An Aerial Robot with a Passive Morphing Design for Efficient Hovering and Forward Flight

With foreseeable applications such as assisted agriculture, reconnaissance, and transportation, research in small, human-friendly micro aerial vehicles has received tremendous attention from scientists and engineers. These small robots, or drones, have potential to revolutionize our use of robots for civilian applications. Compared to conventional aircraft, however, at centimeter scales, small flying robots suffer from radical reduction in aerodynamic efficiency. The elevated energetic cost of staying airborne severely limits the flight endurance.Among a few common platforms, rotary-wing vehicles, such as quadrotors, become popular owing to the simple design and the ability to hover. While being extremely maneuverable, these flying machines rely on direct propulsion force to stay aloft without wings. Compared to fixed-wing aircraft with large aerodynamic surfaces, rotary-wing vehicles are inferior in terms of aerodynamic efficiency and flight endurance. While hybrid machines with dual flight modes have been developed, the use of airfoils for lift generation is still limited to forward fixed-wing flight only.In this proposed research, we will show how a simple passive morphing mechanism can be employed to realize a new class of transformable flying machine that is energetically efficient for both hovering and forward flight. This research will address the issues on flight endurance and functionality of small aerial robots in three steps. First, to create a robot capable of operating efficiently in two flight modes, we are inspired by autorotating flight of a winged achene—samara, and a passive wing pitch rotation found in insects. Herein, we incorporate flexural hinges to allow the airfoils to intelligently adapt its angle of attack according to aerodynamic loads. The morphing mechanism enables the wings to generate lift in both hovering flight (by rotation) and forward flight without requiring additional actuation. Second, by studying the aerodynamic forces and flight dynamics of the hovering robot in a rotating frame, it is possible to design and fabricate the centimeter-scale robot to guarantee passive attitude stability, simplifying the requirements for active control. A similar strategy is applied for a robot performing a forward flight. Finally, we seek to demonstrate hovering and forward flight. To achieve position control in a hovering flight, a time-varying signal is required to disturb the radially symmetric nominal hovering trajectory. For a forward flight, we must deal with the coupling between the altitude, pitch, and longitudinal dynamics.It is perceivable that the proposed research will contribute to advances in the field of micro aerial vehicles by expanding their endurance and functionalities. It is likely that the project would broaden the applications of aerial robots. Scientific merits will come from: (i) the development of the morphing design and corresponding aeromechanic models; (ii) the framework for analyzing dynamics and stability of a rotating hovering flight; (iii) the realization of an energetically efficient robot with a bimodal aerial locomotion.