Body pitching and bobbing shape the aerodynamic force, power, and stability of wild silkmoths

Quasi-steady models of insect flight often prescribe constant body dynamics during a wingstroke. However, many insects experience large fluctuations in body kinematics even during a single wingstroke. Silkmoths use larger, slower wingstrokes more akin to some flapping robot designs than their cousin hawkmoths, which are common models for insect flight dynamics. Here, we test whether silkmoth's body pitch and vertical oscillations (time-periodic body angle, stroke-plane angle and body velocity) impact aerodynamic force production, power requirements, and flight stability. An analysis of digitized wing shapes and forward flight 3D kinematics from nine silkmoth species shows that body oscillation magnitude is strongly associated with flapping frequency and wing loading (p<0.05). We also find that body oscillations directly impact the wing angle of attack within a wingstroke. Incorporating body oscillations into a quasi-steady blade element model of silkmoth flight significantly impacts the wingstroke-averaged aerodynamic forces, reduces profile power, and increases body pitch stability. These results might have strong implications for the design of flapping-wing micro air vehicles (FW-MAVs) that require high stability and low power requirements all while maintaining agility.