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Winged insects vary greatly in size, from tiny wasps (0.015 mg) to large moths (1.6 g). Previous studies on the power requirements of insect flight focused on relatively large insects; those of miniature insects remain relatively unknown. In this study the power requirements of a series of miniature insects were calculated, and changes with size across a range of insect sizes were investigated. Aerodynamic power was computed by numerically solving the Navier–Stokes equation, and inertial power was computed analytically. Comparison analysis was then conducted on the power requirements of miniature and large insects. Despite a 100,000-fold weight difference, the required power per unit insect mass, referred to as mass-specific power, was approximately equal for all the insects examined. This finding is explained as follows. Power is approximately proportional to the product of the wing speed and the wing drag per unit weight (i.e., “drag-to-lift ratio”). When insect size decreased, wing speed decreased (due to reduced wing-length), while wing drag increased (due to increased air-viscosity), resulting in an approximately unchanged mass-specific power. For large or small insects, flight power is derived from the same type of muscles (striated). Assuming that the mean power per unit muscle mass is the same under the same type of muscle, the above size/specific-power relation indicates that the ratio of flight-muscle mass to insect mass is the same for different sized insects.

In the development of MAVs, small sized flapping wing designs mimicking insects have appeared recently and lot of studies have been carried out for various aspects of insect flight. The study of aerodynamics of ground effect is an important venue. In this paper CFD studies has been done to simulate the ground effect in hover flight for a rectangular wing. Various heights from very near to the ground till free stream condition where the ground effect is absent are investigated. Incompressible 3D NS equations are numerically solved and results are presented. Aerodynamic vertical force and aerodynamic power variation has been presented. The study indicates that during hover very near to the ground, average vertical force during a wing beat cycle increases largely as compared to its free stream condition in the absence of ground effect. For the typical case taken a 26% increase in average cycle vertical force and 11% decrease in average specific power is noted near the ground. Maximum vertical force increase is found below three quarters of wing length distance from the ground. The ground effect on aerodynamic force or power vanishes after 2.5 times the wing length height above the ground.

Insects can hover, fly forward, climb, and descend with ease while demonstrating amazing stability, and they can also maneuver in impressive ways as no other organisms can. Is their flight inherently stable? If so, how can they maneuver so well? In recent years, significant progress has been made in revealing the dynamic flight stability and flight control mechanisms of insects and has partially answered these questions. Here the most recent advances in this active area are reviewed. The aim is to provide the background necessary to do research in the area and raise questions that need to be addressed in the future. This review begins with an overview of the flapping kinematics and aerodynamics of insect flight. It is followed by a summary of the governing equations of insect motion and the simplified theoretical models used for analysis of dynamic stability and control. Next, the stability properties of hovering flight and forward flight are scrutinized. Then the flight control properties are explored, dealing in turn with flight stabilization control, steady-state control for changing from hovering to forward flight and from one forward-flight speed to another, and control for maneuvers near hovering. Finally, remarks are given on the state of the art of this research field and speculation is made on its outlook in the near future.

In the present paper, the controlled flight of fruitflies after voluntary takeoff is studied. Wing and body kinematics of the insects after takeoff are measured using high-speed video techniques, and the aerodynamic force and moment are calculated by the computational fluid dynamics method based on the measured data. How the control moments are generated is analyzed by correlating the computed moments with the wing kinematics. A fruit-fly has a large pitch-up angular velocity owing to the takeoff jump and the fly controls its body attitude by producing pitching moments. It is found that the pitching moment is produced by changes in both the aerodynamic force and the moment arm. The change in the aerodynamic force is mainly due to the change in angle of attack. The change in the moment arm is mainly due to the change in the mean stroke angle and deviation angle, and the deviation angle plays a more important role than the mean stroke angle in changing the moment arm (note that change in deviation angle implies variation in the position of the aerodynamic stroke plane with respect to the anatomical stroke plane). This is unlike the case of fruitflies correcting pitch perturbations in steady free flight, where they produce pitching moment mainly by changes in mean stroke angle.

