Frank Williams brought his new creation the "Slot Machine" out to Scobee Field this weekend. It has an implelemtation of the Fowler (Hofackerr?) flaps I was trying on my modified Hofflapper Twister. I didn't get a chance to talk to Frank to get his impressions of the first flights since he was tied up being heckeled by the usual peanut gallery. There are some obvious differences in the treatment of the slot shape in his implementation. I was trying to get the trailing edge of the main airfoil as sharp as possible to minimize turbulence in the slot which I thought would aggravate seperation over the flap airfoil. Frank's main airfoil TE is much thicker. I'm guessing the thinking is to blanket the flap airfoil and to close the slot at low angles of flap deflection, opening the slot at slightly higher angles of flap deflection. This might give the wing flap combination two lift curve slopes: one at small deflections when the slot is closed and a steeper one when the slot is open at higher angles of flap deflection.
It is certainly going to be interesting to see the evolution of this concept!
In the case of the Hofflapper Twister I'm using about half the flap deflecton of the standard "Gwenn" flap. The airplane is very solid and smooth in level flight and around loops. Perahps even "soft". I suspect many experts would not like this soft feel but it makes it easier for a beginner like me to "fly" the airplane aroud a loop. Yet, there is plenty of control for recovering from near disasters. And the airplane doesn't stagger around a corner when over controlled. The Hofflapper Twister is also fairly heavy. But that's a topic for a different post. 