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Jan 19, 2013, 04:30 PM
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Build Log

FMS T28 Part 4: fuselage assembly


Part 4: fuselage assembly

I had just 5 days to cover the complete fuselage, and for the first time assemble all the parts to transport it to the flying club. During winter once a month we gather together for some kind of activity and December traditionally means everybody displays the project(s) we are working on. Early march everybody brings their completed models after working all winter on them. I had covered my fuselage in shoulder to shoulder applied vinyl panels, coinciding with the now filled in deep FMS panel lines. Some panels like the one just behind the canopy required very delicate application because of their complicated concave/convex shape. Remember I had varnished the fuselage to get rid of most contrast between the factory painted parts, and the parts where upon removal of the decoration, the paint had come off with. The varnish makes a nice flat adhesive base, but the vinyl has to be spot on before pressing it down, any attempt to pull it off to reposition or get rid of a crease or bubble, results in the varnish remaining stuck to the vinyl and adhesive capabilities of that area being totally gone. The only solution then is to get rid of that worthless complete vinyl piece, cut another one out, and applying it over the area that has to be sanded with 600 grit paper again to soften the transition between bare foam and varnished foam, because the thin vinyl otherwise would show that.

Before covering the bottom of the fuselage I had to cut out an additional airflow exit. The standard aircraft comes with two open holes and I had read some people had their canopy pop open in flight, presumably due to cooling air being forced in the fuselage with forward speed, but insufficient area to let that air out in the back. The additional cooling holes I drilled in the fake engine and oil cooler channels just augment the need for exhaust capability, whilst I had to discard one of the stock openings to install the bottom speaker. I thus opted to carve out an additional hole in the only part available before the fuselage becomes solid foam. The channel got canted for best efficiency, and both orifices were now flush covered with a custom grille, later painted white.

After covering the bottom panels I glued Nylon M4 nuts into cutouts in foam against the speaker panel, and reinforcement rings into the panel so I can tighten that bottom panel, supporting the sound system during high g maneuvers, with long M4 nylon bolts. After this picture was taken that panel also got vinyled and I must say I was rather pleased with the completed fuselage look. In the meantime I occasionally had tackled one of the wings so I could show the other members what I had in mind with the flaps and aileron modifications, and the difference between a stock FMS wing with crevasse as deep and wide as the grand canyon, and a wing that had been smoothed out with multiple filler and sanding. With just a few hours to spare, I assembled all the parts I had, finished or not. With its cowling, prop and spinner in front of the bulky fuselage, it started getting some elegance. Because I didn’t want to hook up everything nor take transmitter or batteries along, I extended the gear by lowering doors and legs, one by one with the servo tester. Getting the wings together with the rods was simple, but having everything tied up and screwed into the fuselage holes required strong positive actions. Next I just dry fitted the horizontal and vertical stabilizer and fit the cockpit assembly. I liked what I saw and it fitted in the back of a friend’s station wagon.

Entering the club I saw most of the spaces already occupied but a fellow member who just had a small winter model was so friendly as to offer me his table. Next to my T28 I placed the modified and unmodified flaps and ailerons, a printed out copy of the illustrated build log, and the MrRcSound system components. From the start interest was so great I had to quit answering questions after an hour because my throat was dry. A Hoegaarden beer corrected that and I took the opportunity to make pictures of the other displayed aircraft, most being huge close to 10ft balsa wooden aircraft powered by serious multi cylinder gas engines. 2-1/2 hours later we packed and I was glad I had no transport damage, the cushions we took along proved their worth during the trip.

Next morning I looked at the model in the living room and did not feel so happy anymore. I had continuously demonstrated to others how I planned to eliminate the gaps in control surfaces on the wing, versus the solution I had applied to the tail, to get rid of the foam connection limiting movements and being unsafe in the long run. Whilst taking the model apart in its basic components again I grabbed the tail in one hand, and the rudder in the other and started pulling them apart. I was surprised how tight the connection was between the nylon hinges and the slots I had made in the foam, but they finally came apart without damage. I then did the same to both elevators and was convinced reworking the tail would be worth the effort. The problem on this model is the foam being so thick, with flat vertical cuts between machined parts. In order to get some control deflections, you needed a serious gap and that looks ugly. The stock ailerons on the wing are so thick, only minimal deflection is physically possible. The rudder base is 4cm wide, flaps are an inch thick at the root, with just vertical flat cuts at the junction with the wings. Cutting the joining foam and replacing them with standard hinges is not a good choice. I opted to Dremel out a concave curve on all fixed surface ends, and sanded the leading edges of the moving surfaces with a constant diameter so they would fit into each other and being able to move at least 25 in either direction without gaps. Before using the Dremel I carefully cut out the vinyl on those areas because I wanted to save as much of the original covering as feasible. On following picture you can see the round Dremel sandpaper used to hollow out the back edges. Rudder is done but only one side of the elevator to show the difference.

