individual batteries to the wing, then the wings together, and then in turn to forward and aft fuselage halves. To my surprise and relief, I saw no sparks, no smoke, no smells, and every servo moved. The most annoying problem were asymmetric flap angles between both wings, but that got relatively easily corrected after removing the canoe covering the servo arm, and rotating that arm in another angle before fastening the screw again. After some adjusting of the throws and flap percentages I obtained a perfectly working 3-position flap system with 4second travel time. I also had to swap the rudder and nose wheel steering pins at the receiver in order to have the expo on the steering and none on the rudder. Here is the picture of how I tested all the connections whilst all subsystems in nose and tail were still accessible. Some might question my decision to concentrate all the electrics and electronics in that tiny wing box, with only the batteries ending up over the forward wing part in the vast empty fuselage, but the ease of assembling the model in the field was essential for me.

With the assurance that all connections were correct and none short circuited, I applied liberal amounts of liquid rubber to the pins to reinforce the connections and prevent shorts when handling the connectors in the future. After everything dried, I made a construction to hold the wing to fuselage pins pointing vertical on top of the port wing, so I could easily push the fuselage connectors into them through the battery hatch opening during field assembly of the model. With the model semi-assembled and each battery connected in turn, I was able to perform the individual throttle calibrations (essential for twin engine airplanes), and readjust control linkages, basic mixes and differentials, to obtain a ready to fly model (except for failsafe settings, range check and high speed taxi test).

Final fuselage assembly

It was tempting at that point to permanently join the front and back fuselage halves, but I decided not to because the total length makes is more difficult to handle. Vinyling the fuselage in one go is impossible, and once both halves are joined, the tubular shape makes it very unstable to work on. I therefore decided to cover the fuselage in patchwork using the kit crease lines. All 4 separate fuselage parts can thus be substantially covered and detailed with their backs resting flat on a table, but the panels to the nearest junction crease lines were not covered at that stage. First step was to look at pictures of the real aircraft and try to translate that into a straight separation line between the upper blue and lower gray colors of that airline. Due to the application of a straight line on a lower portion of a submarine shaped cylinder, and it had to match the non-scale wing-fuselage fairing and other engraved lines in the foam, I had to redraw that line a few times before I had it right. I uses a worn ball pen for that, so it left sweeping traces even without much rolling over the oily EPO surface. When I finally had it right, I sanded the erroneous lines away, and pressed this used roller pen over the correct line so it created an additional crease line that I could see and feel to make the cuts in the vinyl to obtain a shoulder to shoulder fit of the 2 colors along a straight line. Duplication on the other side was much simpler, the rounded shape at the back was trickier.

Prepositioning the custom made Caliegraphics revealed a few shortcomings. Although the number of side windows might vary from one airline customer to another, fuselage doors are always different between front, emergency wing exit, and aft boarding door. Not only the delivered side strips (doors and windows) didn’t match with the distance between front and back doors, but the emergency exit doors had not been printed, and the four door prints all had the medium size of the back doors. With the deep crease lines of the front doors, this would be unacceptable.

With no window crease lines, I started to slide window positions to the left and right so they looked right and wouldn’t end up on the forward/rear fuselage joint, but was limited in movements by the window that had to end up in the middle of the wing emergency exit panel. From there on I compared forward and aft window gaps between the doors and had to eliminate one window to get it right according to pictures I had. Making a cut between the forward and aft window strip at the fuselage joint, the forward part went back in the box, the forward fuselage relegated to standby, and the aft windows were permanently pressed on the vinyl on the port tail half. Callie’s thick front protective paper made it difficult to exactly position the door outline versus the crease lines, so I used a soapy water solution in between, in order to adjust the final positioning of the door lines (mind the correct side of the door hinges). At that point I also discovered that Callie also forgot to print a European flag on the port side next to the Belgian one, so I will have to produce one of those myself. Aircraft type denomination and registration were then applied, and the whole operation was repeated on the starboard tail part.

First to be permanently glued were the two back halves. That assembly is not too big and yet uncovered seams first could be filled and sanded before vinyl can be stretched over the later invisible seam. That also applied to the APU exhaust and intake tubes, but luckily on the real aircraft this much rounded area is usually left bare metal and in our case can be painted over instead of vinyled. The top of that fuselage part consists mainly of the void for the vertical stabilizer to be inserted, and the front bit can be left unattended until it is joined with the small length aft of the battery compartment. The bottom seam can be easily made invisible at this point, and the intricate shape of the lower fuselage cheat line applied when resting with the belly up. I thus ended up with a completely finished tail assembly, with still nude foam front fuselage halves.

With the lack of Callie produced emergency exits and wrong size front doors in mind, I decided to fill those crease lines with lightweight filler. They would eventually still show sufficiently through the vinyl, but not deep enough to blatantly expose the self-produced custom contour lines. This was also the time to sand away the too pronounced pilot window outlines, and get rid of any mold traces or blemishes crated by past handlings. Both forward fuselage halves were then vinyled except for the nose, top and bottom panels along the longitudinal seams (picture of that stage was shown in the part of the tail feather assembly system). All the rest of the Callie’s decoration sheets were applied, except for the cockpit windows. All the detailed stenciling was applied at this stage, much easier to do with a fuselage half lying flat on the table. I used thin strips of white and light blue to produce the outline of the emergency wing exits, some stenciling of Ming’s sheet in lieu of Calie’s incorrect door handles and her missing door portholes. The fuselage halves were then positioned over the wing to finalize the cheat line on the wing part of the non-scale wing-fuselage fairing (thus cheating even more for an acceptable look).

The forward fuselage half containing the nosewheel assembly and the wiring then was mated to the complete tail, and dry assemblies ensured that alignment, crease lines and windows could be aligned. After liberal application of PU wood glue, the parts were joined and strips of battery holder material used to keep the upper parts snug together during the long dry phase (the bottom stays together with gravity). A few toothpicks through the inside ensured the parts couldn’t rotate away from their perfect horizontal lineup, and regular looks along the top of the fuselage half junction ensured the tailpiece (without fin) was perfectly lined up longitudinally.

At this stage you have the last chance to check all the connections before gluing the remaining fuselage part to the other 3. Using a servo tester at this stage is counterproductive. This complete electrical functional test is better done using the full flight configuration. This means using the intended batteries, ESC’s, BEC’s and all connections inserted as for flight. This can easily be done by placing that 3-part fuselage on its wing saddle, both wings already being mechanically and electrically joined (semi permanently). The remaining fuselage part is only an empty shell, all systems should thus be working properly, but most wires and connectors are still easily accessible if corrections have to be made.

If satisfied with the result, the fuselage can be removed from the wing, the plywood wing tie down plates slid into and glued to their fuselage orifices, and the last front fuselage shell glued to all the other quarts and the nosewheel cave, but still without geardoors. It took me 20 minutes to apply glue on the vast contact surfaces, slow drying glue is a must for this task.

This time toothpicks had to be used externally to better align the nose halves with each other. When dry, filler can then be liberally applied to seal off and contour all joints, and the last bits of exposed white foam sanded and vinyled. With that done, all the semi recessed Led light assemblies could be pushed out to protrude in their final exposed positions, and final decoration touches such as the cockpit windows applied after the smoothened nose got vinyled (good luck on that). Calie’s front windows were much too small and were discarded. Ming included two sets, the one on the large decal sheet has incorrect window divisions, the supplementary ones in the plastic bag were the nearest to scale.

