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Jun 09, 2020, 04:14 AM
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Build Log

Build log of OldGliders SZD9bis Bocian 1c scale 1:4


Pic 11jul20-22crc


Part 1: General info and tail assembly

The choices
After building the Ka2b OO-SZD, Gö4-3 OO-SZC and Foka4 OO-ZEU in their historical Sabena livery, only one glider was missing to have them all, the 1958 Bocian 1c OO-SZE serial P311.

Pic Bocian HFI 2018(19)


For years I compared the available quarter-scale (short)kits, one from the UK, one from Germany and the one from the well-known Polish OldGliders. End 2019 I choose the latter and ordered all their available options (except the oleo gear) including a scale pilot. The reply I got asked me to transfer 805 euro, also covering the shipping to Belgium. Three weeks later DPD delivered a 8,8kg package. It had been extremely well packed with liberal use of triplex-wood around both cartons, then many layers of black plastic to protect all sides during handling. Don’t panic after opening the box, just as with any 1000-piece jigsaw puzzle, it only takes patience to assemble the awesome mess of single loose pieces. After unpacking I roughly amassed similar looking parts in heaps and took following picture of the complete delivery.

Pic 5039c


First thing I noticed was that almost no parts were marked. I thought I would find numbers on the full-size plans but found none. The plans showed a few hand-written amendments but had only a side-view of the fuselage, no top-view. An accompanying CD-Rom had tons of pictures at various stages of build and helps find out how to assemble the model. As there is not a word of text, language is no problem. Although OldGliders sold me the extra wood pack for the model, The CD-ROM shows a picture of required wood strips, most of them longer than a kit-box could contain:

List of strips SZD-9 Bocian 1:4/ Wykaz listewek
Pine/ sosnowe:
15mm x 1mm x2200mm - 4szt
5mm x 5mm x 1000mm - 4 szt
12mm x 7mm x 2200mm - 4szt
Balsa or pine /balsowe lub sosnowe :
5mm x 5mm x 1800mm - 15szt

As I sorted out the bunch of extra wood that was delivered in the pack for 70 euro, I found many similar but only one meter long parts. Here is a list of the contents of the optional wood pack:
Balsa: all lightweight flawless 100x10cm planking
10mm: 2, 6mm: 1, 3mm: 1, 2,5mm: 10, 2mm: 23
Pine wood stringers/strips: 100cm long, all very straight
12x7mm: 14, 15x1,5mm: 14, 6x5mm: 9, 5x5mm: 35

It looks as the extra wood package caters for the needs of the CD-ROM list, just that they are delivered in reasonable transportable lengths. Anyway, so much quality wood for that price is an excellent deal and I highly recommend the purchase of the extra wood packages if you order any models from OldGliders, even if some of it ends up in your stock because at some stages you prefer to use longer one-piece pine wing-spars or balsa instead of pine for the fuselage stringers.

An extensive internet search did not reveal any complete build-logs for quarter-scale OldGlider Bocians, neither for the 1c nor 1e versions, not in English, Dutch, French nor German. The best I could find was a German thread with many excellent illustrations and some good pointers : http://www.rc-network.de/forum/showt...rungsaustausch

I’ll thus attempt to produce that model the way I think is logical, writing an illustrated build-log for other potential builders on the fly. Be aware this is not a designer’s approved build-log and there probably are other equally valid methods to assemble that kit. The Bocian 1c optically differs from the 1e mainly regarding the vertical and horizontal tail’s and wingtips, having rounded tips instead of the latter’s easier to produce square tips, no wheel suspension and a multiple-part single-curve canopy.

Here comes the rationale behind some choices I made. As the early Bocian versions had a rigid wheel and the model apparently lands slow and should weigh less than 9kg, I opted for the rigid gear instead of the heavier later version landing gear with suspension. Due to weight and balance concerns some other modelers deleted the servos in the stab and used long Bowden cables to a forward mounted servo. As I intend to build a realistic cockpit interior and prefer the redundancy of two separate elevator servos, I decided to follow the kit plans. The horizontal stab having no struts, it will be solidly anchored to the fuselage with two screws and a fixed green Multiplex connector, used to make field assembly uncomplicated but allowing for easy horizontal stab-angle adjustments before fixing it for good. Tail flight-control surfaces will be hinged in “hidden” fashion, with the ailerons hinged aft and slightly below the wing to create Frise-type ailerons with a smooth extrados. All servos will be of the high voltage type to allow direct connection to a pair of 2S LiFe batteries.

As in the end the model needed a lot of ballast in the nose it is important to build everything behind the CG as light as possible. If I had to do it again I definitely would replace many heavy plywood or spruce parts by identical parts made of balsa. Building the model as suggested by OldGliders is an overkill regarding strength in the entire aft section

Pre-assembly work

I downloaded all the pictures of the CD-ROM on my PC and created separate folders to order them, one for the tail, one for the fuselage and one for the wings. I then cut the plans into separate parts for these sub-assemblies. Next I grouped the pre-cut wood into relevant similar-shape packages and separated left and right wing parts. To learn how the designer intended the model to be built plus get a feel of the materials and fit, I started small at the tail feathers. I therefore pinned down the plan for the rudder and horizontal stab plus elevators on my construction table and covered it with clear plastic. On the plan I then could position all the individual parts needed to complete the vertical and horizontal stabilizer sub-assemblies. I had to dig into the plastic bag with the numbered parts to find some I needed. I found out that those hand-numbered parts were the ribs of the ailerons and taped them together to form one sequential pack for each aileron before putting them aside. It’s just one big puzzle and when I had all the parts on the plan, I pencil-marked them with a letter (r=rudder, s=horizontal stab, e=elevator, f=fuselage, w=wing) and a sequential number either from middle to outside, front to aft, or from bottom to top.

Basic tail assembly

Pic5049c


A dry-assembly of the rudder was then made to verify the basic fit. All the parts were cut by milling and OldGliders delivers only the parts (already separated from the carriers) without burn marks and a single minimal tab protruding from each part. All the triplex-plywood has an unusual thickness of 3,2mm and the cuts are very clean. Although not aviation grade, that wood is of good quality. Where ribs have to be meshed into spars or stringers into frames, the openings are tight but inside corners are round instead of at square angles. The tight fit of the parts might allow for gluing as is, but I used a square file to obtain even more contact surface for the glue on all the kit parts, a rather boring and time-consuming job. I recommend you to buy a 3mm and 5mm square file, that will help tackling the sometimes 50 square corners in a single fuselage frame. For the entire kit I calculated between 1500 and 2000 corners have to be squared out correctly for a good correct fit. Furthermore the cut of some parts is not precise and filing/sanding has to be done for things to fit properly before gluing. What bothered me even more was that some parts seemed just a tad longer than on the drawings. After much measuring and thinking I can only imagine that the plans have been reproduced a tad under 100% size. I decided to follow the cut on the parts instead of correcting them all to fit the drawings.

I first started gluing the rudder. On the flat-laying forward spar I glued each rib vertically with white glue, then applied glue to the curved aft spar and pressed it in position, all in one go. I then pivoted that assembly horizontally on the plan and supported the aft spar with a pencil while ensuring the geometry followed the one on the plan during drying. With the elevators being similar in build I glued them the same way, no surprises because so far, there is no specific orientation for those mostly symmetrical parts.

The narrow one-piece horizontal stab had too many parts to glue in one go. I therefore elected to first produce the three box structures, one for the middle of the stab with the three traverse connectors, and both servo holders. Here was the first time orientation mattered, be sure the open squares are glued at the bottom of the stab and flanked by a slightly larger inner rib than the outer one. When the boxes had been glued, I squeezed them without glue between the forward and aft spar to ensure correct spacing and alignment when drying. It then was the moment to file the missing cutouts for the aft spar in the longer outside ribs. The positions were marked but the correct cutouts had not been factory produced.

After a few hours dry time I removed the boxes from the spars and applied glue to all the stab ribs, after which I first pushed them vertically against the flat laying aft spar, then pushing the forward spar through the nose slits. One hour later that assembly was lifted and rotated till it lay with the nose-part of the ribs flat against the corner of my table. The nose spar then was forced flat again using pincers, eyeballing along the edge to find the exact locations. The trailing edge pointing slightly up allowed the long tip-ribs to be glued in position. That complete assembly was the left to dry overnight.

Pic5050c


Before planking the stab the servo, attachments had to be made and their wiring installed including the fuselage connectors. Because I like to use fixed Multiplex type connectors the exact place had to be found but that was dependant by the attachment method of the stab on the fuselage. OldGliders foresaw only a single 5mm dowel at the back of the stab, engaging in a slot where it could be adjusted up and down to vary the stab incidence angle. Besides that single dowel there had been holes drilled in the stab plates and on the 3mm wooden base-plate where the stab would rest on, but only for a single screw that would have to take care of all the forces acting upon the entire horizontal stabilizer, especially during ground handling or mishaps. As that was unacceptable to me I choose to use a pair of nylon M6 screws placed side-by-side and grabbing in metal T-nuts that were glued to an extra 5mm reinforcement plate glued under the original base-plate. With the T-nuts having a diameter of 8mm, that meant a lot extra holes had to be precisely drilled before any assembly was done. Therefore next thing I did might sound odd, but was essential for a correct fit at a later stage. At that stage I also drilled a double pair of 5mm holes in the aft of the fixed stab and F21 so a pair of carbon pins could be used instead of the single dowel to attach the horizontal stab to the fuselage for flying. These pairs were drilled at different heights to allow for ample stab incidence angle adjustments through the use of support blocks and the M6 screws during final assembly and after flight testing (the aerodynamic fairing over the stab can only be finalized after flight testing). Because the chord of the stab is only a fraction of the elevator dept I expect the possible stab angle changes to be rather important during test flying..

