Zap flaps

A form of Zap flap — A kind of flap whose leading edge is mounted on a track, while a point at mid-chord on the flap is connected via an arm to a pivot just above the track. When the flap's leading edge moves aft along the track, the triangle formed by the track, the shaft and the surface of the flap (fixed at the pivot) gets narrower and deeper, forcing the flap down.