2

Flight a Retrospect a Brief Review

11

on wing swept area, small mass of the flier and density of the air. Crawford’s formula

holds good for small insects like mosquitoes. Weis-Fogh [19] discussed the hovering

flight in nature by applying the actuator disc concept and momentum jet theory for

insects having the Reynolds number ranging from 10² to 10⁴. Weis-Fogh [20] studied

flapping velocity as a simple harmonic motion for a semi-elliptical wing. Lighthill

[21] found that the wasp Encarsia was using a horizontal stroke plane and circulatory

lift mechanism during hovering.

Bennett [22] proposed a differential velocity model, that is, the downstroke

velocityduringawingbeatisfoundtobesignificantlygreaterthantheupstroke,which

is notable since the downstroke is a powerful stroke and the upstroke is a recovery

stroke. Puranik et al. [23] used classical methods for measuring wingbeat frequency

in the tethered flight of soapnut bugs (Tessaratoma Javanica), by using a hydrophil

balance and adopting Melde’s experiment. Natchtigall [24] described the wing move-

ments of Formia. Norberg [25] recorded the wingbeat movements of a dragonfly

during normal flight. Rainey [26] showed that the elasticity of flight muscles is an

important factor and needs to be considered in insect flight studies. Norberg [27]

used a modified force balance to measure mean lift and drag coefficients. Pringle

[28] has observed that aerodynamic forces are generated during wing movements.

The high wingbeat frequency of insects is attributed to the mechanical resonance

of the Wing-Thorax-System. The wing-thorax system in Diptera appears resonant

which may contribute to propulsion. Ahmed [29, 30] conducted the Fourier analysis

of flight sound of a soapnut bug. They have used a bio-acoustic technique. Weis-

Fogh and Alexander [31] have calculated the mechanical power output of muscle

irrespective of size. Aravind Babu et al. [32] reported the aerodynamic parameters of

a pentatomid bug in detail. Chari et al. [33] reviewed the flight adaptations of insects,

birds and bats. Ellington [34] proposed the vortex theory of hovering based on blade

element models. Baker et al. [35] described wingbeat frequency, flight speed and

altitude in free flight for L.Migratoria. Vogel [16] has calculated the drag coefficient

for Drosophila.

Ellington [36–38] gave a detailed description of morphological parameters related

to flight. Casey et al. [39] elucidated the flight energetics of bees in relation to

their morphology and wingbeat frequency. Broadskii [40, 41] has discussed vortex

formation in the tethered flight of the butterfly and the evolution of insect flight.

Puranik and Chari [42] have explained the theoretical basis for calculating the

frequency of wingbeat depending on aerodynamic parameters based on body and

wing morphology. Recently, lift-enhancing devices have been reported by various

authors.

a.

Clap and Fling Mechanism

b.

Rapid Pitching up Rotation

c.

Wake Capture

d.

Delayed stall of LEV

e.

Tip Vortex and

f.

Passive mechanisms.