Flutter Totally Explained

Everything about Flutter totally explained

In the field of electronics and communication, flutter is the rapid variation of signal parameters, such as amplitude, phase, and frequency. Examples of electronic flutter are:

Rapid variations in received signal levels, such as variations that may be caused by atmospheric disturbances, antenna movements in a high wind, or interaction with other signals.
In radio propagation, a phenomenon in which nearly all radio signals that are usually reflected by ionospheric layers in or above the E-region experience partial or complete absorption.
In radio transmission, rapidly changing signal levels, together with variable multipath time delays, caused by reflection and possible partial absorption of the signal by aircraft flying through the radio beam or common scatter volume.
The variation in the transmission characteristics of a loaded telephone circuit caused by the action of telegraph direct currents on the loading coils.
In recording and reproducing equipment, the deviation of frequency caused by irregular mechanical motion, for example, that of capstan angular velocity in a tape transport mechanism, during operation.

In the field of mechanics and structures, flutter refers to an aeroelastic phenomenon where a body's own aerodynamic forces couple with a its natural mode of vibration to produce rapid periodic motion. Aeroelastic flutter occurs under steady flow conditions, when a structures aerodynamic forces are affected by and in turn affect the movement of the structure. This sets up a positive feedbackloop exciting the structure's 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, chimney and tall building are prone to flutter. While for aircraft and rigid aerofoils such as helicopter rotors, propellers and aerofoils with gas turbines, design to avoid flutter is a fundamental requirement.
   Prediction of flutter prior to modern unsteady computational fluid dynamics was based on empirical testing. As a result many pioneering designs failed due to unforeseen vibrations. The most famous of these was the opening of the Tacoma Narrows Suspension Bridge in mid 1940, which failed spectacularly 4 months later during a sustained 67kph crosswind.
   During the 1950s over 100 incidences were recorded of military or civilian aircraft being lost or damaged due to unforeseen flutter events. While as recently as the 1990s jet engine flutter has grounded military aircraft.
   Techniques to avoid flutter include, changes to the structures aerodynamics, stiffening the structure to change the frequency away from the exitation and increasing the damping within the structure.

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