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Aug 14, 2019, 10:23 AM
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Build Log

Build log of a Göppingen4-3 scale 1:4 from Assmann design


Chapter 1: Introduction to the Schemp-Hirth Gouvier gliders

Black and white picture of the real 1953 Sabena gouvier in flight


During the thirties, soaring became popular but the basic period single-seaters only allowed slow student progress by short hops along slopes. Some two-seaters were developed but in 1937 the first flight of a side-by-side two-seater (developed from the Gö3 Minimoa) opened up a new way of introducing more people to soaring, and offering a better way of teaching. The Göppingen 4 (abbreviated by many to Govier/Goevier/Gouvier but with different pronunciation in German, Dutch and French) had flight characteristics similar to the popular Grunau Baby but at 92cm width, the seating felt rather cramped. Space had been maximized by the wing to fuselage blending root-shape to accommodate shoulder and elbows. That part could be ordered in resin impregnated jute (sackcloth), the very first use of ‘plastic’ parts in gliders. The Gö4 was very successful and used by the Germans to train candidates before they joined the Luftwaffe. After the war the factory developed and built the shorter aft-fuselage version Gö4-3 that didn’t need as much balance weights when flown solo. Of the more than hundred Gö4’s built, as of 2015, only 3 remained airworthy in Germany and 2 in the Netherlands.

In 1952 Belgium’s national soaring centre acquired Werk-nr 415, one of the 21 factory produced Gö4-3 and flew it unregistered till 1954. It then was registered OO-SZC by Sabena (Belgian’s airline), painted beige/light blue with Sabena markings on wings and tail, and offered back to the training centre where it flew as such till 1959. It later sported less attractive liveries and flew out of Knokke, Charleroi, Ghent, Moorsele and Wevelghem until after an accident end-seventies it was abandoned in the old German hangar. When the rotten hangar roof collapsed in 1980, the Govier (and a Grunau Baby) were bulldozed with the rest of the hangar materials into the soil, a sad end for this charismatic glider.

After already having the 1:3 scale Ka2b OO-SZD and Foka4 OO-ZEU in Sabena markings, I was thinking about adding the Bocian 1c OO-SZE and Gö4 OO-SZC (both also in period Sabena markings) to my glider fleet, but as easier to manhandle 1:4 scale models. The Bocian was available on the market, but no short fuselage version of the Gö4. During an international SAM (Society of Antique Modelers for pré 1942 R/C models) gathering at my field I spoke with Jürgen Assmann (a respected German modeler who had flown a Gö4-3 while training in real gliders) and he quickly embraced the idea of adding a short-kit of that glider to his offerings (unavailable online). A few months later he surprised me by asking me to build the prototype, review the kit and test-fly it because his winter was already full of other projects. I agreed and here follows the build-log of that unusual short-kit.

IMPORTANT NOTE: THIS AND THE EVEN MORE DETAILED BUILD LOG WAS WRITTEN REVIEWING THE PROTOTYPE AND THEREFORE MENTIONS A LOT OF SHORTCOMINGS OR PROBLEMS THAT PROBABLY WILL BE RESOLVED BY THE TIME YOU BUILD A PROPERLY DEVELLOPED AND CORRECTED SERIES-KIT AND PLANS. ALWAYS TRIAL FIT ANY PART OVER THE PLANS AND VERSUS EACHOTHER, AND: “ALWAYS MEASURE AND THINK TWICE BEFORE CUTTING ONCE”. IF YOU DO NOT POSSES A FAIR AMOUNT OF TRADITIONAL WOOD-MODEL BUILDING SKILLS AND ADEQUATE WOOD TOOLING, YOU BETTER CHOOSE FOR A MORE PREFABRICATED KIT BECAUSE THIS (SHORT) KIT REQUIRES A LOT OF EXTRA LABOR TO COMPLETE.

TIP: This is the abbreviated build-log that was compressed from a very detailed one that I can mail you if you actually want to assemble the Jürgen Assmann Gö4-3 kit. Please contact me by replying or sending me a P.M. if you want the more detailed build-log. On this abbreviated log you’ll see behind some subtitles the number of hours I needed to complete that specific sub-item. Expect about 500 hours of working time to produce a scale-looking Gö4-3 from this kit

a) Inventory of the supplied short-kit

The compact carton (68x40x2,5cm) packed short-kit consists of 7 sheets of 3mm birch plywood containing 267 parts (mainly frames and ribs), and 4 sheets of 0,8mm birch containing 60 parts of complex-shaped planking and canopy frames. That are 327 individual marked very precisely and well pre-cut parts in high quality wood, a lot more than what I found in short-kits from other manufacturers, and also no problems for safe shipping. The engineering to fit so many parts on so few panels is remarkable. 3D drawings/pictures of the model with and without sheeting were mailed and those greatly facilitate the assembly because no assembly notice was available. Correct plans (one for the starboard wing plus elevator, and one for the fuselage and rudder, were received as two .pdf files. I had them printed in a local shop, two sheets normal and two sheets in mirror, the four sheets coming out in true model size. All that because I want to build each wing on the plan, and the fuselage and rudder are both built in two halves that are later joined in the middle, hence again the two required opposite fuselage plans to build on.

Pic 4746


b)additional parts required

As this is a short-kit, not everything is included and some parts and additional wood have to be purchased (locally) by the builder:
-Wheel 70-75mm diameter
-A 300gr GFK 18mm key of 60cm was delivered in its pre-cut aluminum wing tubing
-Three large 150x50cm sheets of 0,8mm birch plywood for fuselage planking etc
-One each 100x10 balsa planks of 15mm, 12mm, 10mm and 5mm half-hard balsa sheets for edges of flight control spars and shaping ends.
-Twenty 12x3mm (fuselage) and twenty 6x3mm (wings) birch stringers.
- 4m leading edge hardwood 15x10

Does that mean that all other parts are pre-cut? Unfortunately not, some important and complex balsa parts have to be fashioned by yourself, here is the list as I found out:
-Querruderholm=balsa aileron leading edge (30x12mm) spars and wing trailing edge (30x15mm) spars
-Horizontal Stabilizer=everything
-Elevator=all but the ribs
-Seitenruderholm=rudder leading edge spar and fairings
-Wing inner leading edges: 21x5mm 3ea, 20x5mm 1ea

c)personal choices

As my model will be finished in the colors of OO-SZC which was completely painted and had no clear dope covering visible anywhere, it allowed me to deviate when necessary from the see-through internal wing/tail structure. As I wanted the elevator assembly to be removable and I did not like to fumble with elevator connections on the field, I planned on installing two servo’s with minimal length linkage in the horizontal tailplane, with a single MPX connector to the fuselage. The rudder will use pull-pull cables from a servo mounted just behind the pilot seats. Like on the real Gö4, the ailerons are immense and deep, and after having heard from a famous model-tow pilot that most Govier models (irrespective of size) experienced problems of aileron/wing flutter under tow, I choose to use stiffened ailerons on multiple hinges and use two upper-actuators on each side (as visible on the pictures of the real Gouviers), all mounted free of play with four 9kgcm servos.

Most of the model was glued with Titebond original wood-glue but where extra strength or filling was needed I used Bison PU wood-glue. The model has a lower mounted towhook and uses 2S LiFe batteries with 8 High-Voltage servo’s all around. The mechanical spoilers extend top and bottom of the wing and a full cockpit interior was installed. To replicate the period (sagging) fabric I covered the model with Oratex and painted it with water based lacquer. Because of the large ailerons possibly scraping the ground, no provisions were made for operating from hard surfaces. It was not intended to compete in scale competitions but only used for fun-flying a historic model that is rarely seen in the towed model-glider community. This build log describes how that is achieved, but there are certainly different approaches that can be used to finish this CNC-based kit to the level you desire. The historic design inherently restricts the gliding performance of this model, you fly a Gouvier for the looks, not for performance.

d)Some tips and tricks I used

Living in an apartment with limited space, I choose to build the model on a dedicated 200x50cm perfectly flat wooden plate. The LHS (Local Hobby Shop) offered all I needed to make such an 18mm thick table held in shape by gluing and bolting two 45x18mm beams on the bottom. I kept the beams 42cm apart so that assembly can be either deposited on the living table, or saddling my organ support/work stand. The length and width of that plate were selected so it could be stocked vertically, pass under doors, and be suitable for most quarter scale glider model wings and fuselages. Edges of the plate were finished with iron adhesive corner material, screw holes filled out and everything sanded for splinter free handling.

The available 50cm width led me to cut the plans into portions that fit over the plate in order to build directly on them. With a bit juggling it was possible to cut the complete side views of the fuselage halves and top views of the wings to fit, the remainder of the plans could then be used separately for review but after the cut lines were drawn, I made sure to mark all the parts numbers on both sides before using the scissors. I thus ended up with many pieces of the plans to build the port and starboard wings, the stab and elevator, port and starboard halves of the fuselage and rudder.


Pic 4779


When gluing parts on the plans, I first lay down a layer of thin clear cellophane over that plan part for easier separation later. It remains in place over the plans thanks to the high static electricity.

Chapter2: Building the tail feathers

a)Rudder via sub-assemblies: 20 hours
I always like to start a model by making a small part to get the feel of the fit, the materials and the designer’s assembly philosophy. The obvious choice on this Govier was the port-half side of the rudder. When analyzing the plans for the parts it quickly became clear that the ribs have to be found on the 3mm birch sheets, the trailing edge on the 0,8mm sheet, and the top and bottom have to be made from thick balsa, 10mm for the top and a (probably composite) large block for the bottom. On the side of the rudder depiction on the plan are a side- and aft -view of the seitenruderholm 1/2 (rudder main spar half) that has to be carved out of a minimum 12mm thick balsa sheet, and 3mm indentations made as per plan for the ribs to grab into.

IMPORTANT: If you want the rudder to have sufficient throw, modify the bottom of the leading edge so it is maximum 4cm wide (in total). This means shaving a lot off the pear shape of the seitenruderholm (rudder leading edge) and cutting part of ribs sr7, sr8 and sr9 to obtain a slimmer result.

Removing the ribs from the plates is no easy task. The trick Jürgen showed me with one firm chisel impact on the remaining wood stubs works well on the 0,8mm wood, but quickly damages the lamination of the extremely narrow rib ends on the 3mm plates. Even the Stanley knife was too thick and I ended up using the finest modeler’s knife I had to separate the ribs from the plate.

TIP: Buy (or adapt) a square file so it has 3mm sides, this will be extremely useful in building this model, starting with the cutouts for the rudder ribs. I made both half-spars at the same time to have them completely symmetrical by sanding them in shape together. Do not sand the ends at this time, but do that later after the balsa fairings are in place.

First glue se-1 UNTEN and se-1 OBEN together (on the plan) and let dry. Pin the port spar-half on the plan, then dry fit ribs sr7 til sr14 into their slots and if necessary, sand till length and height are suitable taking into account the bottom has to be flat to be glued to the starboard half at a later stage.

TIP: For the (white) glue to strongly adhere on all model parts, I sanded away all the slightly burned wood from the part edges so the glue could better penetrate the to be glued surfaces .This might sound as an overkill but I I think it is worth the time and effort

Cut the top fairings out of the 10mm balsa plate and already cut/sand much of the desired taper away. After a last dry positioning for correct fit on the plan, glue the top fairings and all ribs onto the half-spar and immediately glue the complete SE-1 bow to all its supports, then use pins and weights to press everything perfectly level on your table. This last step is important to ensure maximum adherence when both rudder halves will be glued together. Whilst the port assembly is left to dry, all the identical parts for the starboard side can be prepared on the mirror-plan of the rudder (that is temporarily placed partly over the original for convenience.

