There is a possibility I can get access to a wind tunnel  at local engineering school aero dept. They have done some work with RC aircraft- I'd be interested to know about any wind tunnel testing that has been attempted to investigate aerodynamics of prop or aircraft design for   C/L  PA aircraft , (or speed or racer for that matter).

Hi Keith, I think your advise about deciding what to measure before pursuing any form of empirical testing like wind tunnel work is right on. I do have a couple of questions.

To my knowledge, the only signficant body of wind tunnel data  for slow speed aerodynamics with test samples with model size reynolds number airfoils are airfoils intended for R/C sailplanes.  Do you know of any wind tunnel data created for say R/C aerobatics or similar disciplines in the US or Europe?  I can understand the appeal of the idea to select a proven airfoil and plug it's coefficient of lift into the lift equation and  get a result of what a given wing will do. It seems very neat and clean and precise but you make the case that it is not always so"cut and dried".

This leads to my second question, Wind tunnels go to great pains to straighten the air flow but a stunt plane flys in a circle so even if you had some nice "clean & precise " windtunnel data how much would it be effected
or invalidated by the circular flight path a plane follows or would it be effected at all.  I defer to knowledge on this one Keith but I would guess it would have some effect.
                                                                       Pat Robinson

The circular airflow business - If you test wing and tail in conjunction, I guess you could just set them at the appropriate angle to each other, to experience the "circular" effect. I.e. instead of the airflow being circular, set the wing and tail to be circular. If you'r just testing the circular effect of the flow over the wing alone, I guess you might be able to build your test section "circular", i.e. bend the airfoil chord line accordingly, so you end up with a semi-symetrical section. Intriguing. This is taking design to depths I had never considered before. It sounds so complicated I might just continue building and flying in ignorance and devil take the hindmost!

To: Lyle .  The person you might want to contact is Michael Selig ,
Department of Aerospace Engineering - University of Illinois at Urbana-Champaign, Illinois 61801.  He may be one of the worlds most knowledgeable aerodynamicists about model size low Reynolds numbers airfoils. It would seem that he would provide you with the best advise on setting up your test program. You can find his site online UIUC airfoil Data. 

To Gary and Lyle :
There has been wind tunnel testing on symmetrical stab and elevators that you can read about in Martin Simons book "Model Aircraft Aerodynamics".
This is recomended reading even if you just want to dabble to understand things a little better. Martin Hepperles web site has good data and is worth a look.

You can also go online and download :
NACA Report No. 360 - "Pressure Distribution Over A Symmetrical Airfoil
                                        Section With Trailing Edge Flap" 
Please note*  This report is not for model size low Reynolds numbers so we can only extrapolate its value for stunt size models.

The thing you have to understand is that nowhere else in the aerodynamic world do people use "Plain Flaps" (as opposed to extendable "Fowler" type flaps) to fly radical manuevers like we do in stunt.
This point was clearly brought home to me when I e-mailed the creator of Profili airfoil software. Profili has incorporated X-foil virtual wind tunnel as an optional feature. I wanted to ask Mr Duranti if it would work to scan in and test some stunt airfoils in X-foil.  When I described what a stunt airfoil looked like and how it worked he thought it was the worst aerodynamic idea he had ever heard of and he didn't think X-foil would work.  Guys here is a man who has worked and processed close to a thousand different kinds of airfoils but he had never heard of a stunt wing with a manuevering flap. We take the idea for granted but he an many other aerodynamic types have no frame of reference for what we do in stunt. So guys I just want you to know what you are dealing with when you examine aerodynamic data or talk aerodynamics with non-stunt folks because it may impact how applicable that data is to your needs.

Fortunately, for all of us some very bright guys like Bob Palmer, George Aldrich, Bill Netzeband, Bob Baron, Al Rabe , Ted Fancher and many others have extrapolated design ideas from published data and then they went out and did the hard work of testing and refining those ideas to make them work for our needs.  I believe this was the point that Keith was making.

Lyle, an idea occured to me. you might try selling the idea that studying flapped stunt design airfoils and wings would be a first step in designing a small UAV that is capable of radical manuevering to survive in high threat enviornments. This might even turn up goverment funding and generate some real data for real stunt planes. Hey, It's just an idea.
                                                                     Till Next Time,
                                                                   Pat Robinson               

I don't think the "circular airflow is a problem. At any instant, the plane is seeing at most a airflow at an angle to the longitudinal axis--this depends on your leadout position. It is the lines that pull the plane in a circle. So to do a real test, you would like to include their effect which is adding to the drag of the inboard wing, and potentially giving a torque around the verticle axis (again depending on where the leadouts are).

Personally if you have access to a wind tunnel, I say go for it. Some questions you learn to ask by trying something and not understanding what you see. If you already knew the right questions, you probably already know the answers. This is the experience of a Particle Physics experimentalist.