A Novel Control Allocation Method for Yaw Control of Tailless Aircraft

Abstract

Tailless aircraft without vertical stabilisers typically use drag effectors in the form of spoilers or split flaps to generate control moments in yaw. This paper introduces a novel control allocation method by which full three-axis control authority can be achieved by the use of conventional lift effectors only, which reduces system complexity and control deflection required to achieve a given yawing moment. The proposed method is based on synthesis of control allocation modes that generate asymmetric profile and lift induced drag whilst maintaining the lift, pitching moment and rolling moment at the trim state. The method uses low order models for aerodynamic behaviour characterisation based on thin aerofoil theory, lifting surface methodology and ESDU datasheets and is applied to trapezoidal wings of varying sweep and taper. Control allocation modes are derived using the zero-sets of surrogate models for the characterised aerodynamic behaviours. Results are presented in the form of control allocations for a range of trimmed sideslip angles up to 10 degrees optimised for either maximum aerodynamic efficiency (minimum drag for a specific yawing moment) or minimum aggregate control deflection (as a surrogate observability metric). Outcomes for the two optimisation objectives are correlated in that minimum deflection solutions are always consistent with efficient ones. A configuration with conventional drag effector is used as a reference baseline. It is shown that, through appropriate allocation of lift based control effectors, a given yawing moment can be produced with up to a factor of eight less aggregate control deflection and up to 30% less overall drag compared to use of a conventional drag effector.

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“…The results of the simulation showed that the adverse yaw effect was reduced by 25%. Further reduction of the effect can be obtained using optimization rules (Shearwood et al, 2020). Figure 7(a) shows aerodynamic efficiency vs angles of attack of the aircraft for a few chosen spoiler configurations.…”

“…The results of the simulation showed that the adverse yaw effect was reduced by 25%. Further reduction of the effect can be obtained using optimization rules (Shearwood et al , 2020).…”

“…The single control surface is divided into three segments – Figure 2. This enables additional yaw control augmentation (Shearwood et al , 2020), together with redundancy and reduces servomechanisms loads. The side edges of the control surfaces are aligned with the free stream flow to decrease aerodynamic drag.…”

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