I built a 24"x24" Pizza box Flyer to evaluate the efectivness of a full airfoil on this type of plane. I had hoped that a blunt edge would help with the pitchiness of this type of wing. However I managed to break the foam while bending it whitch resulted in a sharpish leading edge. I used 1/4 pink foam with a max thickness of 2.5". On my next one I will use a heat gun to mold the foam over some PVC. I decided to use wingletts to help the elevons work better at high AoA. It came out to weigh 20 oz.
I used a 200 watt motor witha 12x3.8 prop

http://www.youtube.com/watch?v=8eftSfAjA_E

How about that high speed pitch problem? Did your airfoil have any effect?

Once you get it all sorted out, give this a try................http://www.rcgroups.com/forums/showthread.php?t=1515094

I made some changes to the PBF.
I built a new one with a more rounded leading edge. I also used a foam box spar and a longer nose. This lightened it up quite a bit without sacraficing strength. I also decided to have the rudder hang past the elevons. This allowed me to not have to notch the elevons and allows it to be more effective in high AoA.
The pitch stability is very good. Top speed is pretty slow (~40mph). It is more of a 3d plane than a speed demon with its current set up. I am confident that it would be good at higher speed with a hotter motor.
It is super floaty for its 20oz weight.
Here is a video shot by my 8yo son. (you have been warned)
http://www.youtube.com/watch?v=4OUXfCCazbI

Thicker wing means higher induced drag means exponentually more drag as speed increases. That's why the F-104 was able to go so fast, while the DC-3 never even got close to breaking the sound barrier.

Pavelow, That is a terrible analogy. The f-104 was able to go fast because it had a huge jet engine pushing it along. Not just the wing thickness. There are more factors to all out speed than souly the % of the airfoil thickness.

Sure the frontal area of a typical PBF is way less than my airfoiled model. But a flat surface also causes drag. A curved airfoiled surface causes less drag than a flat surface.
I was specificly trying to reduce the wild pitchiness of the flat wing by using a rather thick airfoil. To this end I would say that I suceeded. The stall is very soft and almost non exhistant. It may not do Mach 6 but it is stable. I may try replacing my 900Kv motor with a 12x4.7 prob with a 2200 KV and a 6x4 to see how the high speed is. But for now I like the 3D style flying it offers.

Originally Posted by Bike Medic

I made some changes to the PBF.
I built a new one with a more rounded leading edge. I also used a foam box spar and a longer nose. ... It is super floaty for its 20oz weight. Here is a video shot by my 8yo son. (you have been warned) http://www.youtube.com/watch?v=4OUXfCCazbI

Nice idea and it reminds me of some of the stuff I have seen in the Armin Wing (if I spelled that right) - "Easy Foamboard True Airfoil Wing Construction" thread. Thanks for sharing.