Pic4781


The starboard sub-assembly can now be adjusted and glued the same way the port one was done. After drying overnight, both sub-assemblies can be pulled away from the protective clear cellophane sheet. Now carefully sand away any protuberances where the two halves have to be glued together. Also sand the inner trailing edges and rib tips as necessary to obtain sufficient adherence surface on both halves along that rather narrow contact line. Often check that both trailing edges meet without effort along their whole length, this might require more sanding of the inner ribs than imagined. Remove sr6 from the plate and use as a template to mark the shape of the lower part of the upper forward balsa block.

Finally joining both halves together is done by using slow-drying white glue that is liberally spread over all the common surfaces, then carefully aligning all parts and pressing together, blocking sliding movements by passing a few pins through and through, then using a lot of clamps to make the solid bond. For the trailing edge, use strong clamps at the rib positions and softer clamps for the wood in-between and let dry.

Pic4785



The plan mentions a Balsa füllklotz (solid balsa block) to be used for the bottom fairing but that seems expensive (and heavy) for a part that has no structural function. I made that part from a block of styrofoam, easier to replace in case of damage and lightweight (every weight saved in the tail means 3-times less ballast in the nose) and capped it with a scrap piece of 3mm birch ply and some Samba wood.

The plan depicts the bottom-line of that as a straight line while all the pictures of real Gö4-3 gliders show a nicely curved flowing line, a little more upwards from the aft-skid line to avoid damage on the ground and tail-first touchdowns. If making this rounded rudder bottom, you’ll later have to produce a tail-skid, that is not foreseen on the plan but pictures of real Gouviers show most with tail skids of various types.

b)Horizontal stabilizer: 5 hours

The horizontal stabilizer has no aerodynamic shape whatsoever and consists of a single-piece constant 15mm thickness assembly with tapering end fairings and none of the parts were pre-cut. I have no access to detailed plans but it seems to me that on the pictures of real Gö4-3 the tailplane appears thinner and more tapered towards the end. A detailed study of ALL plans was necessary before cutting any of that wood. With an already partly used 1000x100x12mm balsa sheet and a single virgin 1000x100x15mm balsa sheet, some serious thinking had to be undertaken to get the maximum out of these two thick sheets. I made the two 15x12 elevator leading edges and the thick part of the elevator fairings and the inner elevator anchor blocks for the control horns. I don’t think more than 2cm² was left of that 15mm sheet, it can be done but is very tricky taking the saw-blade width into account. All parts were laid-out over the plan and leading edge sides cut for the 15° wing-sweep angle.

Pic4789


I then glued the stab parts on the cellophane protected mirror-plan and used clamps because no slits had been foreseen for the fixed stab ribs.When sufficiently dry I added the partially shaped blocks forming the tips. Looking at the rudder and stab, they appeared very massive indeed. That might be the result of producing a solid model, but I couldn’t live with it and undertook the job of intense sanding to taper the tips-ends quite a lot towards all tips (instead of just rounding-off), and making as much of a constant radius as feasible on all leading edges. I later also tapered the trailing edge a bit so it aligned with the 12mm high elevators. For the wide 5mm ribs not to be so visible on the ground through the fabric, I sanded each at a 45° angle towards the top so only about about 3mm will be in contact with the Oratex material. Needless to say, to the dismay of my house cleaner, it produced tons of dust that put a layer over everything in the hobby room. All along I tried to continuously collect as much as I could and had to use a mouth mask to work, it had been a mess but the result was well worth the effort. Note the altered smooth curved wooden bottom of the rudder.

Pic4790


c)Elevators: 10 hours

As mentioned in the horizontal stab part, I had the leading edges of the elevators cut, but now had to make the incisions for the angled ribs to fit into them. The trailing edges are made of four 220x20x0,8mm laminated birch parts that are not on the pre-cut sheets. There is sufficient extra material left on the long edges of the CNC plates to produce those. For a reason still unclear to me, the elevators are made in upper and lower halves just as the rudder, but on a single common 15mm high leading edge. All ribs numbers are thus produced in four pieces with their thickest part being 6mm, tapering to less than a hair at their trailing edges. Although the CNC laser cuts were extremely precise with a bare minimum of waste wood, it again required a very thin knife to cut those 28 ribs free of a postcard sized 3mm birch plate. Thanks to the minimal-size holding-lips the job wasn’t too difficult, but sanding away the burned Laser marks on all surfaces of those narrow pieces is a job for masochists, especially along the hair-thin trailing edges. Here is a picture taken after the day-long measuring, engineering, cutting and sanding preparation work on all individual parts before starting any horizontal stab assembly.

Pic4787


After the straightforward assembly of the fixed horizontal stab, I reflected a complete day and night about the pros and cons of first building those elevators in separate top and bottom halves (on a common leading edge?), then join them together, or alternatively first glue all the half ribs to each-other, then build the elevators as complete left and right units. Whatever method you choose you will have to puzzle with scrap bits to get everything aligned, primarily because when assembled, the ribs are only about 12mm high while the leading edge is 15mm high, and both top and down half-ribs taper equally towards a middle placed trailing edge. As I could find little or no advantages in the former (kit-suggested) method, I went ahead with the alternate one. Gluing those tiny half-ribs together became a rather messy affair with my thick fingers. Traditional model builders better refrain from using I-Phones with sophisticated authentication methods, the glue on your fingers will prevent the smart-phone from recognizing your fingerprint, and a face full of sawdust and a respiratory mask don’t facilitate facial recognition either.

I again worked on the mirror plan and spent a lot of time dry assembling and correcting/sanding parts. The plan’s 5mm rib depictions cause the indentation drawings on the elevator leading edges to be totally useless, you’ll have to draw new indentations yourself and adapt some rib angles to the pairs sit together tight in their cavities. I then pinned down the bits that elevate the ribs 1-1/2mm from the plan, and the 5mm angled support strip under the bottom trailing edge capping. Only after that did I glue all the parts from one elevator together, taking care of the alignments and angles, and let it dry for a couple of hours.

TIP: Take advantage of the total symmetry of both elevators. When the first elevator has sufficiently dried, carefully remove it from the plan whilst leaving all the support pieces (pinned) on the plan.You can now assemble the second elevator on the same spot and supports as on the first one.

You can now glue the other trailing edge to the first elevator, using a straight supporting piece to spread the the force of the clamps evenly over the complete length. After some drying, sand the outer edge of the elevator completely flat and after roughly sanding the 15mm balsa tip block, glue it against the outer rib. Here is a picture of the works at that stage. To the left you see elevator two still supported by various leveling means, held in place by pins, and held flat by various weights. To the right is elevator one with second trailing edge capping still pressed, and the partly sanded balsa tip just glued in place. This is just organized woodworm chaos.

Pic4791


After completing the second elevator I let everything dry overnight before more sanding, this time to match the elevators to the horizontal stab and seriously taper/thinning the thickness of the assembly wherever I could. With the real Gouvier having a mediocre (but top in 1937) 1:20 glide ratio, I knew my model wouldn’t be the queen of the thermals, but by designing the thickness of the horizontal and vertical tail surfaces so thick just made things worse, hence my attempts of putting them on a rigorous diet through very extensive sanding. That could also help reduce the still unknown amount of ballast in the nose. Any blemishes in the surfaces and joints were then eliminated by sanding judiciously applied lightweight filler. Further work installing the hinges, control horns and servo’s could only be done after completion of the fuselage section, see details in chapter 5.

Continue reading on the next posts (published soon) or return to the resumé of all my build logs on https://www.rcgroups.com/forums/member.php?u=430882
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Aug 14, 2019, 11:10 AM
The sky is the limit
BAF23's Avatar
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Chapter3: Building the fuselage

The fuselage is built in two separate left and right halves that at a later stage are glued together. All parts are pre-cut and the final shape obtained by lots of 3x6mm stringers. After that, the entire fuselage is planked with 0,8mm ply sheets before finish is applied. The exploded views offered by the designer are very useful to help in developing an assembly sequence.

Pict rumphhalfte lexpl


VERY IMPORTANT: Neither the plans nor the CNC machined parts have any incidence on the stab angle. Flying it that way is possible but highly uncomfortable (read my maiden flight report for details). I experimentally found out that a whopping -3,5° angle is optimal for the horizontal stabilizer so it is imperative that the aft fuselage at the stab seating is modified during the build to either lower the front or raise the back of the stab to achieve that angle.

The large side by side cockpit is very visible through the greenhouse but by model-design philosophy, the fuselage cannot contain a scale cockpit interior unless important modifications are made to maintain structural strength. For those interested in a detailed interior, the major alterations I made are described in this build log. If you are happy with an empty cockpit with eventually only pilot heads and a completely fake instrument panel, just follow the plans and use the original parts.

a)Nosecone: 2 hours

The nosecone is built-up from 34 arches of 3mm birch-ply, all to be found on one plate spread in-between larger parts. I slowly got more proficient in getting them out of the sheet. The parts were a few mm too small but if not corrected on your kit, use heavy polyester putty/filler and sand to shape AFTER FUSELAGE HALF JOINING.

Pic4807


b)Main fuselage skeleton: 19 hours

TIP: Start by removing all required parts (rh,rr,rf, rs,rl,sr,r) from their support plates and group them into separate piles per denomination, then separate them in left and right sides, then sand blemishes and burn marks away where they have to be glued. That will keep you busy for a couple of days. Some lips were larger than my 6mm chisel and were difficult to cut without damage to the parts. If still pre-cut, do not remove the lower of the 4 lightening holes in rs17 but instead, glue it firmly into place for solidity. Don’t look for rr2,rr4,rr5,rr7 because they don’t exist as they are part of the frames

VERY IMPORTANT: if your plans and rh4 parts show straight angles at the back of that part, modify the shape for the seating of the stab to be at a 3,5° angle. The back needs to be 6mm higher than the front to obtain the necessary “decallage” setting between wings and horizontal stabilizer. At this stage I also suggest you to narrow the width of rs18 at the bottom so it conforms to the width of the narrowed leading edge of the rudder to allow free movement of the latter.

Because of the way the plan was printed, you better start with the port fuselage-half sub-assembly. Start by laying out all the rh contour parts on the plan. There are numbers on their sides that indicate what joins with what, but these are not needed because all the different shapes don’t even allow mistakes in assembly. This is the time to decide if you want to build a model with realistic cockpit or just follow the version that model-designer Assmann has pre-cut but has all kinds of wood crossmembers obstructing the cockpit just below the canopy line. As I choose the former I’ll guide you through my solution attaining that, but it requires extra work and manually cutting new parts from scrap wood.

On the prototype wood-sheets there were a couple of identification mistakes and even essential parts missing, but those shortcomings will hopefully have been corrected after my feedback so you won’t be bothered by that. I did not want the rh5 and rh12 parts to be so obviously visible through the greenhouse, neither the crossmembers of rs6, rs7 and rs8. Just omitting all that would seriously weaken the structural integrity of the nose of the model. Modifications had to be custom made to compensate for the eliminated parts. Here is the sequence of how I did it but I’m sure others could come up with different solutions.

TIP: When gluing the contour frame on the plan, work very meticulously because any millimeter deviation will have to be corrected by filler or sanding after mating both fuselage halves and seriously complicate matters.

Completely eliminating the aft part of rh1 and the majority of rh2 would drastically increase the risk of the forward fuselage breaking-off in case of rash tow-forces, hard landings or even mild crashes. As I already ordered a scale instrument panel from www.scale-cockpits.at and that is to be placed well inside the fuselage as can be seen in following picture of a real Gö4 cockpit, angled panels rs5 were reduced to simply their 1,5cm outer arch resting against whatever is left of rh1 at that spot. Frame rs4 got augmented by a new part that will fill the space where the instrument panel will be screwed into.

