I was using the frisbee as an example of airfoil. It is stable because it spins, and by definition has to be symmetrical. Toss either one without spinning it and see how that goes. I'll wait.
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Ok, back to the original question: what airfoil?
@Vimana89 has an excellent series of desgns along this line and his nutball shows what the typical DTFB round wing might fly like. Could even use a series of steps like a symmetrical KFM wing. At 24" probably would even fly pretty decent
Hmm sounds like a
@Vimana89 challenge. You up for it?