Supra Data:

Wing Span: 134 inches Wing Area: 1052 Airfoil: AG 40 - AG 43, Dry Weight: 49 Ozs, Flying Weight: 60 -65 (fiberglass), 65 - 70 (carbon), Wing Loading: 8.2 - 9.6, Surface Controls: Ailerons, Flaps, Rudder, Elevator, Built-in Ballast tube.

More Supra information: Supra Inst

NOTE: The rear hold down bolt should be at least 20mm in length. Some kits may have a 16mm bolt instead of 20mm. Check the last picture for more information on the rear wing hold down.

Supra # 42 pictures

Just out of the box.

Fuse arrangement. 2.5 ounces of powered tungston mixed with epoxy is molded around the battery as far forward as possible.

Airtronics 95761 digital servos, a 1200 Mah NMh battery, charging switch, Airtronics receiver and ballast tube. Battery pack is available for Kennedy Composites. Ballast is inserted by moving the receiver enough to allow access. The fuse was not cut out to accommodate the receiver to provide as much strength as possible in this critical area.

Measurement is from the front of the fuse with nose cone removed. Tow hook is in middle of adjustment range. Note antenna wire and sheath exiting the fuse. This was recommended by Larry Jolly and seems to work quite well. The antenna is taped to the boom with the last 4 inches hanging down.

Elevator push rod exits the boom about 3 inches forward of the elevator bracket. A slot about 1 inch long and the diameter of the push rod and sheath was cut in the top of the boom. After final adjustment was made, the sheath were anchored with epoxy.

The rudder push rod exits the boom about an inch forward of the forward rudder mount. This location was determined to provide the shortest unsupported push rod length and the least binding. The slot in the boom is about 1 inch long and the sheath was anchored with epoxy after the final location was determined.

The push rods for the Supra seemed to be too large and stiff to make some of the bends in the routing required for an external installation. I used the arrangement of servos as shown in the picture, but put the push rods inside the boom rather than have them exit the fuse. I experimented with the optimum angle to exit the boom and then cut the slots for the exits to accommodate the angle. I used small pieces of packing foam cut in circles to hold the rods agains the side and bottom of the boom. In the fuse, I used 6 inch pieces of aluminum tube to stiffen the rods from the entry into the fuse back along the ballast tube. I also used small pieces of foam inserted through the hole in the pylon to hold the rods in place in the rear portion of the fuse. It took a bit of work, but the results were worth it.

2/8/2006 - Another 1.5 hours with 'ole #42 launching from both a highstart and a winch. The dive and inverted test still indicated a forward CG so another .5 ounces was removed. Dive test now shows a shallow pull out in about 300 feet and the inverted flight test takes a little bit of nose up to maintain level flight. This feels about right for me. Of course DP and JW will take out another 1.5 ounces, but I like a bit more stability. Final weight is 67.5 ounces and the CG is located at 100mm. For windy conditions I will probably add .5 ounces which moves the CG to 98mm

Elevator compensation with flaps was reduced considerably to get a slightly nose down attitude with full flaps. I was pleased to note that deploying full flaps at considerable speed did not produce dramatic pitching modes. Only at high speed was there a little pitch up which was easily compensated for until speed reduced.

Landings were made to a hard ground surface with no grass, no wind and no skeg (F3J configuration). Ground slide was about 12 feet with the flaps raised at touch down and full down elevator, but no dork. The slide probably will be shorter on grass. Approaches were flown with no flaps until final then half flap until landing assured then full flap (raised at touchdown). With even a little wind, half flap may be enough as the model slows quickly.

FAILURE MODES

Notice the gap that developed between the CF cap and the fuse. The CF cap carries the rear wing mounting nut so with loose attachment, the wing could move vertically about 1/4 inch. Some 30 minute epoxy seems to have fixed the problem.

3/28/06 A new problem related to the above problem developed when the wing came off following a landing. As shown in the picture below, the entire cap with the mounting hold down nuts came off with the wing attached.

I have not determined the type of glue used to hold these parts together, but the only good bond is seen along the edges where the CF cap pulled away leaving some fragments attached to the pod.

Pictured is the front hold down bolt attachment that looks like an expansion molly bolt that was inserted into a hole in fuse and then expanded to bond the CF cap to the fuse. This attachment pulled out from the fuse. The rear hold down bolt is encased in carbon and glued into the pylon.

The question is how to fix this problem. Somehow there must be a structural tie to from the cap that carries the wing hold down bolts to the fuse/pylon. At this writing, I have not decided how to fix the problem. If you have a suggestion, email me at hilaunch@aol.com.

THE FIX THAT I ADOPTED

I received many responses to my request for suggestion on how fix this problem. I will quote some of them at the end of this article.

After looking at the problem for a day or so, I concluded that the major contributing cause was the lack of a permanent tie in between the wing and the fuse. The rear hold down was not attached to the fuse, only to the pylon (which is bonded to the fuse). This put the epoxy used to make the bond in sheer stress, which subsequently failed.

It seemed to me the only good resolution would be to attach the front and rear hold down bolts to the fuse. With that goal in mind, I evaluated several alternatives and finally decided to create some special tee nuts to be installed under the top of the fuse and on top of the ballast tube.

The sides of the nuts were ground away to compensate for the curve of the fuse. The balsa shims were placed under the blind nuts and on top of the ballast tube. The blind nuts were epoxied to the bottom of the fuse and the shims epoxied to the bottom of the blind nuts. To ensure alignment, the top cap was installed (but not glued) and wing the installed to pull the nuts into the fuse while the glue cured.

The bottom of the original hold down nuts was ground down to provide space for the top of the blind nuts. The original hold down nuts were drilled to allow the new 6 x 32 bolts to pass through. The old hold down nuts provide a guide for the new bolts to assure alignent and easy installation. They also act as a spacer to provide a hard connection between the wing, the new blind nuts and the fuse.

The depth of the old hold down bolts was carefully tailored to make a close fit between the top cap and the blind nuts.

The final step was to epoxy the top cap to the pylon being careful not to get epoxy into the path of the hold down bolt. The cap was covered with plastic film and the wing installed and tightened to hold every thing in place while the glue cured. The result was very good so some test flights were in order. A series of mild launches and landings were conducted in 15 mph wind. The wing attachment is very solid and I think will not cause further problems.

I noticed that before the failure there was some creaking, snapping, groaning and other sounds coming from the pylon area when the wind caused the wing to rock while I was holding the model for launch. These noises have gone away. I assume that the epoxy had been debonded and the noise was caused by the epoxy rubbing against the plyon. Why it did not fail on launch will never be know, but I guess the hidden expiration date that each model has, had not been reached. Your comments? Suggestions of others.

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