I then fabricated and painted a vhf antenna that I pushed through the foam block used to cover the battery compartment, but 3 inches further back than on the real aircraft. It is retained by a few transverse carbon sticks glued to the underside of the foam, and is now a very handy grip to pull the battery hatch open from its magnets. I left the nose gear-doors out till this point because they already were prefabricated, adjusted and completely decorated. Applying vinyl around the nosegear box at that stage would have been much more difficult with the doors in place, the risk of sticky vinyl adhering to the door decoration was just too big. After the doors were inserted in their pivot holes, and connected to the pushrods, final minor adjustments of their operating endpoints was necessary. The weight and balance was a very nice surprise: total fuselage weight: 1490gr, total wing weight: 1930gr. It means that despite all the modifications my dry weight is only 3420gr, and with the two 5s2700 batteries a very acceptable 4082gr ready to fly ! Even better, with the batteries in the forward side of the fuselage battery compartments (resting against the foam bulkhead, my model balances perfectly just aft of the wingspar/esc’s and needs no additional weights for its maiden. With a calculated wing area of approximately 30dm2 this results in a wing load of 136gr/dm2, which puts it in way above any other of my RC models. I couldn’t resist making a few pictures of the result after 750 hours of work.

Put the model on a table, power it up, savor and enjoy your jewel from all angles, watch all the gimmicks operate after all those weeks/months or eventual years of work, and call family, neighbors and friends to celebrate with you. With such an elaborate model, champagne shouldn’t be considered too extravagant, they do it for real aircraft as well (note you can use a full-size bottle, contents and glasses do not have to match the 1:18,5 scale of your model). Start panicking and have doubts about risking to actually fly that work of art and technique. Better make more pictures and movies at that stage.

Post Scriptum

During the electrical hookup phase a few unrelated problems occurred. Being in the middle of the winter and no flying as such, I decided during a visit of an RC friend to finally implement the 1.06 and 1.08 software updates on my Spectrum Dx10t transmitter. I had delayed that update because I had read that others experienced troubles and a lot of them had to open up the complete body in order to disconnect the battery for a total power cycle. Thanks to being thoroughly prepared and rigorously following the available (but insufficiently detailed) information, the updates went smooth, except that my model numbers were not displayed anymore, I had to rebind every single receiver and none of the 4 stick switches were recognized by the software (I use those for autotrim on helicopter stabilizers or light system paging such as on the B737). A few days of searching the web and talking it over with Spectrum employees on forums, revealed that my problems could not be solved without sending the previously perfectly working transmitter to the German Horizon representative. I got fed up with that, and after due reflections and analysis of costs and options, decided to (despite the expensive transmitter and 25 receivers) abandon Spectrum and slowly change everything over to Taranis SkFry equipment during the course of the year. The latter is an open software system costing a fraction of Spectrum items, and with a flawless reputation regarding range and (temporary) loss of signal. A Spectrum DM9 JR adapter module will allow me to fly my not updated models on their Spectrum receivers during the slow transition.

Why do I mention this on this build log? Because I decided to take the voluminous and expensive (165 euro) Spectrum AR9110 receiver out of the Boeing, replace it with a FrSky 8+4 receiver (dual power still being assured by a Scottsky diode behind the Bec’s) which will allow me to eliminate the Turnigy flap servo reverser (using a separate slaved reversed channel instead), and a 6-position knob for the light module control: Off, nav lights on, +rotating beacon, +strobe lights, +landing lights.

When integrating the German produced light controller in the circuit, I discovered to my dismay that all the lights had a common positive wire, the negative being used to control or modulate the individual lights. This went unnoticed so far because I only had tested each light one at a time during the assembly. Having already wired the complete aircraft with common negative grounding to minimize wires and connector pins, this was very bad news. Changing the wiring for the lights into common positive grounding would not only be a nightmare requiring additional plugs and a lot of soldering, but also to probably destroy the winglets to change the way the 3 lights got hooked up to get their power through the 3 wires embedded in the wing (see part one of the build log how I was able to get the double blitz strobes next to the green/red and white navigation lights). My RC friend again came to my rescue, stating that she could produce a negative ground light controller if she found the suitable transistors and time to produce this custom piece of equipment.

All these alterations and delays drove me to first complete the model as I first wired it (so I can still operate the landing gear for static, transportation or storage), and tackle all the electric and electronic changes at a later day. I thus cannot yet show you the effects of the lights, and probably will first testfly the plane before finalizing the lights connections. Next report will be published on this page after the maiden flight during spring.

To do:

-Make Euro flag decal
-make solid (universal) battery tiedown
-note controls and flaps throws
-remove AR9110 and install 8x+4x with Scottky diodes
-watch rangetest with proximity of carbon wingspar versus Tx positions
-program expos and throws on FrSky
-establish failsafe control positions
-glue Mpx 1 and 2 to bottom wing
-measure watt output and eventually order more c batteries.
-perform high speed taxi tests
-buddy check of model before maiden
-perform shakedown flights as per test card sequence

Spectrum AR9110 hookup
1: Thro = Throttle
2: Ail = Right Aileron
3: Elev = Elevator (via y-cable in tail to both)
4: Rudder = Nose wheel steering (via 70% expo)
5: Gear = Flaps, via y-cable port dct, stbd via reverser (3-pos switch A)
6: Aux1 = Left aileron
7: Aux2 = Gear (2pos switch E)
8: Aux3= Rudder dct from left stick input
9: Aux4= Light system (2pos switch F, reset manually)
Last edited by BAF23; Aug 14, 2015 at 05:23 AM.
Apr 08, 2015, 05:49 PM
The sky is the limit
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Thread OP

Getting ready for the maiden

Spring 2015 update

It took me a while getting all the necessary FrSky parts for this model, and when I finally got them I started removing the Spectrum AR9110 receiver and his 3 satellites. I first tackled the receiver power supply but was unable to guarantee full redundancy. I still have the two separated batteries that feed each engine and separated CC10Amp Bec’s. Unfortunately those BEC’s cannot supply power to a single receiver in parallel, and I had to solder a Shottky diode between them so the receiver power only comes from one BEC at a time. I hate this weakest link in the receiver power supply, but couldn’t find any other practical solution. Soldering had to be done on the wing because of the short bits of wiring that already had been soldered in the previous setup.

The receiver is a SkFry X8R with an additional 4 channels through a CCPM S-bus decoder. This allowed me to install the much smaller receiver on the port side, and via a single connector the decoder on the starboard side. I thus was able to eliminate the starboard flap servo reverser and connect directly to the 10th channel on the decoder. The lights controller also will be connected at a later date through channel 9 on the decoder, and its former wires to the port side receiver were already eliminated. I was glad I had made an elaborate wiring scheme because otherwise I never would have found back how I had done it initially. With so many changes I will need to make a new scheme soon.

Ahead of the port ESC I now inserted a FAS100 power sensor measuring Amps and consumption in Ma/h , and which I connected via a non-precision variometer (used solely for protocol translation) to the receiver’s Smart Port. All this required drastic cutting in excess wire length and soldering different plugs or wires together, but in the end it allowed me to neatly fit everything in the restricted confines of the wing box. Extensive Range testing will be conducted at the field to verify if any interference occurs with all those electronics so close to the antenna’s, but one of the big advantages of using receivers with integrated telemetry is that you continuously can see the receiver’s signal strength (RSSI) on the transmitter, and it audio warns you of low strength at half the distance you would lose it completely, greatly enhancing confidence and safety when operating such less than optimum setups.

I programmed every surface on a separate channel and was glad my new setup showed no errors when I powered it up. Except for the throw reduction on the 3 position flaps to eliminate some buzz, and reversing an aileron, everything moved as I had in mind, including 40% aileron differentials and 20% expos (80% for the nose wheel steering), plus very slow flap operation, all that is not so easy on an open-tx Taranis plus transmitter. Having separate battery supplies allowed me to perform individual ESC throttle calibrations, and by disconnecting a single battery also verify the proper operation of the Shottky diode.

