Ground resonance involves which component's oscillation and what potential outcome?

• A. A tail rotor bearing oscillation leading to yaw instability.
• B. The destructive vibration where the lead-lag hinges of the rotor blades oscillate and, if not corrected, can destroy the helicopter.
• C. A vibration in the landing gear that resolves itself.
• D. A vibration caused by tail rotor failure.

Answer: (B)

Ground resonance is the destructive vibration that arises from the rotor system oscillating about the lead-lag hinges when the helicopter is on the ground with the rotor turning. The blades are free to move fore and aft in their hinge axis, and on the ground, any small movement of the fuselage couples into the rotor and amplifies through the rotor’s dynamics. This can drive a self-reinforcing oscillation that, if not interrupted, can rapidly build to a destructive level and potentially destroy the helicopter.