Pict go real pic 11



Frames rs6, 7 and 8 were doubled up (along the outside arch) against the original to increase lateral stiffness of the cockpit sides, and their cross-members temporarily kept in place to attain the correct shapes and angles during gluing. As I always add pilots to my cockpits, these will certainly touch shoulders and legs in the middle of this cramped environment. This allows me to construct a central almost invisible solid brace-strut between wing key holder and the foot-well behind rs3, to effectively replace the lack of the middle-placed rh2 compression member. I fabricated it in in the same 3mm ply (from a remaining bottom of a CNC plate) with a width of 18mm. The two identical plates will be glued against the surrounding contour parts on each fuselage half and will most likely disappear when flanked by both pilots. rh2 is then cut leaving only the aft vertical short section in place. The main section is not to be thrown away because it forms ideal reinforcements for the cockpit sides just under the canopy. After ensuring that all V-joints of the contour parts are free of burned wood, all these parts can be glued onto the plan including the fabricated compression strut.

Pict4802


I started on the tail again by gluing rs16, 17 and 18 in place. I had to lengthen rs16 by inserting a 4mm part in the middle so the bottom comes level with the lower end of rh7, check that and eventually adapt or you’ll have trouble bending the lower stringer later. r1, 2 and 3 were then glued in place together with sr1 to sr6. The 5x8mm balsa capping of the leading edge was only installed much later in order not to damage it during the works.

The plan calls for assembling frames rs8, 9 and 10 together with wheel box rl 1 and 2, at the same time the r4 wing key boxes are glued. That are a lot of pieces for one go so I went in stages and first glued the two r4 parts to frames 9 and 10, with the alu wing key holder in place to be sure it would fit when dry. Clamps were used to secure that very important process. In the meantime I had dry assembled the other parts and noted the rl 2 spacer to be 3mm too wide. On the other hand, if the wheel support was glued into their pre-cut slots, total width of the box would only be 26mm. The original has balloon wheels and I had a 76mm (the maximum possible tire diameter) aluminum wheel that, although no balloon tire, was 28mm wide. I decided not to cut the rl 2 top of the box, but to widen the slots for the lr 1 wheel lateral supports by 3mm. After filling the old 3mm slot with scrap wood, I expect to have a 35mm wide wheel box, sufficient to insert my wheel with inside spacers/axle blockers. Those 3mm ply lr 1 axle support plates looked flimsy to absorb no-suspension hard-landings or accidental side forces. I therefore decided to double-up those plates by gluing an identical plate to the outside of the original, and sanding the front and back to reduce the drag.

Pict747


In the meantime the sub-assembly had sufficiently dried and formed a solid square box to which the wheel box could be glued, including to rs8. All this could now be glued in one go to the contour plates including my custom crossmember against the wing key tube assembly.

TIP: Frames rs11 and rs12 were then glued in place, and wing rib rf 1 dry positioned over all five frames so as to maintain everything aligned and perfectly square during the drying process. Be sure to glue the fuselage frames with their OBEN marks towards the top of the fuselage. Watch out for rs15 that has no marking but has to be installed with the widest flattest portion towards the top.

A few hours later rf 1-upper and rf 1-lower were adjusted so they fit snug against each-other before also gluing them in position using clamps. I then duplicated the arches of the frames rs6, 7 and 8 and glued them firmly to their originals to increase fuselage lateral strength. rf2 was then glued into position after which rf4 and flared arches rr1 to 12 could be glued in place.

TIP: check all rr parts if the openings are sufficiently wide to accept the 6x3mm fuselage stringers without glue and ensure all rr parts are aligned. Modify as necessary before gluing because once they hang in there it is extremely difficult to adapt them. I found it easier to glue rr 1, 3, 13, 14 and 15 in place after their stringers were installed.

When that had dried and had been sanded flat, rf3 was glued directly on rf2 to cap the hole assembly. All forward frames and the nose where then glued in position together with the remaining arch of what was once rs5. With the horizontal cross-members of rs6, 7 and 8 still resting on the plan, I slightly adapted those parts so the discarded rh12 could be glued to them to form a new cockpit side structure.

TIP: builders who are incorporating the modifications for the more scale cockpit are encouraged to duplicate the altered parts for the starboard fuselage at the same time because once glued into position, it is more complicated to duplicate a part than to just put them on top of each-other and copy the desired lines. Keep in mind that the custom reinforcement will come in a mirror setup, so the sides being glued together have to be watched carefully.

The first 6x3mm stringers can now be glued in place along the upper fuselage, these are one-piece things that go in easily. The two lower stringers are more complicated because none are sufficiently long to install in one go, and the curve that has to be achieved between rs1, 2 and 3 is more than can be achieved by just forcing them to bend.

I started from the tail and cut them at a slant angle between rs9 and rs10. Due to the adjacent wing key, the fuselage is very strong there and I thought of it being the ideal spot to join stringer parts. Before gluing, alterations had to be made to lengthen 16 by 4mm at the middle, please verify with dry assembly. I then made the remainder front part of those long stringers, together with all the other forward short stringers and let those all 8 soak for a couple of hours in hot water. That made them sufficiently weak that I could bend one end (of all those stringers laying flat next to each-other) into a relatively tight curve by using weights and other unorthodox support means.

Pict4804


After drying overnight, the stringers maintained their curves and before they had the chance to straighten out again, I glued them in place using loads of temporary clamps. The long stinger just below the wing was impossible to lead into the foreseen grooves to the nose because you just cannot make bends in the wood in both directions. I let those run straight forward towards the rs1 nose groove intended for the next-up stringer and adapted some enroute cutouts. I also let that short stringer go straight and adapted those grooves as well. A short extra stringer filled-in the void just below the displaced middle one. When everything on the nose had solidified I used a belt-sander to follow the stringer contour lines along the nose and already eliminate some of the excess nosecone material. It became clear it was going to need a lot of filler to get from this to a nice flowing nose shape. The straight horizontal crossbars of rs6, 7 and 8 were then cut off. Here is a picture of that week of work, along the plan on which all prototype problems were noted in red, and the alterations for the cockpit room and suggested gear well in green.

Pict4805


For the ones who don’t understand the thousand words about the changes done to obtain a usable cockpit space, here comes the picture of that area taken from the middle (inside).

Pict0748


c)Further fuselage preparation work: 22 hours

It took me only 11 hours to assemble the starboard fuselage-half to the same skeleton stage. The wing salmon construction was then continued on both sides. The front highly curved rr16 strips were installed one by one on the model. The thin individual strips are sufficiently flexible to more easily be squeezed into the openings of rr8 to rr12. 3 curved strips glued one on top of each-other were sufficient to close the gaps. With a clamp around each rr rib, the built-up front wing-salmon bow looked very good.

Pict 4811


With both half fuselages at the same stage I undertook some serious sanding to obtain perfectly flat surfaces where they have to be joined, and smooth contours everywhere else. The dreaded moment of the first dry assembly came and I slipped the aluminum carry-through wing key holder through the opening whilst slowly mating the fuselage halves. Note that there is still some fore aft play between both so to get the wings square to the fuselage, the halves will have to be carefully glued and held together. Same for the yet not torsion-free vertical stab. I therefore fabricated a foam jig where the model is supported by the wing key and in which it can be mounted right-side-up or upside-down, the tail being kept centered and vertical at the end. I fabricated it oversize so it can hold any of my gliders and also balance them because my Sig balance limits in width and weight couldn’t handle my larger/heavier gliders. It also proved its use for first painting the underside, then turning the model around in the jig and continue straight with the topside joining both before the paint dried and thus having no traces of paint joints.

At that point I had to make a major decision. Although the kit designer suggested me to first glue both fuselages together before planking the lower and then upper half of the fuselage in the jig to avoid any torsion during the process, I looked at the model and its complex shapes plus the limited ways in which the 0,8mm birch ply planking could be forced to take the required shape, and decided to work the other way around.

I reasoned that by keeping the half fuselages flat on the plan, each half could be largely planked separately in-between the highest and lowest stringers, using weights, clamps and elastics where necessary. The thus already more rigid halves could then be mated after which a top and bottom planking could then cap the joints whilst in the jig, adding solidity and structural stiffness.

TIP: This method can only be used when the building is compressed in time. Allowing too much time between partial planking and joining halves will result in fuselage distortion (due to the curved wood trying to straighten itself again). If done in a week or two, mating both halves should be relatively easy and result in a perfectly straight fuselage

As usual I wanted to start by the tail but realized that after planking the vertical stab I wouldn’t be able to make inside reinforcements for the rudder hinges. The way that stab was constructed in two halves also prevented the installation of hinges in the middle unless the structure is locally seriously weakened. I had offset hinges in my stock but those wouldn’t have looked good/scale through the wide gap necessary to allow sufficient rudder movement. The much too wide bottom (4,8cm) of the rudder seriously complicated things and I sanded its width down to 3,6 cm (at the same spot r18 was sanded down to 4,8cm down from 5,4cm). As that took away some material from the sr8 ribs, I added an inside hard-wooden crossmember that also serves as anchor point for the pull-pull control horns. For strength I used 4 of the large variety of Dubro pin-hinges, through holes in the middle of the rudder, but on the stab size drilled into rs18 just along the rh6 middle beam. The hinge-pins were then glued at an angle in the stab so their pivot points end-up at center-line. Balsa support blocks were also added in the rudder, but not as wide as to disrupt or be visible through the future fabric. On following picture you can see how I achieved those results, the funny part on top of the picture is the rudder beam with the top at the left and the too fat bottom on the right, see how much material I already took away on one side of it.

Pict 4818


I also got puzzled on how to fix the horizontal stabilizer stab to the fuselage. On some gliders the stab is just lowered on the fuselage and bolted with some vertical screws, the electrical connection taking place at the bottom with a green MPX plug. On the Goevier the back of the stab slides in a cutout at the base of the vertical stab and a wooden horizontal pin (dowel) keeps it in place there. The front is then bolted to the kind of platform by a long nylon M6 screw. As the MPX plug had to connect to both elevator servo’s, their position had to be pinpointed first. That in turn was depending on the control horns and hinges so a lot of juggling was done before cutting and installing everything after a lot of modifications. For the elevators I used 4 medium type pin-hinges per side and installed them along existing ribs in the stab and elevator, or in the plain balsa plates. For the control horns I used the nylons with sandwich plates held together with long screws. The plates were first countersunk in the elevator balsa spar which had been penetrated by thin-CA glue to solidify those areas. I then had to cut through the first stab ribs to allow the 10mm thick 7,9kgcm torque servo’s to be installed. I used the extra balsa around the hinge pins to serve as attach point for the servo’s. Other custom plates were installed to accomplish the task, including a 0,8mm ply servo cover-plate for maintenance access. I choose for a relatively aft position of those servo’s to allow sufficient space for the wiring to the forward MPX plug, and to keep the distance short to the control horn so I could use light 2mm adjustable pushrods. Results of that can be seen on the previous picture.

It became clear that with the weight of the model, a lot of lead will have to be stuffed in the nose for balance. I still wasn’t happy about the capabilities of the central fuselage to absorb landing forces by just the wheel box along the lower spar. The inertia of the lead in the nose and weight of the wing could easily crush everything together and pull my new forward compression apart. I therefore glued additional vertical and slanted reinforcements between the front and aft of the wheel box and the wing key box (compression), but also side plaques at the front and back of my compression strut to prevent it from separating when the lead pulls the nose down during touchdown. Many of those parts were also added at positions which will be helpful to serve as strong-points on which to attach servo’s (for which no provisions were made on the drawings or in the kit). Here is a picture of the works at that stage.

