Constructal Design and Aeroelastic Stability Analysis of HALE Aircraft

Abstract

In the new generation of the Unmanned Aerial Vehicle (UAV), the capability of increasing the flight duration and altitude is the area of interest for designers. The High-Altitude Long-Endurance (HALE) aircraft can fly farther and for a longer period by using high aspect ratio flexible wings. The primary applications and flight missions of this type of aircraft are environmental monitoring, surveillance, and communications. While using high-aspect-ratio, flexible, light-weighted wings improve the efficiency and reduces the required power, it will bring new challenges into the design of the aircraft. One of the major concerns is aeroelastic instability, which can appear as flutter, divergence, limit cycle oscillation, etc. The main objectives of this research are to investigate the effects of different design parameters on the aeroelastic stability of HALE aircraft. I seek to find the reason why certain configurations can extend the aeroelastic flight envelope and postpone the instabilities. A numerical package is developed that connects three computer programs; Gmsh, Nonlinear Aeroelastic Trim And Stability of HALE Aircraft (NATASHA), and Variational Asymptotic Beam Sectional Analysis (VABS). The Gmsh software provides a discretized model of the wing cross-section of the aircraft. The wing data is then imported to VABS software to obtain the structural and inertial properties. NATASHA uses the structural and inertial properties of the sections to perform stability analysis, and the results of the trim solution are imported to VABS software for stress analysis. VABS uses the trim solution to recover the stresses. Different design parameters such as engine/store location and wing sweep and curvature are considered, and the nonlinear aeroelastic analyses are performed. Most of the studies on the effects of design parameters on aeroelastic stability take a descriptive approach, and they use the state-of-the-art numerical techniques to compare the performance of different designs and reveal the best of the options available. In the present study, I shed light on how a certain design parameter could influence the flow in the system, including the flow of stresses and how changing the geometry in the direction that provides greater access to the currents flowing through it, leads to a better design. I propose how the configuration should evolve towards a better design by facilitating the flow of stresses. This approach stems from constructal law.