It is possible to already assemble just the last seven fuselage frames (F17 to F23) with all their intermediate bits and pieces, including the entire tail-fin and horizontal stab fittings. That way all the tail components can be adjusted for a perfect fit before any planking takes place, minimizing later cuts and adjustments. Follow me through that process. After gathering all the parts except the stringers, I dry assembled the puzzle and found out that frame F19 was too high and had to be modified at the top and where the front of the stab base-plate rested in it. F20 has to be pushed fully down on the keel and not allowed to stick out in the top. I then glued that stab base-plate together with its custom reinforcement and the two T-screws and let them dry. That left me lots of time to correct ALL the fuselage frames. Most of the cutouts for the 5x5mm stringers are too small and not square, and have to be filed to later accept those stringers. That job takes forever but is easier to perform on the separate frames than after fuselage skeleton assembly. Because this was only a partial tail-section assembly it was performed sideways over the plan to ensure the angles between fuselage, frames and vertical tail were correct.

Because there is not a single part of the fuselage that runs flat, unorthodox assembly methods are required at that stage. The way it worked for me was to slide frames F18 to F23 over the central beam but short of their resting place. White glue can then be spread on the respective contact areas and each frame pushed down in it’s own notch. Immediately follow by dry-assembly of the keel to ensure the frames are kept oriented at the correct angles on the plan. Aft fin-frame F23 was held dry against the notches of the keel and central beam, but glued to the horizontal fin base-plate which connects it to the top of F22 and F21. The prefabricated stab resting plate was then glued in-between F19, F20 and F21. Last was the dorsal spine plate between F18 and F19, overflowing via a cross-member to the stab base-plate. Later to be cut rubbers and some pincers were used to keep everything tight during drying. All that was done in one go but the stiffness of the assembly was still insufficient to guarantee the correct geometry at that stage. Things still could be pushed in one or the other way so weights were used to keep the keel and long F23 tail directly over their position on the plan during the drying process. Failure to do so might end in a crooked tail on the model. That is as far as I dared to go before the glue settled, further gluing of parts had to wait till the geometry of the frames had solidified. Here is a picture at that stage of the build (notice the aft fuselage is just resting on the plan with its natural weird angles).

Pic5054c


As I later found out that the aft skid protrusion (being part of the keel) was too large and much too high and thus could easily multiply the side forces on the ground to the point the much too narrow keel cracks or even separates from the tail, I suggest you to at least drastically reduce its external height and augment the interior height of the keel above the skid so it reaches at least the long backbone prolongation, and preferably gets attached to the future lower aft stringers as well. You can read and see all about that later modification under the thread about flight testing, under the part “third flight”

One day later I removed the still loose keel so I could apply glue to all the contact points and used rubber bands to join everything tightly. Then I glued in one go all the remaining elements of the vertical stabilizer in place. All this was again allowed to dry on the plan to ensure the correct geometry but care had to be taken to ensure the correct alignment of the fin with the fuselage axis. After all the already assembled skeletons had dried it became time to dress them up, which I did in series. Leading edges for the vertical fin, rudder and elevators were cut out from the 10mm balsa plank, and I used a 12x7 pine part for the horizontal tail. Contrary to the plan, I allowed all those leading edges to continue well past the last ribs, that way the plain rounded balsa tips have a more solid grip than only against the narrow rib end. Because I still had some 12mm balsa planking in my stock, I cut the horizontal stab balsa strips out of those instead of building up planking. For the top of the fin I used 10 + 6mm balsa to produce the cap.

Again for strength I decided to sand those leading edges straight with the plywood limits, allowing future planking to also be glued along those leading edge sides before sanding them into a streamlined nose. Balsa cap-strips for the elevators was then custom cut from 1,5mm instead of 2mm planking to save weight and because the control surfaces will be covered with strong Oratex at a later stage. Here is an intermediate picture at that early capping stage on one side only at that time.

Pic5055c


Before further planking was made I had to make provisions for the hinges and control horns to be installed. I therefore first had to sand the leading and trailing edges of the horizontal and vertical tails in the correct shape. That was a serious job that got lighter once I started getting used to the Christmas present from my friend: a Proxxon BS/E narrow belt-sander. Checking the parts for fit revealed that the end-ribs of the control surfaces didn’t match at all with the end-plates of the stabs (of the Bocian 1c version). The end-ribs were much too thick and had to be seriously thinned before planking.

As I like to use the Robart 4,5mm (11/64” drill) pin hinges I added some extra support wood in the stabs and moving surfaces, around where I drilled the 5mm holes. The hinge pivot points are deep into the leading edges to minimize the gaps during the movements. I then used Engel GFK control horns that I adapted for this model and glued plus bolted them to the control surface frames. Short 2mm rods with a z-bend on one end and M2 Kwik-link at the other transmitted the servo movements with minimal play. Having read the elevator effectiveness I setup the geometry to achieve about 3cm up and down throw for the maiden trip. Servo wiring was then modified so they only had a short stub that could be plugged within the servo housings into wires that were soldered to a central mounted Multiplex plug. Male and female were mounted on plywood plaques so the horizontal tail assembly also makes all the electrical contacts for the elevators. Positioning is temporary and will be finalized after the correct tail incidence will be achieved during flight testing. Another GFK hinge was installed in the lower rudder to be steered by pull-pull cables. Only after completion of previous jobs was it possible to produce and glue the cap-strips for the elevators and rudder. At first sight following picture might not look very much different from the previous one, but an enormous amount of small tedious work taking about a week work separates both shots. Here you can see the rudder having been capped on the bottom side, with the top side still to be capped with the strips and parts that I shaped by hand out of 2mm balsa. The starboard elevator had already been completely capped and after some more filing and sanding was ready for covering. The port elevator had just been covered by rest bits of white Solartex fabric.

Pic5058c


After all three moving surfaces were covered it was possible to see how far the capping of the fixed stabs had to be extended aft to cover the gap but still allow free control movements. Because these controls are tapered, the overhang also best be of variable depth. I used 5mm outboard and 7mm inboard. For the horizontal stab I first planked both lower halves separately because I choose to saddle the stab over the fuselage instead of just resting on top of the fuselage. For the vertical stab I worked one side at a time and split the surface vertically because of the complex curve at the root. All this planking requires lots of pins, clamps and clothes pegs. Here is a picture taken during the step by step planking.

Pic 5060c


The top of the horizontal stab was covered in one go whilst the long fuselage/rudder spine tackled in turn. Because the overhangs in 2mm balsa were too delicate and too thick at their ends, I home-produced 4mm triangular strips that I glued in the inside corners. That solidified the assembly sufficiently so that I could taper-sand the ends for a smoother transition between the fixed and mobile parts of the tail-feathers. Following the pictures of full-size Bocian 1c gliders I also used a block of balsa to carve a smooth transition between the aft spine and vertical stab leading edge. To further strengthen the balsa I then applied two coats of pore-filler to the entire balsa surfaces I produced so far, and after sanding smooth with 400-grit paper I applied paint-primer to all I finished so far, including the control surfaces. 2mm ply cover plates for the servo openings were then produced. I then final-painted all those surfaces so they were ready for the hinges to be glued because after that, the tight fit wouldn’t allow painting in those areas anymore.

That pretty much completes the assembly of the tail section. It probably could be built much lighter using more balsa and less or thinner ply for the frames, the completely finished horizontal stab with servo’s and elevators installed, weighed 411gr the way I produced it. The entire painted tail sub-assembly weighed 626gr. After that month’s work I took a short break and went to the French Alps with a long time friend for a well-deserved short-ski weekend.
Last edited by BAF23; Jul 23, 2020 at 07:51 AM.
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Jun 09, 2020, 05:49 AM
The sky is the limit
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Part 2 : The fuselage


Assembling the oval fuselage cannot be done straight on the plan. After studying the pictures of how others did it I adopted a similar method by way of a scrap piece of strong plywood screwed along a wooden beam (on my temporarily upside-down model table). The basic idea is to firmly fasten the lower keel to a vertical piece of wood so the fuselage can be kept straight from assembly till most of the planking is completed. Because the frames completely saddle the keel, our wooden aid needs indentations for each frame. Although the keel was expected to have a straight bottom, on the plan it bends very slightly so I recommend to first carefully prefabricate your support plate on the horizontal plan and mark the exact edges of the keel. As I didn’t dare to weaken the keel, I drilled only 1,5mm holes where I attached it to the aid by means of small screws. To keep the fuselage upright I screwed 3 vertical plates in-between some frames as guides, but don’t forget to add 3,2mm spacers to get around the keel. The long front of the keel was then screwed on the aid before everything was mounted vertically on the table. The complete aft fuselage prefabrication can then also be screwed by its keel and kept upright by clamps holding the top beam against the vertical support plate.

Pic 5069cr


Frames F12 to F16 can then be glued on the keel and the spine pushed in position on top and against the spine of the tail. It is essential to work with complete top and bottom assemblies at the same time to get all frame angles correct. That was the easy part of the fuselage, the rest is more complicated and better be built in sub-assemblies. First check the fit by DRY ASSEMBLY FIRST, holding things together with rubbers and clamps. You’ll notice that to obtain a tight and correct fit, besides making the cutouts square you’ll also have to file the sides to allow the slant angles of many parts to be joined with no gaps after gluing, and better also file the tops of frames F3 to F11 so the canopy rail can be seated flat on them when gluing later on. All that filing/sanding is a tedious process and has to be made with delicacy because chipping the triplex wood is all too easy . Don’t forget to dry-install the large cockpit rail DURING EACH SUBSEQUENT PROCESS to keep all frames aligned horizontally and vertically during gluing. A perfectly flat cockpit rail is essential if you build your model with a one piece removable canopy assembly. It also became obvious that a number of panels won’t fit at all without adapting them. Multiple dry tryouts had to be made in-between, especially regarding the fit of the gear-well against the keel and its depth versus frames F7, 8, 9 and 10. There probably are different ways to complete the fuselage but here is how I did mine.

Leave frame F11 unglued until the large upper cockpit frame is finally glued. Start by gluing parts together that were doubled-up for strength around the critical load points around the wing-key and canopy frame. For the gear-well, it will depend if you opt for the amortized version or not. For the fixed gear (version B), the plan and parts only show a single 3,2mm plywood to support the axle on each side of the wheel, that is largely insufficient regarding strength. Furthermore, when the top-plate of the gear-well has to pass under the raised-keel part, the sides-plates show an ill-fit versus the frames. Luckily the furnished 90mm wheel being only 30mm wide at the hub, allows ample reinforcements to be added to the inside of the 57mm-wide well. Using (hidden) axle collars inside the box still left me sufficient space to add extra 4mm thick multiplex side plates inside the wheel-well to absorb the weight of the expected 9kg model during not always so smooth touchdowns or rough terrain. With the model saddling the construction beam it is impossible to slide a completely assembled wheel box up from the bottom.