With the model completely assembled I could position the batteries so the CG would be at 21cm behind the leading edge (or 2cm behind mid cord), as most of my predecessors found out to be the sweet spot. For size I used a 5S2700 25c Zippy and a 5S4300 35c Python. I noted the fore and aft positions of both types and then used scrap solid green foam to make retainers so the batteries couldn’t slide further back. Movement forward is restricted by the models existing bulkhead at the front of the hatch opening, and foam inserts placed either in front or behind each type of battery ensure a correct CG. Because the batteries are just in front of the CG, the hefty increase in weight between both types cause only minimal CG shifts. Fastening such heavy batteries with Velcro might not be such a good idea, I thus figured out a system to block them solely by foam, and used ingenuity to make the positioning foolproof. This is the foam that will be glued against the forward bulkhead. The small battery is allowed almost against the bulkhead, leaving just sufficient space for the NACA cooling ducts to blow fresh air around the outside of the battery. The heavier battery cannot be installed so much forward and the aircraft CG therefore will be exactly the same for both battery types. This simple foam piece also keeps either battery type from floating up.

Whilst the tall battery almost fills up the compartment, it is also kept down at the back by the cross member with the magnets. To keep the small battery in place I formed another piece of yellow foam to fill the room on top of the battery (but allowing cooling air to flow in between) and to prevent it from moving backwards during acceleration or climbs. That yellow piece is not fastened and just slides laterally in position. The same assembly is mirrored on the other side of the cabin, and to prevent anything from moving laterally, I glued another piece of yellow foam to the battery rooftop. When the latter is engaged with its forward lip under the fuselage roof, the foam comes to rest between both batteries and their top retainers, effectively blocking anything from moving, and no forces are applied to the 7 magnets holding the latch in position during flight.

With those last works completed, the Boeing is ready for its range check plus taxi tests, and if all goes well, a few short straight hops on a long tarmac taxi track to check the elevator response during rotation (I have read that others needed quite some up input to rotate). The real maiden flight coming in sight, I took the opportunity of a visiting friend to have some pictures made of me holding my completed winter project in a low setting sun.

Next update soon, after the maiden and shakedown flights.
Just wish me luck, I'll need it because I'm already nervous....
Last edited by BAF23; Apr 09, 2015 at 02:24 AM.
Apr 21, 2015, 06:10 PM
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Thread OP

The Rise and fall of my pride (no joy so far)

Rise and fall of Enjoy

April 10, took the Boeing along to the airfield but my priority was to range-test and adjust eight of my already FrSky converted models for the season start. The Boeing filling the aisle of my camper, it was the first one to be unloaded to gain access to the rest of the fleet. Of course other club members pushed me to witness a maiden flight under superb weather conditions, but I had no envy to shortcut my test-program and kept the Boeing in the shade while first completing the rest of my program. I don’t allow myself to be pushed, and unlike others, prefer to do my thing quietly without too many (sensation hungry) people around. When almost everybody had left, I powered up the B737 and pushed it to the middle of the field where I walked my 30 meter circle around the model carefully looking at the RSSI (receiver signal quality) in range test mode. I had done it numerous times all day for other models, so I was prepared for the numbers appearing on the screen (being alerted by the TX voice each time reception was below the approximate half power value). I noted a critical quadrant by going back and forth when it appeared, but that was only a very narrow sector (maybe 3°) which I could further identify back home. In fact those readings were not very correct, because normally the model has to be put on a wooden table about a meter above the grass. Such large table was not at hand, and I probably had been stamped as more than foolish having performed such circular walks 8 times before, even crossing the active carefully looking around for conflicts or hindrance. With that aspect completed, I was getting ready for the taxi tests when I noted the port aileron didn’t move, a bit strange because I had checked it the night before when dialing in the aileron differential and reduced max flap deflection for the maiden flight. When a couple of pilots came closer to offer help, they quickly realized that with my knowledge and different setup and electronic brands, they were more disturbing my thoughts than helping, and dripped away offering their help if I specifically called them in again.

Next step was guiding the 737 on the taxiway to see if it tracked straight. The nosewheel was vibrating like hell and it was constantly pulling to one side. I initially thought the steering springs were the cause of that, but it later proved to be one of both nosewheels not rotating. This curtailed much of my taxi tests, but after I has at the lineup position I slowly opened up the engines (first separately thanks to the dual batteries) to check for abnormal noises or vibrations. Phaedra had done a superb job balancing them and they ran perfectly at wide open throttle for a 30 second test. The telemetry showed a single engine produced 823 watts of power, which is a lot more than necessary for scale flying this 4kg model. The blocked nosewheel gave me a benefit of having a kind of brake, so I decided to make a rejected takeoff on our 90 meter runway. I did this for two purposes, first to check the acceleration of the model (watt power doesn’t necessarily mean sufficient push out of less than optimum engine nacelles). The second reason was to check the elevator effectiveness to rotate because some previous builders reported needing full up elevator to get the nosewheel off the ground, and my problem could be worse because of my scale slight nose down poise on the ground. I reasoned that accelerating with full up elevator would rapidly alleviate the drag of the sticking wheel, and as soon as the nose lifted, I could abort and the drag of the wheel would help me decelerate to a stop within the remaining runway. At full power, the B737 accelerated well and straight ahead proving that there was no asymmetric engine power, and that the weight on the nose was reduced by the thrust line under the model. I saw the nosewheel come up very quickly just past the halfway point of the runway, the model stayed on the ground so I had not attained flying speed (I had intentionally kept the flaps up). Just before the tail would scrape, I quickly lowered the nose while reducing power. The model decelerated sufficiently fast to be able to be turned around before the grass, and I taxied it back in. I had seen enough for that stage and took the model home for further checking.

That nosewheel problem was so stupid I hardly dare to write it down. I remembered how half a year earlier I choose a larger diameter nosewheel axle within the same leg. The 3mm motor shaft was forced into one wheel , then through the leg orifice, and after the second wheel was on I fastened that one with a C-clip in a groove. The result looked perfect, but because I never moved the model on the table, I never caught the fact that one of the two wheels was not spinning. After just slightly drilling out the hole diameter in the leg, I now have one wheel spin together with its axle, and the other freely inside the C-clip. It might not be everyone’s solution, but at least it avoids exposing ungainly parts to keep the wheels on the axle. The friction between the axle and the one wheel is so strong that I trust it to stay in place without further gluing. This is one item more to carefully check after each flight. Doesn’t it sound ridiculous checking and triple-checking every single component of a model, but forgetting to ensure that all the wheel turns freely?

The aileron problem was just a retracted ground connector pin at the receiver, but getting that JR plug disconnected was not so easy. I had to be very careful not to damage more than I repaired in that rats nest of wires and connections. After carefully feeling how much play I had in some wires, I was able to pivot the receiver just enough so I had some access to the various connectors. Sure enough, during an inspection with the magnifying glass I discovered another discrepancy, unseen so far because it only involved the port navigation light that is still unpowered. Getting the soldering iron through that spaghetti to melt that tiny wire on a pin required the dexterity of a surgeon. With some of the equipment out of the way I also made sure to create more “breathing room” between the antennas and the various other components. An in the house range check of course produced much too high RSSI numbers, but even a 2 meter distance circle around the wing produced sufficiently strong variations to identify problem quadrants. Whilst those angles were causing concern with the model on the ground, having it on the table with the transmitter near the floor allowed me to duplicate more realistically the angles during flying, and those numbers were much better without any weak spots.

