Spin dynamics of F/A-18HARV at a high angle of attack is investigated from the bifurcation analysis results and a brief description of modeling of wind into aircraft equations is presented along with the procedures used to carry out analysis of numerical simulation results for different wind speeds. When the wind speed is increased to a value of 35 m/s, numerical simulation results appear to show aperiodic and uncorrelated motions. The phase portrait resembles a thread bundle, which shows that the trajectories are scattered around and rarely visit any particular region on the phase portrait. The positive slope of the straight line on the curve represents positive Lyapunov exponent, which implies that the motion is chaotic. Evolution of autorotational spin motion of a nonlinear model of F/A-18 HARV in changing mean wind condition is reported.

Nandan Kumar Sinha

Department of Aerospace Engineering

Bifurcation analysis

High angle of attack

LYAPUNOV EXPONENT

MEAN-WINDS

Non-Linear Model

PHASE PORTRAIT

SPIN MOTION

Wind speed

Angle of attack indicators

Bifurcation (mathematics)

Lyapunov methods

Computer simulation

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IIT Madras

Autorotational Spin Evolving Towards Chaos

Journal of Aircraft

Aircraft loss of control is an acute phenomenon that has far reaching consequences irrespective of the class and type of aircraft. In order to ensure safe aircraft operation, loss of control problem has to be addressed efficaciously. This paper investigates various factors that trigger the onset of loss of control events and recovery solutions for the same. Rather than relying on statistics alone, this paper concentrates on simulation-based investigation towards various loss of control scenarios and subsequent recovery schemes. Through bifurcation analysis, distinct abnormal dynamics have been identified and their contributions in driving the aircraft towards loss of control have been examined. The effect of steady wind on aircraft dynamics and the evolution of chaotic dynamics as a precursor to loss of control are presented. Aircraft loss of control under actuator impairment conditions are also probed into. Various loss of control recovery schemes have been investigated and a robust loss of control recovery solution based on sliding mode control is also presented. © IMechE 2019.

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering

An investigation into aircraft loss of control and recovery solutions

High angle of attack maneuvers closer to stall is a commonly accessed flight regime especially in case of fighter aircrafts. Stall and post-stall dynamics are dominated by nonlinearities which make the analysis difficult. Presence of external factors such as wind makes the system even more complex. Rich nonlinearities point to the possibility of existence of chaotic solutions. Past studies in this area confirm the development of such solutions. These studies are mainly concentrated on very high angle of attack regimes, which may not be practically easily accessible. This paper examines the possibility of existence of chaotic solutions in the lower, more accessible areas in the post stall domain. The analysis is composed of the study of effect of external wind as an agent to drive the system towards the possibility of a chaotic solution. Investigations reveal presence of quasi-periodic solutions, which are characterized by two incommensurate frequencies. This solution appears in the time simulation by varying the control parameter viz., wind. The solutions correspond to the values in the lower region of the angle of attack versus elevator bifurcation curve in the post-stall region. A steady wind is considered for the analysis and explores the possibility of chaotic motion by increasing the wind in a step wise manner. It is found that wind adds extra energy to the system which in turn drives the system in to chaos. The analysis is done with the help of phase portrait, Poincare map and amplitude spectrum and a quasi-periodic route to chaos via torus doubling is also presented. © 2017 Author(s).

AIP Conference Proceedings

Quasi-periodic dynamics of a high angle of attack aircraft

Nonlinear Dynamics and Chaos

Flight Dynamics

Appendix E

Journal of Guidance, Control, and Dynamics

Evaluation of Aircraft Performance and Maneuverability by Computation of Attainable Equilibrium Sets

Post-Stall Motions Evolving Toward Chaos

The present paper addresses the problem of spin recovery of an aircraft as a nonlinear inverse dynamics problem of determining the control inputs that need to be applied to transfer the aircraft from a spin state to a level trim flight condition. A stable, oscillatory, flat, left spin state is first identified from a standard bifurcation analysis of the aircraft model considered, and this is chosen as the starting point for all recovery attempts. Three different symmetric, level-flight trim states, representative of high, moderate, and low-angle-of-attack trims for the chosen aircraft model, are computed by using an extended-bifurcation-analysis procedure. A standard form of the nonlinear dynamic inversion algorithm is implemented to recover the aircraft from the oscillatory spin state to each of the selected level trims. The required control inputs in each case, obtained by solving the inverse problem, are compared against each other and with the standard recovery procedure for a modern, low-aspect-ratio, fuselage heavy configuration. The spin recovery procedure is seen to be restricted because of limitations in control surface deflections and rates and because of loss of control effectiveness at high angles of attack. In particular, these restrictions adversely affect attempts at recovery directly from high-angle-of-attack oscillatory spins to low-angle-of-attack trims using only aerodynamic controls. Further, two different control strategies are examined in an effort to overcome difficulties in spin recovery because of these restrictions. The first strategy uses an indirect, two-step recovery procedure in which the airplane is first recovered to a high- or moderate-angle-of-attack level-flight trim condition, followed by a second step where the airplane is then transitioned to the desired low-angle-of-attack trim. The second strategy involves the use of thrust-vectoring controls in addition to the standard aerodynamic control surfaces to directly recover the aircraft from high-angle-of-attack oscillatory spin to a low-angle-of-attack level-flight trim state. Our studies reveal that both strategies are successful, highlighting the importance of effective thrust management in conjunction with suitable use of all of the aerodynamic control surfaces for spin recovery strategies. Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Aircraft spin recovery, with and without thrust vectoring, using nonlinear dynamic inversion

Engineering notes: Autorotational spin evolving toward chaos

Journal	Journal of Aircraft
ISSN	00218669
Open Access	No