Pict 4817


d) Towhook and Rudder Servo: 23 hours

Because it is much easier to install extra stuff in the fuselage with the halves still open, I Decided to install everything including the wiring in the port half. I first looked for an adequate position for the towhook. Pictures of the real Govier show them on the lower middle of the nose but on the model I was afraid this assembly could separate too easily from the rest of the fuselage with a strong pull. I also wanted to reserve all the space available in nosecone for lead that would be poured in after fuselage mating. I therefore elected to install the hook mechanism just behind the nose, along the lower longitudinal rh10 frame. In order to spread the load even more, I glued an additional part that also bridged rs1, 2 and 3, then made a groove in it to accept a medium strength commercial towhook which I glued solidly into place using small hardwood filler blocks and liberal amounts of PU glue. For both hook and rudder servos I used Pichler High voltage digital 3615 servos with 9kgcm torque. Both were mounted on hardwood blocks that were in turn glued to the additional frame reinforcements I previously installed. The for and aft positions of the servo’s were chosen not to infringe cockpit pilot space, but still allowing access for replacement in case of servo failure. The hook was then connected his servo arm by threaded 2,5mm wire with kwik-links on both sides. The completely slimmed down rudder bottom was then machined to install fully countersunk ball-joint control horns that at a later stage will be filled by lightweight putty and connected by pull-pull cables to the central mounted rudder servo.

Pict 4822



Continue reading on the next posts (published soon) or return to the resumé of all my build logs on https://www.rcgroups.com/forums/member.php?u=430882
Aug 14, 2019, 12:13 PM
The sky is the limit
BAF23's Avatar
Thread OP
e)planking the fuselage halves: 66 hours

As already mentioned, the entire fuselage had to be planked with 0,8mm birch 3-ply. This was chosen by the designer because it is strong and less than half the price of the 0,4mm plates. It also can be sanded a bit to eliminate imperfections at the joints. Although more difficult to shape, it doesn’t break as easily as the thinner variety. I decided to start with the most difficult aspect, the tight radius fuselage to wing fillets. It was obvious that just brute force would never be sufficient to bend the ply in such short radius. I first experimented with leftovers of the kit’s 0,8mm ply and first soaked them in water for half a day. I was disappointed that they didn’t really become flexible but using rubber bands, a bottle, pincers and other methods I was able to seriously bend the parts that then were allowed to dry and settle overnight. When let free, the parts slowly straightened out again but by rapidly gluing them in position using lots of pincers to force them into the correct shape, I was able to do almost the full length of the straight intrados in one go.With that knowledge I started cutting strips for the rest of the wing-fillets and proceeded the same way.

Pict 4826


The need for many tools to keep the parts in place and shape during the drying limited me to work one strip at a time. I used PU-woodglue because that solidifies in 4 hours time and expands to fill the space between the kit’s support wood. In order to provide solid joints with later installed fuselage planking, I measured, cut and glued pré-cut panels so they grabbed halfway the fuselage stringers, leaving the other half for the adjacent planking to be affixed to at a later stage. Before the expanding glue solidified, I used a sharp knife to eliminate excess glue so the next panel would fit shoulder to shoulder, good for both strength and flowing lines.

Pict 4823


The extrados fillets were more complicated because besides the sharp radius between fuselage and wings, the planking also had to curve along the upper wing curvature, a nearly impossible feat. On the port side I attempted forcing the process by letting the long strip dry overnight on the model (without gluing), held by many various tools. This proved not to be a success because the supporting ribs became very visible and the smooth shape got disturbed. I used the material’s tendency to stretch back to regain some of the desired shape before gluing it, but it nonetheless was not smooth anymore. That was corrected by lightweight filler at a later stage. I did the starboard side in a shorter piece and that worked out better. On following picture you can see how I pré-bend two soaked pieces on top of eachother around a rod (just resting on the wing fillet) and using clamps overnight to allow tight curve shaping. The parts were then further cut to shape so they would sit right next to eachother before being clamped on the model during gluing (visible at the front of the wing fillet).

Pict 4830


There was no way either the leading edge or trailing edge extremities could be fabricated the same way, so I used scrap balsa to fill those voids and when dry, roughly carved them into shape with a sharp knife.

Pict 4828


Final shaping was delayed till the adjacent fuselage planking was also in position against the balsa. All this sounds very time consuming and it is, it would be much better (faster and lighter) to have those wing fillets formed in plastic or even just canopy material because they have no real structural value and the inner wing rib structure detracts from the scale cockpit aspect. The real Govier had those parts in resin-impregnated jute to provide more shoulder and elbow space for the occupants, all of 91cm width for two cramped persons! Just fabricating and finishing the wing fillets took me 20 hours.

The rectangular shape of the wing root planking allowed me to relatively easily cut a paper pattern around it and that served as a template to produce two large ply parts that allowed me to plank both aft half-fuselages in one go. There were no tight radius curves but as different parts of the plank had different curves, pré-shaping was done differently. The cut wood was soaked overnight, then clamped to shape without glue over the fuselage frame whilst drying out. Here you see the one plate clamped dry with the one for the port fuselage still straight. Both are dark because still soaked.

Pict 4835


After drying overnight I removed all the clamps and applied white glue to all the fuselage frames it would contact, then carefully aligned everything before clamping it again. In order to press the planking shoulder to shoulder against the previously made wing fillets I made a construction with six-packs (yes that is non-alcoholic beer) to keep everything firmly pressed into place. I used tools and other weights at judiciously selected places to ensure frame and planking could bond strongly along the maximum possible surface. On the other hand, all that weight also ensured the fuselage halves remained perfectly flat and could not warp due to the curved wood trying to regain its natural straight shape. Note the gluing was only started when the wood was pale again showing it was completely dry.

Pict 4839


After doing both aft fuselage halves I again used paper to figure out how to plank the front halves. Those curves were much more pronounced and in both directions, meaning I would have to work with narrower strips. I managed to find a way to cut a one-piece part that filled the center-section from the nose till the wing in one go, but with a slit to allow pinching it at the front.

Pict 4840


I made the slit coincide with the extra crossmember that I added during the initial fuselage frame assembly. This now provided adequate support at the right place to keep everything in place using many clamps and tightly placed rubber bands to press at strategic spots. Of course I kept the outlines of those planking parts by drawing them on the back of the plans. It took me time to figure the correct shapes and that had to be kept for possible future use (by other builders)

Pict 4841


When those large parts had dried I drew the adjacent up and down panel. The lower being rather long going from the nose till aft the wheel well, already fully closing the latter. The upper panel is much smaller but curves a lot in both directions. When the four panels had been cut out and soaked in the bath, I used a bottle, and after the neck a smaller diameter spray-can, around which I strapped those panels with a lot or rubbers to help them attain the double curvature.

Pict 4842


TIP: In the end I discovered a better solution to get those double curves pré-formed. Find a carton tube normally used to ship rolled-up plants and place the wet wooden panel along it, but at an angle. I used about 30° so the major bending would still take place around the circumference of the carton, but a secondary bending also occurs along the warped length of the wood. Off course everything is let to dry overnight with many rubbers holding the wood tight around the carton tube. The resulting warping of the piece is easily eliminated when putting the part in position on the fuselage, the part now conforms much better to the required double curvature without having to force it so much. A pity I only discovered that so late but it came to use again when preparing the parts to cap the nose top and bottom after fuselage-half mating

Later gluing to the fuselage proved a real challenge, not only due to the curves, but also because the adjacent panel prevented me to use a row of clamps. I therefore used pieces of scrap wood that were forced to hug the contour shape while fastened by a single clamp on each end. Care was taken to position that beam just inside of the joining line so it wouldn’t attach itself by excess glue spreading when pinched so strongly. The smaller top parts had to be further cut in length, then the joint sanded in a bow to allow it to take the plunge at the nose. Failure to do so would end up with the panel taking the plunge, but without any remaining side bow, later requiring lots of filler and sanding to look curved again. All this was tedious work I really wasn’t fond of, and probably would be the most difficult job of the model.

At the completion of that stage it was tempting to just join both fuselage halves but some other things could still be more easily performed before the mating. Because the interior was going to be visible through the canopy, I found it important to have a better finish of the visible interior if the wing fillets, especially at their leading edges. With everything solidly glued into position I was able to shave a lot from the too prominent rr6 to rr12 guides. With balsa already filling some voids, the rest was filled with lightweight filler to obtain a semblance of smooth elbow room. I also cut a substantial part of the rs8 rib inside the elbow room. That was possible because I previously had doubled-up that rib to strengthen it. A few coats of filler were necessary to obtain a result I could live with.

Pict 4844


TIP: I then cut the openings for the rudder pull-pull cable sleeves but didn’t install them yet because it would seriously complicate sanding of the primer.

Both fuselage halves where then dry assembled using the aluminum wing key sleeves as a anchor point. That is the moment you will discover how well you built those halves on the plan, especially regarding the straight angles of rs9 and rs10. Any minimal deviation during the build would now cause major misalignment of the fuselage halves. Failure to keep the fuselage-halves strictly flat against the plan outline during the build and planking could also cause serious problems at that stage, but my precautions had worked.

That is also the moment to insert the long wing key and position the dry assembled fuselage along a square grid to verify if ALL square angle between fuselage and wing (key) can be attained without forcing. In my case I had to take away a little over a millimeter at the base of the fin because I hadn’t aligned rs18 perfectly square during the initial gluing. I also seemed to have more than a millimeter misalignment in nose length, one more reason not to sand the nose too early during the fuselage build.

I then made the holes and cutouts for the wing connectors. Although that is done by the wing key and a 4mm rod at the back, I also had to drill a 6mm hole throughout the fillet assembly to allow passage for the locking screw and backing plate on f1 rib, plus carving out room for the Multiplex plugs in rf2/rf3 and f1, the latter being just aligned over the wing key for positioning, taking into account the gaps in the f2 rib. It sounds simple, but took me a hole day to get all that done because I wanted the MPX plugs on the fuselage side to float to take care of movements and allow insertion without forcing. That had to be carved out from the 6mm thick double fillet-endplates, a job that would have been infinitely more difficult to perform after fuselage mating. The male MPX plug on the wing side had to be firmly glued into a tight conical custom opening in f1 (preventing it from being pushed further into the wing), exactly across the female embedded floating plug. Wires were soldered onto the connectors, resistance measured, then liquid rubber poured around to eliminate any risk of shortcut, then labeled for future receiver connection. Everything got dry assembled again, including the rudder because this was the best moment to fashion the pull-pull cables and attach everything to the servo to decide and fasten the pivots to obtain the correct throws. The two fuselage halves were about ready for mating.

Pict 4845


e) Interior and mating of the fuselage halves: 24 hours

When preparing for mating I had a try fitting pilot figures in the fuselage. The light foamy one that I had in mind didn’t work because the legs were too wide to fit in one half. The Hangar 9 Piper Cub pilot fits in perfectly and looks period after removing the may-west and the funny flying helmet. He fills his side well and just needs a little butt cushion for correct height. For the other pilot I removed the back-seater from my Blanik, after all those years the front seater can fly solo now. That modified Graupner pilot resembles a bit Mr Jürgen Asseman so as a tribute to the model-designer he’ll fly constantly in his Gö4-3 (as he did for real decades ago). For height he needed a seat so I first cut 3mm balsa for a cockpit floor, then glued another elevated wooden plate to form a base for the pilot’s butt to sit on, but equally to provide a convenient room for the receiver. I then also cut scrap 3mm ply to make a battery box to fit in the nose end and serves as a solid base to which both 2S2800 LiFe batteries can be blocked to.

