Optimization to Support Morphing Aircraft Design
William A. Crossley
Purdue University
September 2003
TA 762-40-31-02
Research Objective. To assess the system-level impact of morphing, systems analysts need optimization-based tools for trading off one mission goal against another. This research creates multiobjective optimization tools for conceptual design problems. These methods differ from traditional optimization methods in that they allow the gross geometry of the aircraft to change from one leg of the mission to another. These methods differ from normal genetic algorithms in that they allow a large number of constraints and they converge to many diverse solutions.
Approach. Compare multiobjective optimization results for aircraft designed with and without morphing capabilities. Develop general rules to anticipate when morphing has a significant benefit. Illustrate findings by using the FLOPS aircraft sizing code to design a military bomber for dissimilar mission goals of high-altitude endurance and low-altitude high-speed dash.
Accomplishment Description. A baseline bomber and morphing bomber are both optimized to meet the mission specifications with the lowest takeoff gross weight. Compared to the baseline, the morphing bomber has increased aspect ratio during loiter, increased wing area during takeoff, landing, and loiter and increased wing sweep during dash (see notional figures). For the specified mission, the morphing airplane has a potential 4% decrease in takeoff gross weight and a 10% reduction in fuel consumption. The potential benefits are based on a traditional parametric weight prediction method and a crude estimate of the weight penalty associated with joints and actuation devices. The system-level optimization results are summarized in a carpet plot (see graph). The heavy black lines indicate constraint boundaries such as the required dash speed and the maximum takeoff field length. These constraints boundaries move to allow a lower take off gross weight, lower thrust to weight ratio (T/W) and higher wing loading for the morphing aircraft. The constraints move because the morphed wing shape has excellent low-speed characteristics that improve takeoff performance as well as dash performance. This allows significant weight savings due to a smaller engine and less fuel.
Significance. Extensive testing of interesting academic problems like this one suggests that morphing benefit is highly dependent on the optimization objective function and on the mission specification. An optimization-based method is particularly valuable when designing unconventional morphing vehicles where the trade spaces are not well understood. Such information enhances the designer's intuition about the tradeoffs and suggests new opportunities for revolutionary concepts.
Future Plans. Optimization-based tools for conceptual design form a fruitful new area of research for the ASCAC. To be practical for morphing vehicles, the system analysis tools must improve (e.g. improve aerodynamic analysis to capture drag change due to twist or camber of wing). Moreover, the optimization problem formulation currently minimizes takeoff gross weight while a performance-based objective such as maximize dash speed could be more appropriate.
Figure: Optimization to Support Morphing Aircraft Design
NASA POC: Sharon L. Padula
Telephone: (757) 864-2807
E-Mail: s.l.padula@larc.nasa.gov
Eric T. Martin, Rania A. Hassan and William A. Crossley, "Generalization of the Two-Branch Tournament for N-Objective Optimization", Presented at the 9th AIAA/ISSMO Symposium on Multidisciplinary Analysis and Optimization, Atlanta, GA, September 4-6, 2002, Also AIAA 2002-5430.
C. Peters, B. Roth, W. Crossley, T. Weisshaar, "Use of Design Methods to Generate and Develop Missions for Morphing Aircraft", Presented at the 9th AIAA/ISSMO Symposium on Multidisciplinary Analysis and Optimization, Atlanta, GA, September 4-6, 2002, Also AIAA 2002-5468.
Brian Roth, C. Peters and William A. Crossley, "Aircraft Sizing with Morphing as an Independent Variable", Presented at the 2nd AIAA Aircraft Technology Integration and Operations Forum, Los Angeles, CA, October 2002, Also AIAA 2002-5840.
Eric T. Martin and William A. Crossley, "Multiobjective Aircraft Design to Investigate Potential Geometric Morphing Features", Presented at the 2nd AIAA Aircraft Technology Integration and Operations Forum, Los Angeles, CA, October 2002, Also AIAA 2002-5859.
Eric T. Martin,:"Multiobjective Optimization for Advanced Aircraft Design", MS thesis, School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN, August 2002.
Brian Roth, "Aircraft Sizing with Morphing as an Independent Variable: Motivation, Strategies, and Investigations", MS thesis, School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN, May 2003.
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Date last updated: April 20, 2006
