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N. Chari et al.

f.

Wingspan Loading (WSL): It is the ratio of mass to the square of wingspan and

is represented as M/L². M/L² is also a ratio of wing loading to aspect ratio. M/L²

is an important aerodynamic parameter that helps in the calculation of wingbeat

frequency and other related parameters. M/L² represents the flight efficiency

better than WL and the aspect ratio is considered separately. Earlier researchers

have not realized the significance of the wingspan loading parameters in bio-

aerodynamic studies involving flapping wing motion. M/L2 becomes important

in comparative aerodynamic studies [1].

Some Useful Definitions

a.

Flight Velocity: The speed and direction of a flier in the air are known as flight

velocity. For insects, it is usually expressed in metres per second (m/s).

b.

Relative Wind (RW): The speed and direction of air impinging on a flier are

known as relative wind. It may be stated that it is equal and opposite to the

direction of the flight path velocity.

c.

Angle of Attack (AOA or α): The acute angle between the relative wind and

the chord line of an airfoil is known as the Angle of Attack. With an increase in

AOA, lift also gradually increases until the stalling angle of attack is reached.

d.

Lift (L): The component L of the aerodynamic force, which is perpendicular to

the relative wind, is known as Lift.

e.

Drag (D): The component D of the aerodynamic force, which is parallel to the

relative wind, is known as Drag. It may be noted that drag always opposes the

flight motion. There are various types of drag acting on fliers such as surface

drag, body drag and induced drag at wing tip which is responsible for the

formation of wing tip vortices.

f.

Centre of Pressure (CP): The point on the chord line where the aerodynamic

forces intersect is known as centre of pressure.

g.

Laminar Flow: Smooth airflow with a little transfer of momentum or energy

between parallel layers is known to be laminar flow.

h.

Turbulent Flow: Flow where streamlines move fast and break up and there is a

considerable mixing up of the layers is known as turbulent flow. There will be

an exchange of momentum between different layers. Unsteady flows can be an

example of turbulent flow.

Wingbeat frequency: It is expressed as the number of wingbeats or oscillations

per second (cps/ Hz). The wingbeat frequency may be empirically calculated as

follows:

Wing beat frequency(ϑh) =

Mass of the flier

(Wing span)² × Beff

× Constant