Papers by Keyword: Thrust Generation

Abstract: In this paper, the effects of angle of attack, camber and camber location on propulsion performance of flapping airfoils undergoing plunging motion were numerically studied at Re=20000 and h=0.175. The unsteady incompressible viscous flow around four different airfoil sections was simulated applying the dynamic mesh. The results show that the time averaged thrust coefficient C_Tmean and propulsive efficiency η of the symmetric airfoil decrease with the increasing angle of attack, and the variation of C_Tmean is more obvious than that of C_Pmean. Both C_Tmean and η for NACA airfoils studied in this paper decrease with the increasing camber and the difference between the propulsion performances of different airfoils is not obvious, and the thrust generation and power of various NACA airfoils gradually increase during the downstroke and decrease during the upstroke. Under the same conditions, the airfoil with a further distance between the maximum camber location and the chord of the leading edge leads to higher propulsive efficiency.

Abstract: Flying robots with flapping wings are preferred over conventionally fixed or rotational wings in terms of hovering capability for a simple mechanical configuration. Until recently, available actuators for such a robot are limited to (1) a conventional motor with four-bar linkage mechanism or (2) a piezo electric actuator, but none of them could provide enough lift because of low flapping frequency, small stroke angles, and/or frequent mechanical failure. A new actuator capable of generating large stroke angles with high frequency is developed. It consists of an out-runner brushless motor with a modified motor driver attached to a torsion spring. The wing is attached directly on the cap of the motor. A prototype is built and preliminary thrust force measurements are performed. Properties of wing materials suitable for powerful and robust actuators will be discussed. The actuator employed in the present study utilizes resonance oscillation, which leads to high energy efficiency. Further study of wing shape and directional stiffness is needed for generating higher lift capability.