I've always been intrigued by the idea of adding powerful flaps to sport planes, to expand the flight envelope and to have something more to play with.

The late Andy Lennon created some bold designs that promoted slotted flaps (and leading-edge slats) for reducing the landing speed of his small, heavy, high-wing-loading designs.

But at the modest chord dimensions and low landing airspeeds that we run, would a model-sized slotted flap actually work as expected and generate a lot of extra lift? Will the airflow stay attached to the upper surface of a model flap at deflections of 20% or more? Or are we really just sticking a fancy flat plate out into the wind like a 3D plane's elevator?

A big increase in the CL at landing would be fun, coming in steep and slow like a hawk. But slotted flaps would be hard to build, especially if you also try to move the surface backwards like a fowler flap. If the slot isn't really going to work, then it would be a lot easier to just hinge a big barn-door surface to the rear of the wing inboard, keep the thrust up through the approach and be happy...

Anyone have a feel for how well a complex airfoil like a slot would actually work at model dimensions?