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responsible for the wing rotation and twist. It is usually assumed that the upper part

of the wing adjoining the fulcrum is responsible for the development of lift and the

next part, which is relatively thin and membranous, is responsible for the thrust. The

wingtip which is very thin being the last part contributes to the induced drag through

the formation of vortices and also contributes to the downwash and forward motion.

In order to overcome the rotation, the wings of the flying insects generate a figure

of “8” or ellipse in space at the wingtips during the wingbeat cycle. This is because

of the superimposition of two Simple Harmonic Motions (SHM) in flapping and

twisting modes. The different segments of the wings perform different functions

during flapping through aeroelastic interactions including structural deformations.

This division of labour is an interesting example of morpho-functional correlation.

Lift, thrust and induced drag as developed by various components of the flapping

wings are notable features. It has to be emphasized that there is a closer correlation

between the structure and functions of insect flapping wings as compared to man-

made aeroplane and helicopter wings, which have limited capability.

The energy required to move the insect wings is supplied by the contraction

of flight muscles of the insect, where the ATP (Adenosine Tri-Phosphate) gets

hydrolyzed. Due to this action of the enzyme ATPase, ATP gets converted into ADP,

inorganic phosphate with associated energy release. In insect wings, the wing motion

is more or less sinusoidal. The resilin at the wing base works as an elastomere. The

elastomere is four times more elastic than conventional rubber and plays a vital role

in the insect flight. If the resilin is cut, the insect is unable to fly. This resilin is

the characteristic elastomere found only in insects and other arthropods and not in

homeothermic fliers such as birds and bats.

The concept of the centre of mass will help in a better understanding of the

wing dynamics and Moment of Inertia computations as described in Appendix. The

general expression for the moment of inertia is given in Eq. 7.1. Detailed studies

carried out by Prof. N. Chari and Prof. M. Prasad at SNIST, Hyderabad, indicate

that the wingspan, in general, increases with the mass of the flier, but up to a value

of about 0.65 to 0.95 gm. It has been observed from various studies that the mass

of T. javanica varies from 0.45 to 1 gm in Telangana, India. A further increase in

the insect mass beyond this value restricts the wingspan typically at around 5.85 cm.

The wing breadth only increases to provide the necessary wing area to support the

flight and associated aerodynamic forces.

During mutilation studies as mentioned earlier [1], the wing was cut into 10 equal

strips and the typical wing length was 21.5 mm. The values of strip wing loading

and strip area as calculated and measured for various strips numbering from 1 to 10

are shown in Fig. 7.1. These studies also further indicate that the area of the strips is

nearly a maximum for strip numbers 2–5 beyond which the area seems to decrease,

indicating a decrease in area and mass as well.

The MI of the moving wing is usually calculated by the strip analysis method. The

wing is carefully cut at the fulcrum where it is attached to the thorax. Subsequently,

this wing is carefully cut into as many equidistant strips as possible (typically 10

strips). The strips are numbered in increasing order from the fulcrum to the wingtip.

The distance is measured from the fulcrum point to the centreline of each strip.