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as a self-induced vibration with practically very little damping effect. In soft flutter,

the net damping decreases gradually up to the flutter point. For non-linear systems,

flutter action acts as a Limit Cycle Oscillation (LCO). The fundamental frequency is

influenced by the length, size and tension of the vocal cords. This frequency in adults

averages about 25 Hz (males) and 210 Hz (females). Young insects (imago), young

birds and young bats also exhibit wing flutter before attaining full flight. Flutter

means to move or flap the wings quickly without being able to fly. Flutter is common

in aviation, aeronautics, medicine and electronics. Flutter can be of hard and soft

type.

Buffeting

Buffeting is a high-frequency instability caused by an increase in load. Buffeting is

usually observed in fast-flying aircraft. It is a high-frequency phenomenon where

instability is caused due to shock waves resulting from high-speed supersonic flow

past the body. It is a random forced vibration, which also influences the tail unit of

the aircraft structure resulting in unexpected vibrations, damage and stall. Buffeting

meansirregularoscillationsofanaircraft,duetoturbulenceleadingtohigh-frequency

instability, leading and stalling. Some of the methods suggested for buffet detection

are as follows:

1.

Pressure coefficient diagram.

2.

Pressure divergence at the trailing edge.

3.

Computing separations from trailing edge based on the Mach number.

4.

Normal force fluctuating divergence.

The model suggested can be used to predict the flutter margin.

The Mach number is defined as the ratio of the velocity of the flier to the local

speed of sound. Mach numbers for insects are very low. As the flying object is in the

transonic range of Mach numbers, moving shock waves dominate the flow and the

intensity of the shock waves affects the stability of the flier. This situation will not

arise in the case of insect flier where the Mach numbers are well within the subsonic

range and M is less than 0.3. However, the Mach number in high-speed fliers varies

from 1.3 to 25. Aeroelastic effects can persist in such low subsonic flow regimes

because of the elastic nature of structural deformation as in the case of flexible

flapping wings of low- and high-frequency fliers (Neurogenic and myogenic).

Aeroelasticity involves the study of structural damping, inertia and mass char-

acteristics of the flying objects besides the external aerodynamic loads and their

dynamic nature. A proper estimation of these loads and vibration characteristics

could help in the design optimization of MAVs as well as the flapping wings. The

model should preferably include details of the interacting aerodynamic forces and

the way their dynamic vibrations act in relation to flight surfaces. These models can

be helpful in predicting the flutter margin and potential problems leading to stall.

Irregular oscillations on the part of an aircraft cause buffeting.