Originally Posted by nmasters
In the few wind tunnel tests that have been performed a vortex does form in the space behind the step just as the original hypothesis assumed and the pressure distribution has a funny bump upstream of the step with a dip downstream then a spike a bit farther aft.
All the testing I've seen concluded that vortices did form ion the step area but they were not stable and were constantly shed downstream. The net result generally being an increase in drag over the non-stepped version.
True that the Witherspoon tests did find some very narrow operating regime where a small benefit was observed for one discontinuity configuration (a kind of notch rather than a step). But that was in comparison to a symmetrical airfoil. non of the results they got showed numbers that would compare favourably to any reasonable cambered airfoil.
As for the claimed Top Flite tests..I take that with a large pinch of salt as they were never published and we have no idea of the test methods, or in fact it the tests even took place. FWIW the testing I did against a conventional Mark Drela airfoil showed a very marked reduction in performance for the KFm3 configuration tested. Other than the much increased sink rate and obvious increase in drag the KFm wing flew in a similar way to the Drela, and it exhibited normal stall behaviour: http://www.rcgroups.com/forums/showt...&highlight=elf