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== Aeroelastic ==
In the field of [[mechanics]] and structures, '''[[Aeroelastic flutter]]''' is an [[Aeroelasticity|aeroelastic]] phenomenon where a body's own [[aerodynamic]] forces couple with its [[natural frequency|natural mode]] of [[vibration]] to produce rapid [[periodic motion]].
Aeroelastic flutter occurs under steady flow conditions, when a structure's [[aerodynamic]] forces are affected by and in turn affect the movement of the structure. This sets up a [[positive feedback]] loop exciting the structure's [[Vibration#Types of vibration|free vibration]]. Flutter is self-starting and results in large amplitude vibration which often lead to rapid failure.
The aerodynamic conditions required for flutter vary with the structure's external design and flexibility, but can range from very low velocities to supersonic flows. Large or flexible structures such as pipes, suspension bridges, chimneys and tall buildings are prone to flutter. Designing to avoid flutter is a fundamental requirement for rigid airfoils (fixed wing aircraft and helicopters) as well as for aircraft propellers and gas turbine blades.
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