Adaptive Compensation at High Angles of Attack

Abstract

High AoA flight poses unique aerodynamic challenges, and these issues are studied extensively over the years [1]. An air vehicle at high AoA allows the pilot to rapidly nose-point to ensures a decisive action on the enemy. That is why next-generation aircraft must be able to operate consistently at higher and higher AoA than before and in a controlled fashion, thereby posing newer challenges in control, especially with the possible deployment of SJAs. Freezing conditions can also promote a local high AoA flow condition where ice accumulation on the tail leading edge may have an equivalent effect of a full-span stall strip [2]. The trend in the next-generation air vehicle design is towards increased exploitation of high-AoA aerodynamics and flow-field interactions. The relevance of high AoA studies is widespread, contrary to the general understanding that the pilot of a light single-engine propeller-driven air vehicle may also encounter high AoA aerodynamics as frequently as the pilot of a modern high-performance fighter.Boundary layer flow separation is an undesirable phenomenon in almost all technical scenarios, and especially the point of flow separation and the AoA at which such an event occurs on the wings of air vehicles is of interest in this work. Flow separation causes loss of lift and (or) increased drag and reduction in retained energy. Therefore, there has been extensive research on the study of flow separation and ways and means to eliminate or delay the event. At high AoA, there is diminished flow attachment, and the separation takes place further and further away from the leading edge, thereby providing a diminished lift force. The resultant flows get controlled by airframe shaping or actively ensured by mechanical, pneumatic or active flow control devices like SJAs. In recent work, Linehan et al. demonstrate a servo-controlled sliding alula actuator to reorient separated flows at high AoA without undesired transients caused by the shedding effect of a stall vortex using a customized autopilot board and a 9-axis IMU for feedback control [3]. Other actuators which are used in high AoA separation control include weakly ionized plasma actuators consisting of