Design of robust control schemes for small scale unmanned helicopter during hover near hover flight

Abstract

Unmanned aerial vehicles (UAVs) are employed for various applications, including newlinedisaster relief, border surveillance/infiltration detection, and agriculture. Nowadays, newlineUnmanned Helicopters (UHs) attract prominence over fixed-wing aircraft for such newlineapplications. This prominence is due to their unique features such as vertical take-off newlineand landing, autorotation, and hovering for long durations with minimum energy newlineconsumption. Despite the advantages, their inherently unstable, under-actuated, newlineand coupled multi-input-multi-output dynamics mark the autonomous operation newlinechallenging. A preliminary approach towards developing a fully autonomous flight is newlineto build a stability augmentation system for the standard hover flight mode. In hover newlinemode, the UH is maintained stationary with respect to a reference position. The newlinehover/near-hover flight condition of a small-scaled UH with a single main rotor and newlinea tail rotor for anti-torque control is addressed in this research. Initially, to develop a newlinecoupled rotor-fuselage linear-time-invariant (LTI) MIMO model representing hover newlineflight, the trim values are calculated from the Euler-Newton nonlinear equations. newlineThen, an analytical method is adopted to calculate the stability and control derivatives newlineduring the flight to arrive at the LTI model. newlineA two-loop control structure, in which an inner-loop responsible for stabilizing newlineattitude angles, its rates, and flapping angles and an outer-loop for trajectory tracking, newlineis used in this research. Primarily, stabilization of the inner-loop dynamics is achieved, newlinefollowed by trajectory tracking of the outer-loop dynamics. In the first and second newlinephases of this work, inner-loop stabilization is addressed. A composite control law newline(CCL) and an adaptive reaching law-based sliding mode control (SMC) that improve newlinethe closed-loop transient response is proposed in the first phase. Fast stabilization and newlinereduction in maximum over/undershoots are achieved using the proposed methods.