TIP: When those extra-interior parts had cured I applied the standard gray paint in the entire cockpit because some places later would be extremely hard to reach after fuselage mating

Next morning the postman brought the 3 instrument panels I had ordered 11 weeks before in Slovenia. Unfortunately they mixed up my order and produced the one for the Foka to scale 1:4 and the Gö4 panel in 1:3 instead of the other way around. There was no way I could modify it to fit in-between the fuselage confines and I sent both back by post. Here you can see the pilots in their respective seats and the much too large but nice instrument panel in place.

Pict 4848


Last job before mating was to produce and install the power wiring. Because those old heavy (500gr ballast) 2S2800 LiFe batteries still have Deans plugs that are used in some of my other older gliders, I choose to glue Deans plugs in the side panels of the battery box. After the batteries are pushed in and plugged in, they can’t physically slide out anymore and everything will be hidden behind the instrument panel. The individual wires were then routed vertically down the starboard side of the cockpit, then under the floor to pop up under the pilot seat where I soldered them to a couple of two-way switches that I installed in the middle of the seat between the pilot’s thighs. That is almost invisible and easy to operate. I glued an extra dowel between the pilot’s crotch and the switches to prevent accidental operation during rough movements in the air. From there the wires were soldered to a Schottky diode from which a single wire feeds the receiver with 2S voltage. To me this is as redundant as the more expensive powerbox systems. To me, the less components are installed, the less chances of one failing. I made some sticks that were glued through the floor onto the traverse beams but without the correct instrument panel that concluded the pré-assembly possibilities.

The day had come that I found no more excuses to further delay the feared mating process a the end of my building method (that had been discouraged by the designer). Everything was checked and double checked because the gluing of both halves was definitely a point of no return. The curved planking on the sides sure had distorted the straight lines a bit, but because it was symmetrical along both halves I had no fear that my fuselage would end up as a banana. Most junction areas could be easily brought together but at the nose this required serious pinching, no wonder after the efforts I had made to force the planking around the bends. I initially toyed with the idea of first gluing together everything behind the cockpit and only when completely dry, join the front ends together. That would cost me an extra day and applying glue to the front wouldn’t be easy through the remaining openings, so that idea was discarded.

The Titebond white glue that I work with has a relatively short open-air dry time, and when parts are pressed together the initial grasp is very solid allowing little to no adjustments, but the recommended time before pulling is a long 24 hours, plus the glue requires direct contact with both pressed surfaces and doesn’t fill voids. I therefore preferred to use the (more messy) Bison PU wood-glue that cures rock-solid in about 6 hours, but allows you to make easy adjustments during the first half hour, and it even fills serious gaps through expansion. I readied my arsenal of pincers and clamps and applied a uniform layer of glue to only one side, staying away far enough from critical spots where the expansion could cause jamming of the rudder hinges or towhook. I then inserted the aluminum key sleeve through both fuselage halves but kept them still separated by a few centimeters. The model now stood stable upright on the wheel supports and tail bumper.

Making sure nothing got jammed (like wiring looms, battery box or elevator blind nut), I slowly joined both halves with the tail part touching first. Here I used clamps to secure the vertical tail-halves, playing vertically and horizontally to obtain the best possible match. I then used stronger tools to symmetrically slowly force-join the elevator platform and bottom of the tail(skid) at the same time. Next I worked my way forward by using pincers along the spine, then closed the gap at the keel with even more pincers. I then forced the top of the nose curve together slowly working forward. I didn’t care the nose wasn’t a perfect match, that could be corrected later by polyester filler and sanding. Closing the forward keel didn’t require much force but all those clamps now prevented the fuselage from drying in an upright position. Because the glue already started expanding at the back, I used a rag to collect the excess glue before it dripped too much or caused harm to finished surfaces. I let the glue cure for 12 hours to make sure nothing would split anymore.

Pict 4851


After removing all the clamps I was very happy to see my fuselage was straight as an arrow, with no visible gaps except along the non-structural cockpit floor. I put some cellophane on the cockpit floor and allowed glue to flow between the extra cockpit brace strut. I voluntarily omitted that first because the necessary clamps for the rest of that space stood in the way to clamp that central beam at the same time. My gambling at producing and assembling the fuselage this unorthodox way payed-off. The earlier produced jig had not been necessary but was later used during painting.

At that stage the fuselage weighed 1726gr and was seriously tail-heavy. I didn’t know yet how much ballast would be needed but with a model built as a tank (very little balsa but very thick birch-ply) it will be a serious amount. The more forward the ballast, the less you need. I therefore hung my model vertically on its nose and used a funnel to fill the entire nosecone with 375gr of air-gun steel balls. I then slid a long straw over the tip of my PU glue container and guided the process to uniformly spread the bonding. You do not want any of those metal balls to come free and jam the hook mechanism or create a shortcut in your electronics.

TIP: (Gu)estimating the glue quantity is difficult, but halfway the balls is the aim. That glue expands so much it will engulf everything, also the forward fuselage frame and spine, creating a rock-solid nose that won’t fall-off at the first hard landing. Care has to be taken not to allow the glue to expand in your hook mechanism space.
Here is a picture before the expansion process started.

Pict 4856


The expanded glue also forms the forward wall against which the batteries rest. With those in place, the fuselage weight already rose to 2650gr and it balanced (without the tail feathers) on the wheel supports.

TIP: Before completely closing the fuselage I used the bottom voids to maneuver another 375gr of lead plates in-between the nosecone and the hook-servo, both left and right of the keel.

I then cut the ply planking strips to the exact shape needed to fill the remaining spine and keel voids. After a few hours of soaking in the bath, I wound the long ones for the back of the fuselage around aligned carton tubes and used lots of rubbers to force them take the shape. The aft bottom narrows much but requires a tight radius, that was obtained by sliding a piece of round plastic till halfway between the carton and wood.

TIP: The wood for the forward fuselage needs double bending so I wound them at a slant angle along another carton receptacle, the more angle, the more double curve.
Ps: any whisky container boxes work fine, I just love the Laphroaig taste...

Pict 4857


The wood was allowed to dry overnight before it was released one by one and immediately glued to their position before they had the time to straighten out again. I then glued them into place using rubbers because clamps could not be used anymore.

Although the fuselage was entirely planked, it still had to be plastered and sanded when I took a week of rest in the form of a ski trip to Italy with friends, I think I deserved that break after working more than 3 months nearly non-stop on two large gliders, the fuselage of the Gö4 already necessitated over 200 hours of labor, not including final shaping, canopy nor finish.

Pict 4862


Continue reading on the next posts (published soon) or return to the resumé of all my build logs on
https://www.rcgroups.com/forums/member.php?u=430882
Aug 14, 2019, 01:43 PM
The sky is the limit
BAF23's Avatar
Thread OP
Chapter4: fuselage assembly and finish: 79 hours

Upon return from holiday various other occupations prevented me from swinging into full build rhythm. Applying filler layers and allowing to dry before sanding also slowed the advance. I also spent some time on the rudder getting everything aligned and flowing over from the very wide fixed to the (now) thinner movable part of the vertical stab.

TIP: I made a solid tailskid with scrap ply saddling the keel, that was necessary because without that higher skid, the rudder of the model on its wheel would touch the ground.

With the arrival of the correct size scale instrument panel I looked for a way to fix it in the cockpit. Most important was to be able to change batteries with the pilots in their seats. The only solution was to add a few plates to the front-sides of the battery case, to which Velcro could be affixed. I also had to remove some useless plastic from behind the instrument panel so an extra plate could be glued to affix the other side of the Velcro. That done, I touched-up the paint of the cockpit interior and while drying, covered all tail surfaces with Oratex. A liberal coat of white primer was then applied to check the seams in the fuselage and protect the Oratex surfaces during further finishing. The first sanding showed that the attained shape looked good with very few depressions.

TIP: Before applying the second coat of primer on the fuselage (none was needed on the tail feathers) I wanted to get the moving surfaces attached with their hinges and pull-pull cables connected. I therefore elected to first paint those fixed and moveable tail surfaces before gluing their hinges.

The paint I had ordered was then rolled-on but quickly proved too dark, more of a mustard color instead of cream. I hoped it would get paler during the drying but that didn’t happen. There are no color pictures of the original aircraft but a text describes it as cream and light blue. As most surviving Gouviers in museums seem to have a pale cream such as often seen on German taxi-cabs, I ordered a pot of RAL1015 and hoped for the best. No way to get new paint on a Sunday so I just applied a second thick coat of primer to the rest of the fuselage and started painting the pilots a bit. Hopefully the blue resembles the Sikkens concept 1041 color S3.56.42.

Pict 4863


The pictures of real Gö4-3 show that except for the ailerons, the control surfaces show huge gaps at the hinges. For that slow-speed training role, aerodynamic efficiency had not been a major concern. This came in handy connecting the rather thick movable surfaces to the fixed ones whilst still allowing sufficient control throws. With the overall painted model inverted in the jig, I glued the rudder (hinges) into place and when dry, attached the pull-pull cables and glued the guides in the aft fuselage. I did all that through the minimal access I had left around the tailskid so it became time to cover that opening too.

TIP: That shape was so complex and curved that I even didn’t attempt using ply. Instead I glued scrap 10mm balsa blocks which were then roughly carved into shape with lightweight filler applied to blend into the existing fuselage curves. This probably will augment the lateral solidity of the tailskid, essential when the model is pulled on a string during sharp turn ground movements.

Pict 4866ch


At that stage I also corrected minor blemishes which only became apparent after painting the complete fuselage. This was done by deepening the imperfections and very locally sanding back to wood grain to provide sufficient adherence for filler and primer. The entire fuselage was then sanded smooth again before a second coat of beige paint was applied. As I was very happy about the overall result, I assembled everything (including the wheel) and stocked the model on the rack on its custom transport cradle where it sat till the final mating with the wings and application of second color and markings occurred weeks later.

Pict 4871


About a month later Jürgen wrote me he had made two prototype canopies over a 3-piece wooden form. He sent one to me by post and upon arrival I noted it to be relatively good quality, with only minor blemished caused by the junctions of the mold parts. He did apply non-permanent continuous marks where the form was supposed to be cut with a comfortable margin, and a dashed line where he thought the final cut had to be made. He also applied dots where the multiple-part frame was supposed to come. All had been very well packed for transport by a slow delivery postal system.

Pict canopy mold


TIP: I recommend you to first position your new canopy over the model and only gradually cut to the outlines you need. The marked lines are only a general guidance and can easily be removed by white-spirit.

On the rare pictures of real Gö4 it looks like bolted or riveted aluminum strips were used over the transparencies to fix them together and to something looking like inside tubing. As I had no detailed pictures of the early-type canopy interior frame it was guesswork as to what material was used and if the canopy was swiveling around the top aft part or just dropped on the fuselage after the occupants took place. Although Jürgen did send me a pdf-file with the shape of the various arches, no material had been specified nor delivered in the kit. I saw no practical way to cut a solid yet sufficiently thin frame at this scale. I therefore went to my friend who is a dental technician and has all the material and proficiency for bending and soldering metals to any complex shape I desire. After 16 hours of delicate work using the plans, the model and the roughly-cut canopy, he came up with a nice 4mm copper tubing assembly to which I could screw the clear canopy. 3mm tubing would have been sufficient but because I only found 1,4x4mm small screws, 4mm tubing was more practical.

