Aerodynamic and flight dynamic study of wings with non-elliptic lift distributions

摘要

Adverse yaw has become a widely accepted nuisance in conventional aircraft design and it is typically solved through either pilot training or implementation of flight control systems. In this paper, the authors address it from the perspective of wing design; specifically via an approach that is based on the assumptions used by Prandtl in 1933. Known as Prandtl wings, such designs provide an opportunity to address adverse yaw characteristics and minimise induce drag while considering structural weight. The work presented aims to investigate the claimed benefits, by coupling aerodynamic and flight dynamic design methodologies that utilize reduced order aerodynamic tools. The study uses a conventional wing with elliptic loading as a baseline and compares its characteristics to those given by two different bell-shaped or non-elliptic lift distributions: that developed by Prandtl and a another defined using a Fourier cosine series. The design methodology yields wing designs that match the predicted aerodynamic behaviour of Prandtl wings. The results confirm that induced thrust is produced locally on the outboard wing areas and overall efficiency is increased, whilst the structural weight is optimized. The flight dynamic assessment shows improvements in the lateral-directional and control coupling characteristics, leading to pro-verse yaw dynamics. Further work should focus on assessing the robustness of this design method to changes in flight conditions and the impact of aileron design on non-elliptic lift distributions in adverse yaw conditions.