FAA Private Pilot Helicopter (PRH)Helicopter Aerodynamics and SystemsMedium
A pilot performs a steep turn at a high load factor while allowing rotor RPM to decay slightly below normal. As a result, the main rotor blades assume a greater coning angle than normal. What is the primary aerodynamic consequence of this excessive coning?
- AA reduction in the effective diameter of the rotor disk, decreasing lift
- BA reversal in the direction of gyroscopic precession
- CAn increase in effective translational lift efficiency
- DAn increase in rotor RPM due to reduced blade drag
Show answer & explanationAnswer & explanation
Correct answer: A. A reduction in the effective diameter of the rotor disk, decreasing lift
Coning angle results from the balance between lift (upward) and centrifugal force (outward) on the blades. Low rotor RPM combined with high load factor increases the coning angle, which reduces the effective diameter (and thus effective disk area) of the rotor, decreasing available lift when it is most needed.
Why the other options are wrong
- B. Coning does not reverse gyroscopic precession, which is a separate 90° phase-lag phenomenon.
- C. Coning is unrelated to airspeed-based effective translational lift.
- D. Excessive coning reduces, not increases, useful rotor efficiency and does not raise RPM.
Rotor Blade Coning
The upward bending of rotor blades resulting from the balance of lift (up) and centrifugal force (outward); excessive coning reduces effective rotor disk diameter and lift.
- Caused by balance of lift and centrifugal force
- Increases with high load factor and low rotor RPM
- Excessive coning reduces effective disk area and lift
- Can risk blade contact with droop stops or airframe in severe cases
Memory trick: Too much cone = smaller circle = less lift.