A trim problem formulation for maximum control authority using the Attainable Moment Set geometry

Abstract

This paper presents a generic trim problem formulation, in the form of a constrained optimization problem, which employs forces and moments due to the aircraft control surfaces as decision variables. The geometry of the Attainable Moment Set (AMS), i.e. the set of all control forces and moments attainable by the control surfaces, is used to define linear equality and inequality constraints for the control forces decision variables. Trim control forces and moments are mapped to control surface deflections at every solver iteration through a linear programming formulation of the direct Control Allocation algorithm. The methodology is applied to an innovative box-wing aircraft configuration with redundant control surfaces, which can partially decouple lift and pitch control, and allow direct lift control. Novel trim applications are presented to maximize control authority about the lift and pitch axes, and a “balanced” control authority. The latter can be intended as equivalent to the classic concept of minimum control effort. Control authority is defined on the basis of control forces and moments, and interpreted geometrically as a distance within the AMS. Results show that the method is able to capitalize on the angle of attack or the throttle setting to obtain the control surfaces deflections which maximize control authority in the assigned direction. More conventional trim applications for minimum total drag and for assigned angle of elevation are also explored.

Flight Performance Evaluation of the Flying-V

“…The toolbox has been developed in-house in MATLAB, using the Simulink and Simscape multi-body dynamics packages. It has already been implemented in several other research applications to unconventional aircraft configurations [27,28], including studies on the propulsive empennage concept [29], and the trim and transient response of staggered box-wing aircraft [30,31]. A top-level overview of the PHALANX flight simulation toolbox is shown in Figure 6.…”

“…If trim is required for a longitudinal-symmetric flight condition, the pilot inputs on the lateral-directional axes, as well as the roll and yaw attitude angles are automatically set to zero, and the trim problem is greatly simplified. In all cases, the solution is found with an iterative, gradient-based optimization algorithm, and is therefore locally optimum [31].…”

Impact of Control Allocation Methods on the Design of Control Surface Layouts for Box-Wing Aircraft under Flying Qualities Constraints

“…The toolbox has been used in several previous studies on novel aircraft configurations like the Blended Wing Body [36], the Delft University Unconventional Configuration, featuring the propulsive empennage concept [37], and other box-wing aircraft [20,21,38]. An overview diagram of PHALANX is shown in Figure 3.…”

“…This flexibility should be exploited to improve the flying and handling qualities characteristics of the aircraft. Redundant CSs can be coordinated to increase safety in case of failure, actively control the aerodynamic load over the wing, and allow innovative techniques in maneuvering flight, such as direct lift control [20][21][22]. A possible way to do so is through the employment of Control Allocation (CA) methods.…”