Aero-Effected Distributed Adaptive Control of Flexible Aircraft Using Active Bleed

The proposed research focuses on the development of a new adaptive control methodology for active control of wing aerodynamic shape to effect distributed aerodynamic forces and moments for maneuvering and stabilization of flexible airframes without moving control surfaces. The new aero-effected flight control will be achieved using output feedback adaptive control of distributed bleed across aerodynamic surfaces, and is particularly suited for high-altitude long endurance vehicles. The large-area air bleed is driven by the inherent pressure differences in flight across the pressure and suction wing surface, and is regulated by low-power, surface-integrated louver valves. Our previous basic research in adaptive control has stressed the ability to model and cancel the effect of uncertainty in output regulation. We also have developed methods for adaptation in the presence of nonlinear actuation, which includes such effects as actuator saturation. These tools are currently being employed in the study of active flow control using synthetic jet actuation, and will be adapted to the problems that are unique to improving aeroelastic performance and active damping of airframe-propulsion-structure interactions using distributed bleed. Phase I will focus on advancing the state of the art in output feedback adaptive control, and demonstration of the capability of aero-bleed to control the dynamic modes of a flexible lifting surface. These efforts will be integrated in Phase-II by using an adaptive controller to regulate a flexible wing flown in three degrees of freedom in a wind tunnel experiment, using an existing traverse mechanism. Another option is to use Atair Aerospace's LEAPP vehicle to flight test a highly flexible wing design. Additional Phase-II and Phase-III transition possibilities include coordinated research efforts with Boeing related to the DARPA Vulture vehicle, and/or with AeroVironment related to the Global Observer vehicle.

The most immediate non-NASA application would be to the DARPA Vulture vehicle. Boeing has recently been awarded a 1-year program for both sub- and full-scale conceptual vehicle design and a system requirements review. There are other department-of-defense programs that could benefit from this effort such as the Zephyr Joint Capabilities Technology demonstrator. Atair is also interested in the development of an active means of flow control for applications to their line of guided parafoils. Guided parafoil control currently makes use of electrically driven left and right servos to pull lines that are attached to strategic points on the canopy. While effective, this approach to control has a number of drawbacks that limit performance in terms of terminal accuracy. The most obvious limitation is that it does not provide a direct means of controlling glide slope. This means that guidance can only be achieved though banked turns since there is no independent means of controlling rate of descent. The proposed development of distributed bleed control could in concept replace the need for conventional servo actuation with embedded active control devices, and provide an independent means of glide slope control.

The most immediate NASA application would be to Global Observer. This vehicle recently completed its first test flight that took it to an altitude of 4,000 feet. Ultimately Global Observer is intended to function as a high altitude long endurance vehicle. As this program progresses, active aeroelastic and vibration control could easily become an enabling technology. Adaptive output feedback control design could be added to the existing flight control system as an augmenting element to mitigate the effects of modeling error and possible failures that can occur when undergoing a long endurance flight. Active bleed control could also be explored for augmenting the existing aero and propulsive means of flight control. NASA has recently funded a variety of adaptive flight control studies under their Integrated Resilient Aircraft Control effort. To date, all of the adaptive methods that have been explored under this program assume the availability of full state feedback. Control of seroservoelastic modes implies that the full state is not available for feedback, and moreover that the full dimension of the plant is unknown. Advancements in adaptive output feedback design contemplated for this effort would ultimately address issues related to control of unmodeled dynamics as well. These advancements would also permit application of adaptive control theory to distributed and decentralized control of large and complex flexible space structures.