Four-Winged Flapping Flyer in Forward Flight - Selected Topics of Computational and Experimental Fluid Mechanics - page 143

Four-Winged Flapping Flyer
in Forward Flight

R. Godoy-Diana, P. Jain, M. Centeno, A. Weinreb and B. Thiria

Abstract We study experimentally a four-winged flapping flyer with chord-wise
flexible wings in a self-propelled setup. For a given physical configuration of the
flyer (i.e. fixed distance between the forewing and hindwing pairs and fixed wing
flexibility), we explore the kinematic parameter space constituted by the flapping
frequency and the forewing-hindwing phase lag. Cruising speed and consumed elec-
tric power measurements are performed for each point in the parameter space

and allow us to discuss the problem of performance and efficiency in four-winged
flapping flight. We show that different phase-lags are needed for the system to be opti-
mised for fastest flight or lowest energy consumption. A conjecture of the underlying
mechanism is proposed in terms of the coupled dynamics of the forewing-hindwing
phase lag and the deformation kinematics of the flexible wings.

( f ,˕)

1 Introduction

Flapping flyers display an extremely rich variety of maneuvers because of the mul-
tiple kinematic parameters that rule the unsteady production of aerodynamic forces.
From a biological point of view, the case of four-winged flyers capable of out-
of-phase motion between forewings and hindwings such as dragonflies is particu-
larly interesting. In the words of Azuma et al. ( 1985 ): “Dragonflies can hover, fly
at high speed and maneuver skillfully in the air in order to defend their territory,
feed on live prey and mate in tandem formation”. Their body and wing kinematics