TIP: Do not use the lines on the clear canopy but continue straight up from the frames on your fuselage, the latter are better guides to obtain a symmetric assembly with correct square angles

Pict 0947c


After getting the model back home I sanded that copper assembly to prepare it for priming and painting. I then wiped away all the black markings from the clear canopy and taped in in position over the frame so I could trim it where needed. I then drilled 1,2mm holes in the copper and drilled 1,5mm holes in the canopy to accept the thirty-eight 1,4x4mm screws. That were a lot of tiny holes that had to be drilled. I then cut and applied thin 5mm strips on top of the canopy to simulate the metallic fixing strips. By pushing on them, I noted the position of the previously drilled holes, opened them up and inserted the screws in position. After the clear canopy had been bolted and adjusted, I used canopy glue to stiffen the entire assembly. Note that as on the real early Gouvier gliders there are no hinges. I have two pins fixing it into the frame next to the instrument panel at the front, and a moving pin on top aft of the greenhouse. This assembly now weighs 227gr and took 34 hours to complete, but is eye-catching on this model. Unfortunately, the canopy quality is so mediocre that everything underneath is very blurred and the detailed instrument panel can only be admired with open cockpit.

Chapter5: The spoiler assembly: 19 hours

If opting for spoilers, assemble them before starting the wings. The model had been designed without spoilers and no provisions were made on the plan for installation. I know such gliders fall out of the sky as bricks instead of gliding out, but just to better control the touchdown point, I prefer having spoilers, plus love the looks of a pair extending top and bottom of the wing. When I picked up the kit I mentioned this and Jürgen suggested I mount a pair of modern spoilers in the top of the wing, but as the real Goevier had wooden plates protruding symmetrically a good distance both above and below the wing, I begged for such a setup. Using 4 spoiler sets with probably as many servo’s to actuate them was insane so I suggested a true reproduction of wooden Schempp Hirth spoilers as per original. Jürgen obliged and made plans to modify one of the similar designs he used on his Ka6 gliders, but adapted the thickness to the Goevier wings.

Pict Gö3 störklappen 001


A few weeks later the postman brought a carton containing a bunch of pencil labeled wood plus small hardware to build the spoilers. As I laid them out on the table it all looked very nice and complete, but stowed them away until the fuselage had been completed. A few months later I undertook their actual build.

Pict 4813


I glued the sub-assemblies as per plan, only to discover (when half-dry) that the swiveling long caps were too wide to fit in the created boxes. As the white glue hadn’t completely cured, I was able to quickly separate the box-assemblies but left the rest to dry overnight. Next day I analyzed the problem and found out that nothing really matched. I thus started calculating the required thicknesses of the different items and discovered to my horror that I had to cut away almost 2mm from all the spoiler cap widths for the arms and the spacers to function without play. As those 4 caps had already hardened I had to use a grinder to separate one of the flat sides, eliminate 2mm and sandpaper flat before gluing them again. As the pivot arms were 3mm thick, adding 2mm spacers each side meant the caps had to be 7mm wide inside. The sides being 2mm thick meant the caps would be 11mm wide outside, but the box end-pieces were designed as to allow slightly less than 11mm inside-box width. Figuring 1mm of play each side wouldn’t be luxury, I had to re-fashion the box end-plates to obtain 13mm inside and thus 17mm outside width to allow the system to operate freely and without excessive play. The metal 2mm spacers had been hand made and there were only 10 instead of the required 16, and they all had to be grinded to flatten the sides. I made the additional ones out of plastic that was easier to sand flat to thickness. The cutouts provided along the inner sides of the higher caps were insufficient to let pass the larger center rings but after a trial fitting the latter were discarded because they were not long enough. I replaced them with pieces of 6mm outer diameter aluminum tubing that were cut to 5mm lengths. That way I also circumnavigated the problem of the cutouts that were too small for the larger supplied roundels.

Everything had to be found out by trial and error, with lots of glue drying time, filing and sanding. I only made one side to start with and only when a satisfactory solution was found, this was copied for the other side. In the end I had one workable system and a second one ready for assembly. This is shown on following picture, flanked on the right side with all the wing ribs, at the left by all the discarded rib centers, and behind it the supporting wood remains. That was another annoying job I catered for whilst various spoiler parts were drying.

Pict 4890


The spoilers were then completely dismantled and painted on the inside (also the boxes) before reassembly. The boxes ended up 17mm wide, 45mm high and 30cm long. Contrary to the supplied exploded view, I opted for the actuator rod openings to be mounted at the lowest point, allowing the servo cutouts to be made on the underside of the wings. That results in spoilers deploying slightly differently but nobody will notice. The exact position of the servo depends on the required throw for the spoilers, that was experimentally measured as 15mm, a small servo arm will thus do the job. On one of the museum pictures the position of a spoiler is visible so I compared that to the plan of the model and figured the best way to install the spoilers (also for strength) was to glue them in front of the wing spars, inboard of rib f11. That meant that part of ribs f6, f7, f8, f9 and f10 had to be modified, and a servo holder plate fit between f5 and f6. In-between spoiler-works I therefore also chiseled-out all the ribs (4 hours work) and sanded away all the brown deposits of the laser-cuts (5 hours). On following picture you can see the partly painted spoilers parts around the inventory of cleaned ribs.

Pict 4891


The 2mm pins between the arms and the spoiler plates were affixed flush in slight depressions so they couldn’t move out due to the PU glue, but form a flat surface for everything to slide smoothly in and out of the box. Wherever they could catch during retraction, the corners were sanded round and the surfaces angled all along. Once that was finished everything except the flattop and bottom of the spoilers received two coats of paint. The top and bottom surface caps will only be glued in place after the wing planking is in position, then sanded smooth to obtain minimal airflow disturbance when retracted.

Continue reading on the next posts (published soon) or return to the resumé of all my build logs on https://www.rcgroups.com/forums/member.php?u=430882
Aug 14, 2019, 02:42 PM
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Chapter6: Building the wings: 171 hours (Ribs prep: chisel: 4hrs, sand: 5 hrs)

Ing Assmann opted for an Eppler 195 rib profile, constant along the entire span (thus varying in thickness according to the length of the ribs) but for ease of construction, modified the profile to have a flat intrados instead of a concave one. I hope the latter won’t detract too much the lift of that good profile. The wings have a unique rather complex shape. The inner third part containing the spoilers is of constant chord, in the middle third part the thickness of the ribs augments because the chord becomes longer due to the ailerons becoming larger. On the outside third, the leading edge has a slight sweepback whilst the rest tapers towards the end, the trailing edge of the bowed ailerons flowing over into a nicely rounded wingtip. The ailerons are really large and on the real Goevier use two actuators on top of the wing to avoid torsion. Hearing horror stories of previous models encountering wing flutter I made modifications to increase overall torsion resistance, both on the ailerons themselves and on the fixed wing part.

I started by removing the 17mm of wood in ribs f6 to f10to accept the spoilers. I cut the removed vertical wood to shape to glue more forward and keep the rib strength. I then laid out all the furnished ribs and spars only to discover that the latter were 10x3mm whilst they should have been 12x3mm. The plan also mentions the wrong size but depicts them correctly. Furthermore they were only 1 meter in length and would have to be joined together, plus doubled to 6mm thickness till halfway the span. I entirely neglected Jürgens e-mail solution of filling-up the voids at the ribs with 2mm balsa strips. I also didn’t like the 18cmx10cm wingtips supposed to be made of a large balsa block, only held by gluing against the seriously hollowed out kit outer rib .

I quickly figured out a way to improve that design. I bought a 2m long spruce plank that I sawed into 4 one-piece spars, 12mm wide with thickness changing halfway from 6 to 3mm. I didn’t cut them off at the tips as per plan, but allowed them to continue right to the wingtips. I also cut the one-piece 19x4mm rib-nose inner spars. Eyeballing the wing taper change between the kit’s outer ribs f26 and f27, I created an additional plain f28 rib that could be glued 5cm further outboard and be a stronger attach point for the much reduced balsa wing tip rounding. These and many other deviations from the original plans were deemed necessary to augment overall wing strength and eliminate weak links. Many more changes were made along the built, follow me through for a description during the actual build sequence.

TIP: Be extremely precise when aligning ribs, both vertically and spanwise, failure to do so will highlight every imperfection later when gluing the rib related planking. It will also complicate cutting if you opt to box the space between upper and lower wing spars.

Pict 4894


I started the assembly by pinning down my one-piece lower wing spar to the plan and glued all the ribs to it, except for inner ribs f1 and f2 but more about those later. When sufficiently dry, I added the top spar to it and let dry overnight. Next I glued the spoiler box in front of the spars and when dry, glued the noses of the ribs to the box.

Pict 4897


I then cut two 19x4 mm spruce leading edges that were sufficiently flexible to bend around the leading edge sweep-back dent. That way I kept the rigidness of these 2 meter long planks to counter span-wise flection. The plan doesn’t mention how to make the 8mm leading edge bend around the curb, and sawing them through and reassemble at an angle would greatly reduce strength, hence my solution. A first 4mm leading edge was glued to the rib noses and then sanded at the correct angle to accept the extrados and intrados nose planking over them. The two outer leading edge parts can only be mounted on each-other after the capping plates are in place.

Pict 4898


TIP: Do not attempt any work on the plan’s suggested method for the wing trailing edges nor ailerons before thoroughly analyzing the hinge problems first. Let’s talk about possible options in next chapter, before resuming any work on the wings.

The Aileron dilemma

The plan suggests you use a 30x20mm plain balsa strip which you have to indent and shape vertically to accept wing and aileron ribs. The ailerons are thus supposed to be built attached to the wings at this stage, a dotted line indicating where they have to be separated later by a vertical cut in the long thick balsa aft spar. You don’t have to be an engineer to figure that such a method, using whatever hinges along the much varying thickness of up to 30mm, will not allow proper aileron deflections unless an enormous gap is left between wing and ailerons. The ailerons having a flat bottom and a very curved top dictate that hinges have to be mounted at the bottom. Pictures of real Gö4 gliders on the internet are not very clear regarding this aspect but also don’t show such pronounced bowing on the aileron extrados. I have a feeling that the problem was created by the model designer when he opted to maintain that Eppler 195 profile even with the considerable variable length of the aileron ribs. The traditional way of making a hollow-curved aft spar receiving a constant radius curved aileron leading edge was impossible to apply because the aileron thickness varied all along from 12mm inboard to 30mm max and back to 15mm outboard. These huge 10cm deep ailerons were probably going to cause serious adverse yaw when deflected but the geometry of the ailerons did not allow for large up movements and thus aileron differential would be limited.

Pict 4901


After a few sleepless nights and many trial drawings I came up with a possible solution. Using 7 low mounted hinges I created Frise type ailerons with all the hinge points 15mm behind the aft-wing spar. That would help eliminate the adverse yaw problem, and minimize the gap between wings and ailerons. It required a complete new approach to building the ailerons and aft-spar, but I couldn’t come up with any better solution to resolve this complex problem. If you chose for the same solution, follow me through the next paragraphs, if not: good luck! For the ailerons I only worked on the plan-view shape of the wing and completely discarded the plans regarding the aft wing/aileron spars and capping strips.

I selected the “large steel-pin Robart hinges” for the job. With the hinge point 15mm behind the spar, that left 2cm to grab into the aft spar. The aileron being so thin at the wingtip precluded the use of even the smallest Robart hinges. The only solution to have a support on the outside of the aileron was by using a 2mm piano wire that was bent at 90° with the aileron pivoting freely around it at the hinge line.

With all that in mind, I cut a 30x15mm balsa spar and positioned it against the wing rib ends. That allowed me to mark the indentation lines and the top of the rib point so I could shave off the extra wood and end up with the nice flowing top curve. I made the indentations for the ribs deeper so the ailerons would keep their original dimensions but the spar was more resistant to torsion (remember the flutter danger).

That spar was then glued to the ribs and the extra (being more than 1 meter length) outboard section added. I then inserted a 12mm balsa block between the main wing spars and glued it to the last (extra) rib, leading and trailing edge of the wing, before cutting it in the curve as per plan and sanding it into a flowing but solid tip.

