What is translating tendency?

Translating tendency is the movement of the helicopter to the right due to the combination of main rotor torque and tail-rotor anti-torque.helicopter translating tendency

If uncompensated, power applied to the main rotor would turn or yaw the helicopter to the right.  To prevent turning, anti-torque is applied via left pedal.  As anti-torque is applied, the tail rotor produces thrust which pushes the tail to the right, stopping the potential turn.  There are now two forces moving the helicopter to the right, and one force to the left.  The forces to the right are greater and the helicopter tends to drift to the right, assuming no pilot inputs.  Translating tendency is often called rotor drift.

Some helicopter designs compensate for translating tendency by various methods, such as tilting the mast or designing a bias into the cyclic.  Most training helicopters, such as the Robinson R22/R44 and the Sikorsky 300CB, do not have any of these compensating characteristics.  In these helicopters, the pilot must counteract the translating tendency, or rotor drift, through pilot inputs to tilt the rotor disc to the left.

Not all helicopters experience translating tendency, specifically dual rotor helicopters such as the CH47.  In these helicopters, the torque produced by one rotor is counteracted by the other, which rotates in the opposite direction.  As such, forces are equal in each direction.

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 2-14
Principles of Helicopter Flight, 2nd Edition, pg. 70
FM 3-04.203-2007 Fundamentals of Flight pg. 1-36

Other Helicopter Flight Conditions

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