FAA Private Pilot Helicopter (PRH)Performance and LimitationsHard
During a low-altitude, low-airspeed departure, a pilot turns the helicopter from a headwind heading to a tailwind heading. What performance hazard is of greatest concern during this maneuver?
- AExcessive rotor RPM buildup due to the change in relative wind direction
- BA sudden reduction in tail rotor thrust caused by the turn
- CAn abrupt increase in retreating blade angle of attack leading to blade stall
- DLoss of effective translational lift as airspeed through the rotor decreases, risking settling toward the ground
Show answer & explanationAnswer & explanation
Correct answer: D. Loss of effective translational lift as airspeed through the rotor decreases, risking settling toward the ground
Turning from headwind to tailwind at low altitude and low airspeed reduces the airspeed through the rotor system relative to the air mass, which can cause a loss of effective translational lift. Combined with low altitude, this can result in a settling tendency or loss of altitude before the pilot can compensate with added power.
Why the other options are wrong
- A. Rotor RPM is governed and does not build excessively due to a heading change.
- B. Tail rotor thrust is not directly disrupted by a downwind turn in this manner.
- C. Retreating blade stall occurs at high forward airspeeds, not low-airspeed downwind turns.
Downwind Turn Hazard
Turning downwind at low altitude and low airspeed reduces airspeed through the rotor system, risking loss of effective translational lift and an unexpected settling toward the ground.
- Most critical near the ground and at low airspeed
- Groundspeed increases but airspeed through rotor decreases
- Pilot must add power/anticipate sink during the turn
Memory trick: Turn downwind, lose your wind — watch the sink!