Pict 4938


Trailing edges fe1 were then glued over the inner wing ribs with additional spruce bits in between to avoid distortion later. Ribs f1 and f2 were then glued on eachother and the aluminum wing-key tube dry-inserted in place. With the GFK wing-key in the fuselage and the 4mm rod in place, the inner f1/f2 rib is slid over it and the rest of the wing as well. With the inner wing rib pressed against the fuselage outer rib, the angles can be finalized for a perfect match of both. With everything still in position, I glued the f1/f1 rib assembly to the leading edge, main wing spars and trailing edge, and 4mm rod on the ribs, and let dry before separating the wing from the fuselage again.

That was the easy part, building the ailerons was a lot more challenging.
With such enormous ailerons I figured throws of +25° and -10° would be sufficient, in conjunction with the Frise type movement and generous rudder use as in real ancient gliders. Using the drawings at various rib cross-sections I figured and calculated the optimum cut angles to obtain such throws without having any visible voids and mostly respecting the original aileron size. I came up with 20° aft canted aileron leading-edge produced from a 12mm balsa plank, rounded-off at the top, and a 15mm aft extension of the wing capping (supported by a 5x5mm triangular balsa strip under the void).

To obtain sufficient rigidity of the aileron and have a solid base to build on, I cut a piece of 0,8mm ply in the shape of a single-piece aileron bottom. On this I then drew the 15mm (from the front) hinge line and the position of the various aileron ribs. I positioned it against the wing so I could figure out and mark the optimum position of the hinges. Note that all hinges have to be installed square to the aileron hinge line and not parallel to the wing ribs. This method also means that the lower cap strips fe2 and fe3 are not used and that in turn requires you to completely flatten the bottom of aileron ribs qu2 to qu15. With the flutter still in mind and desiring to have the hinges embedded in the aileron ribs at their end, plus the two actuator servo horns along the ailerons, I opted for the use of 6 Robart hinges plus that single 2mm piano wire spread at about equal distance for each aileron.

Pict 4942


Assembling further sub-parts

Instead writing a detailed story of the continuation of the wing/aileron build, I think just a sequential list of action is sufficient for any wood builder with a certain experience.

TIP: I built one wing at a time on the plan, even pinning it down to keep it straight with a few nails around the main spar. The other wing than then be easily copied from the first.

Drill extra hole in rib f5 for longer 4mm rod to pass
Cut 30x15 balsa wing trailing edge spar
Position along wing ribs and mark desired heights
Cut and smooth top balsa to follow rib curves
Make indentations and glue trailing edge of wing to ribs
Split fq1 and fq2 in half
Glue half of fq1 to fq2 and to bottom of trailing edge wing at position as per plan
Glue remaining half of fq1 and fq2 on leading edge top of aileron
Add custom balsa end of wing.
Cut away all overhanging material and sand smooth
Cut entire bottom aileron 0,8mm plywood baseplate
Mark position of all qu ribs on it
Decide on position of hinges according wing and aileron ribs and mark on baseplate, square to aileron line.
Cut slots for hinges in baseplate and qu ribs, cut lower qu ribs into straight line.
Mark positions of hinges on lower wing trailing edge balsa and drill holes
Make 20° slanted aileron leading edge and glue to baseplate
Slant-sand aileron trailing edge baseplate and fe2 plus fe3 trailing edge bottoms
Cut part of front of all qu ribs and make indentations for them in ail leading edge
Glue hinges on baseplate and add qu ribs at the same time.
Glue fe2 and fe3 to aileron bottom plate
Reinforce trailing edge gaps with balsa (not on aileron).
Make support plates for aileron servo’s + slightly larger ones for other wing
Make and glue servo plate pedestals on f16-f17 7mm high
Make and glue servo plate pedestals on f21-f22-f23, 8mm high
Make aileron servo plates install square to aileron line
glue upper capping on aileron leading edge
Eliminate ail lips on upper fq1 and fq2
Dry fit aileron and sand top bow to slide smoothly under overhang at all angles
Glue hollowed-out triangular strips aft-top of wing-aileron gap (except last tip part).
Fill and sand aileron upper leading edge smooth in a curve
Adjust angle of wing gap for overhang capping
Glue fq1 and fq2 and glue in place with 14mm overhang
Use lightweight filler to smooth out inner curve of gap

Pic 954


Make horns and glue to aileron.
Mount servo’s in wing and cut linkages
Inner pushrod 70mm, outer pushrod: 90mm, all 2mm
Cut wires for all servo’s and solder to MPX in w1 rib
Mount wing on fuselage to position and glue w1 rib at correct angles
Glue wing spar alu tube and 4mm rod in ribs
Fabricate ply reinforcements between alu tube, spars and ribs.
Install end of wing-key device to keep it centered
Glue fe1 trailing edge top in position
Glue trailing edge in-between strips
Glue additional wood to create strong box structure around alu wing tubes

Pic956


Make access cover plates for all 3 wing servos and install
Make inter-spar ply reinforcement plates at wing key, 1,5mm balsa till f24
Sand top of f16 and f17 ribs for plain capping
Install spoiler and servo for good and test
MAKE PORT WING IDENTICAL WITH OPEN STBD ONE AS EXAMPLE
(STBD wing 928gr, PORT wing 916gr at that stage)
After planking: port 1222gr, stbd 1231gr

Pict 4944


Glue fb1, fb2 and fb3 on ribs
Cap upper then lower front of wings

Pic 959


Produce capping over both aileron servos and make pushrod holes
Sand inner leading edge of wing straight
Glue outer leading edges to inner and sand to shape

Pic 961


Cap upper and lower spoiler and adjust to wing surface
(Planking+leading edge: 40u)

Chapter7: Finnish and final assembly: 78hours

After planking, using filler and sanding everything smooth, it was time to cover the wings. Pictures of real Gö4’s clearly show they only were covered with fabric in-between the plywood planking so I duplicated that method on my model. After custom cutting all required panels and marking the limits of those with a pen, I first applied liquid heat-activated Oracover on the wood. When dry, I applied the Oratex and first used the heat iron on a moderate setting to fix the sides of the fabric to the wood. Only after drying did I start to increase the temperature to shrink the Oratex where necessary in-between the wooden sides.

Next I applied two coats of white primer to the entire wings and still loose ailerons. After delicate sanding all imperfections the height difference of the fabric had mostly disappeared. A single coat of beige was then applied over the entire wings and ailerons. Both wings were then mounted on the fuselage so the contours of curved blue lines could be drawn, after which masking tape could be applied on the beige. The to be over-painted beige was then lightly sanded to get better grip for that blue layer. Taping was a tedious job because of the required symmetry of the complex curves all over the plane. I used up many meters of masking tape in widths varying between 4mm (for the medium turns) and 40mm (for the straight lines, and anything in between for the sharp turns and and continuity.

Pic 962


Immediately after applying the second coat of blue I removed the yellow tape to avoid peeling blue if done after drying. Next came the 4mm Corsair-blue 4mm strips over the color separation lines. I used a complete 15m Oracover roll for that but admit Orastick would have been easier because heating the glue on the narrow strip without melting the paint with the heat-iron was no sinecure, especially in concave area’s. Such 4mm strips were not sufficiently soft to follow many of the curves so I was forced to use bits of 6mm strips that I cut into 4mm bow-parts and Ironed with some overlap to form a single smooth bow. That was a lot of work but the result was worth the effort. Next I applied the (Calliegraphics) artwork to the top and bottom of the wings before gluing the ailerons in the wings. Both were delicate operations because they had to be done in one go, the huge artwork because it is very sticky, and the ailerons because of the small tolerances along the gaps and critical alignment of the Frise lower corner along the flat wing intrados. Just the right amount PU glue was inserted in the wing holes where the hinge tips had to be inserted. These then were pushed in those holes without pulling them out for adjusting because that would allow the glue to expand and spread into the narrow gap and locking the ailerons to the wings in a flat position. Throughout the drying, weights were on top of the wings and ailerons to keep their bottom completely flat on the table. I crossed my fingers as after a few hours I lifted the assembly from the table and moved the ailerons for freedom. Everything worked fine and the model was then completely assembled for weight and balance. Ing Assemann had calculated that a 116mm distance between leading edge and center of gravity would result in 29% MAC, but the MAC was very difficult to calculate with that partial swept wing leading edge and aft protruding bowed trailing edge. It was supposed to be a safe starting point for the maiden but I was sceptical, and afraid the short arm of the aft fuselage would be insufficient to compensate if the value was wrong, I therefore programmed a larger elevator deflection than normal for the maiden. I had to add much more lead in the nose to balance the glider at that 116mm. Besides the 500gr of batteries, I had a total of 1168gr of lead spread around the nose. Total weight in flight condition thus became a hefty 8100gr, resulting in an acceptable 70 gr/dm² wingload. After all the programming and the adjustments were done, I stopped the clock at a total of 477 working hours spread over 6 months.

Continue reading on the next posts (published soon) or return to the resumé of all my build logs on
https://www.rcgroups.com/forums/member.php?u=430882
Aug 14, 2019, 03:04 PM
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Chapter8: Maiden and development flights

The development flights took place during the hottest week ever recorded in Belgian history end of July 2019 at the model-airfield of Pottes near the French-Belgian border. The model had only been finished a few days prior to this annual international BiGGS meet. Although the field is sloping, it is 130m long and obstacle free on 3 sides. Furthermore, very experienced modelers from all over Europe attend the meet and are always available with good advise and necessary materials and tools for field repairs or alterations. With Danny Dewispelaere being the field coordinator, I also was certain to have an expert tow pilot on hand with his Wilga that can tow at slow and constant speeds. Meteo was not perfect with temperatures varying between 32 and 40°C, and wind always blowing across the runway and the last days in rain. Sometimes we flew upslope but most of the time downslope.

The maiden flight was in the downhill direction. After a thorough second opinion preflight analysis and assistance programming workable throws by well known model-pilot John Greenfield http://www.ghostsquadron.co.uk/home.html I hooked-on behind Danny after we discussed the tow. Still being afraid of possible flutter, we agreed on him reducing power after takeoff to allow a turnout at slow speed. After a call from me that I had it under control, he slowly would augment the speed till normal. Anything abnormal I would immediately release. I had asked BiGGS president Bert to film the entire maiden for later analysis, and Danny installed a rearward facing camera on his Wilga

Pict Potes maiden 4


First flight

John kept one wing from the ground (you don’t want Frise ailerons to grab the soil) and soon the Gö4-III thundered down the runway without a sign of willing to fly. Although I knew it was heavy, this was not normal and I slowly increased the back-pressure on the stick. Seeing the Wilga already lifting, I augmented the movement and when it finally broke ground I released some back-pressure to avoid climbing too high, but the model immediately settled on the ground again. I yanked it airborne again and struggled with the pitch and bank throughout the first turn. Thanks to using cross-trim on my transmitter I was able to quickly trim fully up, but that was still largely insufficient so I needed a serious amount of manual up elevator throughout the entire maiden, without ever finding the sweet spot.

As briefed, Danny reduced power, but having not seen or heard any signs of flutter, I told him to open up again and slowly accelerate to normal tow speed. With so much elevator deflection, I needed the airspeed to keep the nose up so I wouldn’t end-up below the flight-path of the tow-plane. As my brain and fingers were working hard on pitch, I admit not taking sufficiently care about left-right positioning. As we had gained sufficient altitude and I felt increasingly uncomfortable maintaining position under tow, I announced I was opening the hook. The release produced less erratic pitch movements than expected, but controllability was poor and I was unable to turn away to the right as I should have done.

