Body flexion effect on the flight dynamics of a hovering hawkmoth

Abstract

The position and attitude controls of flapping wing flyers are challenging because of their inherent instabilities. Insects can cope with such difficulties by finely and quickly tuning their wing kinematics. In addition, it is known that insects change their posture through the joint between thorax and abdomen in response to visual stimuli. In this study, the effect of the body flexion on the flight dynamics of a hovering hawkmoth are investigated numerically by using an in-house computational fluid dynamics (CFD) and a flexible body dynamics (FBD) solvers. For an integrated understanding of the effects of the body flexion, the curved or flexible body models, which replicate the longitudinal active and passive body flexion respectively, are developed. Our computational results indicate that the slight change of the center of mass (CoM) caused by the active body flexion alters the total aerodynamic torque, which result in the large pitch-up or pitch down of the body within a few wingbeat cycles. It is also found that, even though the rigid body pitches up in free-flight with a measured wing kinematics, the mild flexibility in the body can maintain the body attitude without any control. These results point out the importance of the CoM position on the flight dynamics and control of a flapping flight and, furthermore, the possibility of the simple but effective flight-control system with the body flexion for a bio-inspired MAV.

Biomechanics and biomimetics in insect-inspired flight systems

“…Although there arise difficulties in separating the active controls that stabilize the inherent instability from the natural flight dynamics of an insect, by tethering the insect and measuring its control response to a properly designed stimulus, it is revealed that the insect's sensorimotor system could be modelled reasonably by a proportional-derivative controller with delay times [46,53]. For large insects such as butterflies and hawkmoths, there is relative motion and body flexion between abdomen and thorax [54], which may inherently influence passive flight dynamics and hence flight control [55][56][57].…”

Aeromechanics of Hovering Flight in Perturbed Flows: Insights from Computational Models and Animal Experiments

“…Although these experiments were conducted on tethered hawkmoths and the extent to which these responses play a role in free hovering flight is not yet fully resolved, it has been suggested that this is a plausible feedback control based strategy that is employed by hawkmoths in free flight [15]. Furthermore, Dyhr [39] also showed that abdominal flexion can be used to redirect lift forces and this mechanism could be sufficient to stabilize the hovering flight of a hawkmoth [4]. Additional evidence of such a mechanism can be seen in recordings of freely hovering hawkmoths; Fig.…”

The effect of the abdomen deformation on the longitudinal stability of flying insects

“…The wing planform is considered as a rigid flat plate with no mass and divided into 50 elements for the application of the blade element theory. The lift, drag and moment at each aerodynamic strip along the span-wise direction z WF are given in equations (6) to (8). ( cos ( 2 ) sin ( 2 )…”

“…Their results indicate that the control of the abdomen stabilizes the hovering flight but has a slim stability margin. Also, Noda 6 , who numerically investigated the role of the body flexion using a coupled computational fluid dynamics and flexible body dynamics solver, concluded that the change of the center of mass caused by the body flexion, which alters the total aerodynamic moment, plays important role in the flight dynamics and control of the flapping flight. Here, we derive nonlinear equations of motion of a flying insect with two bodies connected with a torsion spring.…”