Conceptual design and optimization methodology for box wing aircraft

Abstract

A conceptual design optimization methodology was developed for a medium range box wing aircraft. A baseline conventional cantilever wing aircraft designed for the same mis- sion and payload was also optimized alongside a baseline box wing aircraft. An empirical formula for the mass estimation of the fore and aft wings of the box wing aircraft was derived by relating conventional cantilever wings to box wing aircraft wings. The results indicate that the fore and aft wings would use the same correction coe cient and that the aft wing would be lighter than the fore wing on the medium range box wing aircraft because of reduced sweep. As part of the methodology, a computational study was performed to analyze di erent wing/tip n xities using a statically loaded idealized box wing con guration. The analy- ses determined the best joint xity by comparing the stress distributions in nite element torsion box models in addition to aerodynamic requirements. The analyses indicates that the rigid joint is the most suitable. Studies were also performed to investigate the structural implications of changing only the tip n inclinations on the box wing aircraft. Tip n inclination refers to the angle the tip n makes to the vertical body axis of the aircraft. No signi cant variations in wing structural design drivers as a function of tip n inclination were observed. Stochastic and deterministic optimization routines were performed on the baseline box wing aircraft using the methodology developed where the variables were wing area, av- erage thickness to chord ratio and sweep angle. The conventional aircraft design showed similar performance and characteristics to the equivalent in-service aircraft thereby pro- viding some validation to the methodology and the results for the box wing aircraft. Longitudinal stability investigations showed that the extra fuel capacity of the box wing in the ns could be used to reduce trim drag. The short period oscillation of the conventional cantilever wing aircraft was found to be satisfactory but the box wing aircraft was found to be unacceptable hence requiring stability augmentation systems. The eld and ight performance of the box wing showed to be better than the conventional cantilever wing aircraft. Overall, the economic advantages of the box wing aircraft over the conventional cantilever wing aircraft improve with increase in fuel price making the box wing a worthy replacement for the conventional cantilever wing aircraft.