MORPHING AIRFOIL SHAPE CHANGE OPTIMIZATION WITH MINIMUM ACTUATOR ENERGY AS AN OBJECTIVE Brian C. Prock* Terrence A. Weisshaar† William A. Crossley‡ Purdue University School of Aeronautics and Astronautics West Lafayette, Indiana Abstract Morphing aircraft are multi-role aircraft that use innovative actuators, effectors, and mechanisms to change their state to perform select missions with substantially improved system performance. State change in this study means a change in the cross-sectional shape of the wing itself, not chord extension or span extension. Integrating actuators and mechanisms into an effective, light weight structural topology that generates lift and sustains the air loads generated by the wing is central to the success of morphing, shape changing wings and airfoils. The objective of this study is to explore a process to link analytical models and optimization tools with design methods to create energy efficient, lightweight wing/structure/actuator combinations for morphing aircraft wings. In this case, the energy required to change from one wing or airfoil shape to another is used as the performance index for optimization while the aerodynamic performance such as lift or drag is constrained. Three different, but related, topics are considered: energy required to operate articulated trailing edge flaps and slats attached to flexible 2D airfoils; optimal, minimum energy, articulated control deflections on wings to generate lift; and, deformable airfoils with cross-sectional shape changes requiring strain energy changes to move from one lift coefficient to another. Results indicate that a formal optimization scheme using minimum actuator energy as an objective and internal structural topology features as design variables can identify the best actuators and their most effective locations so that minimal energy is required to operate a morphing wing. Background A morphing aircraft is a multi-role aircraft that, through the use of morphing technologies such as innovative actuators, effectors or mechanisms, changes its state substantially to complete all roles - with superior system performance.1 For instance, for a hunter-killer aircraft, role A is long-duration loiter while role B is high-speed dash and role C is some form of energy deposition to neutralize the target. Morphing aircraft are a major part of a system that requires technology integration to manipulate geometric, mechanical electromagnetic or other mission critical features - on the ground or in-flight - to match vehicle performance to a well-defined environment and mission objective. Modern aircraft already contain complex morphing devices to allow them to balance one mission demand against another but still perform a mission well. The simplest example is the use of landing and take-off flaps to allow transport aircraft to operate from shorter length airports and still cruise at high speed. The trade-off that favors morphing is the fuel saved when a smaller wing is used for efficient high-speed flight and deployable flaps generate increased lift at low landing and take-off speeds. The cost of this system performance balancing is expressed in metrics such as weight, complexity and cost. * Graduate Student, School of Aeronautics and Astronautics, 1282 Grissom Hall, West Lafayette, IN 47907-1282 † Professor, School of Aeronautics and Astronautics, 1282 Grissom Hall, West Lafayette, IN 47907-1282, currently on leave at DARPA, Arlington, Virginia. ‡ Associate Professor, School of Aeronautics and Astronautics, 1282 Grissom Hall, West Lafayette, IN 47907-1282 9th AIAA/ISSMO Symposium on Multidisciplinary Analysis and Optimization4-6 September 2002, Atlanta, GeorgiaAIAA 2002-5401Copyright © 2002 by the author(s). Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.2 Morphing Aircraft Potentialcombining many systems into oneAttack mission:high speed dash, high speed turnsISR mission:high altitude, long range / enduranceHunt: soar, observeAttack: dive, maneuverAttack: dive, maneuvercombine functions / reduce system complexity Figure 1 – Combining system functions Morphing shape/state changes are also necessary when long loiter time is coupled with a high-speed dash requirement or when stealth features are not required during the entire mission. In the latter case, morphing into a “faceted brick” shape like the F-117 for the stealthy portion of the mission would then change the aircraft radar cross-section “state” while preserving aerodynamic performance during long cruise segments. Modern morphing aircraft concepts address system problems such as that depicted in Figure 1. The upper part of Figure 1 shows the different sensor aircraft required to identify targets for combat aircraft to engage and attack. In addition to the variety of aircraft used, this “observe, identify, target and attack” system requires command and control as well as human operators. The result is a complex system with large time lags that impede its effectiveness. The lower part of Figure 1 shows nature’s answer to a sensing and attack system. All capability, including system operation, is concentrated onboard the vehicle. Wing morphing cannot be applied to all systems and all missions. In fact, it requires a major effort to identify the new missions that might result from modern morphing. However, once these missions and system architectures are identified and the aircraft that use them are developed, the result will be to create “game-changers.” Minimizing actuator energy required to generate lift Modern morphing concepts include wings with a variety of moving surfaces, such as: articulated flaps and slats; surface flow control devices; and continuously deforming surfaces. In the latter case, the deformation of the surface is generated either by internal elements that exert forces and moments on the aero structure to deform it or external devices such as continuously deforming trailing edge surfaces. The latter case includes Active Aeroelastic Wing concepts (AAW).2 Because wings are lightweight, structural flexibility and aeroelasticity are essential features of morphing wing design. The energy required to change wing cross-sectional shape to generate lift has two parts, the energy required to strain the structure and the energy required to move against the air pressures on the wing surface. The strain energy stored during the