Structural Modeling and Optimization of the Joined-Wing of a High-Altitude Long-Endurance (HALE) Aircraft

Abstract

Recent research trends have indicated an interest in High-Altitude, Long-Endurance (HALE) aircraft as a low-cost alternative to certain space missions. These missions require a lightweight vehicle operating at low speeds, high lift and minimum drag. These conditions necessitate high-aspect ratio wings. Due to its large span and light weight, the wing structure is very flexible. The wings undergo significant deflections as a result of the fluid loads acting on them, and require the consideration of aeroelastic effects. To reduce the structural deformation and increase the total lift, a sensorcraft model with a joined-wing configuration is employed. The results of the simulation of the complex, three-dimensional flow past the joined wing of a HALE aircraft are used as an input for the structural analysis. In the existing studies to date, only simplified structural models have been examined. In the present work, a semi-monocoque structural model is developed. All stringers, skin panels, ribs and spars are represented by appropriate elements in a finite-element model. Linear and nonlinear static analyses under the aerodynamic load are performed. The stress distribution in the wing is explored. Starting with a structural model with uniform mass distribution, a design optimization is performed. The optimized model has a maximum stress 42% lower and a maximum deflection 26% lower than obtained for the initial model. Linear and nonlinear buckling analyses are performed as well. The nonlinear analysis yields a critical buckling load 18% lower than that predicted by linear analysis. This paper will discuss the details of the structural modeling as well as the results obtained before and after optimizing the model.