Unsteady Propulsion of a Two-Dimensional Flapping Thin Airfoil in a Pulsating Stream.

The cruising velocity of animals, or robotic vehicles, that use flapping wings or fins to propel themselves is not constant but oscillates around a mean value with an amplitude usually much smaller than the mean, and a frequency that typically doubles the flapping frequency. Quantifying the effect that these velocity fluctuations may have on the propulsion of a flapping and oscillating airfoil is of great relevance to properly modeling the self-propelled performance of these animals or robotic vehicles. This is the objective of the present work, where the force and moment that an oscillating stream exerts on a two-dimensional pitching and heaving airfoil are obtained analytically using the vortical impulse theory in the linear potential flow limit. The thrust force of the flapping airfoil in a pulsating stream in this limit is obtained here for the first time. The lift force and moment derived here contain new terms in relation to the pioneering work by Greenberg (1947), which are shown quantitatively unimportant. The theoretical results obtained here are compared with existing computational data for flapping foils immersed in a stream with velocity oscillating sinusoidally about a mean value.The authors acknowledge support from the Advanced Grant of the European Research Council GRIFFIN, Action 788247, and from the Junta de Andalucía, Spain, Grant UMA18-FEDER-JA-047. Ernesto Sanchez-Laulhe also acknowledges his predoctoral contract at the University of Malaga

Model-Based Lateral Tracking for Bird-Size Ornithopters in Perching Scenario.

An improved tracking method for ornithopters in perching scenario is presented. Based on previous works, this article develops a model-based approach for the lateral controller of the ornithopter. The paper shows how a simple dynamic model can be used to track autonomously a target point in a constrained confined space, that requires accurate and fast maneuvers. The lateral control follows a cascade architecture to transform the actuator movement, which for this kind of platform is the deflection of the vertical tail, into an effective trajectory tracking in the horizontal plane. Results show an improvement in the accuracy of the perching maneuver, reducing the errors in the horizontal plane from the perching position to the target point, the center of the branch in this case. In addition, the improved lateral control allows the ornithopter to reach the perching objective from different initial positions and directions, so it can perform a real 3D perching, compared to the previous experiment where the launching direction was aligned with the branch. This new controller can also be implemented for 3D trajectory tracking, leading to a complete ornithopter-based autopilot architecture.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. ERC Advanced Grant GRIFFIN, action 78824

Design of the High-Payload Flapping Wing Robot E-Flap

Autonomous lightweight flapping-wing robots show potential to become a safe and affordable solution for rapidly deploying robots around humans and in complex environments. The absence of propellers makes such vehicles more resistant to physical contact, permitting flight in cluttered environments, and collaborating with humans. Importantly, the provision of thousands of species of birds that have already mastered the challenging task of flapping flight is a rich source of solutions. However, small wing flapping technology is still in its beginnings, with limited levels of autonomy and physical interaction capability with the environment. One significant limitation to this is the low payload available. Here we show the Eagle-inspired Flapping-wing robot E-Flap, a 510 g novel design capable of a 100% of payload, exceeding the requirement of the computing and sensing package needed to fly with a high degree of autonomy. The concept is extensively characterized, both in a tracked indoor space and in outdoor conditions. We demonstrate flight path angle of up to 50° and velocities from as low as 2 m/s to over 6 m/s. Overall, the robotic platform has been proven to be reliable, having performed over 100 flights. Through mechanical and electronics advances, the E-Flap is a robust vehicle prototype and paves the way towards flapping-wing robots becoming a practical fully autonomous flying solution.Consejo Europeo de Investigación 78824

Model-Based Approach for Lateral Maneuvers of Bird-Size Ornithopter.

A model-based approach for lateral maneuvering of flapping wing UAVs in closed spaces is presented. Bird-size ornithopters do not have asymmetric actuation in the wing due to mechanical complexity, so they rely upon the tail for lateral maneuvering. The prototype E-Flap can deflect the vertical tail to make maneuvers out of the longitudinal plane. This work defines simplified equations for the steady turning maneuver based on the body roll angle. The relation between the velocity of the prototype and the turning radius is also stated. Then, an approach to the attitude is proposed, defining the relation between the deflection of the vertical tail and the roll angle. We prove that, even though this deflection causes a yaw moment, the coupling between yaw and roll dynamics generates also a roll rate. To validate this simplified model, a simple control is presented for continuous circular trajectory tracking inside an indoor flight zone. The objective is to track circular trajectories of a radius 2 times greater than the wingspan at a constant height. Results show a very good agreement between the theoretical and experimental turning radius. In addition, the direct relation between the vertical tail deflection and the roll rate of the ornithopter is identified. Even though the desired radius is not reached, the FWUAV is capable of maintaining a closed turning maneuver for several laps. Therefore, the insight provided by the model proves to be an appropriate approach for aggressive lateral maneuvers of bird-size ornithopters.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. ERC Advanced Grant GRIFFIN, Action 788247