Automatic recovery of a combat aircraft from a completed Cobra and Herbst maneuver: A sliding mode control based scheme

Abstract

Cobra and Herbst are two complex post-stall air combat maneuvers popularly executed by the present-day fighter aircraft. At the end of these maneuvers, the aircraft usually develops either a high negative flight path angle or a high negative flight path angle rate apart from a considerably low velocity. Therefore, the aircraft needs to recover from such undesired flight conditions as quickly as possible. Usually this recovery is achieved manually by the pilot. In the present paper, a novel automatic recovery strategy is proposed. Two recovery schemes - a partial recovery scheme to get back to a level flight condition quickly without worrying about velocity and a full recovery scheme to restore the initial steady level trim completely (both velocity and altitude wise) are presented. As these maneuvers are executed in high angle of attack regions, the aircraft flight dynamics becomes highly nonlinear and coupled requiring use of nonlinear control methods. In the present work, sliding mode control technique is considered as, apart from handling the nonlinearities effectively, it also provides robustness to uncertainty in the aerodynamic data. MATLAB simulation results are presented to first demonstrate the execution of the maneuvers and thereafter to validate the proposed recovery schemes.