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Importance of Aeroelasticity

Aeroelasticity plays an important role in the transonic, supersonic and hypersonic

flights in addition to subsonic flight. The application of aeroelasticity concepts to

insect, bird and bat flight remains to be elucidated in detail. In the early days, aeroe-

lasticity was almost ignored during the process of flight designs. However, many

accidents were attributed due to aeroelastic problems in various fields of study.

Gas turbines, rotor wings of helicopters, long bridges, transmission lines, ships and

offshore structures, very tall buildings and biological phenomena involving cardiac

failures and bio-aerodynamic accidents come under this category. A large number

of structural failures in man-made fliers such as blade and wing flutter, buffeting and

uncontrolled structural vibrations causing excessive fatigue forced the scientists to

attempt a deeper study and understanding of the subject of Aeroelasticity. A lot of

information about aeroelasticity is available in standard textbooks and the following

sections are mostly reviewed from [2]. Structures such as wings, aerofoils, chimneys

and bridges are exposed to aerodynamic forces. Blunt shapes create a continuous

stream of vortices. Bridges are destroyed by aeroelastic fluttering.

Static Aeroelasticity

Static aeroelasticity deals with the static response of an elastic body moving in a

fluid flow. These aeroelastic effects cause typically divergence and control reversal

phenomena.

1.

In divergence, there is a sudden elastic twist of the wing due to resistance to

overcome deformation.

2.

In control reversal, the ailerons and control surface functions get reversed due

to deformations and may lead to the opposite effect.

Divergence

The uncoupled torsional equation for motion is given by

GJ ^d2θ

dy^{2 = M ′}

(9.1)

where y is spanwise dimension and θ is the elastic twist of the beam in radians.

For some special boundary conditions where an airfoil is tested in a wind tunnel,

it is possible to eliminate the phenomenon of divergence (Hodges and Pierce 2002).