The reason I said I would like to see wind tunnel tests is that I can't quite grasp why it is producing better lift without the wing overlapping the slot. This is the kind of stuff that turns my brain into a pretzel!
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Given that simple flaps seem to work perfectly well, and will turn a well-trimmed stunter on a dime with no hint of stall, I'm not sure that the Velvet flap
is acting as a slotted flap. It could just be that it's a very complicated way of getting essentially the same aerodynamic effect as a simple flap, but with a lot of mechanical 'woo'.
OTOH, it could be that having a lot of overhang on a slotted flap is good, but not necessary to get at least some positive result. I landed head-first on the rear window of a car during rush hour in the mid 1980's commuting home from school, and haven't been able to work out computational fluid dynamics problems in my head since*.
Speaking from personal experience, I've flown a heavy Ringmaster in the pattern, so I know what a stall feels like out at the end of the line. I've also had a couple of planes that will turn fast enough to burn off a lot of speed in a corner, and the feeling is not like a stall -- it's a lot more consistent with scrubbing off speed due to induced drag (and
that's consistent with high aspect ratio stunters being able to corner better, although I haven't had that experience).
I really don't think that flaps, done the way we do them, are particularly high-lift devices. I think they mostly increase scores by letting the plane groove better in the rounds and level -- and in fact, Igor Burger's logarithmic flap mechanism changes the flap/elevator ratio with deflection, essentially letting the flaps max out in the corners for more "turn" without more lift. And Igor Burger seems to be a
reasonably good pilot.
* Not that I ever could before, but definitely not since!