Effects of morphing on aeroelastic behavior of unmanned aerial vehicle wings

Ünlüsoy, Levent
Morphing aircraft technologies became the center of attention in aviation industry through the last decade. Although the intended optimization of the aircraft in terms of aerodynamics and/ or flight performance resulted in advantages like reduction in carbon dioxide emission and noise levels; that also brought some structural borne problems such as the possibly deteriorating change in the aeroelastic behavior of the structure. These structural problems should be clearly identified and attempted to be eliminated even at the conceptual design stages. This study intends to provide a broad view for the effects of morphing especially on the linear aeroelastic behavior of unmanned aerial vehicle wings. The study considered four different flight phases, namely take-off, climb, cruise, and loiter. An unmanned aerial vehicle wing, which was considered to be used in these four phases, was assumed to undergo chord, span, sweep and camber change with the help of certain morphing mechanisms such as the leading and the trailing edge mechanisms and the telescopic ribs and spars. Four different wing geometries were then obtained by considering the aircraft design requirements, aircraft performance requirements and aircraft structural requirements. Those four different wing shapes so obtained, which satisfy the minimum requirements for design, performance and structure and by no means optimum for any of those requirements, were studied for linear aeroelastic instability problems. An in-house computer program was developed and used for the prediction of the flutter and divergence speeds at different stages of the flight, in which the planform of the wings were changing. Aeroelastic models of morphing wings at different flight phases were developed as reduced order models having two-degrees-of-freedom and threedegrees-of-freedom. Theodorsen theory was used to represent the unsteady aerodynamics. Structural properties of the wings were obtained by conducting a series of finite element analyses on the developed equivalent plate models representing the planform of each morphing wing shapes. Two different classical solution methods were used during the aeroelastic analysis; k-method and pkmethod. Aeroelastic analyses conducted showed that the flutter and divergence speeds drastically changes up to 58 percent and 75 percent respectively among different wing configurations, when compared to the highest flutter and divergence speeds achieved. A series of analyses were conducted throughout this study, in order to identify the structural problems which arise due to the inclusion of the morphing phenomenon in aircraft design. It was realized that, the aeroelastic tailoring due to the morphing should be an essential part of the structural design procedure.
Citation Formats
L. Ünlüsoy, “Effects of morphing on aeroelastic behavior of unmanned aerial vehicle wings,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.