I started by gluing the wing-key attach plates in-between the doubled F9 and F10 frames (watch out for their correct orientations). Don’t glue those frames to the keel yet but allow that sub-assembly to dry in their future position (using the dry-positioned innermost wing rib for correct spacing and alignment). Next, dry-install F7 and F8 and assure yourself that the flat top of the wheel well (installed from below) will fit snug against the raised part of the keel. When all conditions are met, glue those four frames on top the keel and the wheel-well roof plate under the keel, making sure it is laterally horizontal. Again don’t forget to use the innermost wing-rib as a guide for correct spacing at the extremities of the frames, failure to do so at this stage causes troubles when at a much later stage you finally glue those fuselage/wing-ribs in place.

Pic 5075c


You can then dry assemble the wheel-well side plates and cut part of the aft lip of the inner plate so it will fit snug against the top of wheel well. Glue the 3,2mm and custom produced 4mm axle support plates against each-other but not yet against the wheel well side plates. The holes in the plates have no use for the fixed-wheel. When dry, put both sub-assemblies together and drill a 5mm hole through those 4 plates at the same time so the wheel axle will be aligned. It is easier to already sand the protruding axle-support extensions in a more aerodynamic way at that stage. The long vertical sides of the wheel-well can now be glued uniformly to the horizontal top-plate and the 4 frames so the loads will be spread evenly over that complete fuselage section. When dry, glue the thick inside plates with the wheel support in the box and press them firmly against the outer and top wheel-well plates.

For the moment, skip F5 and F6 but produce the forward sub-assembly by gluing F2, F3 and F4 on the keel and with the tow-hook servo plate in which you better first drill the holes. Next dry-fit the canopy rail on them and use a plumb rule to certify the top of F2 remains horizontal during the drying. Note I didn’t glue F1 at that stage because I will only install it together with the hook mechanism and wooden nose. The delivered wheel had to be drilled out from 5,7mm to 6mm before a copper tube could be inserted so it had no play on the 5mm piano-wire axle. It then became time to finally glue F5,6 and 11 in place and cap everything with the cockpit rail, this time using glue. To square out frame F11 use the indentations in the wing’s inner rib to keep align it during drying. When all clamps are removed it is possible to add the rudder-servo plate in which you already drilled the desired holes.

Pic 5077c


Before installing the rudder pull-pull wires I had to figure out their outlet positions and therefore had to install the fuselage stringers. There are a lot of the four (per side) that are more than the provided one meter lengths, I decided to use random lengths at the start so their joints would not be at the same section of the fuselage. To glue all those pine strips I used PU wood glue because of its longer working time and shorter drying before rock solid, plus it better fills the voids. Because of the large forces caused by the stringers that have to be seriously bent around some sections, I recommend working symmetrically to ensure the fuselage remains straight. When I clamped and glued a stringer on one side, I immediately followed by gluing its counterpart on the other fuselage side, and as such mirrored the entire sequence.in following manner: port upper stringer, starboard upper stringer, starboard lower stringer, port lower stringer, port middle stringer, starboard middle stringer, then filling remaining the gaps using the same principle. I also dry-installed the horizontal stab and wing key so I continuously could monitor no twisting of the fuselage took place in the process. Allow the stringers to protrude about a centimeter forward of the F1 frame position.

The sheer number of stringers and the limited amount of clamps I have necessitated dividing the process over a number of days. In the meantime I prefabricated the nosecone. On the plan the shape of it forward of F1 is indicated as a block of balsa. I find that a stupid idea because the nose needs ballast anyway and balsa is too soft to resist impacts during transport or landing accidents. Besides that, I want it to be solid to firmly anchor the tow-hook. I therefore used scrap heavy wood from an old dresser which I glued around where the hook-mechanism tube could be slid into in the correct angle. That cone on F1 now weighed about 100gr at that pictured stage (before further shaping, filling, filing and gluing to the keel and stringers). The hook servo being offset to port leaves just sufficient space for two 2S1700 LiFe batteries on the starboard side, all having easy access below the future instrument panel.

Pic 5080c


After further refining the shape the nosecone was attached to the rest of the fuselage. Don’t expect the stringers to fit nicely into frame F1, when after serious wetting you can bend them witch much force around the nose, mark where they end up and at which angle, and make new slits in the nosecone. Because most of the tow-force will end-up along the cone and F1, I preferred to route and glue all those forward stringers well into the nose instead of just on the narrow edges of the F1 frame. As it was impossible to keep all those forward stringers tight together during drying I worked in steps. The first one consisted of producing the upper stringers (between the angled canopy front panel) in a correct length with F1 pressed firmly against the keel and servo plate structure. All this was then glued in one go and after drying, roughly sanded into on continuous upper nose-shape. Second step was pressing the lower stringers on place one by one, ensuring they fit into the cone and adapting their length and end-angle to the receiving slits in the cone. When all were correct, glue was applied and all of them were held together with clamps to force them into their final positions.

Pic 5083c


The rudder servo was then installed so the 0,8mm pull-pull cables could me made and guides along the fuselage fixed at regular intervals between some frames. Only the contour wood of the inner wing root was then glued in position but the rest not yet because it would hinder basic vertical fuselage planking. Just behind the first frame I was able to install 550gr of ballast by inserting 15 custom cut lead plates that are saddling the hook assembly and rest on the hook-servo plate. A wooden plate keeps them in place and also forms the back of the battery compartment. The solid nose, lead and batteries account for 850gr fixed ballast, A 14x5x4cm box was then built and slid under the hook-servo plate where further (adjustable) lead plates can later be inserted to obtain the correct CG after the build and flight testing. As weight and strength in the nose is not critical, all the extra wood for the nose is cut from the delivery protection triplex that surrounded the carton boxes during shipping. Here is a picture of the fuselage at that stage, just before planking. The lead plates and pre-curved planking are also visible.

Pic 5088c


Before planking, ensure all wiring (electrical and pull-pull) to the tail has been installed with all intermediate supports, then carefully sand the entire fuselage skeleton to ensure proper adherence of the planking over all the already assembled items. It is written nowhere but some of the pictures on the CD-ROM show the fuselage planking to have been done with 2,5mm balsa. I suppose this was done to be able to better sand the joints because 2mm would have been sufficiently strong and easier to bend around the frames. As there were 6 of those 2,5mm sheets in the wood kit, I used them but only after pre-shaping them by soaking and forcing them with rubbers around an 8cm diameter carton tube. Before planking the tail section I dry assembled the wing key in the fuselage (also using the wing/fuselage joining rib) and mounted the horizontal stab firmly in position. The V-angle between wing and stab can then be measured accurately for the first time. On the plans it depicts 3°, I came out to 2,5° which is within limits for the maiden flight. More important is that looking at the model from the nose, you can now perfectly parallel the tailplane to the wing key by using spacers under the stab. This will correct any fuselage twist and if held in place during the planking, will ensure the glider’s surfaces will all be square to each-other and to the fuselage after completion. The temporary vertical fuselage supports can now be completely removed, upon which the planking of the top of the fuselage can also be undertaken. I started with just that and after precise cutting/adjusting/sanding the four curved upper panels were glued to every frame/stringer/bow that it touched. For that I used quite a bit of clamps, pins and pincers till the white glue settled. For this I used my second Titebond canister, the first one being already totally empty from all the previous gluing.

Pic5089c


The idea was to to first plank the entire upper-fuselage with two halves of pre-shaped sheets joined in the middle, then use straight planking for the entire relatively flat middle fuselage, all being done symmetrically left and right to avoid twisting.I worked my way forward in order to overlap the planking over the nose section. When all these panels had dried, a first rough sanding took place, also over the spine where I had added a 5mm layer to make it curved instead of relatively flat. With the horizontal stab having been measured within limits, it was possible to already produce a top cover that ensured a smooth transition between the spine and the vertical fin. As I saw on pictures of real Bocians that such fairings were pivoting on hinges, I duplicated that feature, not in true scale, but facilitating the insertion and removal of the horizontal stab on the field (while completely covering the two M6 screws in the process.

After finer sanding the area around the wing root area, I glued the remaining fuselage parts and inner wing rib in place so I could also plank the wing filet area. It took time to prepare those because they are twisted and curved (had to be forced wet) and as such need to be very much shaped to conform to the fuselage. Furthermore, much angled sanding was performed both on the fuselage wood and rib in order for the planking to adhere flat against it instead of just touching a narrow corner. On the pictures you can see that I intentionally omitted to install the leading edge bits on the short wing stubs as their final shape can only be found out after the wings are finished and installed. With the rest of the fuselage being closed, it became increasingly difficult for my tools to grab something solid to press those fairings against the skeleton and fuselage planking. Acupuncture seemed the best alternative.

Pic 5096c


All the previous work was enough to make the fuselage sufficiently rigid for it to be unscrewed from the construction beam so it could be turned upside down to mount the pre-curved lower halves bits of the planking. Compared to other gliders, the Bocian had a relatively narrow fuselage resulting in the underside to having a short radius that 2,5mm balsa has trouble to follow, especially at the back of the fuselage. I therefore had to pre-shape some of the parts even tighter along a smaller chord carton roll. On the back of that the same rubbers pressed “normal” curve planking for the forward fuselage.

Pic 5098c


With the underside of the nose having a pronounced curve up an inwards, I had to glue much smaller pre-shaped pieces to conform to the overall shape. To obtain a smooth transition between the planking and the solid nose, I applied a liberal coat of automotive fiberglass putty that was later sanded with the more squarisch nose balsa pieces into a nice and smooth continuous 3D nose contour.

Pic 5102c


Because of my fixed wheel I added frames just forward and aft of it, plus closing down the remainder of the small well so dirt could not be thrown around in the rest of the fuselage when operating from wet muddy grounds. The planking was then continued right to the wheel, also forming a solid surface for the custom cradle to support the heavy nose.

