Nonlinear dynamics and control of a laterally mass varying fighter aircraft

Abstract

This paper presents dynamic analysis and nonlinear control of laterally mass varying combat aircraft based on a six degree-of-freedom model derived for a variable mass system. The objective is to investigate the effects of asymmetric lateral mass variation, due to mass ejection, from two different perspectives – the open loop dynamic behavior through bifurcation analysis; and the closed loop control performance while carrying out some demanding maneuvers. Bifurcation analysis reveals considerable coupling between the longitudinal and lateral-directional channels even for a modest lateral shift in the center-of-mass due to store ejection, which in turn is observed to give rise to a spiral-dive like divergent mode even at low angles-of-attack. Thereafter, the well-known high angle-of-attack cobra maneuver is implemented for the symmetric center-of-mass case using sliding mode control technique and using a new single loop control formulation in contrast with the conventional inner-outer loop formulation. The proposed single loop control formulation is further extended to handle the lateral movement of center-of-mass due to asymmetric store ejection using the asymmetric dynamics model proposed and derived in this paper.