Flexible clap and fling in tiny insect flight

Abstract

SUMMARYOf the insects that have been filmed in flight, those that are 1 mm in length or less often clap their wings together at the end of each upstroke and fling them apart at the beginning of each downstroke. This ʻclap and flingʼ motion is thought to augment the lift forces generated during flight. What has not been highlighted in previous work is that very large forces are required to clap the wings together and to fling the wings apart at the low Reynolds numbers relevant to these tiny insects. In this paper, we use the immersed boundary method to simulate clap and fling in rigid and flexible wings. We find that the drag forces generated during fling with rigid wings can be up to 10 times larger than what would be produced without the effects of wing-wing interaction. As the horizontal components of the forces generated during the end of the upstroke and beginning of the downstroke cancel as a result of the motion of the two wings, these forces cannot be used to generate thrust. As a result, clap and fling appears to be rather inefficient for the smallest flying insects. We also add flexibility to the wings and find that the maximum drag force generated during the fling can be reduced by about 50%. In some instances, the net lift forces generated are also improved relative to the rigid wing case. Supplementary material available online at

Kinematics and aerodynamics of avian upstrokes during slow flight

“…To provide a rough estimate of the net forces that the clap and peel mechanism may provide relative to the subsequent downstroke, we adopted two models: a momentum-jet model (Vogel, 1994) focusing on downstroke, and a reverse peel model (Miller and Peskin, 2009), focusing on the clap. Both models assume steadystate flow conditions and circulation averages are representative of the wingbeat.…”

“…Among birds, there exists aerodynamic evidence that Japanese white-eye (Zosterops japonicus) and Gouldian finch (Erythrura gouldiae) capitalize on a ventral clap, wherein the wings are brought together beneath the body to contribute to the downwash (Chang et al, 2013). Here, we differentiate between a clap and fling versus a clap and peel, as defined by Miller and Peskin (2009): we define a clap and fling as minimal flexibility in a rigid wing structure, wherein changes in shape are from external mechanisms, such as aerodynamic loading and inertia; clap and peel, then, has flexibility spanwise and chordwise along the wing, and shape changes are both passive and active via musculoskeletal control.…”

The hydrodynamics of swimming at intermediate Reynolds numbers in the water boatman (Corixidae).

“…Such a mechanism could break down at higher Re, as a result of less viscous cohesion in the flow field. Although unsteady mechanisms of this sort have been shown to be ineffective at lower Re values in insect flight (Miller and Peskin, 2009), the geometry and motion of water boatmen may offer a contrast. Future flow visualization and mathematical modeling studies could resolve how a water boatman creates the very large force coefficients that we report here.…”

Rolling with the flow: Bumblebees flying in unsteady wakes

“…Volant insects employ a variety of unsteady fluid-mechanic phenomena to remain airborne, including leading edge vortex generation (Ellington et al, 1996), wake capture during hovering (Dickinson et al, 1999), rotational circulation during pronation and supination (Dickinson et al, 1999), and reduction of the Wagner effect via clap and fling (Miller and Peskin, 2009). Over the past two decades, our understanding of these phenomena has been significantly improved by studies exploring the flow field over insect wings in free and/or tethered flight conditions, and through the use of dynamically scaled robotic models (for reviews, see Sane, 2003;Wang, 2005).…”