Design and comparison of tails for bird-scale flapping-wing robots

Abstract

Flapping-wing robots (so-called ornithopters) are a promising type of platform to perform efficient winged flight and interaction with the environment. However, the control of such vehicles is challenging due to their under-actuated morphology to meet lightweight requirements. Consequently, the flight control of flapping-wing robots is predominantly handled by the tail. Most ornithopters feature a tail with two degrees of freedom but the configuration choice is often arbitrary and without indepth study. In this paper, we propose a thorough analysis of the design and in-flight performance for the three tails. Their design and manufacturing methods are presented, with an emphasis on low weight, which is critical in ornithopters. The aerodynamics of the tails is analyzed through CFD simulations and their performance compared experimentally. The advantages and performance metrics of each configuration are discussed based on flight data. Two types of 3D flight tests were carried out: aggressive heading maneuvers and level turns. The results show that an inverted V-tail outperforms the others regarding maneuverability and stability. From the three configurations, only the inverted V-Tail can perform an aggressive stable banked level turn with a radius of 3.7 m at a turning rate of 1.6 rad/s. This research work describes the impact of the tail configuration choice on the performance of bird-scale flapping-wing robots.

How ornithopters can perch autonomously on a branch

“…S2 for actuator comparison). The selected conventional tail configuration yields high pitch authority, an important metric for precise vertical positioning (35). Low weight and extended pitch deflection are possible using the new direct drive, carbon fiber tail design, see description in Text S6 and Fig.…”

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

“…However, it is more interesting to define the conditions by the frequency needed to fly at a certain velocity or a certain angle of attack. Then, we can obtain the deflection of the tail needed by equation (8). To complete the formulation done here, we need the aerodynamic coefficients formulated in section IV.…”

“…The coefficients have been identified with a regression factor greater than 97 percent, and are as follows: C max L,t = 0.94, a α = 2.92, C max d,t = 0.36, C 0 d,t = 0.04 and b α = 4.23. For further information about the design, aerodynamic simulations and performance analysis and maneuverability we refer to [8], where three different tails at the range of interest were modeled and analyzed experimentally.…”

“…For large flapping-wing aerial robots, those common birds tasks become a challenge, which is the case of study in this work. Thus, in the context of the GRIFFIN Advanced Grant of the European Research Council, we have developed a fully operational large aerial robot with available payload and low-speed operational range (2-6 m/s) [7], with characterized aerodynamics [8], [9], to perform real-world applications based on the perception of the environment. As a new addition to this prototype, a fuselage body has been designed in order to get a bird appearance, providing also impact resistance and better aerodynamic performance in forward flight.…”

“…Two cases are analyzed with and without fuselage. Dynamic analysis is based on aircraft flight equations, using results of CFD experimentally validated [8], [9] for the formulation of the aerodynamic forces. In order to model the aerodynamic performance of the fuselage, a new CFD analysis is also developed.…”