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.

Automatic Control of an Asymmetric Fighter Aircraft Performing Supermanoeuvres

“…Sliding Mode Control is a robust nonlinear controller design technique particularly suitable for dealing with structured or parametric uncertainties [18][19]. This control approach is found to mitigate a wide range of uncertainties in the case of asymmetric aircraft [7][8][9]. However, the manoeuvre performance considerably deteriorates when the controller does not have an accurate information of the asymmetry.…”

“…This approach is, indeed, appealing because of the excellent capabilities of the feedforward neural networks for adapting to various changes in its input parameters even if the dimensionality of the data to be learnt is too high. Following the formulations as proposed in [8,9], first an SMC controller is designed using the actual asymmetric dynamics. From this simulation, the ∆F(x, u) values are stored as per Eq.…”

“…The outer loop sliding mode controller, which generates the desired body rates i.e. x1d, is designed in the conventional way neglecting the asymmetric dynamics altogether [7,8]. Further, the control moments demanded from the controller are converted to control surface deflection commands through the standard pseudo-inverse control allocation method [10] and availability of full state feedback is assumed.…”

“…Aircraft having lateral asymmetry in inertial and aerodynamic properties inherent in their structure have recently gained prominence in aircraft flight dynamics and control research [1][2][3][4][5][6][7][8][9]. In civil aircraft, such an asymmetry may generally arise due to asymmetry in fuel consumption, partial structural damage in the wing etc.…”

“…In many cases the asymmetry induced due to the aforementioned reasons cannot be accurately identified and quantified. For example, identification of the asymmetry due to firing of stores needs online centre of gravity estimation in order for the controllers to be able to compensate for the changed dynamics, as considered recently in the literature [5][6][7][8][9]. Further, the changed dynamics is far more complex and control design based on them requires considerably more online computation power.…”