I have a G.W.S. Slow stick and I built an under camber wing for it out of foam board. the problem I have is with the new wing on, it will hardly turn to the point it is uncontrollable. but has plenty of lift. With the factory wing it will turn on a dime. Would improper incidence cause it not to turn? I tried two other wings of the same shape, one longer, one shorter with the same results. All the new wings had the same chord and C.G. . Any thoughts on what the problem is?

If you have not already added dihedral, then add some now and try it again, or add some more.

Bob

Without ailerons, you will need some dihedral, probably 5 degrees or more, in order to turn with rudder only.

Impossible to say without seeing it, but besides making sure the dihedral is about the same as the old wing, what about stiffness? If it's bendy or sloppy you will have control problems. If the incidence is off a little all that will happen is you'll have to change the elevator trim.

In a very weak personal moment I bought a GWS Slo Stick to see what all the fuss was about and to get an idea of what the then currently acceptable yardstick was for performance and controllability. I was seriously disappointed in the results in stock form. I only flew it one flight before I added a thread to pull the wings together and up to form more dihedral.

Having said this there WAS some small amount molded into the wing. But if you formed flat wings from the foam board there would be ZERO dihedral. And for a rudder controlled model to roll into a turn it MUST have dihedral. The more dihedral the more the model will respond with roll from the yaw angle of a given rudder input.