Needless to say, much sanding also was required to the rest of the fuselage balsa to obtain a seamless continuously curved transition between all the previously glued panels. Having 2,5mm to play with helps a lot, the structural strength coming more from the pine stringers than from the planking. To obtain the smooth curves I desired, I applied two heavy coats of primer, each of them being almost entirely sanded away. To ensure a uniform colorization of the dark blue, I reapplied primer to the previously painted but later altered tail section. Only when satisfied that I couldn’t see or feel any joints between all the partial panels did I undertake the final hand-sanding with fine-grit paper and applied the first coat of lacquer with the roller. I already did this finish not for the eye, but because the balsa is so tender that if left blank, it is all too easily dented when performing other work. The more than ten hours of sanding before and in-between the coats so far caused my apartment and myself to be covered with a layer of dust which I cleaned up before calling it quits and head for my annual ski trip to Italy. I deserved another break after two months of intense work on that Bocian project. This is how I left the Bocian for thorough drying, next to its custom made cradle and hanging into a jig in which I can paint an entire fuselage in one single go (starting inverted with the underside).

Pic 5104c


Due to the outbreak of the Corona virus pandemic we changed our destination to Austria a mere 5 minutes prior to hitting the road. All went well but upon return I decided to go into voluntary quarantine in order to avoid any risk of infecting others. As a lot of countries/areas went into lockdown it promised weeks/months of time to work intensely on my Bocian. Instead of starting on the wings I choose to first complete the rest of the fuselage, beginning with the very prominent canopy.

Cockpit and canopy

A first dry fit of the clear canopy over the supplied frame immediately shows you that a well-defined order will have to be followed to get any chance for a good fit. You quickly realize this is a catch22 situation. Not only the square-edged canopy rail doesn’t fit nicely to the fuselage shape, the acetate mold cannot be cut to shape before it is stretched over the rail that first has to be cut and angled (especially at the back), but you need the clear canopy angles to see how much material has to be taken away of the rail. First thing to do was to glue the angled front wood to the rail. This was done on the fuselage itself using cellophane to keep the expanding PU glue from sticking to the fuselage. PU glue was used here to fill the voids between that angled joint. Further sanding to obtain better contact surfaces would have caused the top of the angled part to sit too low versus the nose, and the back of the rail to end up too short to conform the canopy to the fuselage shape. Before cutting any excess wood it is essential to determine the exact final position of the frame on the fuselage, therefore the latches and catches are the next things to construct.

Here again, much will depend on how you want your canopy to operate. Small holes on top of the frames behind the canopy suggest to use a long sliding wire to lock the back of the canopy into place but I didn’t like that. The size and shape of the canopy probably create a lot of lift and to keep it tight against the fuselage I elected to use multiple catches along the length. At the front I glued two 3mm piano-wire stubs perpendicular to the angled wood, then drilled 4mm holes in their prolongation in the angled fuselage frame and glued 4mm copper tubes in those. On the aft side I fabricated a wooden lip that catches under the enlarged fuselage hole when slid forward. A perpendicular spring-loaded pin slides behind it to prevent the canopy sliding aft (and thus unlatching) in flight. The useless recesses in the cockpit rail were modified as to allow L-shaped custom-made wooden hooks to also slide under the rail. Additional L-shaped hooks were mounted under the canopy-rail cross-member to catch in and under extra holes made in the cockpit rail. All that took a while to fabricate and adjust, but provides a much better attachment of that large canopy to the fuselage, easy operation and fool-proof mechanical latching via a small pin on the aft side of the canopy seating.

With the canopy rail in its closed position it is then possible to mark the wood so you can cut and sand where necessary to shape that rail to conform to the surrounding fuselage shape and angles. As the top frame is more narrow than the bottom, I cut away the inside of lower one to eliminate this obvious visual hinder. I used pre-bent 2mm balsa to create the small turtle deck forming the aft end below the canopy and for which a bowed frame is in the kit. I then produced the instrument panel so it could be mounted in the canopy frame, covering my hook servo and locking my batteries in position when closed, but allowing good access on these items when the canopy is removed. The kit parts intended to produce the instrument panel fairing are twice the length and height of what it measures on pictures of full-size Bocian 1c gliders. I therefore first cut the main box to be maximum 30mm high and the eliminated the first half of the box plus had the front follow the slant angle of the forward canopy frame so that it could be completely closed. This means the instrument panel itself ends up situated along frame F4, just aft of the hook-servo plate.

The instrument panel itself has holes in the correct places and if you purchased the added instruments, these fit very nicely into them. The face-plates are nothing more than a picture of a period instrument panel printed out in the correct scale so they can be glued as one entire set behind the holes (but I replaced the small magnetic compass face for clarity). Don’t forget to sandwich a trimmed out plate of included clear acetate between the wood panel and the instrument faces. The bag of only 10 2x12mm screws is useless and the panel is much inferior to what scale-cockpits.at can deliver, but provides an acceptable view in my semi-scale Bocian. I cut the instrument panel so I could glue it a little deeper in the box to minimize the sun glare as per real. Add some custom-made panels to reproduce the top box around the sticking-out needle and ball. Sand the corners of all this into a smooth assembly. The plastic instrument roundels look good at the outside, but their inside better be painted before you snap them in place after the panel has been painted satin black (together with its entire box).

With the batteries under the removable instrument panel, it became time to take care about securing them without the use of tools on the field, and find a place for the connectors. As all this had to be integrated in the cockpit space I decided to first make the interior cockpit fairings/planking. To make those relatively one-piece multiple curved custom panels that had to fit between the frame bottoms I used curved 1mm aviation grade plywood I had inherited from the Air Cadets when after they sold their last wooden old full-size gliders, they offered me a 1989 roll. Part of that can be seen in the background of following picture. The starboard cockpit planking clamped in place, in the foreground the prefabricated curved port inner side, left forward lays the canopy rail with instrument panel and aft turtle deck.

Pic 5108c


This also felt like the good time to glue the fuselage wing-key furrow and aft anti wing-twist copper tube into place. Unfortunately the openings in the fuselage and outer rib were slightly too wide and too high for the former. 1mm plywood first was glued inside the openings before the furrow was glued solid in place with PU glue. I still don’t understand why the wing key was designed to be inserted horizontally instead of vertically (in an aerobatic capable glider). As I didn’t trust the solidity of this simple inner wing/fuselage rib to cater for the forces of a wing getting caught behind an obstacle, I decided to drill 8mm holes slightly ahead of the furrow, also through the very solid wing-key’s inner support plates so I could use long M6 nylon bolts to secure the wings to the fuselage. Proper alignment was ensured by also drilling the holes in the wing’s innermost ribs.

Then came the time to fabricate the seats, but for that floors had to be installed. Because of the kit’s internal structure regarding the rudder servo and the wheel well, the floors end up in 3 different heights. To fabricate them I used the lesser quality plywood that was around the kit for transport protection. I also used those for a front panel that blocks the batteries in place and hide the hook servo from sight. All that unfortunately eliminates of lot of space normally used for the pilots’ legs and feet so that in my model, the front pilot sits rather cramped, even after intentionally omitting to install his parachute. Nothing compared to the back-seat that is so narrow (due to the wing-key support wood) that I only could fit a Ken (Barbie’s boyfriend) in between. I grafted an older looking head to his body because that is what sticks out above the canopy rail, and swapped his Bermuda for long trousers plus painted his thick-soled white beach shoes black. I had to install a thick parachute for his knees to come sufficiently forward (over the rudder-servo seat cover) so his lower legs could be bent down.

All seats and floors are removable without tools to allow access to the receiver, power supply wiring, rudder servo and various connectors and antennas. With no plans or parts for an interior, all this took days of trial and error cutting and gluing before the complete interior and loose parts got painted in period PZL gray. Sticks, spoiler handles, trim and vent knobs were custom produced on the hand of the scarce available Bocian 1c cockpit pictures, then installed together with seat belts to complete the interior. Power wiring with switches and diode were then installed below the underside of the forward floor.

Pic 5111c


Last item was the canopy that had to be fixed over and around its frame. The optional acetate molded shape is a whopping 85cm long with lots of extra material that has to be cut away for fit. Bocians 1c’s had angled canopy styles but the provided one is entirely smoothly curved as used on the later Bocian 1e gliders. On the factory fresh Bocian 1c’s, a small straight front part remains fixed against the nose, a side-pivoting middle part is constructed by two straight parts joined by rivets all along a transparent bow in the middle, and an aft part also made from two riveted but curved parts that slide backwards on rails. While duplicating that would look very nice, the lack of bow drawings, poor rigidity of the 0,6mm clear material, and delicacy during field operation, led me to use the rounded one-piece canopy over the provided (flat horizontal) frame, with decorations to suggest the bows and separations. After everything dried I wasn’t satisfied about the rigidity of that huge unsupported bubble so I cut two custom adapted 1cm bows out of 4mm plywood and glued those in place inside the canopy, thus eliminating this all too weak clear part. Scale freaks better fabricate their own Bocian 1C canopy with single-curved thicker clear polyester panels over custom produced individual canopy frames instead of ordering the optional clear compound-curved thin canopy of the Bocian 1E.

Before starting the wings I gave the fuselage multiple coats of white and applied the light blue stork sticker I had ordered with the kit. With only a few black/white pictures of the period glider available, it was difficult to figure out the exact colors. On a single color picture showing the tail of Bocian OO-SZE along the entire Ka2b OO-SZD, it is obvious they were painted with the same period dark Sabena blue. On the balck/white picture it is clear that the nose and stork are much lighter in color and that led me to assume those parts remained as factory delivered in light blue, Sabena working around them with their later applied darker blue graphics. So after hours of masking on the fuselage and canopy, light blue and dark blue were applied. Canopy and cockpit assembly and paint took a total of three weeks to complete but I admit, a lot of that was glue and paint drying time.

