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P. Mukkavilli et al.

Lift-Enhancing Mechanisms in Insect Flight

There are six additional lift-developing mechanisms. This has been reported to be

operative in at least 20 types of insects after experiments by various authors.

1.

Clap and fling mechanism

2.

Wake capture (wing-wake interaction)

3.

Passive pitching mechanism

4.

Tip vortex formation and figure of eight (8)

5.

Rapid pitching rotation and

6.

Delayed stall of Leading Edge Vortex (LEV).

Such flight techniques are practiced by various insects, based on their specific

requirements as well as on environmental conditions.

1.

Clap and Fling Mechanism

• The two wings together clap above and then fling them open apart in quick

succession.

• As a result of clap and fling action around each wing, circulation of air is

enhanced for generating additional lift at a low Reynolds number.

• Due to the clap action, there is a certain amount of damage to the dorsal

structures as they come in contact with each other.

Ex: Butterflies, Moths, Fruit Flies (Drosophila), Wasps, Thrips and Soapnut

bugs.

The importance of clap and fling is that it helps in generating additional lift and

some thrust. The clap and fling mechanism is also exhibited by pigeons occa-

sionally [6, 11]. Flying insects appear to increase their lift force by contralateral

winginteractionduringtheclapandflingmechanism,however,thisneedsfurther

study.

2.

Wake Capture (Wing-Wake Reaction): The wing is exposed to the wake

region produced by the previous stroke in a flapping cycle. This mechanism is

usually observed during a wing-wake interaction. This makes interaction with

the wing during stroke reversal by the rotating wing and contributes to the lift

production [12]. This is termed as wake capture. The wake capture helps in the

aerodynamic lift by a transfer of momentum to the wing at the beginning of each

stroke. The wake capture was considered as a lift-enhancing mechanism,that is,

a wing can recover lift from fluid motion created in a previous half stroke [13].

Both the wing acceleration and the wing-wake interaction should be taken into

consideration when modelling wing design.

The fruitfly wing model may be taken as an ideal example of low Re flight.

Wake capture force represents an unsteady phenomenon that involves changes

in distribution and magnitude of vorticity during stroke reversal. It is interesting

to remember that as compared to regular wing rotation, they exhibit enhanced

downstroke contributing to aerodynamic loading [14].