Indirect actuation reduces flight power requirements inManduca sextavia elastic energy exchange

Abstract

In the vast majority of flying insects, wing movements are generated indirectly via the deformations of the exoskeleton. Indirect measurements of inertial and aerodynamic power requirements suggest that elastic energy exchange in spring-like structures may reduce the high power requirements of flight by recovering energy from one wingstroke to the next. We directly measured deformation mechanics and elastic energy storage in a hawkmoth Manduca sexta thorax by recording the force required to deform the thorax over a frequency range encompassing typical wingbeat frequencies. We found that a structural damping model, not a viscoelastic model, accurately describes the thorax's linear spring-like properties and frequency independent dissipation. The energy recovered from thorax deformations is sufficient to minimize flight power requirements. By removing the passive musculature, we find that the exoskeleton determines thorax mechanics. To assess the factors that determine the exoskeleton's spring-like properties, we isolated functional thorax regions, disrupted strain in an otherwise intact thorax, and compared results to a homogeneous hemisphere. We found that mechanical coupling between spatially separated thorax regions improves energy exchange performance. Furthermore, local mechanical properties depend on global strain patterns. Finally, the addition of scutum deformations via indirect actuation provides additional energy recovery without added dissipation.

Hawkmoths use wingstroke-to-wingstroke frequency modulation for aerial recovery to vortex ring perturbations

“…This is consistent with evidence that elastic energy exchange substantially reduces the power requirements of insect flight [3,4,5,6,7,8]. As the wing decelerates, elastic elements store excess kinetic energy and subsequently return this energy to reaccelerate the wing.…”

“…Because inertial and aerodynamic power requirements both scale with frequency cubed [24], increasing wbf by 16% would increase mechanical power requirements by over 55%. Spring-like structures in the insect flight system have a finite capacity for elastic energy exchange [6], therefore the musculature would have to supply this increased power demand. Under tethered in vivo conditions, Manduca sexta power muscles produce only 50% of peak power and this power can be modulated with precise timing [41,2].…”

“…Like resonant oscillators, insects store excess kinetic energy during a wing stroke in spring-like structures and return this energy to reaccelerate the wings. This strategy effectively reduces the inertial necessary for flight 1 [3,4,5,6,7,8,9]. Recent work directly measuring resonance properties in bees suggests that wingbeat frequencies are directly tuned to match resonance frequencies [10].…”

“…[5][6][7][8] as factors. Normalized wingbeat frequency modulation (95% quantile width/mean wbf) was the dependent variable.…”

Wing damage affects flight kinematics but not flower tracking performance in hummingbird hawkmoths

“…Inertial power is often not considered as a cost, because it is assumed that minimal power is required for the inertial acceleration of the wings due to energy storage and return. However, it has been shown that the inertial power, while significantly reduced, is not perfectly compensated by elastic elements (Gau et al 2019). Thus, the amplitude-based strategy of M. stellatarum should be beneficial from an inertial power point of view, and equally good as far as aerodynamic power is concerned.…”