Pic 5116
Jun 09, 2020, 07:31 AM
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Part 3 : Basic wings assembly


Analysis and preparations

After studying the pictures of the various wing assemblies on the CD-ROM it became clear they were from two different builders who used different methods than what’s on the plan. The pictures with the hand-written numbers depicting the various heights for the support planking during the construction puzzled me. If built that way the wing clearly would have a pronounced washout(twist) that would aggravate instead of diminishing tip stall tendencies. As on the real Bocian tailerons are of the Friese type that are hinged well below the wing line to counter adverse yaw, I decided to build them separately from the wing so their rounded upper leading edge could nicely match into a concave shaped modified deeper aft-wing spar. As all that eliminated the need for a 2mm support under the main wing-spar, I only needed a single support one meter in length and tapering from 14 to 10mm height to put under the trailing edge between the root and the aileron. Make that a stable support because you will use it a lot, even, during planking to ascertain no warping occurs. The few other parts that needed support got it by using scrap 2 and 3mm balsa. The aim was to easily build a wing with a 1° washout in the right direction. I obtained that by building the wing with its lower main spar flat against the table with the custom trailing edge support in place and ensuring an 11mm height between the table and the trailing edge of the outer rib. This is a deviation from OldGlider’s plans, if you wish to build it the way I describe here, don’t blame them for the flight behavior of your finished model.

If using the maximum one meter-long extra-wood from OldGliders you’ll end up with (weak) joints all at the midpoint of each wing, an unacceptable result for me. I bought 2m50 straight pine wood from a local do-it-self store and used my Proxxon FKS/E table saw to cut four 12,5x7mm main spars and two 18x4 and 18x5mm leading edges (OldGlider mentions balsa leading edges of 3 and 6mm which I find too delicate). As I care less about weight and prefer a robust model that can cater for hangar rash plus transport and field damage, these deviations from the plan tremendously augment the rigidity of my model.

As I fly from a variety of fields in various countries, some being bordered by high trees or crops, plus my heavy models needing speed in the pattern, I opted to install spoilers/airbrakes on top and below the wing. Instead of making those myself on long pivots as per original, I just ordered four 300mm mechanical spoilers instead of two (from OldGliders). The wing ribs are just sufficiently thick as to allow that setup but additional cuts had to be made in 3 ribs (the one just outboard of the spoilers can be left closed if you use 300mm ones. Before starting to assemble anything I recommend you file each opening in the ribs to the point that that the spars and stringers drop in easily and lay flush with the intrados and extrados. Even if the supporting stringers for the spoilers are only 5x5mm, I recommend opening up the cuts in the ribs to 6x6mm at this stage. This will allow the spoilers to drop in with their slightly wider rivets and plastic end-capping, and sit deep enough so the 2mm planking can later be applied over the spoiler frames (deepen the rib cutouts if necessary) . All this is a lot of preparatory work but is much easier to perform at this stage instead of later and ensures less sanding and better adherence of the planking.

Wing skeleton

I started by pinning the plan with its thin plastic on my table. The Bocian 1c wing being 2m15 wide (round tips) and my builder’s table only 2m, led me to following solution. As the two inner wing ribs (that have to be glued together) can only be glued in place AFTER the wing skeleton has been adjusted to on the fuselage-wing stubs (for correct angles with the wing key in place), that inner wing part was left in overhang with the wooden parts initially made slightly longer than on the plan. Idem for the outer rib and later to install rounded tip. Instead of cutting the leading edge and spars off at the last wing rib, I allowed them to continue outboard to the end of the rounded tip for solidity.

Step one was pinning the lower main wing spar directly to the plan, ensuring it is all the way straight. I then positioned my tapering (14mm to 10mm) support under the aft part of where the long ribs would come. It is good practice to first write down a number on all the ribs at this stage, all on the same side and position, ensuring the more rounded extrados curve sits on the top side. This might sound elementary but errors could easily occur with the less pronounced outer ribs or half-ones. Next all ribs were dry positioned over the lower spar to assess the span-wise alignments and measuring the incidence angles at different intervals. By supporting the trailing edges of the smaller ribs with 3mm wood inboard and 2mm wood outboard, wing incidence remained constant. This seemed a simple way to construct the wings, a slight outboard washout can easily be applied later during planking.

Pic 5125c


Just a few scrap wood supports were necessary to support the lower one meter 6x5 mm aft spar. Wood glue was then applied to each rib before pressing them on both lower spars, resting on their aft temporary supports. Dry position the frames for the aileron and spoiler servo access covers to ensure correct spacing, but do not glue them yet.

Pic 5124c


Then I added the few intermediate inboard leading-edge short false-ribs but supported them in the front with 3mm scrap as to allow a straight leading edge line all along the wing. The upper main wings spar was then glued on the assembly. The “eyeball Mk1” was the primary instrument to ascertain leading edge and trailing edge alignment remained perfect before all that was left to dry overnight.

Pict 5126


Step 2 was gluing the leading edge inner pine strip to the the rib noses. That was the proof of the pudding regarding rib alignment and came out perfect. By moving the trailing-edge support slightly forward I was able to glue the one meter 15x2mm pine kit-extra trailing edge strip under the rib ends.

Pict 5130


I then glued the 5x5mm pine strips providing the shoulders for the spoilers to drop into. As I use spoilers on top and below the wing I tried to compensate that weak structural spot by allowing those strips to continue against the next (normally unaffected) ribs. When the lower trailing edges had sufficiently dried I filled in the voids between the ribs at that position with 3mm balsa strips. I saw plenty of large gliders with mountain-ridge like trailing-edges and absolutely wanted to avoid that. Sandwiching balsa in-between the pine flat trailing-edge strips helps solidifying that area and allows the edge itself to later be sanded into less thickness. Allow all to dry overnight at that stage.

Pic 5131c


Step 3 consisted of removing the pins holding everything in place and allowing the wing to be slid backwards to the edge of the table so the latest applied balsa could be sanded flat with the rib’s extrados aft ends. If done properly the pine strip can be sanded in the prolongation of the wedge to obtain an ultra-thin edge that will increase the bonding surface for the upper strip. I then reversed the wing in different directions in order to be able to sand the leading edge smooth in the prolongation of the upper and lower arches of the rib-noses. With the wing upside down I also glued the lower spoiler shoulder strips in position, but this time only prolonged outboard because inboard there is the support bracket for the spoiler-servo access plate. After turning the wing right side up I let it rest on the aft tapering support and glued the 15x2mm pine upper trailing edge on top of the flattened rib/balsa-fill ends and let everything dry overnight.

Step 4 consisted of gluing the outer leading edge to the inner leading edge before dry assembling both inner wing-ribs in the wing skeleton and pencil-marking their presumed position from the plan on the various contact points with the skeleton. The wing was then mated to the fuselage with the wing-key, their furrows and the anti torsion bar in position, then gradually the protruding excess wing skeleton material was cut/sanded till the inner ribs were completely snug against the fuselage rib. New marks were applied on each the inboard wing stub and after wing separation, both inner wing-ribs were first glued together, then slid into the latest marked position with sufficient glue to form a solid bond. A combination of needles and my complete array of clamps was needed to fix everything in the correct angles and to each-other during drying. Note that the wing furrow was not glued at that time because it has too much (adjustment?) play within the ribs holes and can only be blocked during the next fuselage/wing mating. All this was then left to thoroughly dry overnight.

Pic 5133c


Step 5 was the dusty job of sanding the forward leading edge. Not yet to the nice rounded shape, but in line with the prolongation of the nose rib shape. The idea is to have more surface for the 2mm balsa planking to adhere to when that will be glued at a later stage. Only after that, the final sanding the nose of the leading edge can be done. In the meantime I mated the wing to the fuselage again and used wood leftovers of 1 and 2mm to block the furrow in the wing ribs (with the wing key inserted). Also slide the aft torsion bar through its fuselage guide and eventually adapt the holes for the copper sleeve in the inner ribs as to allow everything to glide effortlessly in and out. That is also the moment I glued the wing retaining nylon plate in place so all three wing attachments were perfectly in line with the elements of the fuselage. I then started planking the main wing spars, for and aft, first custom fitting around the angled furrow with 3mm plywood, then further from the inner rib till one rib further outward of the wing key, and from there on with 3mm balsa (all with vertical grain) till just aft of the aileron servo plate, outboard of that got boxed with 2mm balsa. As this box tremendously increases wing rigidity and resistance to torsion, it is imperative to check the incidence angles along the wing during that work. As the future capping continues to the aft spars, I decided to also apply 3mm balsa strips to fill the aft void in-between those upper and lower spars. Only after the boxing of all spars you can glue the support frames for the aileron and spoiler servo cover plates in place.

Pic 5137
Jun 09, 2020, 08:57 AM
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Part 4: ailerons and planking


Step 6 was the design and realization of the ailerons and their mechanisms. The real Bocians use hinge points aft and below the aft-wing spar, attached to a central aileron spar with deep cutouts in the leading edges and an upper internal pushrod actuator, to create a continuous Coanda effect, whatever the throw. The lowered nose during up-aileron position is typical for Frise-type ailerons, minimizing adverse yaw. Here is a picture of the hinge, actuator and air channel on a real Bocian.

Pic real hinge


The model’s ailerons only have a forward spar and modifying that would require major redesign and fabrication of about 100 new aileron-rib parts. The ailerons being 118cm long and have to be pivoted preferably without ungainly gaps to the aft wing (that even without planking tapers from 25mm to 15mm). Even after trying hard with multiple drawings of cross-sections of both ends of the ailerons and aft wing sections, I was unable to figure out a design that was workable and combined a relatively constant aerodynamic slot with a leading edge of the up-going aileron protruding under the wing to counter adverse yaw. I wasn’t the first one that tried that because in a book of Polish gliders I saw drawings of how SZD experimented with various methods on their previous glider, the SZD8 Jaskolka an later SZD11 Albatros gliders. Here you see that picture together with my experimental drawings regarding gap-shapes, hinge points and types, with possible max throws.

