WOW, this is a good one!
George Hicks did a whole thing of why a flat plate airfoil is best compromise for this area of flight IE very low RE#'s and wing loads for 3D flight not RC training, after he designed the Tribute, i forget where it was posted though, if you don't know George Hicks he is a aero engineer for Gulf-stream and an excellent pilot part of Team JR.
And as far as designing a better airfoil for these models, sure it could probably be done, but i bet it resembles a flat plate, like thin and blunt. I would love for somebody to compile a list of airfoils that harrier well for 46 size planes
I know I shouldn't let it, but this whole flat plate thing grates on me. Each of us needs a neurosis, I guess. I think two issues are being confused: thin and flat. It is definitely true that as the Reynold's number gets smaller, the airfoil section should get thinner. Now, if you take some 'standard' airfoil section and make it thinner, it will start to look more and more like a flat plate, at least from a distance, but there are important differences. With no exceptions that I can think of, performance will be enhanced if the leading edge is rounded (perhaps with a fairly small radius, if one wants to stall on command for some maneuvers), and the trailing edge is tapered. For a particular plane, it may well be that the effort of modifying the leading and trailing edges this way is more trouble than is justified for the performance gain, but that doesn't mean the flat plate is better. The only real superiority that I can think of for the flat plate is that it is much easier to get it truly symmetric than a traditional airfoil section. Strength is NOT an advantage of a flat plate. For the same construction technique, strength depends very strongly on the thickness, and very little on the shape of the section. In fact, the strength to weight ratio would almost certainly be better for a traditional airfoil section of the same thickness.
If you value the simplicity of a flat plate wing, and find the performance to be good, then you should use it happily. If you think that the flat plate performs better, I think you are mistaken. With any luck, this little outburst will get it out of my system, and I can lurk quietly for a while.
banktoturn