  Tiny flying insects, such as Drosophila melanogaster, fly by flapping their
wings at frequencies faster than their brains are able to process. To do so,
they rely on self-oscillation: dynamic instability, leading to emergent
oscillation, arising from muscle stretch-activation. Many questions concerning
this vital natural instability remain open. Does flight motor self-oscillation
necessarily lead to resonance - a state optimal in efficiency and/or
performance? If so, what state? And is self-oscillation even guaranteed in a
motor driven by stretch-activated muscle, or are there limiting conditions? In
this work, we use data-driven models of wingbeat and muscle behaviour to answer
these questions. Developing and leveraging novel analysis techniques, including
symbolic computation, we establish a fundamental condition for motor
self-oscillation common to a wide range of motor models. Remarkably, D.
melanogaster flight apparently defies this condition: a paradox of motor
operation. We explore potential resolutions to this paradox, and, within its
confines, establish that the D. melanogaster flight motor is likely not
resonant with respect to exoskeletal elasticity: instead, the muscular
elasticity plays a dominant role. Contrary to common supposition, the stiffness
of stretch-activated muscle is an obstacle to, rather than an enabler of, the
operation of the D. melanogaster flight motor.
