Hysteresis Effects on Wind Tunnel Measurements of a Two-Element Airfoil
Wind-tunnel tests were conducted on the GA(W)-2 airfoil with 25%-slotted flap at Reynolds number of 2.2x106 and Mach number of 0.13. The tests were made for flap nested and flap deflected cases of 30 and 40 deg with optimum and narrow gaps. Stall characteristics on the airfoil elements were examined through plots of force, moment, and surface pressure data and flow visualisation. Flap deflected configurations indicated a two-stage stall and hysteresis phenomenon. The hysteresis loop appeared to be a function of flap angle, gap geometry, and history of changes in air speed or angle of attack.