When pushing all the electronic gimmicks against their Velcro or double sided Scotch type tape, I noticed that the receiver was quite warm. With the fuselage on top of most of that compartment it would be even worse in the air, and I decided to make a gutter between both wing halves to place a small cooling pipe to bring air to that compartment when flying. If that still proves insufficient I can drill some holes in the extended plastic cover over the ESC gutter. A thorough visual inspection in the nacelles assured me that even at full power the fan blades had not touched the casing, and that the bullet connectors in the direct exhaust still were solidly engaged. My unorthodox way of holding the loose propulsion train in place showed no traces of movements, and thus seemed adequate. Seeing no more discrepancies, I declared the model fit for further testing on the field, with the fail safe on the receiver, it is now fit to fly when I feel the plane, myself, and the weather to be ok.

Second high speed test

Sunday was a cold and windy day, but on the positive side the wind was straight in the runway at force four Beaufort and relatively steady. I decided to join Phaedra for lunch at the airport and just before we left for lunch we witnessed the crash of a Jet engine Viper. His flight went well up to the point he lost all control doing a simple 180° turn at pattern altitude to come overhead again. I felt sorry for the experienced pilot losing his expensive model without understanding why it started a roll without him doing any input.

After lunch we first watched the (full scale) T28 Trojan making a local flight and talked to one of the maintainers. By that time some courageous modelers got their gliders towed up, but it was obvious when watching either the full size or the model gliders that it was very turbulent in the air. Not wanting to waste the day, I asked Phaedra to buddy check my Boeing and I later returned the favor on her motorized/towed Ka8b. We also performed range checks, and when she held my Boeing 1 meter from the ground and turned it around, also in pitch, it showed I still had about half signal strength at 85m distance. That means that according to the book it could be flown at full strength transmission power to 30 times more or an astonishing 2400 meters!

Both of us already made up our minds not to fly our new models in this strong wind and bumpy conditions, but this kind of headwind was a blessing for some mode acceleration and rotation tests down the runway. To get a better feel for the conditions I took my faithful FMS B25 out and got it tossed around the sky by the heavy turbulence, but I managed to land it. It was a rather hard landing and due to the flex of the entire engine nacelle (not too strongly secured to the wings), one propeller blade was town off and a new prop had to be installed.

When the glider boys took a break, I taxied the Boeing to the runway and was glad to see that the nosewheel behaved well and the steering was precise. I first repeated the previous rotation test by accelerating down the runway without flaps, and short of takeoff speed briefly applied full up elevator rotating the nose up and quickly brought it back down, then stopped the aircraft and taxied back to the lineup point. With CG and elevator throw obviously within capability to get off the ground, I made another acceleration to stop run but now with the nosewheel remaining in contact with the runway at all time, to check the sensitivity of the steering at high speed, and ascertain no shimmy would occur if I lowered the nosewheel too quickly after touchdown. My 80% steering expo seemed right on the mark, so I taxied back and selected flaps-one to obtain liftoff, after which I would throttle back and allow the model to settle down again, all without leaving ground effect. On this intended third and last run I rotated the model as I would for flying, reduced the throttle but as I was airborne, kept the body angle till touchdown. This bit went very well, but because I had chosen to do that maneuver at a time the wind wasn’t blowing so hard, I knew I would not to be able to stop on the runway. I touched down just past the tarmac, in the grass overrun but still at speed. With the engines at idle, I even didn’t attempt to steer (afraid of sheering the nosegear off) and allowed the model to go its own way. Just before it stopped I saw the left wing drop, and as we approached the model we saw the left main gear leg had sheared off about a meter before stop.

During the complete test, Phaedra had been filming along the midpoint, but forgot to point the camera while watching at awe where I would end up upon landing. She also filmed at the “crashsite” so we could eventually use it for better understanding, but after picking up the gearleg she was quick to point out this had been a clean crack, possibly due to a weak point in the metal. Luckily there was no other damage at all, and the rest of the retract also was intact and hadn’t moved a mm from the pedestal. I found that very strange, because during assembly I had used nylon bolts to fasten it, just to create a weak link so I wouldn’t damage the gear or wing. I had hoped that excessive forces would have allowed the complete gear assembly to be torn off by having the soft nylon flat bolt head slipping in the hard plastic. I carried the plane back to the pits thinking I might have been better off flying a pattern and landing on the runway threshold. Here is the short film about those ground tests.

Jetair B737 hi-speed taxi tests (1 min 31 sec)

When talking it over with some other experienced builders, they pointed out that using 4mm engine drive shafts was not the best solution because the hardened steel snaps instead of bends at excessive load. Piano wire is much better for such joints because at least they just flex a bit under load.
Back home on Monday 13th, it wasn’t too difficult to extract both pieces of the shaft, and putting them together it was obvious it broke along the machined groove for the C-clip. I remembered I had used those in the assembly to ensure the axle wouldn’t protrude more than intended behind the metal trunion. This can be seen on the pictures of the landing gear modifications earlier in this build tread. Those C-clips having no real use, I machined the 4mm piano wire bits (recuperated from an old landing gear of a petrol trainer) without this groove, but with flat spots to secure the grub screws so the wheels would keep tracking straight. Doing the other gear would have been even easier, had a screw not broken in the aluminum leg during reassembly. With everything completed and tested I loaded the batteries and started putting everything in the camper.

Finally the maiden

By 16h I was taxiing out in light but variable wind, with the sun piercing through high clouds. Everybody was watching from a distance as I positioned behind the model and selected takeoff flaps, with the intention of leaving them (as well as the gear) deployed for the duration of the maiden flight. No need to wait any longer, I resolutely opened up the throttles and as the acceleration looked good, I slowly brought the nose up after passing the hallway point taxiway. As it majestically left the ground, I held that body angle for the short climb to downwind altitude. During the climbing turn I noticed that the aileron response was perfect, and felt the same for the elevators after the level off.

I quickly reduced some power in downwind because I have no clue as to how strong those flap hinges are, and wanted to keep the airspeed down to about 1-1/2 times the speed I lifted off the runway. As I intended to make this a short flight to measure the batteries after landing and have a feeling of their temperatures and capacities, I didn’t climb but elected to make a few traffic patterns to trim the model out. With the crosstrims on my Taranis it was a piece of cake, the model being rock steady longitudinally and laterally. Although when flying directly overhead the model seemed to have no crab, directional stability was poor at that speed and configuration. The air was calm, and I was glad I had not taken the Boeing really airborne the day before in the turbulence, it probably would have been gyrating wildly. One of the reasons might be that I kept the gear down and thus the area of the wheels and geardoors reduced the effectiveness of the large tail area. On the next downwind I became bold and retracted the flaps completely, keeping my finger on the flap lever during the 4 second process to reverse if necessary. It only needed one click of trim, for the rest there was little change in behavior.

Next pattern I lowered the flaps again and I extended the downwind a bit for a first approach attempt. The turn to finals was very steady, and the glide slope very easy to control with the throttle. As my Boeing was flying on rails, I adjusted the speed to attain about the same body angle as during liftoff, and it looked very realistic. As it didn’t fishtail anymore and was going for 10 meters past the threshold on an approximate 5° glideslope, I started reducing the power slightly and flared just a bit when a foot high. I made a textbook smooth landing and stopped without a swerve with about 30 meters of runway remaining. I heard the applause and taxied back proudly. Unfortunately on weekdays only retired pilots are flying, and none are very proficient or tempted to exchange their direct view for that through a cellphone screen to immortalize such moments digitally. Furthermore I refuse to fly with a hatcam over my coiffure.

After the flight I looked at my telemetry screen and that showed only 1250 Mah consumed, which would be less than half the capacity of my 5S2700 measured battery. When I took it out and measured with the Lipo tester, it indicated 48% remaining. To be followed up, but next time I will aim for a 6-minute flight and measure again. Even with the additional cooling airflow that I created, the battery felt warmer than expected, having flown mostly at ¾ power. That also was more than expected and I’m anxious to see how much difference a clean airframe (gear and flaps retracted) will make. Overall I’m very pleased with what I’ve seen so far, CG throws and expos can remain the same, but might consider installing a gyro on the rudder channel if the directional instability persists.

