Helicopter Dynamics
Teetering Rotor Mast Bumping & Low-G Pushover Hazard
FAA Ref: FAA-S-ACS-15 Area VIII Task J (Low Gravity (G) Recognition and Recovery)
Scenario & Physics Summary
Catastrophic structural contact between rotor hub underslung trunnion and mast during low-G weightless maneuvers on semi-rigid rotors.
Interactive 3D Visual Plates & Scenario Media
Plate 1: Teetering Rotor Mast Bumping & Low-G Pushover Hazard
Plate 2: Teetering Rotor Mast Bumping & Low-G Pushover Hazard
Plate 3: Teetering Rotor Mast Bumping & Low-G Pushover Hazard
Plate 4: Teetering Rotor Mast Bumping & Low-G Pushover Hazard
Plate 5: Teetering Rotor Mast Bumping & Low-G Pushover Hazard
Plate 6: Teetering Rotor Mast Bumping & Low-G Pushover Hazard
Aerodynamic & Operational Physics
- In a low-G pushover (abrupt forward cyclic), main rotor thrust drops to near zero.
- Tail rotor thrust continues pushing above CG, causing rapid uncommanded right roll.
- Pilot applies left cyclic; with zero disc loading, cyclic flapping exceeds mechanical stops, causing rotor hub to strike and sever the rotor mast.
- Recovery: Gentle AFT CYCLIC FIRST to reload the main rotor disc before correcting roll.
FAA Exam Gotcha Alert
FAA Exam Trap: NEVER apply lateral cyclic to correct roll during low-G condition. You MUST apply gentle aft cyclic first to reload the rotor disc.
Frequently Asked Questions & Exam Explanations
What causes mast bumping on semi-rigid helicopters?
Low-G weightless conditions combined with lateral cyclic input causing rotor flapping to exceed mechanical mast clearances.
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