Helicopter Dynamics
Helicopter Ground Resonance Destruction Trap
FAA Ref: FAA-S-ACS-15 Area VIII Task I (Ground Resonance)
Scenario & Physics Summary
Self-exciting destructive oscillation on fully-articulated rotor systems when lead-lag dampers fail during hard ground contact.
Interactive 3D Visual Plates & Scenario Media
Plate 1: Helicopter Ground Resonance Destruction Trap
Plate 2: Helicopter Ground Resonance Destruction Trap
Plate 3: Helicopter Ground Resonance Destruction Trap
Plate 4: Helicopter Ground Resonance Destruction Trap
Aerodynamic & Operational Physics
- Occurs on fully-articulated rotor systems when blades shift out of phase (unequal lead-lag angular spacing).
- Center of gravity of rotor disc shifts off-center, creating violent eccentric shaking.
- If frequencies match helicopter natural airframe frequency on skids/wheels, total structural destruction occurs within seconds.
- Recovery: If rotor RPM is normal, IMMEDIATELY TAKEOFF to hover. If RPM is low, reduce collective completely and apply rotor brake.
FAA Exam Gotcha Alert
FAA Exam Trap: Ground resonance CANNOT occur on rigid or semi-rigid teetering rotor systems. It happens only on fully articulated systems.
Frequently Asked Questions & Exam Explanations
How do you recover from ground resonance if rotor RPM is operating range?
Immediately pull collective to lift the helicopter off the ground into a hover, freeing the airframe from ground contact excitation.
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