Effective translational lift occurs at an airspeed of

• A. 8-12 kts
• B. 16-24 kts
• C. 0-4 kts
• D. 30-40 kts

Answer: (B)

Effective translational lift is the extra lift you gain when the rotor disk starts moving through air that’s already flowing relative to the helicopter. In hover, the rotor must produce lift primarily by accelerating air downward in its own downwash, which requires more power. As you move forward, the rotor encounters undisturbed air, so the induced velocity needed to produce the same lift falls and the rotor becomes more efficient. This translational regime kicks in noticeably in the mid-teens and grows through the low-to-mid 20s knots, giving the best practical gain in lift without yet hitting the high-speed aerodynamic limits. That’s why the 16–24 knots range is the correct answer. At very low speeds you’re still mostly hovering with little ETL, and at very high speeds other effects begin to limit the benefit, so the mid-range is the typical effective window.