Influence of flight control law on spin dynamics of aerodynamically asymmetric aircraft

In this paper, we analyze the spin dynamics of an aerodynamically asymmetric aircraft in
open-loop configuration and also evaluate the performance of gain scheduled flight control
law in improving dynamic characteristics of aircraft spin. A look-up tables based aerodynamic
model is developed from static, coning and oscillatory coning rotary balance wind
tunnel test data. As a starting point, all possible steady spin modes are identified by solving
the aircraft dynamic model comprising moment equations. The influence of high-alpha
yawing moment asymmetry on predicted right and left spin modes is discussed. Six degree
of freedom simulations of left and right flat spins are performed in open-loop and closed-loop
configurations with the flight control law. Our studies reveal that large amplitude oscillations
in the angle of attack and sideslip observed in the open-loop configuration are significantly
damped by the control law. The control law reduces the recovery time of the left flat spin.
However, the aircraft natural tendency to rotate rightwards due to yawing moment asymmetry
at high angles of attack renders flight control law ineffective in aiding the recovery of
the right flat spin.