A temporary end

Wednesday the 15th was an early summer day, almost 25°C temperature due to a southerly wind that was forecasted to be and stay in the runway. Upon arrival at the airfield I was surprised the wind was not force 1-2, but more like 3-4 and sometimes completely cross. Only 4 other pilots showed up on that beautiful day. As the wind calmed down a bit around 1600 I taxied the Boeing to the takeoff position for its second flight. I had consulted my testcard and decided that following items were on the program: no flap takeoff, gear retraction on downwind, reposition for a low pass to confirm all gears were up and doors closed, climb to pattern altitude and execute horizontal figure eights to check for gear-up directional stability plus adverse yaw during the outbound reversals. After that I would climb to altitude and perform clean stall checks and a cg-dive check. Next on the program would have been partial an full flap movements on downwind to get a feel for the need of flap-elevator mix. If all went well, the gear would be lowered and a full flap landing executed.

Nothing went as planned because upon gear retraction I noted the nosewheel somewhere was halfway the doors and stopped there. During the overshoot after the visual check I lowered the gear again and observed all were down on downwind, so I retracted the gear again and turned back in for another visual inspection. This confirmed that the problem persisted so the stalls and directional stability checks were meaningless. I thus was curtailed to flap movement longitudinal stability influences. I left the gear as it was and in downwind lowered the flaps to takeoff position, noting it didn’t cause any pitch change at the moderate speeds I had been maintaining so far because of the gear problems. With the Boeing perfectly maintain its downwind altitude, I initialed a 180° turn with 30° of bank at the end, the idea being of repositioning for an upwind pass halfway the downwind leg where I could observe the first slow full flap extension and eventual pitch change. My speed during that turn was definitely superior to the speed I had flown the takeoff flap (final) landing turn during the maiden. His time after having reached 30° of bank, I stabilized everything but shortly thereafter ( almost on base) my Boeing started rolling into the turn without me able to stop the movement. The nose quickly pointed vertical and cut the throttle and applied full up elevator, hoping to be able to break the impact a bit. In a stall you would give full power and apply opposite aileron and rudder, but there also was a possibility I had an ESC/engine failure on the engine inside the turn, in which case I had to reduce the asymmetry by cutting the good engine. In this case I didn’t perceive any reduction in the bank angle, but with the nose pointing straight down, it was too late to try anything else but try to raise the nose a bit from the vertical.

During that flight I flew with my earphones plugged into the Taranis but did not hear any messages that my RSSI (receiver’s reception strength) was low or critical. The only call I got was just after impact, telling me that telemetry was lost, completely normal when the model is in the grass about 150 meters from the transmitter. Knowing the place it crashed, I switched my transmitter off, quickly changed in the camper from skirt and flip-flops to jeans and sneakers with socks, then caught up with a fellow pilot and his father who already had set course towards the presumed point of impact. When we spotted the model, it was clear we first had to cross twice over the horse’s alley between the house and the delimited playground. That alley was about 5m wide delimited by poles sporting isolators. A detailed look made me conclude that only the top cable was electrified, the bottom being a simple nylon rope looped through the insulators. Pushing the bottom one down with my rubber sneakers, I was able to bend and crawl under the dangerous wire. My helpers stayed on their safe side and after crossing the second parallel wire I got to my aircraft that was resting wings level on the grass just 2 meters beyond the wire.

As usual I mentally noted all clues on the model before picking it up. All pieces were present at the crash site, none had separated before the impact. The vertical tail had sheared off the pins holding the horizontal stabilizers in place. The impact therefore must have been rather brutal with the vertical tail laying completely separated within half a meter of the model, the horizontal ones still in their slits but the right one without the carbon guide missing. The starboard engine nacelle had separated from the wing, but still hung by the 3 engine wires to the wing. Although both winglets had separated and laid close to the wing, they could be reassembled because the rest of the wing miraculously looked completely intact. The ailerons were in neutral positions, but one flap was up and the other down, had that been the cause? The fuselage didn’t look that good, a few cracks left and right made it difficult to transport, and it was in fact the wing connection that kept it all together. I disconnected the batteries and because they looked intact and weren’t hot I stowed them in my pockets for the return, but crashed batteries are always a hazard.

My helpers did a good job getting the model and myself through both wires, and after joining the pits again I put the model on the table and powered everything up again. Within a second all controls were streamlined and everything worked ok, including the flaps. On purpose I didn’t check the gear, the mains were nicely retracted but the nosewheel had taken a serious pound. The model must have impacted seriously on the nose because it wasn’t aligned anymore and had seriously compressed the geardoors and nosewheel leg to the point the doors were broken midpoint, and not only the leg had bent in an angle, but even the motor axle worm wheel was bent before it sheared off with the gear in its semi retracted position. Connecting the batteries after disconnecting a few times, I noticed the same momentarily asymmetric flap condition during binding as on the crashsite. Although I has programmed the failsafe on the receiver, the servo reversal in the transmitter apparently causes this one-second problem (as most other models encounter with undesired very short landing gear inputs during receiver power-up. I interpreted those indications as that although I didn’t get any loss of signal report, the receiver obviously had lost my signals, and was binding again just before impact. After disassembling the fuselage from the wing, the former was barely holding together the 3 solid portions.

Back home I made some more pictures of the snaking fuselage and immediately thereafter got my hairdryer out because I heard it is easier to straighten out damaged foamies just after the distortion, compared to leaving it compressed for weeks or months before tackling the repair.

Having no envy to rapidly order a new set of Calie-graphic stickers, I initially applied heat to the compressed fuselage portions from a safe distance. Was able to carefully remove the starboard cockpit windows and then cut away the frontal portion of the vinyl. This allowed me to apply more heat directly to the foam.

The worst wrinkles were eliminated in an hour time but I was afraid to further manhandle that fuselage without enlarging those substantial cracks even more. I thus decided to first glue one crack at a time, and used many hidden 6inch flat carbon strips (which I pushed in stencil knife made slits) to solidify the repairs made with PU wood glue. The expanding nature of this slow curing glue helped it finding its way through the entire surface of the cracks and around the carbon strips, an important point on the thick foam on this Boeing fuselage.

After 24 hours all cracks had been solidly repaired , which allowed me to use cushions and weights to further straighten the fuselage. I then removed the nose gear and was surprised to see how much of it was broken internally, most forces came from the compression and sideway during impact on the nose. The original joining axle was bent and thus impossible to push through the trunion. The servo worm wheel was bent and broken, and even the print plate had a bend in it.

Without the nosewheel I was able to dip the nose of the Boeing in a large bowl of boiling water. It had been compressed so much that hot air on the outside was insufficient to get it back in shape.

The boiling water was allowed to enter the nose on the inside as well and quickly weakened my fillers and made it possible to apply finger pressure to push cavities out again.

When the nose was straight I still had a banana shaped fuselage because of the very bad compression just forward of the port wing. Impossible to dip in boiling water, I got my paint stripping gun out and after half an hour of 195°C blowing at less than an inch away from the vinyled foam, it straightened out very slowly with a cushion behind the fuselage , and me simultaneously applying side knee pressure on the nose and hand pressure on the tail.

Using so much heat of course caused the foam to seriously bubble, but that can be taken care of later.

Having the camera not exactly in the middle when taking those pictures of the results from close by creates an optical distortion, but believe me when I say that the fuselage is nearly straight.

I never thought I would get it that way again without major surgery, but that definitely is an advantage of foam over any other model materials. One small crack around the main gear openings also was quickly repaired, but having not found a satisfying way to reattach the starboard engine nacelle to the wing yet, I put the Boeing in its support box and it will rest for a few weeks or months before tackling the rest.

