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Jan 19, 2013, 04:40 PM
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Build Log

FMS T28 Part 5: modifying the wing

Part 5: wing modification

As you read in previous chapters, whilst mainly concentrating on the fuselage, I already started working on the wings when time available. A test of all electrics showed, although I have a version one, the flap servo’s are of the slow type. Lights were of correct colors but mounted so deep in the foam, much of their effect was lost. The transparent covers had been glued excessively and were anything but flush with surrounding foam. All had to be removed because my wingtips would be blue, and the transparent covers had been applied over the red painted foam. Removal of the covers without cracking them required some delicacy, but removal of all the glue from them proved impossible. The thick lights bulbs were pulled out from their recesses and glued only at their base, shining much better now. The area around the wingtip lights was painted blue, and the one around the landing light silver. Covers were again glued, but now as flush as possible. Traces of factory glue excesses requires partial covering of the transparent area during the vinyling phase. I then removed the factory applied plastic tapes that covered electric wirings and servo’s, and applied several coats of lightweight filler to fill all surface creases and wire channels. After much sanding I obtained really smooth surfaces as a good base for later vinyling. Ailerons were cut off because their thickness and foam joint only allowed minimal deflection. They got the same treatment as the elevator and rudder (see part 4), being covered after the control horns had been flush mounted and excess screw lengths dremeled off. Ailerons were test fitted but not yet glued into position because the flap problem had to be resolved first.

Large very thick flaps were factory hinged by a narrow foam junction at the bottom of the wing. That allowed a serious deflection, but also created an enormous wide and deep gap on the top or the wing. Those flaps definitely could create drag, but it is doubtful they would generate any lift because the airstream over that gap would make everything behind subject to turbulence (or even stall). On the FMS P51 Mustang they hinged the flap on top of the wing, at least allowing better airflow over the all-important extrados, The reverse installation method on the T28 Flaps was obviously unacceptable. Flaps were thus separated from the wing, and their straight front sanded off top and bottom to create an nice airfoil. The wing end got Dremeled out to accept this airfoil, but that still left a slight gap on top and bottom. I then cut out a narrow strip of foam on the top part of the wing junction, to flush glue a plastic strip of 1,5mm thickness and about an inch deep over the flap gap. With the use of flap hinges with a pivot point below and behind the wing, the top of the wing will be completely flush with the flaps up, but when deflected they will move backwards and down, allowing the positive pressure along the bottom of the wing to enter the small gap and be expelled under that plastic cover and over the top of the rounded flap nose. The gap in fact creates a venturi effect that will increase the lift and delay stall onset over the flap. On the picture of the real aircraft with flaps down you can clearly see how the rounded shape of the flap keeps hugging the top plate, whatever flap position. At least this configuration will give the airflow a chance to bend around that corner. The silver part is completely hidden with flaps up, indicating how much the flap extends to augment the wing area.

Having removed so much foam of the wing and flap, the total wing area flaps up has been reduced, but the fowler flap effect when extended more than restores the lost portion, and will allow effective partial flap use for takeoff. My model’s increased weight will benefit more from extra lift as from drag. The picture shows the cutoff in the wing areas and the reshaping of the flap and ailerons

Following picture clearly shows the stock starboard wing on top, with the flap held by a thin foam link at the bottom, and the resulting huge gap with square corners even at moderate flap positions. The aileron of that wing is held by a small foam strip in the middle, and the top and bottom ends quickly hit the vertical flat back of the wing at very moderate deflections. The bottom port wing got the modifications to flap and aileron, but the flat coverplate had not yet been installed in the carved out strip, at the time I did dry fittings during the final sanding of the flap nose to obtain the essential correct rounding. Belgian customs delays are notorious (even when not on strike) and without delivery of the ordered HK flap hinges, further work on the wing got stopped after vinyling the wingtips and ailerons.

In the meantime an airfield mechanic (also a superb model builder and pilot) informed me our original T28 got some paint applied to the nosecone and propeller hub. Those are now red and I hate having to strip the chrome plating on those FMS parts so the plastic paint will hold on those fast rotating elements, and the constant speed unit dome which is the grab to tighten the prop on the engine now painted flat black. I don’t think all that is a visual enhancement but I want to keep my model as faithful as possible to the one pictured by the mechanic in the hangar along our rc facilities.

Click here to read part 6 of the T28 build log
Last edited by BAF23; Jan 25, 2013 at 04:11 AM.
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