Aeroelasticity
No aircraft structure is completely rigid, so when it is subjected to aerodynamic forces it will normally deflect by a small amount. This effect can become very important at high speeds because any change in the shape of the body can cause the applied aerodynamic forces to change, leading in turn to further deflection and further changes in load. This vicious circle can rapidly develop into aeroelastic phenomena such as flutter and wing divergence.
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2 Wing divergence 3 Prediction and cure |
At its mildest this can appear as a "buzz" in the aircraft structure, but at its most violent it can develop uncontrollably with great speed and cause serious damage to or the destruction of the aircraftFlutter
Flutter occurs when a lifting surface deflects under aerodynamic load so as to reduce the applied load. Once the load reduces, the deflection also reduces, restoring the original shape, which restores the original load and starts the cycle again. In extreme cases the elasticity of the structure means that when the load is reduced the structure springs back so far that it overshoots and causes a new aerodynamic load in the opposite direction to the original. Even changing the mass distribution of an aircraft or the stiffness of one component can induce flutter in an apparently unrelated aerodynamic component.
