Flight-dynamics, flutter analysis, and control of mdao-designed flying-wing research drones

�The flight dynamics, flutter, and control design for two flexible flying-wing research drones are discussed. The drones, with wing spans of 10 to 14 feet, aspect ratios of over 10, and control surfaces along the entire wing trailing edges, are being developed for flight research into the modeling and control of highly elastic aircraft. The dynamic modeling is based on a mean-axis formulation, and quasi-steady aerodynamics. Flutter-modeling results are shown to agree with those from NASTRAN and flight tests. The vehicles exhibit body-freedom flutter in their flight envelopes, while well below the flutter speed the fight dynamics are quite conventional. Control systems developed for these aircraft include an autopilot and several active-flutter-suppression systems. The autopilot includes an airspeed command/hold plus pitch-and roll-attitude command/holds in the inner loops. Outer loops such as an altitude hold are also employed, but except for the landing-localizer coupler are not discussed in detail. A thrust-command-to-pitch-flap cross feed is also employed to reduce the pitch disturbances from the thrust-cg offset on the vehicles. Three different approaches for active flutter suppression are also discussed and compared. The approaches range from fairly classical to modern MIMO methods. Flight tests revealed that all three designs achieved the goal of actively damping the targeted first aeroelastic mode at the design flight condition, and two of these designs also expanded the flutter boundary. Research is currently underway to further expand the flutter boundary using all three design approaches.