Flight Instructor for Rotorcraft Category Helicopter Rating › VII. Hovering Maneuvers › Task A. Vertical Takeoff and Landing

HI.VII.A.R3

Risk management

Ground resonance.

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Helicopter Flying Handbook p. 11-11
Chapter 11: Helicopter Emergencies and Hazards › Ground Resonance
Ground Resonance Helicopters with articulating rotors (usually designs with three or more main rotor blades) are subject to ground resonance, a destructive vibration phenomenon that occurs at certain rotor speeds when the helicopter is on the ground. Ground resonance ... balance rotor. The unbalanced rotor disk vibrates at the same frequency (or multiple thereof) of the airframe’s resonant frequency, and the harmonic oscillation increases because the engine is adding power to the system, increasing the magnitude (amplitude…
Helicopter Flying Handbook p. 11-11
Chapter 11: Helicopter Emergencies and Hazards › Dynamic Rollover
rollover angle is exceeded, the helicopter rolls on its side regardless of the cyclic corrections made. Figure 11-4. Ground resonance. Dynamic rollover begins when the helicopter starts to pivot laterally around its skid or wheel. For dynamic rollover…
Helicopter Flying Handbook p. G-3
Glossary
results from a reduction in upwash, downwash, and bladetip vortices, which provide a corresponding decrease in induced drag. Ground resonance. Selfexcited vibration occurring whenever the frequency of oscillation of the blades about the lead-lag axis of an articulated rotor…