7

Moment of Inertia and Mutilation Studies of an Insect Wing

95

2.

Knowledge of the MI also helps in describing the acceleration and deceleration

pattern during the angular motion of the wing.

3.

A 3-D study including the wing thickness variation along the wingspan gives

more specific information needed for the design of membranous wings for

MAVs.

4.

Modern techniques like zooming and the use of a nano-balance will be an added

advantage during experimentation as the total mass of each wing is less than

10 mg and each strip is about a milligram or so. Such studies will yield more

accurate data for the MAV/ NAV Design.

5.

The moment of inertia around the axis is I = mK²

where K is known as the radius of gyration.

6.

Study of MI and the radius of gyration is also necessary to calculate KE, torque

and inertial power requirements in connection with MAV/ NAV flight studies.

7.

The moment of Inertia data is very much helpful in the experimental evaluation

of the wingbeat frequency of an individual flier as well as for the comparison

with the other species for possible generalization of such studies.

Mutilation Studies of Insect Wings

Mutilation studies of insect wings were carried out by various researchers both on

neurogenic and myogenic fliers. The neurogenic fliers are also known as synchronous

fliers where the wingbeat frequency usually varies from about 2–100 Hz. The

myogenic fliers are also known as asynchronous fliers, where the wingbeat frequency

varies from 100 to 1000 Hz. These studies have been in the tethered state.

It was observed that in the case of neurogenic fliers, if we cut the wings inwards

from the wingtip, the frequency of wingbeat does not increase. In myogenic fliers,

however, the frequency of the wing after mutilation gradually increases so long as the

coupling between the wings is not affected. Further, if the wing coupling is destroyed

during cutting, both the wings start moving independently. It may be observed that

the female fliers have relatively higher mass (by 20% approx.) and higher wingbeat

frequency (by 10% approx.) compared to male counterparts (Fig. 7.3).

For a myogenic flier like Tessaratoma javanica, the wing mutilation studies show

that a decrease in wing length by 5–40% and breadth 1–28% leads to doubling in

frequency from 55 to 110 Hz (Fig. 7.3). The typical weight of the insect under

study was 940 mg and in another case, the weight was 1130 mg. The present studies

indicate that a variation in aspect ratio for the wing may create additional aeroelastic

problems due to increased wingbeat frequency. The decrease in strip area has been

depicted in Fig. 7.4.

Further, it may be stated from the wing analysis of the loading experiments on

T. javanica conducted in 1975, by increasing the wing loading gradually in steps of

0.5 mg at the wingtip to an extent of 7 mg, the wingbeat frequency was observed

to decrease by almost 50% in tethered flight. This aspect has to be carefully studied