Nandan Kumar Sinha

Though conceptualization of nonlinear sliding mode control has gained great emphasis in mechatronics and nonlinear systems in general, little attention is given to real time implementation owing to its inadequacy in handling mismatched uncertainties. This work contemplates on a robust nonlinear control scheme with sliding mode control and extended Kalman filter in closed-loop to estimate and handle bounded uncertainties. Stability of this closed-loop framework is established through Lyapunov analysis. The proposed formulation is first validated on a simulation platform and then implemented on a 2-DOF experimental gyroscope setup. Efficacy of this approach is evident from its rigorous tracking performance attained with a smooth and bounded control profile, despite induced uncertainties in various forms.

Aircraft dynamics are dominated by nonlinearities that may drive the aircraft into chaotic motions under certain conditions. Past studies in this area have explored several factors leading to the evolution of chaotic dynamics. However, a proper route or sequence for the evolution of chaotic dynamics has not been adequately substantiated. In this context, this paper systematically examines possible routes to chaos in the post-stall dynamics of an F-18 High-Alpha Research Vehicle model with external steady wind as the driving agent. Using tools from nonlinear dynamics based on bifurcation analysis, phase portrait, Poincaré map and amplitude spectrum analysis techniques, existence of quasi-periodic, period-doubling and intermittency routes to chaos are established. An eighth-order nonlinear aircraft model incorporating wind effects has been used for generating time responses from different post-stall flight conditions.

Recent interests in Loss-of-Control (LOC) related accidents of aircraft bring back focus on the need for construction of realistic simulations not only of impending accident scenarios but also of recovery of aircraft from fully developed accident scenarios. Developing control schedules for both the activities thereby becomes crucial. In this paper, a novel approach based on constrained numerical continuation procedure is presented to effectively compute open-loop control interconnect schedules for a six-degree-of-freedom aircraft model. For illustrative purposes, the approach based on a new formulation of constraint equations is used to design open-loop control interconnect schedule for recovery of an F-18 HARV model from auto-rotational spin condition.

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.

Aircraft loss of control is one of the largest contributors to fatal accidents in the aviation environment. The unprecedented change in aircraft dynamics due to loss of control onset and the associated structural constraints make loss of control prevention and/or recovery a challenging task. State-of-the-art autopilots are generally designed for nominal aircraft operations and disengage under off-nominal conditions, hence cannot be viewed as a safety solution during loss of control onsets. Herein lies the importance of providing training to pilots so as to equip themselves to rescue aircraft from loss of control events. Current pilot training methodologies have significant limitations when it comes to loss of control prevention and recovery strategies. In this context, a simulator for improved pilot training based on bifurcation and continuation techniques is presented in the paper. Augmenting these techniques with the current pilot training procedure can significantly improve the quality of training. This methodology can help pilots to distinguish various loss of control scenarios and aid them in taking appropriate recovery decisions intuitively. Meanwhile, a robust control-based loss of control handling module is also presented for developing non-intuitive strategies for loss of control prevention and recovery. This module can simulate adequate control profiles that the pilot can follow to get in and out of various loss of control scenarios. Moreover, it can be used as pilot activated recovery system in case of pilot disorientation and as a fully autonomous recovery system for much complex scenarios. The simulator is developed in MATLAB/SIMULINK platform and is shown to realize diverse loss of control events like spiral, spin, etc., and subsequent recovery from the same.