Measurement of free-play on an aircraft control surface

Device greatly simplifies the identification of loose ruddervators

Military Technology

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The Navy inspects ruddervators for free-play after every flight

Free-play is the positional or rotational variation in mechanical parts. All aircraft include movable control surfaces for directional control during flight and these include the rudder, aileron, elevator, and the all-moveable horizontal tail of an aircraft. These control surfaces, particularly those operated in a military environment, must be regularly monitored for the free-play as excessive free-play can result in flutter, vibrations, fatigue, divergence, or other instabilities. Freeplay is typically tested by applying a known load to the control surface and measuring the corresponding deflection. This test involves the use of complex apparatuses and is time consuming, expensive, and labor intensive.

Navy researchers have developed an alternative method to test free-play of the ruddervator (the pair of control surfaces on a v-tail design that perform the function of both a rudder and an elevator). The device attaches to the forward portion of the tail assembly and to the rear control surface. It is connected to a load applicator and measurement instrument for recording the amount of deflection in the control surface relative to the fixed portion of the tail. Deflections are observed on two dial indicators and measurements are taken in increments of 10% of the maximum desired load until 100% load is achieved.

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