Pat:
Thanks for the inquiry, sorry for the delay responding, just got back from a couple days on the road...
Without building a thin flap & thick flap on the same design Its hard to single out JUST the flap effect. I can tell you that the total package worked pretty well, but there might also be room for more. Some facts and/or factoids:
My first high AR airplane was the "Orange Crate"; used 18% airfoil with a very blunt (modern) leading edge and "normal" 3/8" flaps. The airplane flew well but I thought it could do better. I thought this was under optimized. I did not like the thick leading edge more than anything. Looking back on it, other factors might have also contributed, but I thought the eclipse was clearl better. My next "Orange Crate" (if there was such a thing) would have more in common with the Eclipse than vice versa.
* If I may borrow one of Ted's mantras, flaps are NOT separate flying surfaces from the wing, "blended" flaps take this message completely to heart.
* Eclipse used a stock NACA 0018 root airfoil. The tip was NACA 0021 modified by moving the highpoint forward from 30% to 25%. These are nice friendly airfoils with plenty of bluntness, good max lift and are easy enough to build. Eclipse 1 & 2 were foam wings, Eclipse 3 a balsa ribbed D-tube.
* Flaps were 2.5" at root and 1" at tip - same as numerous predecessors. This works out to about 20% of chord (average)
* Trailing edges of the flaps were capped with a piece of spruce so I could thin out the trailing edge as much as possible. This increases the control effectiveness, reduces drag - and it looks REALLY cool!
* I'm jumping around a bit but bear with me. One BIG payoff with thick flaps is STRUCTURE. The flaps are extremely stiff in torsion, meaning that ALL of the control input really happens, the flaps do not wash out. Combine this with LONG control horns and slow controls (max throw around 25-30 degrees) all yielding exceptional mechanical leverage available.
* After all of the above, Eclipse 1 WOULD NOT FLY until hinge gaps were sealed. After test flight day I was ready to throw the bird away; thankfully my brother took it and sealed the hinge gaps, test flew it and brought it back. Then he had to CONVINCE me that it flew different before I would even try it again. The transformation was beyond profound. Since Eclipse 1 I have not built a single airplane (CL or RC) without sealed hinge gaps - and NEVER will again. (MEMO: Ted Fancher had similar experience with his 1982 NATs winner, but I forget which "-ation" that was!)
* The total wing package was thus high AR, blended flaps, structural stiffness, good mechanical advantage - and sealed hinge gaps.
* Of these the next thing I think I would like to explore is to recontour the aft part of the airfoil through the flap, but slightly "unblend" the airfoil. I attribute this idea to Al Rabe, since he is the first one to tell me about it but I see it on some of Bob Palmer's stuff too. The premise is that CLPA birds do not work very hard in level flight, so why not make the airfoil to be at its best when manuvering?
* I want to try redesigning the airfoils such that the TOP surface has a smooth transition when the flaps are deflected about 10-15 degrees. I believe this would help keep the air flow smooth and maximize lift when the controls are deflected.
...and the hinge lines WILL be sealed too.
Topic: Design Question for Dennis Adamisin (Read 1039 times)