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

Abstract

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. Keywords

A review and historical development of analytical techniques to predict aircraft spin and recovery characteristics

“…Hence, it is the balance of aircraft moments, which must be attained to ensure the existence of a steady spin mode. The aircraft moment equations in steady spin phase are given as (Malik et al, 2017):…”

“…Using 3-DOF spin model, left and right spin modes were predicted for a fighter configuration exhibiting yawing moment asymmetry at high angles of attack (Malik et al, 2017). Figure 4 illustrates the two-dimensional plots depicting the locations of the predicted left and right spin modes for different elevator settings.…”

Spin flight mode identification with OEEMD algorithm

“…It happens because of shallow and downward autorotation around the vertical axis. It is explained by Malik et al (2017aMalik et al ( , 2017bMalik et al ( , 2017c, that the spins can be entered intentionally or unintentionally, from any flight attitude if the aircraft has sufficient yaw while at the stall point. In a normal spin, the wing on the inside of the turn is stalled while the outside wing remains flying; it is possible for both wings to be stalled but the angle of attack of each wing, and consequently its lift and drag, will be different.…”

“…The spin maneuver has caused a significant amount of air crash incidents, and so many people lost their lives up to now because of this phenomenon (Brinkworth and Hants, 2015). As it showed by Malik et al (2017aMalik et al ( , 2017bMalik et al ( , 2017c, a particular reason of this event refers to difficulties and imprecisions in estimation (or miscalculation) of the dynamic flight characteristics in such nonlinear conditions.…”

“…Recovery of the flight stability and balance after the spin maneuver is a vital issue and in basics, it requires precise estimation of the nonlinear behavior of the air plane, which lets calculation of the recovery reactions correctly (Malik et al, 2017a(Malik et al, , 2017b(Malik et al, , 2017cAkhtar et al, 2017). In other words, we need to estimate flight dynamic modes and extract their characteristics for analyzing airplane flying quality, airplane dynamic stability and response-to-control.…”