A Control Allocation approach to induce the center of pressure position and shape the aircraft transient response

Abstract

This paper presents a Control Allocation formulation aimed at altering the dynamic transient response of an aircraft by exclusive means of the aerodynamic effectiveness of its control effectors. This is done, for a given Flight Control System architecture and, optionally, closed-loop performance, by exploiting the concept of Control Center of Pressure, i.e. the center of pressure due to only aerodynamic control forces. Two formulations are proposed, and their advantages and disadvantages presented. The first is based on the straightforward augmentation of the control effectiveness matrix, the second on a weighting matrix to prioritize control effectors. The latter is implemented in three application studies on a box-wing aircraft configuration with redundant control surfaces: a simple pull-up maneuver, a trajectory tracking task, and an altitude holding task in turbulent atmosphere. Results show that the proposed formulation can significantly impact performance metrics that are closely related to the aircraft transient response. In the best case scenario, the aircraft is able to completely cancel the non-minimum phase behavior typical of pitch dynamics, hence achieving a sharp initial response to longitudinal commands. If compared to a standard Control Allocation algorithm, the proposed formulation results in improved tracking precision, better disturbance rejection, and a measurably improved feeling of comfort on board.