Helicopter Dynamics · AERO

Teetering Rotor Mast Bumping & Low-G Pushover Hazard

CASA Ref: CASR Part 61 MOS Schedule 3 AD(H) 2.2 · FAA Ref: FAA-S-ACS-15 Area I Task E (Helicopter Aerodynamics)

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

Teetering Rotor Mast Bumping & Low-G Pushover Hazard Plate 1

Plate 1: Teetering Rotor Mast Bumping & Low-G Pushover Hazard

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Plate 2: Teetering Rotor Mast Bumping & Low-G Pushover Hazard

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Plate 3: Teetering Rotor Mast Bumping & Low-G Pushover Hazard

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Plate 4: Teetering Rotor Mast Bumping & Low-G Pushover Hazard

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Plate 5: Teetering Rotor Mast Bumping & Low-G Pushover Hazard

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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.

CASA & FAA Exam Gotcha Alert

CASA / 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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