Initial Characterization of Self-Activated Movable Flaps, "Pop-Up Feathers"

Self-activated movable flaps or pop-up feathers are used by a preponderance of feathered creatures as a means to modify foil characteristics during landing or incurred high angles of attack (gusts). When flow would normally separate, causing drastic decreases in lift, these pop-up feathers will activate, thus delaying the effects of stall. Although these flaps can almost entirely eliminate the stall region in a common UAV foil (NACA 2412), they have yet to be used commercially on any aircraft. The absence of these flaps is attributed mainly to the lack of understanding in their characteristics. This paper uses wind tunnel testing in an attempt to initially characterize the use of such flaps in low Reynolds number regions (1x10-5x10), including their placement, size and ideal material characteristics