Performance Analysis of Flight Control Laws Applied to a Simplified Analog of the Dual-Aircraft Platform Concept

Abstract

Dual-aircraft platform (DAP) is a novel atmospheric satellite concept that features two gliderlike unmanned aircraft connected by a long, ultrathin cable, which uses the persistent levels of vertical wind shear in the lower stratosphere to sail without propulsion. This article presents a comparative design and analysis of three control strategies applied to a simplified analog of the DAP concept, which involves one aircraft connected by a thin cable to a steadily moving ground vehicle (GV). Similar to the DAP, the goal is to sustain flight without thrust (“sail”), and without being towed by the GV, using a sufficient persistent crosswind, despite uncertainties in the cable aerodynamics and disturbances associated with turbulence and changes in mean wind velocity. These control strategies, which include a linear nonadaptive architecture, a nonlinear dynamic inversion, and a L1 output feedback adaptation, are designed following an unorthodox control allocation. The robustness and performance of these control strategies are characterized using a set of metrics designed to capture control actuation energy and thrust impulse used to maintain sailing flight conditions. The results show that including an adaptive layer prevents instability of the vehicle under unforeseen extreme flight conditions and enables sailing with minimum use of propulsion.