Fuselage Aerodynamics and Weight Trade-Off at Low-Speed Ornithopter Flight

Abstract

This work presents a thorough study on the effect of the inclusion or not of a fuselage in flapping wing robots, for which no clear criterion has been found so far. The study consists in a dynamic analysis for level flight conditions at both configurations, of an actual prototype. An overall aerodynamic model based on CFD simulations are used for modeling the average in-flight forces performed by the ornithopter elements, wing, body and tail. Experimental thrust correction is developed to include the effects of wing flexibility, thus increasing the accuracy of the results. Results show a better performance at low speeds when the ornithopter does not carry the fuselage. At higher speeds, the lower drag provided by the fuselage becomes important. However, the increased weight always need a higher flapping frequency for the low velocity range of our prototype, creating a disadvantage for this regime. The results highlights a fuselage design criteria, which can be extrapolated to other bird-scaled flapping wing robots performing slow maneuvers, as perching, as well as to hybrid flapping-fixed wing UAVs.