I have a Jerry Bates Bearcat plans and wanted some foam cores cut for them... The problem is that its not anywhere near the actually NACA airfoil of the full size counter part. Is there a reason why it should not be the same airfoil as the full size?

In comparison, the NACA airfoil is 1/2 inch thicker than what is shown on the plans. I am sure it might even be better to get the gears in the wing.

fw190

Yes, but you'd need to get into the fluid dynamics of that airfoil, the renolds numbers and the down side of scaling them.

The bottom line is that low speed aerodynamics are different. The full-scale aircraft was designed to product the desired lift, drag, and weight at a certain speed, temperature and altitude, none of which an RC plane is going to match. Generally speaking the real airfoil, on the scale planform, won't perform well in the RC arena.
I've been out of the fluid mechanics game for a while so don't dump on me if this wasn't technical enough for any readers.

Thanks for the response, I printed out the original airfoil on the Bearcat and its at least an inch thinker than the Bates airfoil. Totally confused on which to use now. I have to check some other designers....

fw190

At full scale the boundary layer is very thin compared to model sizes and speeds. The boundry layer is where the flow goes from zero velocity at the airfoil surface to the full velocity of the air stream past the airfoil. As size and speed decrease, the boundry layer thickens. The energy in the flow decreases as the square of the airspeed. Because the energy in the flow over a model wing is much less, the flow does not stay attached as well and the airfoil stalls at a lower angle of attack. Because the airfoil stalls at a smaller angle of attack, the airfoil on a model can't produce as high a lift coefficient. Because the boundry layer is thicker, the model airfoil has a higher coefficient of drag.

The extra drag of a thick airfoil will require more thrust for the same performance. The delimma for the scale model flier is that it is very hard to get the model to fly at scale speed without using a non scale airfoil. What do you want? Scale outline or scale flying speed? BTW, achieving scale flying speed also requires very light weight construction because airfoils on models can't achieve as high lift coefficients as airfoils on full scale aircraft.