Translating Tendency or Drift

Rotorcraft Flying Menu >Aerodynamics of Flight >Hovering Flight >Translating Tendency or Drift

During hovering flight, a single main rotor helicopter tends to drift in the same direction as antitorque rotor thrust. This drifting tendency is called translating tendency. [Figure 3-2]

Figure 3-2. A tail rotor is designed to produce thrust in a direction opposite torque. The thrust produced by the tail rotor is sufficient to move the helicopter laterally.

To counteract this drift, one or more of the following features may be used:

• The main transmission is mounted so that the rotor mast is rigged for the tip-path plane to have a built-in tilt opposite tail thrust, thus producing a small sideward thrust.
• Flight control rigging is designed so that the rotor disc is tilted slightly opposite tail rotor thrust when the cyclic is centered.
• The cyclic pitch control system is designed so that the rotor disc tilts slightly opposite tail rotor thrust when in a hover.

Counteracting translating tendency, in a helicopter with a counterclockwise main rotor system, causes the left skid to hang lower while hovering. The opposite is true for rotor systems turning clockwise when viewed from above.