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in aeroelasticity, self-excited oscillations of parts of an aircraft, mainly the wing and the tail, that occur when the critical flutter speed is reached. Flutter may result in structural failure. Flutter is associated with the relative location of the center of gravity and the center of twist of the wing or tail and with other characteristics of a given aircraft.
An aeroelastic self-excited vibration with a sustained or divergent amplitude, which occurs when a structure is placed in a flow of sufficiently high velocity. Flutter is an instability that can be extremely violent. At low speeds, in the presence of an airstream, the vibration modes of an aircraft are stable; that is, if the aircraft is disturbed, the ensuing motion will be damped. At higher speeds, the effect of the airstream is to couple two or more vibration modes such that the vibrating structure will extract energy from the airstream. The coupled vibration modes will remain stable as long as the extracted energy is dissipated by the internal damping or friction of the structure. However, a critical speed is reached when the extracted energy equals the amount of energy that the structure is capable of dissipating, and a neutrally stable vibration will persist. This is called the flutter speed. At a higher speed, the vibration amplitude will diverge, and a structural failure will result. See Aeroelasticity
Aircraft manufacturers now have engineering departments whose primary responsibility is fluffer safety. Modern flutter analyses involve extensive computations, requiring the use of large-capacity, high-speed digital computers. Flutter engineers contribute to the design by recommending stiffness levels for the structural components and control surface actuation systems and weight distributions on the lifting surfaces, so that the aircraft vibration characteristics will not lead to flutter within the design speeds and altitudes. See Airframe, Wing