Pic 5140c


I finally settled for a hinge point slightly under the bottom of the ailerons but 15mm back from their leading edges and differential throws of 30° up and 15° down (real Bocians are aerobatic gliders). In order to have sufficient wood to sand the necessary convex and concave rounding for the airflow to blow over the ailerons, I cut the adjacent balsa trailing edges/leading edges from 15mm balsa (not provided) instead of 10mm as indicated on the plan. I would like to see an OldGliders produced Bocian to see how they resolved that aileron hinge problem without having huge gaps. With judicious tapered cutting, a single 15mm balsa plank is almost sufficient, some of the outboard appendixes can be made by first sandwiching wood leftovers. When everything is cut and adjusted, the appendices were joined to the one metre leading edges with 2mm plywood strips glued in custom made middle-slices, plus some ply strips glued flat to the inside joints. Do not neglect those strong junctions because all the torsion of the outboard aileron appendices are transmitted to the main aileron leading edges via that single junction. All this was left to thoroughly dry before sanding those leading and trailing edges to the necessary curves at the aerodynamic gaps. That will allow you to obtain the identical 10mm balsa trailing edge bottom as depicted on the plan, thus allowing all provided ribs of the wing and the ailerons to be assembled/glued after making indentations but without further modifications.

For the actual aileron construction I first laid out the 25 kit-ribs. Although they had been hand-marked by ball-pen, this had been done disregarding the orientation and that is important because of the under-camber of the ailerons. After sanding the mould stubs I thus applied new pencil-marks right side up and all on the exterior side to avoid assembly errors. I then marked and filed the 5mm indentations on the backside of the 15mm deep leading edge, that is not on the plan but to me essential to obtain torsional solidity (and respect the plan’s overall wing dimensions because of my deeper leading edge). As I feared excessive forces on the outboard tip of the ailerons due to contact with the ground during accidental downward deflections during takeoff and landing, I replaced outboard ribs nr25 with longer custom made ones that could be glued next to the leading edge balsa end instead of against the back, increasing the contact area. The following picture gives an idea of how the preparation work looked around that stage.

Pic 5142c


Before the actual gluing I taped the leading edge and bottom of the trailing edge on the plan. I then held the future upper trailing edge loosely aft of the leading edge so all ribs could be capped flush at a later stage. The front of the trailing edge was slightly lifted by use of pins, just enough so the under-camber aft of the ribs could be glued flat against the trailing edge to continue the hollow intrados curve. After every rib got angled and checked, I applied a liberal amount of glue and used weights to hold everything in place during the overnight drying process.

Pic 5143c


I then glued 2mm balsa strips in-between the rib ends to completely fill the voids. When dry, I sanded everything flat along the top of the ribs and thinned substantially the back of the the trailing edge bottom, then glued the upper trailing edge in place.

Step 7 was the installation of the 70mm long Robart pin-hinges along some of the ribs. To allow sufficient up movement, gaps were cut in the leading edge. With part of the hinges floating in the gap between the wing and ailerons, it was imperative for the rest of it to be solidly anchored. I therefore glued balsa blocks along or in-between the ribs for the pin-hinges to slide into and also to reinforce the structure where the relatively large gaps had been cut. Pin-hinges were inserted at an angle, both in the wing and in the aileron to obtain the correct Frise-type effects and keep the gap between both relatively constant at any deflection angle. On following picture you can see how everything looks on the underside before mating.

Pic 5144c


After some of the hinge-ends had been filed at an angle to stay within the ailerons, I started capping the ailerons. This number and position of the triangular capping deviates from the ones on the plan to conform and hide the 5 hinges per side as per real Bocian. During top and bottom capping care has to be taken to follow the convex and concave rib design but the extra balsa for the hinges is hidden very well in the end. Note the third small jar of Titebond glue that is already empty, after gluing a single wing/aileron, even before capping or sheeting the wings!

Pic 5146c


After sanding the aileron capping flush with the leading/trailing edges, the aileron was dry-assembled onto the wing and a connection with the aileron servo was built-in. This necessitated partial cuts in the wing trailing-edge and aileron leading edge, the latter compensated by gluing a plywood reinforcement where possible. In order to be able to adjust things before planking the wing, the ailerons had to be glued into their own slots, but as the ailerons are easier to cover without sticking-out hinges, the Oratex got applied first.

The Robart pencil hinges were then glued into their aileron receptacles and when dry these hinges were then pushed without glue into the wing for fit. After some corrections to ensure exact lineup and free movement within the adequate throw movements (4cm up, 2cm down), the connection with the servo was finalized in a way that 50% differential was already entirely obtained mechanically with a complete servo movement. In the meantime I had dismantled the spoilers to paint the visible sides red as that seemed standard on Bocian 1c gliders. After reassembly I dropped them into their boxes and and used triple-wire connectors to connect upper and lower servos to a single 7kg flat servo (Master DS3010HV). That seemed an easy solution to cater for the freedom of movements of the 3 different actuator wires. It also allows easy adjustments to be made through the servo cover panel.

Pic 5148


Step 8: Last job was gluing wingtip curve base-plate which I cut from 2mm plywood and glued in-between the main wing spars and firmly against the last rib. The balsa on top and below that plate can only be added after the wing has been planked. I choose not to plank that wing yet so I had an entirely visible starboard skeleton available as an example to duplicate on the port side. That single wing took me about 3 weeks to complete but as I already duplicated custom produced parts for both wings, I expected the second one to go much faster. Note that on the plan the second last port outer rib had not been drawn so pencil that in first.

Just a single sentence now to tell you that the entire port wing only took seven days to duplicate to the same stage. I then assembled the model again and used my Robart incidence meter to check all along both wings and to verify the decallage (seemed to be about 2° but difficult to measure because of the very deep elevators). As both wing inner ribs were verified at 0° incidence it became obvious how nose-down a Bocian flies to provide a superb view for the instructor in the back, long before the idea got incorporated in modern turboprop/jet military trainers. The incidences along the (not yet stiffened) wings were within tolerance and the few deviations could be easily corrected during the planking.

Pic5150c


Step 9 Planking wings of this size is a tedious job, especially when only a minimal aft section is left open for soft semi transparent cover material. OldGliders provided 23 planks of 2mm balsa, so judicious positioning and cutting has to be done to limit the planking to five per side. Some pictures of Bocians are shown with the outer wing portions covered with fabric aft of the main spar, others and the plan show that section to be planked as well. I opted for the latter solution because of the many reinforcement blocks I installed for the hinges and large servo hole, hoping the planking in that section also helps resist torsion during aerobatics. That 2mm balsa planking is sufficiently thick for strength and just soft enough to follow the leading edge curves without having to be made wet. As these planks are forming the noses’ D-section, I found it important to have them mostly uninterrupted from the leading edge till halfway the main spar. As this will stop most of the wing torsion, it is imperative to hold the wing in the desired 1° final washout warp all along the planking process.

I therefore started with the planking of the extrados, with its trailing edge support plate again in position and the wingtip rib clamped to the table with its trailing edge 11mm up. With the wing’s main spar flat on the edge of the building table, the leading edge is standing free to accept the many clamps that are essential to bend the planking around the nose, the rest can be held in place with pins. Prefabricating the planking so the wood can be joined shoulder to shoulder midway over a rib increases overall strength. I started with the outboard forward section, then the outboard aft section that was cut with an 7mm overhang aft of the trailing edge (to help the airflow bridging the ailerons). When the glue at the leading edge had dried sufficiently to keep its grab, I replaced one by one the clamps by pins. The clamps were then used for the gluing long middle section. Shortage of clamps and pins caused me to thoroughly let that assembly dry overnight, my Titebond glue needing hours to resist the tension of that curved wood). Here is a picture of the planking process at that stage.

Pic5159


I intentionally omitted capping the aft ribs at that stage because these were too delicate with the wing still needing a lot of handling. I preferred to first plank the second wing the same way so both would have the same corrected washout before tackling the undersides. Following picture shows what can be achieved after about 15 hours of planking. Note the relatively few small bits of scrap from the ten 2mm balsa planks.

Pic 5161


After some initial sanding I turned the wing upside down and analyzed how I would plank the intrados. As the curves were much less pronounced I decided to plank that side with minimal cutting of the widths. The most pronounced curve was at the root and with the extrados already planked, it was impossible to use normal clamps to force the leading edges together. I therefore started gluing only the forward side while pressing the wing down at an angle against the table, using adjustable tools that were prevented from slipping by using firmly pushed pins in the hard leading edge. I used the wedge shape of an aileron to push the first few centimeters of the rest of the planking against the ribs.When dry, I applied glue where the remaining 75% of the wood had to adhere to the structure and that could easily be held by pins.

Pic 5164c


After the rest of the underside was planked and wingtips filled with balsa I was able to perform a first rough sanding to obtain an aerodynamic leading edge. Time again to mount the wings on the fuselage and carve the missing leading-edge blocks between both. Because of their exposure during handling I used scrap hardwood. This time I also trimmed the elegant fuselage trailing-edge fillet to perfectly join the one on the wings. Incidences were measured again and still proved perfect at the root and mid-wing, but washout at the wingtips was slightly different and needed correcting. I then applied a liberal amount of lightweight filler in the aft hollow area for the ailerons so a continuous smooth S-curve was obtained for the air to flow in the gap from the underside of the wing’s intrados to the aileron’s extrados (as per original). That also reinforced the overhanging extrados planking along those sections.

That initial planking was performed in a single week, but then the time consuming capping of the ribs plus making of servo access doors and spoiler caps was on the order. There was ample cut-off 2mm balsa-rests to produce all that in that I still ended up with 3 unused 2mm intact sheets. After a second sanding I applied a coat of lightweight filler over all the wood seams and dents. When dry, a finer sanding took place to obtain the smooth flowing aerodynamic intrados and extrados curves. As the 10cm distance between the ribs allowed the soft balsa to be pushed in at some places, and the trailing-edge in front of the ailerons had become rather thin, I decided to apply Zap Z-Poxy finishing resin over the entire wing. Half of the canisters was sufficient for both entire wings, and after sanding produced a smooth solid base for further finish. Using clamps during the application at this stage helped finalize and settle the last incidence corrections. I also applied resin to the balsa servo access doors and spoiler caps and it stiffened them without warping. Taking away the brush streaks or dirt particles was quickly done by rubbing with 180grit sponges, creating a perfectly smooth surface.

Previous model constructions showed me that even with a prevailing amount of planked area, covering the entire wings with Oratex (compared to only the see through parts) much facilitate obtaining a uniform finish without much sanding. Furthermore, paint doesn’t grab well on finishing resin. For that reason I also brushed Oracover liquid glue on all the cap strips (especially on the hollow undersides), wherever the edges of the Oratex would grab, plus around the orifices such as for spoilers and access panels, plus on those smaller parts as well. The concave intrados requires the fabric to be positively affixed against the entire cap strip lengths before it is slowly heat-shrunk, failure to do so could straighten that area into a flat zone, thereby eliminating the essential curve of the rib-bottoms.