My plan is to find a solid solution for the right nacelle, replacing the nose gear servo assembly and build it in a much narrower cavity without geardoors, then testfly the aircraft “as is” and if everything works well, cosmetically repair the fuselage and apply new portions of vinyl and decorations over a filled and smoothened fuselage. I realize it will never be as beautiful as it had been, but still will be an attractive model that I hopefully will be able to fly regularly in the 2016 season and beyond.
Last edited by BAF23; Apr 21, 2015 at 06:27 PM.
Aug 31, 2015, 04:13 PM
The sky is the limit
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Third attempt

Shortly after posting the crash report and pictures of the repair attempt, Ming from Windrider contacted me with some exceptional offers concerning spare parts. I was very grateful because I hadn’t bought my model from him, and here he takes the initiative to help me in getting a better looking fuselage than my repair attempt. After we came to an agreement he surprised me even more when in July I opened the huge box from Hong Kong, He actually sent me a complete glider kit instead of just the parts we agreed upon and which I had paid! I soon made up my mind and decided to further summarily repair the crashed B737, fly it like that for the rest of the year in order to get fully proficient on the type, then make a completely new fuselage with Ming’s kit during winter, and mate it with the existing wings to get a near perfect model for the 2016 season. By the end of the month I dismantled my Boeing to work on it. That is when I experienced the benefits of having thought of multiple plugs for the wiring between both wings. In a nick of time I had them disconnected and just slid out both wings from the carbon tube to separate them from each other, greatly facilitating the handling during the repairs.

First job was to find a way to get the broken-off nacelle structurally mated to its wing. Ming’s kit contained those precious CNC cut plywooden 3mm and 2mm shapes that have to be glued together, but although they were ideal to use as a template, it was impossible to get the old ones out because the wings spars and extra wing reinforcements pass right through them, and wiring for the ailerons and lights were glued on it in the wing as well. The idea of gluing those things together helped me find a solution. After pulling out the hinges of the lower nacelle half (easy because I intentionally used sticky glue instead of solid bonding one) I started out by cutting and carving out a 3mm gutter on both sides along the length of the broken parts, but only as deep as not to get into wires nor carbon spars. Next I took a piece of 5-layer multiplex wood and faithfully cutout two mounts based upon the original part.

After some trial and error positioning and cut refinements for foam and wood, everything seemed to match. The old wood was treated with the knife to remove any remaining glue traces, then liberal amounts of PU wood glue was smeared on each new lateral nacelle mount before it was pushed into position. When everything seemed aligned I used clamps to keep everything tight together, both on the remaining foam wing assembly and on the nacelle half. I had to continuously wipe off the expanding glue for the next 3 hours, but at least I knew that everything bonded with everything along its complete surface, and no air pockets could form weak gaps into this structurally very important part of the model.

After leaving it alone for 24hours, I used the Dremel to blend the exposed surface and parts touching the fan shrouds, and after applying and filling some excesses, I could paint the areas before inserting the fan and closing the nacelle again. A few patches of vinyl now completely hide the repair, which I expect to be as solid (if not even more) than the original. Being rather close to the fuselage and lightweight materials having been used, I feel there is no need to add balance weight in the other wing to keep things equal.

When attempting to assemble both half wings together I was unable to push the carbon wing spar to the end of the repaired wing, even using force. Using an endoscopic camera That I pushed 23cm deep into the 8mm foam channel I discovered to my horror that the expanding glue had almost completely filled the hole in the wood for the spar to pass through. Being so deep there was no way to poke that now rock-hard glue through with anything and I searched the internet for a 30cm long 8mm wood drill. Of course that was a special order item and I had to wait two weeks for it to be delivered.

Awaiting the drill I attended the nose of the fuselage. The nosewheel assembly had been completely ruined, even rendering it difficult to remove and dismantle the parts, but my strong custom plywooden base showed no sign of damage. Mating the saved items with a new nosegear assembly produced a drop-in nosegear with the same steering mechanism. The compression impact on the nose also had deformed the modified T28 nosewheel box and ruined the geardoors. Rebuilding that on this temporary fuselage made no sense. I thus straightened out what I could, then dry assembled the nose retract assembly and figured out the contours of a removable foam insert to cover all the free space in the opening, leaving just enough for the gear to retract in between. It won’t be as pretty as with geardoors open, but won’t be too disruptive for looks or aerodynamics with the gear up. Without gear doors hanging down so much in front of the CG, I hope to get rid of the directional stability problems I felt during the gear down test flights.

After making sure everything worked well, it became time to put vinyl around the nose again. As can be seen on the pictures of previous threat, the boiling water and heat gun application had mostly straightened out the heavily damaged nose section, but left it with enormous orange peel bubbles. I initially thought of applying lightweight filler, but abandoned the idea because a lot of stretching and reapplication of nose sections had to be done with the vinyl over this highly compound curved shape, and probably the filler would be torn out during each reposition lift of the material. I thus had no other option than to sand away the bubbles with coarse emery paper. Although this necessitated taking quite a bit of foam away, the result was very pleasing, and a much better base for stretching the blue vinyl.

I admit I wasn’t as meticulous as the during the actual build, but most people will not see the overlaps, pinches and cuts on this temporary fuselage. For the starboard cockpit windows I now used Windriders’ original discarded stickers with incorrect window frames, but from a distance that doesn’t really matter. I then used scrap bits and pieces of blue vinyl to apply over the PU glue residue at the fuselage repairs, vastly enhancing the overall appearance and making those drastic repairs much less obvious. The repair of my custom designed attachment method for the 3 tail feathers was straightforward and caused no problems.

Next on the list was eliminating a possible cause of the crash. An R/C friend of mine also did experience strange phenomena when in her models she had coupled an SkFr X8R with an Sbus PWM decoder to add 4 channels. She experienced the burnout of gear servos and uncommanded flight control inputs during configuration changes with different models. The link to such occurrences had been that analog servos had been connected to the extra channels and apparently some internet colleagues posted warnings of such combinations. When I ran some test on my Boeing with intentional temporary loss of signal, I noted that my starboard aileron and flap (both running on the Sbus decoder) behaved completely different to the other servos during the process of rebind. I remembered my uncontrolled right bank happened when I initiated the final turn, exactly the point where I lowered the flaps. Coincidence or not, we’ll never know, but I wanted to eliminate that possibility from the equation by changing the receiver system to two independent X6R receivers coupled to the Tx. I reprogrammed my Tx so I had all the primary controls (rudder, throttles, starboard aileron, elevators, port aileron and telemetry) on the primary Rx, the accessories like lights, stbd flap, port flap, gear and nosewheel steering on the secondary Rx, thereby minimizing the danger of asymmetric deployments due to uncommanded rx inputs. Receivers had to be bonded individually to the Tx, and I used a spare servo to confirm everything responded correctly before even attempting to install and connect everything in the immensely cluttered wing center section.

This third change of receiver system for only 2 flights was not my idea of having fun with models. It again was of such basic philosophy change that it necessitated yet another wiring diagram drawing. So far these diagrams have proved absolutely necessary because of the complication factor and tendency to quickly forget how things had been rerouted in the compartments. I also found out that during the crash the wooden fuselage support for the aft wing screw had cracked inside the foam. It thus became necessary to cut some foam away and produce a new support plate that was integrated to the old one before being encrusted by new foam.

