Maneuverability, Load Alleviation, and Ride Qualities of Transonic High-Aspect-Ratio-Wing Aircraft

Abstract

Reducing the environmental impact of aviation is driving civil transport aircraft designs toward longer, high-aspect-ratio wings with higher aerodynamic efficiency. However, high-aspect-ratio-wing configurations show increased structural flexibility compared to contemporary, stiffer and lower aspect-ratio-wing ones. This increased wing flexibility causes higher loads and degrades maneuverability. These issues require novel solutions to guarantee load alleviation and maneuverability while maintaining pilot and passenger ride comfort.

This work explores conventional and unconventional control effectors such as distributed trailing- and leading-edge control surfaces and flared folding wingtips for improving load alleviation and maneuverability of very flexible, transonic high-aspect-ratio-wing aircraft representative of a potential future civil transport configuration. The impact on aircraft ride qualities during gust encounters is also investigated. The studies utilize a coupled nonlinear aeroelastic-flight dynamics framework (UM/NAST) that can model different control effectors. It was enhanced in this work with the capability of modeling flared folding wingtips and evaluating an acceleration-based ride quality metric among other things.

A spanwise placement study of trailing- and leading-edge control surfaces showed that ailerons of high-aspect-ratio-wing aircraft should be placed at a more inboard location relative to the wing span than in aircraft with typical aspect ratios to provide adequate roll maneuverability. The study showed that the peak of control-surface effectiveness along with the wing span moves inboard (and decreases in value) for higher wing aspect ratios. The simulations showed that inboard leading-edge control surfaces are ineffective compared with trailing-edge control surfaces at the same spanwise locations; however, outboard leading-edge control surfaces provide higher load alleviation capability than their trailing-edge counterparts while avoiding control reversal. Releasing flared folding wingtips while deploying control surfaces alleviate loads with no significant impact on roll maneuverability at flight conditions where aeroelastic effects are moderate. However, it causes higher loads and degrades roll maneuverability in the presence of strong wash-out effects at higher dynamic pressure conditions or with increased wing flexibility. Increasing wing stiffness improves flared folding wingtips' load alleviation performance and their ability to enhance roll maneuverability. The results also showed that these devices degrade ride quality due to their flapping-induced vibrations. However, this negative impact is smaller than the ride quality enhancements resulting from higher wing flexibility. Therefore, the ride qualities of high-aspect-ratio-wing aircraft with released flared folding wingtips remain higher than for stiffer configurations with a typical wing aspect ratio. Finally, these results demonstrated the importance of considering the impact of wing flexibility when exploring different control effectors for enhancing roll maneuverability and/or explore load alleviation.