FAA Private Pilot Helicopter (PRH)Helicopter Aerodynamics and SystemsMedium
A pilot lowers the collective too rapidly during a rapid descent while at low rotor RPM, causing the main rotor blades to reach an excessively high angle of attack for the available RPM, resulting in a rapid decay of rotor RPM despite full engine power being available. What condition has occurred?
- AMast bumping
- BOverpitching
- CSettling with power
- DRetreating blade stall
Show answer & explanationAnswer & explanation
Correct answer: B. Overpitching
Overpitching occurs when a pilot raises (or fails to lower) the collective beyond what available engine power and rotor RPM can support, driving blade angle of attack too high and causing induced drag to increase faster than lift, which rapidly decays rotor RPM even with full power applied.
Why the other options are wrong
- A. Mast bumping involves the rotor hub striking the mast, unrelated to RPM decay from pitch demand.
- C. Settling with power involves descending into one's own downwash at low airspeed, a different mechanism.
- D. Retreating blade stall occurs during high-speed forward flight on the retreating blade, not from collective mismanagement.
Overpitching
A condition where excessive collective pitch demands more power than the engine can supply, causing rotor RPM to decay dangerously even with the throttle at full power.
- Common at high density altitude or heavy gross weight
- Blade angle of attack increases beyond what available power can sustain
- Correction requires lowering collective promptly to restore RPM
Memory trick: Overpitching = asking the rotor to climb a hill steeper than the engine can push.