Ornithopter studies in the past have focused on ornithopter construction, power sources, wing design, maximizing thrust, energy efficiency, steady flight trajectories, and flight stability. The next step is to control unsteady maneuvers: the transition from hovering flight to forward flight, turns, and vertical takeoff and landing. The design of stable trim conditions for forward flight and for hover has been achieved. In forward flight, an ornithopter is configured like a conventional airplane or large bird. Its fuselage is essentially horizontal and the wings heave in a vertical plane. In hover, however, the body pitches vertically so that the wing stroke in the horizontal plane. Thrust directed downward, the vehicle remains aloft while the downdraft envelops the tail to provide enough flow for vehicle control and stabilization. To connect these trajectories dynamically is the goal. This study of the transition from forward flight to hovering uses two approaches: to first achieve adequate trajectories, and then optimal trajectories. The object is to connect an initial state—in this case forward flight—and a final state—a steady hover at a designated point—through a feasible flight trajectory. A simple approach is to immediately switch between feedback controllers that regulate each trajectory. When the forward flight trajectory approaches the desired location, the computer switches to a control law that regulates the desired hovering trajectory, which—barring instability—should cause the vehicle to settle. A second approach is to select a range of intermediate trims to stabilize. Starting with the full forward speed, the controller will successively stabilize a trim with lower forward velocity. After a finite number of controllers, the system will achieve a stable hover. This approach would lessen the jump between trim conditions, increasing the likelihood of a stable transition. A third approach is to establish an open-loop trajectory through a trajectory optimization algorithm—optimized for shortest altitude drop, shortest stopping distance, or lowest energy consumption. This path itself could be stabilized. This serves to establish the feasibility of new maneuvers in mechanical flapping flight. It also will make it easier to perform the maneuvers by computer assisted control or by providing an example for a pilot to use.

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