A Method for Including Control Effector Interactions in the Control Allocation Problem (Preprint)

Abstract : Much emphasis has been placed on over-actuated systems for air vehicles. Over-actuating an air vehicle provides a certain amount of redundancy for the flight control system, thus potentially allowing for recovery from off-nominal conditions. Due to this redundancy, control allocation algorithms are typically utilized to compute a unique solution to the over-actuated problem. As the number of control effectors placed on a vehicle increases, the likelihood of the occurrence of control effector interactions increases. For example, deflection of an aerodynamic surface that is upstream of another aerodynamic surface may cause the forces and moments produced by the downstream effector to differ from those produced when the upstream effector is not deployed. Another example can be found on launch vehicles that can use a combination of differential throttles and gimballed nozzles for attitude control. The effectiveness of gimballed nozzles are clearly influenced by the engine thrust. The above are examples of the control effector interaction problem. In this work, a method is devised, which utilizes linear programming methods in an iterative framework, to take into account control effector interactions. While nonlinear programming techniques could be directly applied to such problems, the lack of convergence guarantees precludes their use in flight critical systems. The use of linear programming methods is appealing because an optimal solution to each linear programming sub-problem can be determined in a finite amount of time.