Combination of Aileron and Flap Deflection for Minimum Induced Drag Roll Control

Abstract

Induced drag has a significant impact on the performance of flight vehicles. If a considerable amount of the airborne time is spent in maneuvering flight, optimization of vehicle performance requires the minimization of drag associated with maneuvering. In this study only the increment in induced drag due to aircraft lateral control and lateral control induced adverse yaw is analyzed theoretically, using all induced drag minimizing three-dimesional potential flow computer program. The effects of varying single segment aileron span and employment of double segment ailerons with an optimum combination of inboard and outboard corltrol surface deflection angles and the merits of differentiating the upward and downward aileron deflection angles are investigated. The influence of wing induced sidewash onto the vertical tail induced drag due to aircraft yaw trim side forces is accounted for. The optimum size of conventional ailerons is found to be in the order of 70% semispan. Double-segment aileron systems exhibit a slightly lower induced drag incremetlt. They also require smaller control deflection angles and, therefore, should yield additional reductions in viscous profile drag.