I made some built up ailerons to replace the heavy balsa stock that came with a kit I am building. Now that I have the plane covered with the ailerons in (hinged but not glued yet), I notice that the leading edge of the airelrons are about 1/16th inch thicker than the trailing edge of the wing that they butt up against.

I remember reading somewhere that it is bad to have the ailerons thicker than the wing, but I dont' know how much thicker it has to be before it becomes a problem. Can anyone give me advice on this? I am trying to decide if I should rebuild new ailerons.

Andrew

It would seem to me that it would make more drag,and the turbulence would be increased to. If you can ,I would say to thin them down as much as you can.

Some years back, thicker ailerons were sort of a fad in C/L stunt. Of course, they were acting as flaps on our stunters, but that's not actually relevant. And matter of fact, C/L is about the best test environment you can ever hope for.

The idea that was touted for the deal was that the depression along the hinge line insured the boundary layer had to break up along that line so....... by having an effective dam in the flow, the depression (there still would be one) would fill up with stagnant air and the boundary layer would basically have a more constant surface to follow (even if the surface had a section made up of trapped air) and wouldn't detach. The idea was that the boundary would have a somewhat constant and positive path to follow. Nothing it encountered would be encouraging it to detach. Everything it ran into would encourage it's continued attachment. Or so the story went.

Turns out that the only negative anyone (with the flying skills to know) discovered was that the flaps were somewhat more effective. And it appeared that some designs and some retrofitted models seemed to be a bit faster. And it appeared that was only when there was no control input.

It appeared that the initial control input gave a quicker move into the turn. And it appeared that the amount of deflection you held didn't change at all. And that the neutral position was somewhat cleaner for drag. All that made some sense.

We got sharper turns and really didn't have to re-rig the control systems. Only problem was the airplanes were a bit "hunty" in level flight. Turned out that minor control input got quicker results. And we didn't want level flight to be harder to fly smoothly. And we didn't have exponential to take care of the situation.

I wouldn't worry a bit about your problem. It actually isn't a problem at all, but could be considered a design enhancement. At least if you're flying before judges, you should make sure to loudly explain all the magic positives you are getting from you very clever and superior design. That's what we did at all the contests.

You got no worries with that deal. For heavens sake, don't build new ones.

My wonderful old Akro-Knat has ailerons that are 9/16" th. at the leading edge while the wing trailing edge is 1/2" th. The plan note says: "boundary layer capturing device". The plane flies just great. For a photo see: http://www.rcuniverse.com/forum/m_66...tm.htm#6616653

BTW, C/L actually IS about the best test system ever devised for leisure-time-engineers. Every flight is extremely controlled in speed. Timing is extremely accurate since there are no unknowns. And model response to input is not only perfectly seen but you feel it as well.

When we were trying to see what that "fat flap" deal was doing for us, we had it made. A stunter had to fly level, make threshold turns, fly round stuff, and the exact speed mattered. And all that was easily seen and felt or timed. And we did it again and again and again. We got to see what a change of a couple mph did. And knew the exact mph. Most people can't tell the difference in 60mph and 70mph with an R/C plane and have no simple way to time them.

whatever............ keep those ailerons on that airplane.

(A threshold turn is a MAXIMUM, at the threshold of what the model can do without breaking apart, turn. Setup your next ARF to make close to a 5' radius turn and see what it does. Take a sandwich bag to bring home the trash.)

My research and experience says just the opposite. Many years ago Diamond Dust RC accidentally shipped out some kits with 1/4" ailerons when the trailing edge of the wing was 3/8". Most of the planes built with strong engines for speed had flutter.

If anyone digs back fur enough --they will find in a Model Avaition(I think) a article by AL Rabe concerning flat plate FLAPS/ vs smoothe streamline sections, on stunter wings for control line -- He made short wing sections which he affixed to front of hood on a 52 Ford as I recall and then recorded lift at various degrees of flap angle .
Made for good reading at he time --in mid '70's as I recall and had to do with a scale like stunter he was building
all very entertaining and he was quite methodical about the tests .
Having also flown stunt control line competitively -a little - I enjoyed it

My own findings were somewhat varied.
as long as nothing vibrated - the stunt flap need only be rigid and follow inputs - other than that - just get the throws correct to work with the elevator setups. big/small flap whatever
It all was on a case by case thing for me. My last stunter ? very light and no flaps -but then I did not do the "5 ft radius" turns (NOBODY DID) as that looked to me to be a figment of someones imagination.
when it was all said n dun- a flex free wing and flap (oraileron was my goal -at the least possible weight -- I also redid the 33% EXTRA ailerons on the H9 model to have a tapered section and counterbalanced tips and one servo -made a variety of structural models /redo's settled on a section cut from the foam/1/16" balsa sheeted cores.
The model was the best of any of the layouts in response . I balance ailerons at 20% of aileron avg chord.
solid wood ailerons --not my cup of tea as they are invariably too heavy at TE of aileron. try to balance one at 20% of chord ,which I do to help stop flutter -- btw --simply closing gap is not a flutter cure unless it severely attenuates movement.

C/L Stunters also get judged on looks and flaps that blend smoothly into the airfoil help shed the "toy plane" image. Having the flap slightly slimmer at the hinge line is supposed to contribute to smoothness. Minor movements of the thinner flap don't get into the airstream, so the plane is supposed to groove better. This idea was brought up to me in a book written by Dick Mathis and I've used it since then with no complaints.

I can't think of any full scale examples of planes [that fly at a decent clip] with control surfaces that stick out above and below what they are hinged to. It doesn't even look "right" to the untrained eye. I don't even think the design engineers at Blum und Voss would disagree here.

Yeah, there is "proof" that with our model airplanes, anything works. Or more often than not, if anything works ok it's proof of something. So it's not strange that thicker flaps work and that thinner flaps work.

Al Rabe was developing his P-51 and then BearCat stunters. He not only did a bunch of airfoil work, but came up with a number of innovations. His working rudder for C/L stunters was a shocker. It not only deflected more to contribute additional line tension to deal with P-effect, it deflected less to deal with the same. Al was an airline pilot who also did odd jobs delivering restored and rejuvenated P-51 Mustangs to their owners. Did he have a tough life or what. His Bearcat really proved the impossible was possible.

BTW, Al was one who would say that if you thought your idea/change/design worked, then it did. He was right.

Build enough different types on differet types of models -you will see that there is no cut n dried approach
Even the "correct" aileron area for a wing panel is totally dependant on application
some are fine at 10% - my small low speed models get up to 40 % which some good old aero school grads may say is prepostrous but on these models , is very workable .

Andrew....

I would think it a blessing on what you found. For in my experience in obtain solid slabs of balsa wood, they all tend to run thinner than advertised. This "too Thinness" runs from maybe .020" to 1/16" too thin, or less than advertised.

I drove over to a wholesaler a few years ago to obtain some 1/20th balsa. None in the bins. But they sure had a lot of extra-extra thin 1/16th stock that was marked at a more appropriate price.

The lump-bump was caused by the designer not taking in to account the actucal dimensions of the wood being used for construction. Most plywood today is metric based and thus thinner, and in my plans I account for this different thicknesses.




Wm.

Thanks for all the good feedback everyone. I'll see how it flys when the weather gets warm.