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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.
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