Minimum‐series twist distributions for yawing‐moment control during pure roll*

Abstract

AbstractThe main wings of most aircraft produce adverse yaw during roll. In order to control the lateral direction of the aircraft during the roll, the rudder is often mixed with the aileron. Lifting‐line theory is used here to develop spanwise lift distributions that require the minimum number of terms in the Fourier‐series solution for controlling the yawing moment during pure rolling motion using only the main wing. It is shown that the yawing moment can be controlled for arbitrary rolling moments and/or rolling rates by adding symmetric twist in the main wing. The induced‐drag penalty for using this method to control the yawing moment is significant and discussed in detail. For example, it is shown that if zero yawing moment is prescribed, the induced drag can increase by 108% for a prescribed rolling moment or by 300% during a steady rolling rate relative to the induced drag in steady level flight. Because this is the minimum‐series solution, it does not represent the solution for yaw control with minimum induced drag, since more terms could be used in the Fourier series describing the lift distribution to control yaw with less induced drag. However, the solutions presented here can be useful for aircraft with continuous trailing‐edge technologies that are limited in spanwise deflection gradients, and provide a theoretical upper bound on the minimum induced‐drag that can be expected if the main wing is used for yawing‐moment control during pure roll.