[romad]

For an RC airplane I would not over think it. I believe what you are trying to describe is a Fowler flap, a fowler flap is doing two things, its changing camber and increasing area. a simple flap would be more than functional for RC planes.

Newton's third law is the real explanation. Bernoulli's principle is the mechanism of how a wing makes lift. What a wing is doing is creating a down ward flow of air, in simple terms a push of air in the opposite direction of the lift. Thats were the term "with enough power you can make a barn door fly; or how airplanes fly upside down, and the reason the split flap works on fighter aircraft. Boundary layer and complex air flow are all considerations in making lift, but if just flying RC aircraft is your interest the more complex anaylsis falls under just good to known. Now if you are more interested a wind tunnel might be in your future.