9

Aeroelasticity

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The study of aeroelasticity assumes greater importance in relation to insect flight

as they have semi-elastic thorax, elastic resilin and membranous flexible flapping

wings made up of chitin, which is a polysaccharide amine. Even the contracting

muscle is also elastic in nature. Although knowledge of the insect bio-aerodynamics

helps in a systematic understanding of insect flight and acts as a guide in the design

of MAVs. However, it may not be possible to bio-mimic a natural flier in totality

since it represents a highly complex type and our understanding of natural objects

and their functioning is quite inadequate for the design.

Transonic Aeroelasticity covers a transonic range of high Mach numbers, where

a moving shock wave dominates the flow. The intensity of the shock affects the

stability of the flier and this is known as a transonic dip.

Dynamic Response

Dynamic Response is analogous to aero-servo elasticity. In biological flight response

to gust/ landing is almost instantaneous and more accurate as compared to that of the

man-made aerial vehicles because of fast feedback systems due to sensory organs

prevalent in the biological fliers involving the brain.

Aeroelasticity in Insect Flight

Extensive wingbeat frequency studies were performed on a wide range of insects by

the author and his team at Kakatiya University, Warangal, and at SNIST, Hyderabad.

The natural wingbeat frequency of T. javanica was found to be 50 Hz. Further

experiments showed that.

1.

The frequency increases with a reduction in wing area (mutilation).

2.

It progressively decreases through wing loading with the addition of loads at

the wing tip.

3.

Resilin at wing base contributes to aeroelasticity in neurogenic and myogenic

fliers.

4.

This is also true for C. purpureous which has a frequency of about 100 Hz.

The frequencies were measured by a stroboscope and confirmed by Mass Flow

Theory. The above method of loading or unloading the wings can possibly be adapted

to decrease or increase the natural frequency of the MAV [4].