Multi-Objective Flight Control Optimization Framework

Composite materials are being used in aerospace design because of their high strength-to-weight ratio. On modern airplanes, composite wings offer a greater degree of aerodynamic efficiency due to weight savings, but at the same time introduce more structural flexibility than their aluminum counterparts. Under off-design flight conditions, changes in the wing shape due to structural flexibility cause the wing aerodynamics to be non-optimal. This effect could offset any weight saving benefits realized by the composite wings. Structural flexibility could also cause adverse interactions with flight control and structural vibration which can compromise aircraft stability, pilot handling qualities, and passenger ride quality. NASA Ames Research Center has developed a novel technology that employs a new multi-objective flight control optimization framework to achieve multiple control objectives simultaneously. This technology leverages the availability of distributed flight control surfaces in modern transports. The multi-objective flight control technology comprises the following objectives all acting in a synergistic manner: 1) traditional stability augmentation and pilot command-following flight control, 2) drag minimization, 3) aeroelastic mode suppression, 4) gust load alleviation, and 5) maneuver load alleviation. Each of these objectives can be a major control system design in its own right. Thus, the multi-objective flight control technology can effectively manage the complex interactions of the individual single-objective flight control system design and take into account multiple competing requirements to achieve optimal flight control solutions that have the best compromise for these requirements. In addition, a real- time drag minimization control strategy is included in the guidance loop. This feature utilizes system identification methods to estimate aerodynamic parameters for the on-line optimization. The aerodynamic parameters are also used in the multi-objective flight control for drag minimization and maneuver/ gust load alleviation control. As aircraft wings become more flexible, adverse aerodynamic interactions with the wing structure can result in changes in the wing shapes due to aeroelastic deflections that can prevent the optimal aerodynamic performance from being realized. The flexible wing structure can also be more susceptible to vibration due to atmospheric turbulence and wind gusts which can affect passenger ride comfort and compromise the structural integrity. NASA Ames Research Center has developed a new multi-objective flight control optimization framework that can achieve multiple control objectives simultaneously. These control objectives comprise rigid-aircraft stability augmentation control, flexible mode suppression, drag optimization, and maneuver / gust load alleviation, while still maintaining traditional pilot command-tracking tasks. The technology addresses the operational constraints and the efficiency goal of modern transports simultaneously in order to arrive at optimal flight control solutions.