4

Flight Morphology and Flight Muscles

49

9.

The wing movements consist of the upstroke, downstroke, flexion and forward

and backward movements. Rotational movements along the longitudinal axis

of the wing contribute to forming an approximate figure of eight “8” at the

wing tip. The downstroke of the wing is brought about due to the elevation of

the tergum.

10.

The downstroke is also accompanied by a forward movement. The upstroke is

associated with the backward movement of the wing.

Flight Parameters

The basic and derived flight parameters of an insect are as follows:

Basic Parameters:

a.

Body Mass (M)

b.

Wing Length (l)

c.

Wingspan (L)

d.

Wing area (A)

e.

Area of two wings (2A)

f.

Disc Area (Sd).

Derived Parameters:

a.

Average Breadth of Wing: Average breadth of the wing is calculated as 2A/2 l.

Beff is an important wing characteristic parameter in calculating wing area and

wingbeat frequency of the flier. It may be mentioned here that a change in camber

through a differential change in the value of Beff will contribute to additional

lift in insect flight. Beff is also calculated by the strip analysis method which is

also used in the study of Moment of Inertia (MI).

b.

Wing Loading (WL): It is the ratio of body mass to total flight surface area

(2A) and is expressed in gm/cm².

c.

Disc Loading: It is the ratio of mass to disc area. It is expressed in gm/cm².

WL helps in calculating frequency and other related power calculations. The

weight of the flier gets distributed over the flight surface as wing loading during

flight. It may be mentioned that the effective wing area will be changing during

flapping of the wing due to which the wing loading values also vary.

d.

Aspect Ratio (AR): It is the ratio of the square of wingspan (L²) to total flight

surface area (2A). The aspect ratio in insects usually ranges from 3 to 5. The

aspect ratio has an important impact on flight performance. Insects having a

high aspect ratio can fly more efficiently as compared to those with a low aspect

ratio. MAVs designed on flight principle have low AR.

e.

Airfoil (Aerofoil): Transverse Section (TS) of the wing is known as the Airfoil

section. In insects, TS is very small and airfoils are very thin. The section varies

along the wingspan in terms of the chord, thickness distribution and camber. The

wing is flexible and hence, the camber can be changed and get altered during

different strokes, and hence can modify the aerodynamic forces as well.