An Integrated Trim and Structural Design Process for Active Aeroelastic Wing Technology

A new method for concurrent trim and structural optimization of Active Aeroelastic Wing technology is presented. The new process treats trim optimization and structural optimization as an integrated problem in the same mathematical formulation, in which control surface gear ratios are included as design variables in a standard structural optimization algorithm. This new approach is in contrast to most of the existing AAW design processes in which structural optimization and trim optimization have separate objectives and are performed in an iterative, sequential manner. The new integrated AAW design process is demonstrated on a lightweight fighter type aircraft and compared to a sequential AAW design process. For this demonstration, the integrated process converges to a lower weight, and offers an advantage over the sequential process in that optimization is performed in one continuous run, whereas the sequential approach requires pausing and restarting the structural optimization to allow for trim optimization. Introduction An emerging and promising technology for addressing the problem of adverse aeroelastic deformation, such as control surface reversal, is Active Aeroelastic Wing (AAW) technology. It has recently been a key area of study for both the government and industry and is defined by Pendleton et. al., as "a multidisciplinary, synergistic technology that integrates air vehicle aerodynamics, active controls, and structures together to maximize air vehicle performance". AAW technology exploits the use of leading and trailing edge control surfaces to aeroelastically shape the wing, with the resulting aerodynamic forces from the flexible wing becoming the primary means for generating control power. With AAW, the control surfaces then act mainly as tabs and not as the primary sources of control power as they do with a conventional control philosophy. As a result, wing flexibility is seen as an * Ph.D. Candidate, Student Member AIAA † Research Engineer II, Member AIAA ‡ Boeing Chair in Advanced Aerospace Systems Analysis, Associate Fellow AIAA Copyright  2001 by P.S. Zink, D.E. Raveh, and D.N. Mavris. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. advantage rather than a detriment since the aircraft can be operated beyond reversal speeds and still generate the required control power for maneuvers. Hence, there is potential for significant reductions in structural weight and actuator power. Figure 1 illustrates conceptually the differences between AAW technology and a conventional control approach for a rolling maneuver. The hypothetical example shows the cross section of two wings deforming due to aeroelastic effects. The upper wing, employing AAW technology, is twisting in a positive way with the use of both leading and trailing edge surfaces, while the conventionally controlled, lower wing, which uses only the trailing edge surface, is twisting in a negative way. This adverse twist due to the deflection of the trailing edge surface is associated with reduced control surface effectiveness and control surface reversal, in which the increase in camber due to the deflection of the surface is offset by the negative twist of the wing. LE deflects up TE deflects up Wing twists positively