flutter (redirected from mediastinal flutter)
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1. Pathol an abnormally rapid beating of the auricles of the heart (200 to 400 beats per minute), esp in a regular rhythm, sometimes resulting in heart block
2. Electronics a slow variation in pitch in a sound-reproducing system, similar to wow but occurring at higher frequencies
3. Aeronautics a potentially dangerous oscillation of an aircraft, or part of an aircraft, caused by the interaction of aerodynamic forces, structural elastic reactions, and inertia
4. Music a method of sounding a wind instrument, esp the flute, with a rolling movement of the tongue
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.
Distortion that occurs in sound reproduction as a result of undesired speed variations during the recording, duplicating, or reproducing process.
A fast-changing variation in received signal strength, such as may be caused by antenna movements in a high wind or interaction with a signal or another frequency.
The irregular alternating motion of the parts of a relief valve due to the application of pressure where no contact is made between the valve disk and the seat.
Rapid, regular contraction of the atrial muscle of the heart.
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
The wing twist as it flaps up and down. This up and down motion causes changes in the angle of attack. The changes in angle of attack mean that the aerodynamic forces are always tending to help the motion, which do not, therefore, damp out, resulting in flutter.
A vibration caused by the combined effects of the changes in pressure distribution over the surface of airfoils as the angle of attack is altered and the elastic forces set up by the distortion of the structure itself. In the worst cases, there may be a total loss of control and a consequent crash. The flutter may affect the control surfaces such as an aileron, or the main planes, or both. The flutter can be avoided by using mass balances, increasing structural rigidity, and having irreversible controls. Flutter also occurs with propellers, compressor blades, and turbine blades. Flutter is an aeroelastic self-excited vibration in which the external source of energy is the airstream. It depends on the elastic, inertial, and dissipative forces of the system in addition to the aerodynamic forces.