With the control surface now laying much deeper, the total wing and tail area are reduced a bit, and the control horns hit the bottom, so an additional cutout has to be made. With the foam being too rough to be vinyled, I chose to coat those exposed surfaces with filler which was then sanded smooth before being painted with Revell plastic model paint. After many trial and error fittings and additional sanding and touching up came the critical job of installing the hinges. I used pin type hinges because these penetrate the foam deeper. The pivot point has to come not in between the surfaces, but in the center of the radius in the leading edge of the control surface. It therefore was necessary to make small indentations in the surface so the other half of the fin could move freely around 30 each direction, and the pivot point was in the open air but deep into the foam cutout.

I tried many different glues so far but have obtained the best results for bonding foam and nylon, wood or even metal, with cheap Bison PU wood glue. It doesn’t penetrate the foam, but attaches very well to the surface of it. Any irregularity in the surface will act as an anchor for the expanding glue that becomes rock hard after half a day. The problem is it doesn’t cause much friction initially, and starts to seriously swell and expand in the 3 to 5 hour bracket. On previous aircraft I often had to cutout and replace all kind of hinges because after half a day I found out the expanded glue had crept into the mechanism. Although it would have been possible to just push the pin hinges in the foam behind the cutout joint area, having multiple hinges on each control surface I wanted to have them perfectly lined up to minimize friction. I thus use a 3mm drill bit between my fingers to twist it straight into the foam as a guide. Using mechanical means would have made the hole too wide or at an angle. I then dry trial fitted every hinge and made mental notes of how deep I had to get them to obtain the desired result. In order to eliminate the chances of glue expanding on the hidden deep pivot point, I then used a soft ear stick dipped into olive oil (I was working in the kitchen but for you guys in the garage any oil is good enough). Every pivot point was then carefully soaked, but care was taken not a trace could be found on the pins, because that would prevent the glue catching on. I then applied just sufficient glue to of the pin and pushed it into the middle of the cutout without glue touching the sides. After one surface is done, the assembly is raised vertically with the still unused pins lined up flat on the table, to be sure the pivot points are all in one line within the foam. After the glue starts to settle, I pivoted the free arms up as far as they would go so I could check their parallel vertical alignment to minimize friction. Every half hour I carefully moved every pin joint to ensure freedom, and on a few I felt the glue must have surrounded the pivot a bit, but after a few gentle movements the oil took care of any tightness and next morning everything worked perfectly.

On previous picture you see the pin hinges inserted deeply into the control surface, with the pivot point approximately at the center of the leading edge radius, exposed pin free to move up and down for about 30. Concave receiving fixed surface painted and pin hole manually drilled out. The remaining length of the pin is still sufficient for a good grip into the foam. After 12 hours of drying, the other ends can be inserted and the surface movement checked so the pins are sufficiently deep to close the visual gap, but without any foam part touching in its operating range. With the lowest rudder hinge in the fuselage instead of vertical stabilizer, it now became time to first permanently bond the tail to the fuselage and I did that with the FMS glue so if necessary, I might be able to take it apart. It all sounds very tedious and nitpicking, but when you compare the before

and after pictures you have to agree it is a major improvement worth two extra days of work.

With the fuselage now completed (except for the application of the Callie graphics, it becomes time to deal with the wings, but I’m still awaiting the delivery of different sets of flap hinges so I can experiment and choose the optimal hinge to create the desired fowler flap effect out of a very bad basic stock FMS setup.

Click here to read part five of the T28 build log
Last edited by BAF23; Jan 25, 2013 at 04:09 AM.
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