Because of the periodically varying aerodynamic and inertial forces of the flapping wings, a hovering or constant-speed flying insect is a cyclically forcing system, and, generally, the flight is not in a fixed-point equilibrium, but in a cyclic-motion equilibrium. Current stability theory of insect flight is based on the averaged model and treats the flight as a fixed-point equilibrium. In the present study, we treated the flight as a cyclic-motion equilibrium and used the Floquet theory to analyse the longitudinal stability of insect flight. Two hovering model insects were considered—a dronefly and a hawkmoth. The former had relatively high wingbeat frequency and small wing-mass to body-mass ratio, and hence very small amplitude of body oscillation; while the latter had relatively low wingbeat frequency and large wing-mass to body-mass ratio, and hence relatively large amplitude of body oscillation. For comparison, analysis using the averaged-model theory (fixed-point stability analysis) was also made. Results of both the cyclic-motion stability analysis and the fixed-point stability analysis were tested by numerical simulation using complete equations of motion coupled with the Navier–Stokes equations. The Floquet theory (cyclic-motion stability analysis) agreed well with the simulation for both the model dronefly and the model hawkmoth; but the averaged-model theory gave good results only for the dronefly. Thus, for an insect with relatively large body oscillation at wingbeat frequency, cyclic-motion stability analysis is required, and for their control analysis, the existing well-developed control theories for systems of fixed-point equilibrium are no longer applicable and new methods that take the cyclic variation of the flight dynamics into account are needed.

The effects of corrugation and wing planform (shape and aspect ratio) on the aerodynamic force production of model insect wings in sweeping (rotating after an initial start) motion at Reynolds number 200 and 3500 at angle of attack 40° are investigated, using the method of computational fluid dynamics. A representative wing corrugation is considered. Wing-shape and aspect ratio (AR) of ten representative insect wings are considered; they are the wings of fruit fly, cranefly, dronefly, hoverfly, ladybird, bumblebee, honeybee, lacewing (forewing), hawkmoth and dragonfly (forewing), respectively (AR of these wings varies greatly, from 2.84 to 5.45). The following facts are shown. (1) The corrugated and flat-plate wings produce approximately the same aerodynamic forces. This is because for a sweeping wing at large angle of attack, the length scale of the corrugation is much smaller than the size of the separated flow region or the size of the leading edge vortex (LEV). (2) The variation in wing shape can have considerable effects on the aerodynamic force; but it has only minor effects on the force coefficients when the velocity at r 2 (the radius of the second moment of wing area) is used as the reference velocity; i.e. the force coefficients are almost unaffected by the variation in wing shape. (3) The effects of AR are remarkably small: when AR increases from 2.8 to 5.5, the force coefficients vary only slightly; flowfield results show that when AR is relatively large, the part of the LEV on the outer part of the wings sheds during the sweeping motion. As AR is increased, on one hand, the force coefficients will be increased due to the reduction of 3-dimensional flow effects; on the other hand, they will be decreased due to the shedding of part of the LEV; these two effects approximately cancel each other, resulting in only minor change of the force coefficients.

Recently, much progress has been made in revealing aerodynamic force mechanisms and predicting power requirements in insect flight. In this study we have experimentally measured the wing kinematics of a hovering hoverfly (Episyrphus balteatus) and numerically analyzed the flapping mechanism of it. Using multi-digital high speed cameras, we photographed the continuous images of flapping wings and body from different viewpoints, and then we captured kinematics data and modeled the flight motion of the hovering hoverfly. Three-dimensional unsteady computations of the flow past the hoverfly under hovering flight conditions prescribed from above experimental observations were computed. The computed time average force and moment coefficients were validated with expected equilibrium values and were in well agreement. The computational result shows that the major part of the mean lift comes from the mid-portions of the down- and upstrokes.