Distinct forms of resonant optimality within insect indirect flight motors

TL;DR

This paper reveals that insect flight motors operate through multiple distinct resonance states, enabling robustness and efficiency across a range of wingbeat frequencies, challenging the idea of a single optimal resonance frequency.

Contribution

It introduces a new conceptual model showing resonance as a complex cluster of states, not a single frequency, explaining how insects maintain efficient flight despite frequency modulation.

Findings

Resonance in insect flight motors comprises multiple distinct states.

Insects can sustain negative work absorption over wide frequency ranges.

The model explains robustness of insect flight to environmental and structural variations.

Abstract

Insect flight motors are extraordinary natural structures that operate efficiently at high frequencies. Structural resonance is thought to play a role in ensuring efficient motor operation, but the details of this role are elusive. While the efficiency benefits associated with resonance may be significant, a range of counterintuitive behaviours are observed. In particular, the relationship between insect wingbeat frequencies and thoracic natural frequencies are uncertain, with insects showing wingbeat frequency modulation over both short and long timescales. Here, we offer new explanations for this modulation. We show how, in linear and nonlinear models of an indirect flight motor, resonance is not a unitary state at a single frequency; but a complex cluster of distinct and mutually-exclusive states, each representing a different form of resonant optimality. Additionally, by characterising the relationship between resonance and the state of negative work absorption within the motor, we demonstrate how near-perfect negative work absorption can be maintained over significant wingbeat frequency ranges. Our analysis leads to a new conceptual model of flight motor operation: one in which insects are indifferent to their precise wingbeat frequency, and robust to changes in thoracic and environmental properties - illustrating the extraordinary robustness of these natural motors.