Biomechanics and biomimetics in insect-inspired flight systems

Abstract

Insect- and bird-size drones-micro air vehicles (MAV) that can perform autonomous flight in natural and man-made environments are now an active and well-integrated research area. MAVs normally operate at a low speed in a Reynolds number regime of 10(4)-10(5) or lower, in which most flying animals of insects, birds and bats fly, and encounter unconventional challenges in generating sufficient aerodynamic forces to stay airborne and in controlling flight autonomy to achieve complex manoeuvres. Flying insects that power and control flight by flapping wings are capable of sophisticated aerodynamic force production and precise, agile manoeuvring, through an integrated system consisting of wings to generate aerodynamic force, muscles to move the wings and a control system to modulate power output from the muscles. In this article, we give a selective review on the state of the art of biomechanics in bioinspired flight systems in terms of flapping and flexible wing aerodynamics, flight dynamics and stability, passive and active mechanisms in stabilization and control, as well as flapping flight in unsteady environments. We further highlight recent advances in biomimetics of flapping-wing MAVs with a specific focus on insect-inspired wing design and fabrication, as well as sensing systems.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.

Keywords: aerodynamics; bioinspired flight system; biomimetics; flight control; micro air vehicle; sensing.

Figure 1.

Bioinspired flight systems: a closed-loop system to achieve flight control through overarching an external mechanical system and an inner working system. (Bottom) External mechanical system: a passive open-loop system to generate aerodynamic force and perform manoeuvring by integrating kinematics, aerodynamics, flight dynamics as well as flight stabilization associated with flapping wings and body. (Top) Inner working system: a nonlinear dynamic system consisting of sensorimotor neurobiology and musculoskeletal mechanics to mediate the external flight system.

Figure 2.

Biomimetics in insect-inspired flight systems. Scaling issues in bioinspired flying vehicles require a systematic-level design consisting of a biomimetic design system and a control autonomy system. (Bottom) Biomimetic design system brings challenges in aspects of flapping mechanisms, wing design, manufacturing as well as systematic design. (Top) Control autonomy system consists of two level autonomy of controlled flight autonomy and reactive flight autonomy.

Figure 3.

Kinematics and prominent aerodynamic features in insect flapping flights. (a) Wing morphologies of hawkmoth, honeybee, fruit fly and thrips as well as relationship of wingspan versus Reynolds number. (b) Wing kinematics of a hovering fruit fly. (c) Near-and far-field vortex dynamics in fruit fly and hawkmoth hovering and unified explanation of three-dimensional flapping-wing aerodynamics [33]. (d) Flexible wings aerodynamics in hovering hawkmoth: fluid–structure interaction model and near-field vortex dynamics [19]. (e) Vortex dynamics around a bumblebee flying in turbulence [34].

Figure 4.

Flapping micro air vehicles. (Upper panel) Relationship of wing span versus mass in flapping air vehicles powered by DC motor, piezoceramic actuator, rubber band, human power, etc. (Lower panel) Three prototype bioinspired flapping micro air vehicles: X-wing MAV [9,10], Nano-hummingbird [11] and Robobee [13].