Autonomous Flight Control Development on the Active Aeroelastic Wing Aircraft

A highly modified F/A-18 aircraft is being used to demonstrate that aeroelastic wing twist can be used to roll a high performance aircraft. A production F/A-18A/B/C/D aircraft uses a combination of aileron deflection, differential horizontal tail deflection and differential leading edge flap deflection to roll the aircraft at various Mach numbers and altitudes. The Active Aeroelastic Wing program is demonstrating that aeroelastic wing twist can be used in lieu of the horizontal tail to provide autonomous roll control at high dynamic pressures. Aerodynamic and loads data have been gathered from the Phase I AAW flight test program. Now control laws have been developed to exploit aeroelastic wing twist and provide autonomous flight control of the AAW aircraft during Phase II. Wing control surfaces are being deflected in non-standard ways to create aeroelastic wing twist and develop the required rolling moments without use of the horizontal tail. Wing control surfaces are also being deflected to provide maneuver load control during pitching maneuvers. Simulation of the AAW control laws shows acceptable flight performance using this new control surface scheme. Time histories of these simulations will be presented to demonstrate the performance capability of the AAW aircraft while maintaining structural loading within pre-specified limits. Although structural loading is not currently being used as a feedback to the controller, the control law design was developed with load constraints as one of the driving parameters. Flight testing for Phase II should begin in the fall of 2004. At that time, we will be able to verify that the control laws work as they did in the simulations. An example of how this technology can be used would be to design future aircraft with good performance and maneuver load control (MLC) but without horizontal tails. The design space could also be opened up to thinner wings, higher aspect ratio wings, or morphing wings. The goal is not to provide a stiff wing for conventional control, but to allow optimization of the structure to make use of more flexible wings. Control inputs would be the same as for conventional aircraft, but rolling and pitching moment can be achieved through a variety of autonomous control surface inputs, including the wing as a control surface in and of itself. This program was developed under contract from the Air Force Research Laboratory’s Air Vehicles Directorate with flight test development sponsored by NASA-DFRC.