Translational Lift

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Translational lift is present with any horizontal flow of air across the rotor. This increased flow is most notice-able when the airspeed reaches approximately 16 to 24 knots. As the helicopter accelerates through this speed, the rotor moves out of its vortices and is in relatively undisturbed air. The airflow is also now more horizontal, which reduces induced flow and drag with a correspon-ding increase in angle of attack and lift. The additional lift available at this speed is referred to as “effective translational lift” (ETL). [Figure 3-12]

Figure 3-12. Effective translational lift is easily recognized in actual flight by a transient induced aerodynamic vibration and increased performance of the helicopter.

When a single-rotor helicopter flies through translational lift, the air flowing through the main rotor and over the tail rotor becomes less turbulent and more aerodynami-cally efficient. As the tail rotor efficiency improves, more thrust is produced causing the aircraft to yaw left in a counterclockwise rotor system. It will be necessary to use right torque pedal to correct for this tendency on takeoff. Also, if no corrections are made, the nose rises or pitches up, and rolls to the right. This is caused by combined effects of dissymmetry of lift and transverse flow effect, and is corrected with cyclic control.0

Translational lift is also present in a stationary hover if the wind speed is approximately 16 to 24 knots. In nor-mal operations, always utilize the benefit of translational lift, especially if maximum performance is needed.