Tensilon (oz6861)

About this Plan

Tensilon. RC pattern plane for .40 power.

Quote: "Here is the .40 powered aerobatic machine to beat the nitro shortage while practicing for your pattern competition. Tensilon by Duane Gall.

A fellow in our club once entered a beat-up Fledgling in a pattern contest. He dubbed it "Castor Oil" just for the occasion, bragging that it would "make a lot of Phoenix flyers sick." And he did manage to place with it, thus proving two things: first, that anything is possible here in America; and second, that it's not what you fly that counts, but how you fly it. Practice is all-important, whether you're competing on a national level or just trying to hit the ground wheels first.

The airplane presented here was designed to get you through many hours of practice on minimum fuel, and - when you're ready - to compete on a nearly equal footing with the bigger ships. I would have called it Compensator, but somebody already used that one, so I have named it after the drug Tensilon, the antidote to Curare (oz5527). And it flies even better than a beat-up Fledgling.

Fine, you say, but what about all the other .40 size airplanes on the market? Why shouldn't I just buy a Kaos 40 or a Curare 40 (oz6141)? Well, go ahead! But if you expect these airplanes to perform properly, be prepared to get a new Schnuerle ported engine, maybe with a tuned pipe, and a bigger fuel tank to match. The Tensilon was designed to fly with a standard .40 such as you may have sitting around the basement. It is smaller and lighter than the others, and has a few notable features to make it more efficient. If you want to know what those features are, read on; otherwise just send for the plans and make Dewey happy.

Design Philosophy. Maybe I should explain that I'm not really a pattern flyer at all, since my first love is racing. Nothing irritates me more than an airplane that dawdles around Point A when it should be kicking for Point B. And, if you hadn't heard, speed is important to an aerobatic ship because it makes deviations less apparent. (The current folly of tuned pipes and fuel pumps is an attempt to squeeze the last smidgen of speed out of those big majestic .60 ships.) So Tensilon relies on speed for smoothness. The airfoil is a 15%, sort-of-laminar section with a sharp leading edge, instead of the usual blunt, 17-18%, Kaos-type section. Now I know Mr Bridi sat up nights developing that blunt airfoil just so the airplane would have a nice constant speed in the maneuvers. Well, mine gives constant speed too, it's just a little faster. And if you're worried about that sharp leading edge causing a vicious stall, relax. Wing loading and balance are far more important than leading edge radius, as any pylon flyer will tell you. If you're afraid of tip stalling, just sand the outer 6 in or so to a slightly larger radius. Voila! Gentle like unto a newborn lamb.

Now in my vast experience of one season of pattern flying, I've noticed that it's always windy at contests. This is no doubt due to the large vacuum created by competitors extolling the virtues of their latest handy device, or swapping tales of past glory. In any case, the wind - or, more properly, turbulence - tends to upset the smooth flight of an airplane. Many flyers make a habit of building heavy, massive airplanes to minimize the effect of turbulence. This is good thinking as far as it goes, but as Pappy DeBolt points out, even commercial jets will get tossed around. Since a model doesn't weigh as much as a 727, or shouldn't, anyway, there's no way we can eliminate the bumps through massiveness alone. Remember, we still have to take-off, climb, and maneuver using that little bitty engine. I believe that wing loading is the important factor here, and that a small wing is as good as another pound of lead. Tensilon has about 10% less wing area than standard .40 ships. This makes it better in the wind, with the added bonus that it doesn't mess around on landing - nothing scary, mind you, just a noticeable absence of 'float.' You, too, can get it in the circle.

Another factor that affects performance is the tail moment. This has to do with periods of oscillation and certain prehistoric fungi, which we needn't go into here. Let's just say that longer is better, and that Tensilon has just a tad less than the big Phoenix 6.

The wing construction is slightly unusual. It is a normal foam core, but planked with leading edge sheeting and capstrips as one would plank a conventional wood structure. There is no spar or dihedral brace except for the landing gear blocks, which are bound together by the center fiberglass tape. This construction is actually lighter than a built-up structure, and has proved quite successful on racers and pattern planes alike.

Besides being lighter, this method also allows adjustment of the wing after it is built, in case (Heaven forbid!) you should have a warp. Just twist the wing slightly in the desired direction while reheating the MonoKote. Be sure to use enough heat so the stuff doesn't sag a week later. There is a point, just below the melting point, where it will stabilize..."

Hi Steve - Here is Duane Gall's Tensilon from RCM magazine issue 07-79.

Direct submission to Outerzone.

Supplementary file notes

Article pages, text and pics.

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