I allowed the glider to continue its left turn as I attempted to stabilize the glide, but being free also meant that yaw stability became critical. Things didn’t go straight as I rolled out and searched for a stable glide. Additional aileron and rudder trim inputs didn’t produce the desired results. My model seemed to display an inherent tendency to turn left (later confirmed by 1/2° incidence difference measured between left and right wing). Countering that by right aileron input had the Frise ailerons produce a left yaw (probably the reason that during the tow I constantly drifted to the left of the towship center-line). As there was no way I could get things stable at normal speed, I augmented the speed to get more stability and that helped during the straight lines. During re-positioning I also noted a fair amount of adverse yaw so I made a turn reversal when the model flew away from me, mentally noting how much extra rudder I needed (besides the Frise 50% differential ailerons I had mixed 20% of rudder to aileron input) to minimize adverse yaw when rolling out of the turn to final. That was about as much as I could do during this first short maiden that fell like a brick out of the sky. The towship already had dropped his line and made a short pattern for landing after I told him I was making one more 360 in downwind before having to perform my landing. After his landing, Danny turned his Wilga so his camera would face my expected landing spot and that produced following film.

Laurence maiden goevier (3 min 34 sec)


My 360 turn in downwind was fairly stable, proving that speed was adequate for the landing pattern. I maintained that dive angle and flew a track that would bring me lined-up to the runway. It all felt very erratic and the serious updraft in short finals (causing problems to many gliders and motor planes during that whole day) necessitated popping out the airbrakes. As these are rather efficient but had not been assessed in flight regarding pitch change, plus already much of the up elevator being used to just keep the nose along the glide, I wasn’t going to wait too late to break the rate of descend. I broke it too much and my glider leveled off much too high for comfort. As I didn’t want to disrupt the equilibrium by raising the spoilers again, nor losing elevator control due to lack of speed, I released back-pressure and allowed the model to promptly resume it’s glide angle, catching it to break that rate of descend again just before impact. Had the field been uphill, I would for sure have used less or no spoiler, but was very happy to have the model without damage back on the ground. Here is the movie of that maiden taken from the ground

Göppingen4 III Gouvier R/C scale 1:4 maiden flight (3 min 2 sec)


I decided not to fly the model anymore before finding out what went wrong, but at that time had no access to the previous movies for analysis. Back under the tent, a brainstorm with John and some others concluded that the CG was not the culprit, so we used very rudimentary materials (tables and beer plates) to assess the angles of the flying surfaces. John quickly came to the conclusion that the horizontal stab had zero incidence and was the most probable culprit. The glider needed much more decalage (V) but how much exactly? I figured that measuring the amount of up elevator (including up trim) I had to apply during flight and dividing that amount by two, was a good starting point as to how much wood had to be added at the back of the fixed-stab before the next test flight. Note that if I hadn’t had the green multiplex plug at the front, the same amount could have been cut away from the front without having to change the holding pin position at the back.

After measuring, we agreed that about 5mm could be needed, and thus the hole under the fin had to be displaced upwards by the same diameter it originally had. Luckily Alexander, another specialist at large wood-model building, visited the field and proposed to drive home to retrieve the necessary material to perform that delicate operation. After a quick supper, my friend Eric joined and soon the 3 of them made a template and drilled a new hole (touching the old one) by using a serious power drill. I hardly dared to look until that was completed. The old hole didn’t have to be filled because the pin would be held against the top by the temporary filler plate inserted between the aft fuselage and the trailing edge of the stab. That was also necessary to maintain lateral stability of the entire stab (before I installed scale struts later on). A piece of 6mm wood was then cut oversize and sanded into a slight angle before it was fastened by normal tightening of the stab-screw. As a temporary fix to further flight-test and adjust, it was adequate but looked awful and exaggerated.

Pic 973



We agreed not to fuzz with anything else before evaluating that modification in flight. It is wise to only change one parameter at a time because otherwise it is very difficult to analyze what model change exactly caused what behavior change.

Second flight

Pic Pottes maiden 1


Next morning I had no qualms taking it up behind another towship because I was convinced I built my wings and ailerons sufficiently strong and flutter would not be a problem, at least at normal speeds. The elevator trim had been reset to obtain adequate pitch trim range again, and this time the model lifted by itself and was a bit more docile to handle. With nothing done to the rest of the model, this proving flight had the sole purpose to evaluate the new tail angle. This time trimming was possible within the transmitter trim buttons and a much slower glide could be established. It still wasn’t stable but a CG dive check was performed, revealing neutral stability. Of course the adverse yaw had not disappeared but landing it (uphill) was much easier from a more normal pattern, even with a moderate full crosswind.

We didn’t change anything to the angle of the tailplane anymore, but added 50gr of lead in the nose. That amount was chosen by John and seemed a lot to me but later proved correct.

Third flight

The purpose of that third flight was solely to trim the elevator for a normal glide speed before performing a new CG dive test and some turn reversals. Being towed by my friend’s Cessna182 was different because he was still adjusting that airplane and flap retraction resulted in an abrupt pitch change, not what you want during the glider’s pitch setup flights. I managed to stay behind till 300 meters before releasing. The CG dive check proved the weight distribution to be correct, but the model still was not directionally nor longitudinally sufficiently stable. This caused my corrections to catch the full crosswind to induce a crab landing that was too much for my rubber tire. The tire broke in half, and more separation lines were seen in the remaining rubber.

Having no spare wheels of 3 inch anywhere on the field, my friend said he could try glue the rubber with cyan, then glue the tire to the rim, hoping it would last a few more flights so I could continue the development flights. This was completed during the afternoon when temperatures rose to 30°C+ and flying was suspended because neither the tug engines nor the pilots could handle such temperatures for any length of time. I used the free time to adjust the pushrod lengths of the elevator so they were streamlined on the stab at the proven trim angles, but this time with zero electronic trim deflections.

Forth flight

After supper the temperatures had fallen a bit and flying resumed. I proposed John that he flew my Govier during this forth flight so he could feel it for himself and suggest further improvements. As expected he flew it much better than I and his smooth landing didn’t cause the glued wheel to break. After the flight he immediately commented that the elevator was much too sensitive. My suggestion of augmenting the expo was immediately turned down because he rightfully thinks that during the flare it could cause over-controlling the pitch. He convinced me that less expo and less elevator throw are a much better way to achieve smoother response at all speeds. He also looked at the ailerons and thought those were not really in line with the aerodynamic shape of the wing profile. As the bottom of the wings are flat, we “measured” it by holding an inverted beer-plate against the bottom of the wing and sure enough, both ailerons drooped a little.

All that gave me sufficient work and one of the other pilots offered his incidence meter (something I’ll have to acquire soon) to measure everything accurately.
In the field we used one wing (the port one) set at 0° incidence (where the fixed part ends and the aileron starts) as a reference for all the other measurements. The warp on the starboard wing caused it to average +0,5°, and with the elevator in trimmed neutral (and streamlined) position we noted -3,5° tailplane incidence. I later heard from the designer that his wing roots had been designed and cut for +1,5°incidence versus the fuselage, meaning the total decalage to be a whopping 5° of V, surely the result of having such a limited moment for the stab in this short-fuselage version.

With normal ailerons it is easy to turn their neutral points upwards slightly, effectively augmenting lateral stability and avoid tip-stall at the detriment of total lift. On my model with pronounced Frise ailerons you are very limited in such adjustments, less you create serious shape drag along more than half of the lower wing. Minor adjustments were used to stop at the point the lower aileron leading edges started to protrude under the wing. This was still sufficient to result in a minuscule up position when neutral. Later back home I sanded away some wood where it protruded, to minimize shape drag with slightly-up elevators at neutral roll.

Having no further outboard position on the elevator control-horns, the only solution to physically reduce the elevator throw was to use the further inboard hole in the elevator servo-arms, but that then caused a problem of clearing the servo access-hatch at certain arm angles. Whilst attempting to bend the pushrod with pliers, I succeeded in breaking one at the Z-bend, effectively preventing any further test-flying that evening. Luckily local club-member Marc returned home for the night and made me another threaded pushrod with Z-bend at the correct length. He brought it next morning but those 2 following days flirted with 40°C in the shade causing nearly all towing to be canceled. I just further reduced the electronic elevator up-throw a bit and waited for suitable weather. During those hot and windy days I performed some flights with my Blanik.

3 more flights for the Govier

After a very stormy Friday midnight, the weather completely changed (except for the eternal crosswind) and the sky was completely covered on Saturday morning. Before the wind picked up and the briefing for the weekend was conducted, Danny towed me twice to the cloudbase around 250 meters. The first tow confirmed my glider had gained much stability, and I couldn’t believe it didn’t sink as fast anymore. It even wanted to grab the minimal thermals probably issued from the still hot wheat underground. I glided for five and a half minutes, a figure I never could have dreamed of a couple of days earlier. As I was close to full aft stick before the glider nodded in a gentle stall, I needed to augment that throw a bit. It finally flew majestically and stable in pitch and roll, but despite the Frise ailerons and aileron rudder mix, still showed some adverse yaw that had to be countered by manual rudder inputs during initiation and recovery from turns. The landing was uneventful and the tire still held.

Here is the movie of the tow portion that flight
Laurence goevier 2flight (3 min 56 sec)


With nobody else in the air, I quickly hooked-up behind a Zlin for another flight, just for pleasure this time. This sixth flight was my first relaxed one, but probably too early because my test program was not yet completed, I still had to perform deeper stalls, check out a higher number of aileron/rudder mix, and finally perform the so much delayed test of the effect of spoiler deployment/retraction on pitch. Just after the landing I noted everybody had already gathered for the briefing so I attended as well, but after the briefing immediately hooked up for flight number seven. This again was a pure fun-flight but the full-spoiler landing was a bit more brutal (I had insufficient speed/up-elevator to break the sink rate) and a quarter of the tire separated from the wheel-rim, effectively meaning the end of the proving flights for that week. I took the receiver out of the Gö4 and installed it on the Foka4 to testfly that one with a real airspeed indicator.

After the weekend I came home and my first task consisted of measuring the throws to have a reference for further adjustments and inform the builder of settings that so far have proven to work. Further refinements will be published after a couple of more fine-tuning flights. Here are the figures measured at the highest deflection points:
Elevator throw: 25mm up , 30 mm down, no expo
Rudder: 80mm left and right, no expo but 35% aileron mix
Ailerons: 36mm up, 18mm down using 50% electronic differential and 30% expo
Reverse measured CG: ...mm behind the leading edge of the wing.
In a mail and picture/movie exchange with the designer he doubted my model had the prescribed 2% dihedral angle on each wing. I didn’t measure that but as I built the wings from his pre-cut/pre-drilled ribs, the dihedral was not adjustable so I had no choice and as the inner wing ribs had to be glued at at angle to lay flat against the wing fillet wing ribs, I suppose I did everything I could. The shape of the wing (with varying thickness of the identical profiled ribs) makes it very difficult to judge the actual wing dihedral.

Pic pot maiden 3 crop


That week I changed the wheel for a new Dubro 3”one, installed end of wing removable tie-down loops to prevent the ailerons from grabbing the soil, Sanded away some protruding wood at the bottom leading edges of the ailerons, made a wedge balsa insert for the horizontal stab to rest at -3,5° and contoured it to blend with the fuselage, installed struts to augment rigidity of the horizontal stab, touched-up the paint where works had been done and added 50gr more lead in the nose to compensate the latest modifications to the tail. Expect further paragraphs when the model has been fully developed.

Pic 975


TEMPORARY END OF PUBLISHED BUILD-LOG
Continue reading on the next posts (to be published soon) or return to the resumé of all my build logs on
https://www.rcgroups.com/forums/member.php?u=430882
Last edited by BAF23; Aug 19, 2019 at 11:15 AM.
Aug 18, 2019, 07:32 PM
Registered User
WOW !!! I am going to come back and read, in detail, all that you have done here. Very impressive !! Mike


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