Accessible Regions for Controlled Aircraft Maneuvering

DESIGN of maneuvers for carefree access of an aircraft to its complete flight envelope including poststall regimes is useful not only from a combat strategy point of view, but also for devising recovery strategies from an accident scenario. Maneuvers for an aircraft can be efficiently designed if a priori knowledge of its maneuverability characteristics is available to the control designers. Different types of agility metrics that characterize aircraft maneuvering capabilities have been proposed in literature based on different criteria [1,2]. A recent approach to define maneuverability characteristics is based on computing “attainable equilibrium sets,” as suggested in [3] and [4]. This approach involves computing a two dimensional (2-D) section of attainable equilibrium sets of a particular maneuver using an inverse trimming formulation. Construction of maneuvers based on attainable equilibrium sets involves accessing desired aircraft states in the attainable equilibrium set from a normal flying condition, such as a level flight trim condition. Computing an attainable equilibrium set for a given aircraft model and developing control algorithms to switch aircraft states between different operating points lying within the accessible region defined by attainable equilibrium sets are thus essential ingredients of aircraft maneuver design. For aircraft models, which are inherently nonlinear due to nonlinear aerodynamics in the poststall regimes, and because of various couplings, use of nonlinear control design techniques based on dynamic inversion (DI) or sliding-mode control (SMC) have been proposed for control prototyping to design maneuvers [3,5–7]. Using bifurcation theory and continuation methods, Raghavendra et al. [5] computed spin solutions for the F18/high-alpha research vehicle (HARV) model, and demonstrated use of the DI controller to recover the aircraft from a flat oscillatory spin motion. Recently, the authors have proposed a systematic approach using bifurcation analysis and continuation methods in conjunction with a SMC technique to design maneuvers for a nonlinear aircraft model