I recently built a small 3D model , which featured a very scalelike aerobatic airfoil.
I did this because the model was almost exactly same size/shape weight as many of the flat foam 3D models I have flown.
(The model is very inexpensive)
Anyway In flying it, I wanted to see if there was any noticable difference in how it performed -- due to the nicely shaped wing.
The one notable difference was absence of wing flex - so it was quite smooth and steady at higher speeds .
Higher being probably 20 mph.
The big question tho for me was -- how would it react at slow speeds - bordering on a stall.
Two of us flew it and as far as we could tell --it got "loose " at the same speed as other same size/weight flat wings .
Here is what I mean.
You can fly any of these easily down to the speed whare stall sets in -- BUT --if you try to hold it there -- it starts dropping from side to side - and will snap out if great care is not exercized .
HOWEVER-- If you apply power -then raise the AOA to past 45 degrees - the control becomes easier.-- until you reach an almost vertical hover -when it really tames down.
All in all -other than the inherant stiffness of the curved airfoil - we found no improvement-or inferior character in the wing.
Wing loading by the way was about 8 oz per sq ft.
I just did another model with wing loading of just under 4 ozs (3D model.) Exactly same type results in stall angle - just slower .

At very low Reynolds numbers the flat plate is at least as effective as a good design airfoil. I know it sounds strange but in all the books I l ooked there are only 5 airfoils tested in the wind tunnel for small Re and the flat plate is more stable, the separation point is almost independent of Reynolds.
All airfoils with thickness have a hysteresis and for Re=40000-80000, Cl drops significantly (20%-40%) with 1 degree variation of AOA. That's why the wings are rocking so violently.
For a 3D foamie you want to fly slow, the flat plate ( with or without curvature ) is the best airfoil money can buy.

Boby

Dick, quick question, did you notice that when you turned the power off it didn't fall like a brick like many of the flat winged planes do? Built the GP Yak 55 the other day and this was one of the first things I noticed. From any altitude at all you caould make a couple of large circles befroe landing.

Otherwise, it was very much like you described.

Ed M.