When the drill finally was delivered I was able to just use my fingers to delicately turn it around and slowly extract the excess hardened glue in the engine pod mount, without enlarging the deep foam access tunnel of the center wing. Once this was finished, I assembled both wings, connected the contacts and transported the model to the field for its third flight. After a successful range check of the new receivers I taxied to the runway and got the nose wheel tracking straight before taking her in the air using takeoff flaps. With the directional instability experience of the first flight in mind, I soon retracted the gear and I was pleased with the takeoff and climbout, but soon in downwind encountered uncommanded wing dips. Raising the flaps to the flush up position didn’t affect these strange inputs. During the following pattern I pattern lowered the flaps again to half but with the possible tip stall of the second flight in mind, kept the speed up (the wings had definite dihedral) till final when I lowered the gear for an immediate landing. Speed had not been the problem this time because on a normal final in landing configuration, I encountered two more of those wing dips and was able to counter them, but to the detriment of keeping the model aligned with the runway. Because pictures tell more than a thousand words, here is the movie about those scary seconds.

B737 uncomanded input (0 min 16 sec)

No matter it landed in the grass , my Boeing was completely intact, including the beefed-up retracts. Post flight investigation still hasn’t revealed a clear reason for these occasional lateral incursions. Are the two receivers interfering with each other? Are the flaps subject to (turbulent) air loads that cause asymmetry? I don’t know but a fact is that those flaps are anything but rigid because there is no way to attach the hinge mechanism solidly directly to the foam wing. I better should have made plywood beds under the canoes to create a more solid base. With my system of making a Fowler flap movement with Ventury effect, any slightest asymmetry even in the fully up position could cause a substantial lateral imbalance. My plan of just replacing the fuselage during winter would not result in frequent flyer for 2016, other things had to be done so my model flies as well and stable as the videos of other Windrider B737’s I see on the internet.

Fourth flight I got it right

I finally found the cause of the power cycles , a loose contact somewhere in the rat's nest causing the digital flap servos of that brand to momentarily assume full deflection during power-on, but because of the reverse setup in the wings this resulted in the port flap going fully up and the starboard fully down, causing a terrible wingdrop whatever the choosen flap setting. Having eliminated the root cause, I decided to fly it again, but when I'll make the wings for the -800 I for sure will use flap servo's that don't bind in snappy 100% position, thereby eliminating nasty results after a harmless power cycle. I just had to wait a couple of weeks for good flying conditions to attempt a fourth flight.

With a calm wind from northeasterly direction I lined up my repaired JetairFly 737-700, talked the flight profile over with Phaedra who came along me at the runway to call out the wind direction during this testflight, I took the bull by the horns and opened up the throttle when the wind blew down the runway. Having pushed the plane out instead of taxiing it to the takeoff position, I had forgotten to set the takeoff flaps as I normally do before engaging the runway. I noticed it halfway the takeoff roll but decided not to divert my attention and pursued the takeoff, just allowing it to gather more momentum before rotating. Real airliners need a checklist, but I'm seriously thinking about starting using checklist for some of my more complex models, those things aren't toys anymore!

She raised majestically in the air and I kept a moderate 5° climb angle during a 200° left turn that bought her back towards me again. By that time I had reached pattern altitude, so I leveled off and watched the gear retracting completely. After next reposition turn I flew overhead into the wind and worked the trims to obtain straight and level flight (for reasons I still don't completely understand that necessitated full right aileron and a bit of right rudder). As she then felt stable and not fishtailing anymore (probably because I finally got that nosegear completely up), I climbed for some stalls in the various configurations. My copilot faithfully continued to give me the headings according to the windsock, which was a tremendous help. First upwind run was for a clean stall. Because I prefer to execute the stalls like in real airplanes, meaning level flight with a speed decreasing about one knot per second, I just reduced the power to about one third instead of chopping the throttle (having no airspeed indicator it remains educated guesswork). The stall was clean and easily recovered using only partial power.

I took her around the pattern again and dropped the flaps to takeoff position in base whilst Phaedra guided me further left in the shifting wind direction to eliminate side effects during the stall. This time it stalled benign again, but dropped the right wing to about 30° of bank doing it. Recovery was again straightforward but it got me puzzled a bit. With full right aileron trim, the starboard wingtip should have less alpha (angle of attack) than the left, yet it was that wing that stalled first, maybe due do the slight right rudder I trimmed to obtain straight and level flight (in a clean configuration). I left the takeoff flaps and took it slowly around the pattern again.

During the final turn I dropped the gear and lowered the flaps to full, barely reducing the power because the draggy configuration did the rest. I was amazed how slow it flew when it finally stalled, but even more about the magnitude of it. It abruptly wing dropped to 90° of bank and that quickly quickly dragged the nose down to vertical as well. Not being prepared for that I had to make some very quick thinking (it's amazing how a person can do that whilst others just would freeze or use power/ailerons/up elevator to make the situation even worse). Knowing the delicate nature of the full-flap forces (just on 2 hinges glued to foam) on an airliner plunging down to earth, my first reaction was to close the throttle, release the stick back-pressure (although the stall only occurred with half up elevator), then slowly pull the nose back up with wings level, whatever the heading was.

Retracting the flaps to half would just mean a loss of recovery time because of the 4sec slowdown function I had built in. As I quickly regained controlled flight, I was able to turn away before flying in our no-fly area (we share airspace with real airplanes), but my planned test profile and been completed and whilst in landing configuration, decided to continue in a descending pattern for a low approach without modifying the configuration. Because my telemetry wasn't reporting all aspects and I was flying on light 2 x 5S2700 batteries, once I turned to finals in a short Spitfire type approach, it all seemed stable enough to proceed, and after floating a bit (I flew fast enough not to get another wing drop) I got it down halfway the 90meter runway with ample room to stop.

Taxiing the Boeing back I felt relieved as my heart resumed its normal 65 beats, a feeling of achievement overwhelmed me. 18 months of work and troubleshooting finally translated in a superb model (people even don't notice my visible repairs because they are mesmerized by this majestic shape of an unusual RC model, even when they are very close to it on the ground). When taxiing-in back to the pits I raised the flaps and was both proud and glad that after all those working hours and troubleshooting, I finally had a flight (the fourth one) where she gave me satisfaction instead of pure terror. Once back home, it didn't take me long to mechanically adjust the kwik-links of ailerons and elevators so the next flight can be flown with neutral trims. After a while I also found the cause of the telemetry problems (no wonder after the 3 receiver major configuration changes in 3 flights). My B737 is finally ready for “getting acquainted flights” instead of test-flights, so I can fly that unique model and enjoy pleasure doing it. The idea is to gather as much experience as possible with it before my next step into a stretched B737-800 version for which I still haven't decided if it will be a simple flying model, or one with all the gismo's incorporated.

What did I learn from this flight, first the airplane flies extremely well without stabilization (that day I also flew my FlyFly Aeromachi MB339, the Dynham DC3 and Art-Tech T6 Harvard, the latter two in dire need of gyro stabilization in the relatively turbulent air of the day). Ming's Boeing 737 penetrates that turbulence well, as long as the nose gear and associated doors are fully up, but watch out with full flaps in the pattern, just as during the second flight when I went full flaps during the base turn, a few knots airspeed difference (not obvious flying downwind) can cause a wingdrop that is impossible to recover from from a pattern height (I'm now convinced what caused the crash on my second flight). Ming's737 is a fantastic flying model, but has to be treated with respect if you load it up with heavy mods and change the wing aerodynamics by adding fowler type flaps.

