Longitudinal aerodynamics of rapidly pitching fixed-wing micro air vehicles

Some fixed-wing vertical-takeoff-and-landing aircraft can transition between two flight modes: forward flight and near-hover. This study was conducted to improve the transition performance of such vehicles. The experimental model consists of a rigid Zimmerman wing and a propulsion system with contra-rotating propellers. It was rapidly pitched about its aerodynamic center at an average freestream Reynolds number of 86,000. Five nondimensional pitching rates were used, along with two elevator deflections and three propulsive settings. The model was tested statically, and several observations were made. At constant throttle setting, from 20 to 70 deg, both advance ratio and thrust coefficient increase linearly with angle of attack. Higher throttle setting results in greater stall delay, causing the maximum lift coefficient to increase. When throttle setting increases, lift and drag coefficients increase throughout the tested angle-of-attack domain. Rapid-pitching tests showed that nose-up pitching delays stall and nose-down pitching hastens it. Lift and drag coefficients generally increase with positive pitching rate and decrease with negative pitching rate. Wing aerodynamic efficiency is virtually independent of throttle setting, elevator deflection, and pitching rate between 30 and 70 deg angle of attack. The propulsion system is not sensitive to rapid pitching with regard to thrust, normal force, or propulsive moment.