HELICOPTER AERODYNAMICS WORKBOOK
above). Not all helicopters experience these troubles, but for those, which are susceptible, a
common symptom is a sudden increase in rate of turn.
POWER REQUIRED GREATER THAN POWER AVAILABLE
The name of this state defines itself. Indications of this state include:
1. Uncommanded descent with associated maximum torque and/or rotor rpm droop.
2. Decrease in tail rotor effectiveness.
Factors which can cause or aggravate this situation include:
1. High G loading.
2. High gross weight.
3. Rapid maneuvering.
4. Engine spool up time from low to high power settings.
5. Loss of wind effect.
6. Change of wind direction.
7. Loss of ground effect.
This condition is especially dangerous when operating in close proximity to obstructions
where enough altitude/maneuvering space is unavailable to allow for safe recovery from the
situation. Recover by:
1. Nr -- Maintain.
2. Rpm switch -- FULL INCREASE
3. Airspeed -- INCREASE/DECREASE TO 50 KIAS (min power required airspeed).
4. Angle of bank -- LEVEL WINGS.
5. Jettison stores -- as required.
If impact is imminent:
6. Level aircraft to conform to terrain.
7. Cushion the landing.
Pilots can easily avoid this situation through proper preflight planning and using sound
judgment when considering entry into a high power required flight regime.
Ground resonance is normally associated with fully-articulated rotor systems. In order for
this to occur, at least one landing gear or skid must be in contact with the deck. A destructive
oscillation may be encountered if the blades move excessively about their lead-lag hinges to the
FLIGHT PHENOMENA 5-7