III.

Flutter

A dangerous type of vibration is the sudden, violent oscillating motion known as flutter. This occurs most frequently in the control surfaces of aircraft, but is also seen in the “galloping” of sleet-covered electrical transmission wires in high winds. One of the most spectacular instances of flutter caused the collapse in 1940 of the Tacoma Narrows Bridge in Tacoma, Washington. The collapse resulted from a gale that blew at a speed that enhanced the swaying of the bridge.

The amplitude of vibration of a structure might increase so rapidly when subject to flutter that the structure disintegrates almost instantaneously. Prevention of flutter is therefore an important consideration in the design of bridges and aircraft. Flutter analysis for aircraft is usually supplemented by tests on model aircraft carried out in a wind tunnel.

See also Harmonics; Oscillograph; Oscilloscope; Sound; Wave Motion.