Effect of aspect ratio on wing rock at low Reynolds number

Wing rock phenomenon has been studied extensively on slender delta wings but a little is understood about wing rock occurring on rectangular wing planforms, which is the focus of this paper. Specifically, a systematic procedure is discussed for experimental studies of single degree-of-freedom wing rock on rectangular wings. The characterization of limit cycle oscillations in terms of amplitude and frequency is based on the free-to-roll tests in wind tunnel. Rectangular wings with aspect ratio from 2 to 4.5 (with increment of 0.25) are studied at low Reynolds numbers (less than 0.1 million) and low Strouhal numbers ( 10 − 2 ) that are typical for the flight of micro air vehicles in urban environment. The changing trend in oscillation amplitude and frequency of the resulting sustained limit cycle oscillations is analyzed. The results indicate that wing rock occurs in post-stall regime (14–16° of angle of attack) and its amplitude tends to increase from aspect ratio 2 to 3.25 and decrease thereafter. The wing-rock frequency shows a decrease from aspect ratio of 2 to 3.75 and increase thereafter.