Pic 5166c


After a coat of primer and sanding with 320grit sponges, two coats of lacquer were rolled on to produce a superb finish. The wingips were then painted, including the side along which the outer ailerons move. Only after that was it possible to glue the ailerons in place, taking care to align their bottom side with the trailing part of the wing. That is essential in order not to create drag in level flight, but lots of extra drag as the leading edge of the raised aileron drops into the airstream. Final individual adjustments were then made to the spoiler caps before they also got painted and installed in the wing. After connecting and adjusting the ailerons and spoilers to their servo’s (using a servo tester), the cover plates were screwed in place. Assembling the wings took a full 6 weeks working an average of 8 hours/day.
Jun 09, 2020, 10:02 AM
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Part 5: Final assembly and test flights


Final assembly

After the first final assembly I measured the incidences again and was glad 5 positions zeroed out perfectly and only the reading of the port wingtip showed a 0,5° twist in the good direction. I then put the model on the balancer and was surprised I needed another 700 grams in the nose to obtain the aft CG of 90mm, and yet another 200gr extra for the 80mm recommended forward CG for the maiden. That means that on top of the weight of the solid oak nose and the 200gr batteries, the total lead in the nose amounts to 1440 gram, pretty much filling the sides and the entire ballast box. Following picture shows lead in and around the entire nose section. Resting on the side is one of the many layers of custom-shaped lead that can be slid in the box under the hook servo. This allows easy field changes during flight testing. The red stripes allow me to easily identify before takeoff if the canopy latches didn’t engage correctly.

Pic 5173


On the scales the flight-ready model topped 8700 gr, which with a 125dm² wing area corresponds to a very acceptable 69gr/dm² for a standoff-scale sturdy-built model with 4m50 span. With power to the model all control throws were measured and equalized, with 50% aileron differential, 10% mix of aileron into rudder, and initial fail-safe set with open hook and spoilers plus a little left rudder. Next morning the Callie-graphics arrived by post and were applied, and protective bags for the wings and horizontal tail produced. I can now admire the fuselages of all four Sabena ornated gliders in my living room every day, what a sight !

Pic 5176


The model was then trial fit into the camper with sufficient space for the fuselage, but a mere 2cm room between the wings and the door. As the weather was good I assembled the Bocian and photographed it in company of my other 3 historic Sabena glider models in the garden.

Pic 5190c


I then took a ladder to climb on the roof of my garage to get a helicopter view of my Sabena-glider collection. After 4 years I finally got them together.

Pic 5194c


Technical recap

Dimensions: L:204cm, span: 450cm, height: 44cm, single wing lengths: 215cm
Ballast: 550gr: batteries: 2x98gr 2S1700 LiFe
Total weight including ballast for 80mm CG: 8700gr. Wing load 69gr/dm²
Reduce ballast by 200gr for 90mm CG
stab: 410gr, Fuselage: , left wing: 1688gr, right wing: 1644gr
Measured on plan: V=3°, first verification: V=2,5°, final
CG: initial 8cm , final cm
Throws: Ail: +17 -10mm, Ele: +15 -10mm, Rud: LR 25mm
Ail illustration: +25 -15mm. My Frise ailerons on plan +40 -20mm
My initial throws: Ail: +35mm -20mm °, Ele: +40mm -60mm, Rud: 75mm l&r
My final throws: Ail: + mm - mm, Ele: + mm- mm , Rud: mm L&R
Servos: Elevators+spoilers: 4x Master DS3010HV 7kgcm
Ailerons, rudder, hook: 4x CYS-S0150 analog 15kgcm
Colors: Basic White, Sabena blue RAL 5005, Nose blue RAL 5015

Maiden flight

Crosswind had been the reason the maiden got delayed by two weekend. On the first day of June after a couple of flights with my heavier Blanik operating diagonally over our field, and the wind finally losing some of its strength, I took up all my courage and assembled my Bocian on the field. Here is a picture after that, showing the Covid-19 restrictions with the mandatory 5m separation between the parked models and all pilot having to wear masks.

Pic preflight maiden c


I gave my i-phone to Winnie so he could make some stills and movies of that maiden. You never know what happens and studying the images afterwards can point out the problem you hadn’t seen because all happens so fast on a towed maiden. I placed the model for the start of the takeoff run in the corner of the field where a picture was taken showing how attractive that Bocian 1c turned out to be.

Pic holding for maiden c


As the Bidule towship connected and ran-up its engine I stood on the cable and overlooked my glider for a last visual check while I was mentally going through the test sequence I intended to perform.

Pic last visual


With a crosswind from the left (clearly visible at the windmills in the back) we agreed to takeoff and let the combo drift to the right during the initial climb, the make a shallow 90° left turn and climb to 300 meters. After an intentional left wing low takeoff I was surprised the relatively light model didn’t climb higher up behind the towship so I used pitch trim but with negligible result. I didn’t know if it was the wind or turbulence but I experienced difficulty maintaining wings level.

Movie maiden bocian takeoff
maiden flight oldgliders bocian 1c takeoff (0 min 31 sec)


Passing 300 meters I announced disconnect and was surprised how the model immediately banked. I used aileron and trims to keep it under control and soon heard a max trim of the rudder call. Something was wrong but I somewhat regained control and after stabilization I initiated the upwind CG-dive test. As the model didn’t show any sign of recovery I knew longitudinal stability was marginal so I slowly pulled out of the dive and made a turn downwind to evaluate the pitch coupling when deploying and retracting the spoilers. As I observed no drastic secondary effects but saw the model losing altitude fast, I decided to position myself for a high long straight final. I did not want to take the risk of executing normal base and final turns in the turbulent windy conditions under the observed doubtful lateral and longitudinal stability. I came in with a steep decent from 80 meters and those 4 spoilers plus the seriously blowing wind helped me develop the sink rate I needed to land on the field. The irregular crosswind and erratic aileron control forced me to keep the speed much higher than desired for a maiden. Partially retracting the spoilers in short final to break the decent was too effective so I extended them half to come down again. As after the flare the speed decreased, the ailerons became less effective and the weathervane effect played havoc with my flight path sot I let it go straight onto the wind and the model stopped dead on his track without any damage.

Movie maiden landing
maiden Bocian landing (0 min 11 sec)


Back in the parking I was astonished to see a slight left rudder input even with full right trim selected, plus both ailerons deflected about 5mm for right bank with half trim deflection, something was definitely wrong. I then remembered having knocked out one of the pull-pull cables when accidentally hitting the rudder with my foot a few days before. I re-clamped the cable with pliers but forgot to readjust the neutral, hence the deflection with neutral trim that is clearly visible on the images at the start of the tow. That had been enough excitement for the day so I returned home to fix those problems.

Next morning I assembled the model and powered it up. I couldn’t believe how little rudder deflection resulted from full left and right trim inputs, but proceeded to adjust the pull pull cables to neutral trim anyway. I then checked the aileron response to the trim, none! but the rudder moved more than with its own trim. That is when I checked the elevator-trim response and that was also nothing. I quickly pointed out the problem to be faulty trim input selections. I usually setup my models with cross-trim inputs but forgot to select that on the Bocian. Couple that to a programmed 70% rudder expo and 20% aileron to rudder mix, and you can imagine that any trimming I did only aggravated the bad flight behavior. The up elevator trim inputs I gave also only resulted in spoilers slightly extending ! I really goofed-up programming that model, mainly because I started binding the model for a quick check on the wiring to the just completed tail feathers very early in the build, instead of programming it entirely in one go after model completion. One lesson learned, luckily not the hard way because there was no damage. I nevertheless loosely added 22gr of lead in the nose but that will probably come off again after the second flight.

Second flight

A week later conditions were perfect for testflying and this time the Bocian behaved correctly. She glided much better but the CG-dive check still demonstrated a too quick recovery so I didn't even try to stay up longer and brought het back in for a textbook landing. I then immediately removed that 22gr of lead and sson after lined up for the third flight

Third flight

This time the height behind the towship was much better during the climb and after releasing again around 300m she glided much slower so after another CG-dive check declared it as the perfect balance. Stalls were ok but something was wrong with the turn reversals: to the left everything happened as predicted but to the right the glider initially developed a very pronounced skid (which I had not expected with my Friese type ailerons and aileron-rudder mix). That was confirmed after a few other reversals so I brought her in. Although the pattern and glide angle got better each time, after landing she veered abruptly to the left, so hard that it broke the aft skid from the fuselage. When I got to the glider I Immediately saw that the right pull-pull cable of the rudder had lots of slack. Back in the pits I discovered that after only repairing the cable at the rudder horn, I should also have checked it on the servo side because that one also had become loose at the servo arm. That meant repairs back home for a more thorough check all over.

The forward skid also showed some signs of lateral movement so white glue was injected into the narrow split separations to solidify that section. The aft skid as delivered in the kit was much too large and too high (for scale), resulting in the complete skid to exercise too much momentum on the single thin lower keel frame during this and the maiden side-way landing. Instead of rebuilding it I checked the rare pictures of real early Bocians where the tailskid is visible and confirmed they are minimal not tall at all. I suspected that large OldGlider aft skid to also have induced excessive weathervane effect during the landing of the maiden. I cut the sides off and custom built a strong 6mm multiplex scrap wooden assembly consisting of a horizontal base plate resting on the complete fuselage width on the two bottom fuselage stringers, then carved side plates to keep the new skid in place. That strong support assembly was glued with expanding PU wood-glue to the existing structure, ensuring a large contact surface squeezed between the formers of the vertical fin and the one in front of it. The actual skid plate was shaped aerodynamically and is only roughly half as high and as long than the one in the kit. This will tremendously reduce torsion during accidental side forces, and it is only kept in place by elastic fix-all glue so it will hopefully separate before it could cause structural damage to the rest of the tail. After using filler and paint, this assembly looks better and is definitely an improvement of the kit’s structure at that point.

pic 5202c


Fourth flight

The fourth flight confirmed that all the changes I made worked well and without efforts I remained in the air for half an hour and performed a normal approach and landing. The fifth flight confirmed the settings but the CG dive check before the stalls and spin showed it still to be a tad nose heavy. I removed another 10 gram from the nose and will keep the rest of the settings for the future. An elevator servo had to be replaced, probably due to transport forces on the very large elevator easily causing teeth to rip from the small flat servos inside the little stabs.