This woman is very happy with her repaired/finally reliable/stable/attractive B737, and is looking forward learning to fly it realistically before switching to the stretched version for which I have most of the components already in the house. Phaedra usually has her camera along to make shots of my mishaps, but this time forgot her camera, and superstition allowed me therefore to make a relatively uneventful (test)flight :-) Hopefully we'll be able to break the spell soon so I can post video shots of that beauty in the air.
Last edited by BAF23; Sep 27, 2015 at 04:56 AM.
Oct 05, 2015, 05:08 PM
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Getting used to the B737 during flights 5 and 6

First weekend of October a nearby high pressure system caused the winds to drop off and blow from the Southwest, meaning the best runway for testing because of the immense grass overrun in case of takeoff problems. I called Phaedra to bring her camera along and due to an RC event elsewhere we were just a few pilots on the field that chilly Saturday morning. The calm winds led me to first fly my Art-Tec T6 Harvard and Dynam DC3 to verify and further refine the gyro pot settings. I then wanted to get some EDF training with touch and go landings and got the FlyFly MB339 out for the first flights on camera (see elsewhere on my blog page). With the confidence in high gear I then prepared the Boeing and took my time to verify everything and make sure I didn't forget to select takeoff flaps.

During the previous flights I always stood right next to the runway, but this time stood behind the pilot line which for safety is set a huge 20 meters from the runway centerline. With Phaedra filming next to the runway, I made sure not to allow the plane to drift to the left for takeoff nor landing. This was the first time I was able to see the speed during the roll because on previous flights I almost stood right behind the model to steer, and as such had little idea of rotation speed, I just let her roll till the end the tarmac then lifted her in the air. Until further stall tests, speed is my only insurance and I will not allow any comments about too fast for scale, to reduce speed and risk falling into the wingdrop zone again.

Acceleration was normal and when past halfway the runway I started to rotate, I was surprised how quickly the nose raised so I put it down again and made a new slower rotation just before the end of the tarmac. I kept the nose in a shallow climb angle and banked moderately during the figure eight climbout to altitude where I reduced the power and started trimming her out. Despite my ground adjustments, I still needed considerable inputs on all 3 axis to get her to fly smoothly, but after about 3 racetracks I got it right and she became very stable and harmonic in the responses. With the camera on the field I decided to skip the stall tests and brought her down for a couple of low passes, including a top view one centered around Phaedra's position. These passes were made with about 2/3rd throttle, proving 5S batteries to be sufficient for this model.

After a gear down pass to visually check “the 3 greens” I turned to downwind and lowered the flaps to half. At the end of the downwind I selected the flaps to full and counted 5 seconds (I use 4sec servo slow) before initiating the 180° descending right turn to intercept a shallow glide path and allowing the speed to slowly decrease. Body angle is your best airspeed indicator and I'm sure it can be flown slower, but at this stage keeping the nose slightly up with full flaps is all I dare to keep out of trouble. Concentrating so much on minimum speed and glide angle for an early touchdown, I neglected the alignment. I still have to get used to the size of the Boeing to estimate its distance. An airline fuselage on a 2meter span wing is a complete different sight to a jet or warbird of similar span, and standing so far away from the centerline with recent left-eye surgery just complicated things even more.

During the flare I realized I was too close to the right runway edge for comfort and made a last correction to the left hoping the starboard wheel would avoid touching in the grass, and it worked. With full flaps the model slows down well and I stopped in less than 50 meters. Walking towards the model I turned it around and engaged the taxiway where I started to raise the flaps. Phaedra quickly repositioned and made a beautiful shot from ground level of the incoming Boeing, a pity of the grass remains from the recently lawn-cut. I cannot tell you how long I flew because my 3-1/2 minute countdown timer uses procentual throttle inputs rather than real time. I think I flew about 4 minutes and my timer still indicated one minute to go. I mostly rely on the telemetry providing me voice calls about the battery power consumed at 1000, 1500, 2000 and 2250 mAmps used out of the 5S2700 battery, assuming the battery of the other engine consumes just as much. With the lipo tester indicating 35% on both not too warm batteries, this power setup appears ideal by combining light weight with adequate scale-power. I will wait a little longer before flying with my heavier 5S4300 batteries. I noted down all the figures and trim settings and joined Phaedra for a well deserved Spaghetti on the terrace of the clubhouse. Here are the shots of part of the flight against a cloudy sky.

Jetair B737 oct 2015 (2 min 12 sec)

Sunday the flightline was very busy with lots of helicopters, EDF's and motorgliders, but as I noted everybody left the air for me as I flew my realistic sound-equiped delicate Dakota, they probably would do the same for the Boeing, and as the clouds dissipated I started assembling the 737. I had hesitated to do so because on Saturday I noted how well I could track the blue fuselage line, but how difficult it was to judge the bank angle of the gray wings against a backdrop of clouds. This time I wouldn't climb out for stalls either, but make just a few passes for the other guys and many visitors at our field, thus remaining closer for better visual clues.

As I pushed the Boeing towards the taxiway, all pilots dropped their stuff and a lot of them walked with me towards the pilot line. As they started joking about flying to Allicante (most Belgians have traveled to their holiday with such a Jetair 737), I asked them to please remain silent next to me because I needed all my concentration to fly that model at that stage, luckily they kept their promise. After lining up I looked at the windsock, but wasn't afraid of the steady relatively light 45° left crosswind. After I mentally reviewed my flightplan and looked at my fingers and switches I was going to operate after takeoff, I opened up the throttle and this time made a smooth rotation after a 45m ground roll, immediately raising the gear after liftoff and flying a kind of noise abatement climb attitude until over the tree-height, then lowering the nose whist raising the flaps to up before making the climbing accelerating turn towards us. I didn't need to trim but a few clicks this time and she felt solid as a rock, with excellent roll rate and soft but crisp longitudinal control.

I didn't fly higher than downwind that flight, and made nothing but nice flyby's at eye level, many of the pilots making tons of pictures. After about 5 passes with the last one being the gear check, I positioned for a long airline type final and this time concentrated on the correct lineup for the middle of the runway. The touchdown was well centered and about 3 meters after the threshold, but concentrating so much to get all that correct, I didn't sufficiently flare and the 737 touched down a bit too fast and bounced for about 20cm before during the next sink I started raising the nose to see how much I could do it before a wing dropped. None did and I made a beautiful touchdown with the stick well aft. As after the touchdown I slowly continued to full back stick and the nose stayed in the air for aerodynamic braking for a while, and when the model stopped, I measured just 50 meters between the first bounce and the coming to a stop. Half flap for takeoff and full flaps for landing for sure make a difference.

As I taxied in, the other pilots followed me on the taxiway and I started paying some attention to their comments. I felt proud of my achievements, building, setting up and correcting the model during those nerve-wracking test flights, all now paid off and proved that my methodical step by step approach worked well (for me). Another club member (who next time will bring his scale RC tow-truck to give me push-back and tow me to the runway) also has a 737 box at home and will assemble it next winter, just as Phaedra, so next spring we might have 3 Winrider B737's operating from our field, each in different Belgian airliner markings. After the completion of my flight tests, I will post the exact figures I will end up for throws, expo, weight, CG and other goodies, please be patient in the meantime or use the unrefined figures earlier in my blog.

ps: During assembly on the field it became increasingly difficult to engage the 4 long screws through the wing attach points into their fuselage receptors. The foam with the slit over the plywood plate does not provide sufficient guidance for the screws and over time you increasingly have to search by trial and error before the screw engages. Being tired of that, I decided to make my own guides to ensure consistent good alignment. Unable to find the appropriate diameter tubes in my scrap box, I used scissor cut lengths of a drinking straw which I lightly glued with expanding glue into both fuselage and wing foam passages, filling the adjacent slits with crap foam. The tricky bit is to align the top and lower guides without the expanding glue grabbing each-other, nor expand on the screws . Once dry, the remaining voids around the straw-bits can be filled with additional glue to obtain a very solid guide for the screws to be inserted immediately in the unreachable bolt assembly deep in the fuselage. This lightweight modification is easy to make and greatly facilitates repeated assemblies on the field.
Last edited by BAF23; Oct 08, 2015 at 10:59 AM.

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