The aerodynamics of insect flight

Insects owe much of their evolution success to flight. Compared with their flightless ancestors, flying insects are better equipped to escape from their predators, search food sources and get adjusted to new habitats. Because their survival and evolution depend on flight performance

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Because of their high wing flap frequencies and small size, it is difficult to inspect the wing motions of flying insects. For example, Drosophila melanogaster is an insect measuring 2–4·mm in length and flaps its wings at a rate of 220·Hz.

The insect flight mechanism is inspected based on the Quasi-steady assumptions. According to this, the aerodynamic forces on an insect flapping wing are equal to the forces during a steady state of motion of the flapping wing.

Physical modeling of insect flight:

• The difficulties in studying insects or any other calculations of their flight mechanics have led scientists to use flying mechanism models to study and inspect an insect flight performance.
• During constructing these models, the wing velocity and Reynolds number are matched to that of an insect. This condition, called ‘dynamic scaling’, ensures that the underlying fluid dynamic phenomena are conserved.
• As it is easier to measure and analyze the flow on insect wings, these models have proved useful in the analysis of unsteady mechanisms of flying insects.

Unsteady mechanisms in insect ?ight

1. Wagner effect:

• When an inclined insect wing starts from a rest position, the circulation around it does not attain its steady-state value immediately. Instead, it rises slowly to the steady-state.

• This delay in reaching this state may result in two phenomena.
• First, there is a delay in the sticky nature on the surface of the object.
• Second, during this process, the whirling motion is generated at the trailing edge.
• This slow movement in the development of circulation was ?rst proposed by Wagner, often referred to as the Wagner effect

2. For the 2-D motion: The leading-edge swirl grows larger until flow will never attach again.
3. The Kutta condition stops working as a whirling motion forms at the trailing edge and sheds into the wake region. At this point, the wing is not effective. Because of attachment of the leading-edge swirl, it is possible to obtain very high lift, a phenomenon termed ‘delayed stall’
4. Kramer effect (rotational forces):

At the end of every stroke, flapping insect wings undergo forward and backward rotation about an axis. 

Future research:

Finally, it is necessary to account for wing ?exibility since the mechanical models are based on rigid wings.

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The aerodynamics of insect flight