Conclusion

The attractive Bocian 1c from Oldgliders is a nice solid basic kit for which an extra wood package and some accessories can be delivered in one go. The majority of the parts are well-cut and the model’s construction is sturdy, maybe too sturdy and thus too heavy with all kit parts being cut from uniform-thickness 3,2mm plywood, plus constant-thickness wing spars from root to tip. The lack of construction information should not deter an experienced wood-builder from tackling this kit. There are very few real difficulties constructing this glider, but you’ll need months to complete it and a solid dose of ingenuity in the process. The foreseen rudder-servo plate and very solid way the wings are connected to the fuselage make it impossible to build a scale-type aft cockpit. The way the kit delivers the tow-hook servo attachment plate limits the space you normally need for a scale-pilot’s legs and feet. If you want to fill the very visible cockpit space of a Bocian in a true-scale manner, you better order one from a different brand or seriously modify the fuselage during initial assembly.

If you are not prepared to work intensely during at least 4 months, a standoff scale built of this kit is not for you. Oldgliders charges a mere 1150 euro to deliver an Almost Ready to Cover Bocian. If you think time is money or are afraid to tackle traditional woodwork, this is a tempting option that still allows you to add more details before covering. For about 1700 euro you’ll get the fully covered version but that has just an empty cockpit and takes all the “fun” away from producing a jewel that wears your own personal stamp.
Last edited by BAF23; Nov 18, 2020 at 04:24 AM.
Nov 11, 2020, 12:22 PM
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Thread OP

A crash at the annual Bastogne glider meet


A few more scale details

During the summer months as the crosswind had been a nuisance and I still had to test and adjust a lot of others models on their new receivers I hadn’t flown much with the Bocian but custom-fabricated a period looking vent-window and fake overlap junctions under the clear canopy. At that moment I thought all the intense work on my jewel had been completed but that proved too much optimism.

Pic 0030c


Pole dancing at Bastogne

Early September I took it to Bastogne where I attended the only Belgian international glider meet of the 2020 season (due to Covid-19 restrictions). The first day I flew the Blanik because the wind was fully cross and I had to get used to that sloping field again. On the second day the wind was calm and I assembled the Bocian. The first flight was uneventful and I managed to stay up for 20 minutes. The second flight was even better but when coming in for landing I forgot to adapt my mind to the pronounced nose-down flying attitude of the Bocian. I still had the body angle of the Blanik in mind but duplicating that on the Bocian really brings you very near the stalling speed, especially with the 4 spoilers deployed. At that point in final the controls became sloppy and adverse yaw more prominent. My glide angle looked good to cross boundary road and hedge, but my lineup and speed weren not. I erroneously thought I was going to land close to the middle but apparently was lined up on the far right side.

As it hit the bushes at the side of the runway my model stopped dead in the tracks. I quickly crossed the runway and saw that my Bocian had a wooden corner-pole deeply embedded in the starboard wing. The canopy seemed intact but the starboard forward fuselage had substantial damage from the nose till the wheel, but less serious on the port side.

Pic 0048c


The pole had penetrated till the main wing spar but not damaged the latter. The pole was there to attach the barbed wire fence that was hidden inside fencing with relatively thick wild branches that caused widespread damage to the entire forward and bottom section of my fuselage

Pic 0051


A long crack was also visible on the starboard elevator support spine, probably from the horizontal tailplane being twisted, but the latter was completely free of damage.

Pic 0049


Another pilot helped me to delicately extract the model from the barbed wire and hedge without further damage, and after a first look was reassured not much structural had been hit, but the serious damage would take time and dexterity to repair. That was the moment I decided to equip all my large models with FrSky airspeed sensors. You can read more about that on my specific blog page: https://www.rcgroups.com/forums/show...-installations

Wing repair

In November I gathered my courage and started the repair job on the starboard wing. After some cutting of the fabric I was able to unfold the covering and broken structural elements to better inspect the inside and figure a way to repair that nasty looking area.

Pic5295


I inserted the wing key and also looked with a light inside the furrows to ascertain no damage had been caused to that essential structure. My thick ply reinforcements around the furrows had done their work well. Next I started cutting away all loose parts and used a pencil to copy the outline of the remainder of the nose ribs onto a paper to use as a pattern to cut new 3 ribs from plywood leftovers. Whatever was left of those also got cut out and I made channels in the wing spar to better grab the new ribs. Those were cut with a figure saw out from 3 and 4mm leftover ply and sanded to obtain a shape that matched the curves of the leftover 2mm planking or root-rib. I then prefabricated the new leading edge portions and adapted the old one to have sufficient overlap. To add strength I also made an additional strip to keep the entire aft of the leading edge well together to cater for forces in any direction. I started by gluing that strip and the slightly shortened new rib to the existing structure and used PU glue to fill any voids while drying under pressure of clamps.

Pic 5297


After a few hours that was sufficiently dry to add the rest of the leading edge spar and glue the other two rib-noses in-between the structures, but still no glue to the root-rib.
When that had dried it had sufficient strength to be used as anchors to squeeze the root rib tight against the parts using longer clamps whilst verifying the rib remained perfectly straight to avoid gaps with the fuselage. A thicker wooden beam was then glued to the leading edge spar to form the nose.

Pic 5300c


When dry, a belt sander was used to form a flat extensions to the ribs to which the planking could easily be glued. Ribs were further refined with a ruler over all of them to ensure a between the existing planking and the root rib. 2mm balsa planking was prefabricated to fit exactly shoulder to shoulder to the existing balsa (that had been cut halfway the ribs and other supports).

Pic 5301


All was glued shoulder to shoulder and held in place by pins while drying. Note how easy the front can follow the shape at that stage because the leading edge had not been rounded yet.

Pic 5302c


Heavy sanding was then performed to form the rounded leading edge shape and the wing assembled a few times on the fuselage to sand the mating area correctly. A layer of filler was then applied to get all the wood transitions smooth by more sanding.

Pic 5303c


Oratex was then ironed-on shoulder to shoulder to the existing Oratex (that had again been cut slightly shorter to allow some overlap over the original wood. Another few coats of filler and primer were then applied and sanded before the wing was put aside, priming and painting had to wait to be done together with the fuselage. Stay tuned for the entry covering the fuselage repair.
Nov 18, 2020, 04:54 PM
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Thread OP

fuselage repair


For starters I performed an in depth check on the canopy assembly and discovered some more damage. The locking hooks at the back had been damaged and were repaired. The two wooden canopy bows under the canopy were not sitting correctly on the frame anymore but displaced to the port side. This was rectified and the clear canopy glued to the bow and the frame where necessary. The cracks in the starboard forward windscreen were glued with clear canopy glue and the end of the cracks drilled out to prevent from spreading further. The clear parts that showed marks from rubbing with branches of hedges were then polished with rubbing compound.

The damage on the tail was so minimal that I refrained from cutting the planking away. As I was barely able to open the long crack any further I elected to use a sharp knife to just cut a minimal V over the entire crack. After putting the fuselage on its side I allowed thin CA to run in that channel whilst I tried to force the crack open and close a few times. Hopefully the CA had penetrated sufficiently deep to close any hair-gaps and after drying I applied lightweight filler to completely close the crack.

After taking all loose stuff out of the cockpit the detailed inspection revealed no structural damage at all to the keel. In fact, except for a single short stringer portion on the starboard side, nothing structural was broken. The blow of the impact had caused the stringers (still under stress from bending into the curves of the fuselage) to become unglued and spring straight again, taking with them the balsa skin that also tried to resume their flat forms wherever heavily curved. This can be clearly seen on the port side of the fuselage. All that was easy to repair using nothing more than “UHU endfest” glue for the stringers, and Titebond wood glue for the planking.

Pic 0046


The starboard side got the most damage from the pole and had to be stripped of a major portion of its much damaged planking to first tackle some structural repairs. The broken stringer was taken out and the remaining extremities cut at shallow angles to augment the grab surface of the new inset. Other stringers were glued together at their weak junctions and the broken canopy rail portions glued together again, all using the strong “UHU endfest” glue that got hot air blown over it during curing. That was to augment solidity but unfortunately also caused some dripping that was later milled away.

Pic 5314c


The bottom fuselage had been a mix of cracks, deep scratches and missing wood, nothing really structural and relatively easy to repair.

Pic 5309c


More wood was cut away where it was ruined, but re-glued where still solid. Lots of time was spent adjusting the new 2,5mm balsa to be a tight fit against the remainder of the planking before any glue was applied. This is how the heavily damaged starboard side was completely closed before any sanding or filler was applied.

Pic 5316


After milling away the expanded PU glue at the joints I applied about 3 layers of lightweight filler that was each time sanded wit ever smoother sandpaper, first with a block to obtain straight lines, and later by hand to conform to the multiple curves. In the meantime I received the new stork stickers that were just a little different and thus necessitated both sides to be replaced. After the old ones were removed the port fuselage could be sanded and corrected the same way as the starboard side. I then applied three coats of primer to all the treated surfaces (including the wing and tail repairs) and those were delicately sanded by hand with 320grit paper on sponge to obtain smooth new surfaces without visible transitions to the old ones.

Pic 5327c


Next came the application of the new stork stickers after which it was possible to mask-off around them and prepare everything for the blue with a roller.

Pic5329c


While awaiting the 3 coats of blue to dry I took the time to install the custom produced functional pitot static system in the hope that will help me prevent similar crashes. Tubes, sensor and wiring were all installed invisibly behind the instrument panel and under the floor, the copper pitot-tubes were bolted on the fuselage in an agle I expect is correct to measure the airflow’s total and static pressure. The copper pedestal was not on the original Bocian but looks so good I elected not to paint it blue.

Pic5332


You’ll have to inspect really close to see any repairs. That complete job only took 2-1/2 weeks and I’m proud my jewel looks as good as before the crash.

Pic5330c


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