Which Helo taxi is subject to 'ground resonance' and may, on rare occasions, suddenly lift off the ground to avoid severe damage or destruction?

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Multiple Choice

Which Helo taxi is subject to 'ground resonance' and may, on rare occasions, suddenly lift off the ground to avoid severe damage or destruction?

Ground resonance is a dynamic instability that happens when a helicopter is on the ground with the rotor system connected to the airframe through the landing gear. During ground taxi, small disturbances can set up coupled motions between rotor flapping and fuselage vibrations. Because the craft is in contact with the ground and the damping is limited, this vibration can grow and cause the helicopter to shake, and in rare cases, it can even hop or lift briefly off the ground to relieve loads, risking severe damage if not controlled. Hover taxi or being in the air removes the ground coupling, so ground resonance isn’t a concern in those modes. Manual taxi and air taxi don’t describe the on-ground, rotor-tied condition that leads to the instability.

Ground resonance is a dynamic instability that happens when a helicopter is on the ground with the rotor system connected to the airframe through the landing gear. During ground taxi, small disturbances can set up coupled motions between rotor flapping and fuselage vibrations. Because the craft is in contact with the ground and the damping is limited, this vibration can grow and cause the helicopter to shake, and in rare cases, it can even hop or lift briefly off the ground to relieve loads, risking severe damage if not controlled.

Hover taxi or being in the air removes the ground coupling, so ground resonance isn’t a concern in those modes. Manual taxi and air taxi don’t describe the on-ground, rotor-tied condition that leads to the instability.

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