Which phenomenon is a self-excited vibration related to rotor dynamics and fuselage frequency?

Which phenomenon is a self-excited vibration related to rotor dynamics and fuselage frequency?

• A. Ground Effect
• B. Ground Resonance
• C. Vibration
• D. Coupling

Answer: (B)

Ground resonance is a self-excited vibration that arises from the coupling between rotor dynamics and the fuselage/landing gear natural frequencies when the helicopter is on the ground with the rotor turning. A disturbance causes the rotor flapping and the landing gear to interact with the airframe in such a way that the gear and structure vibrate at their natural mode. This vibration feeds back into the rotor forces, reinforcing the motion, so the system continues to oscillate without an external periodic input. The energy sustaining the motion comes from the rotor drive, not from an outside force, which is why it is self-excited. Ground effect is simply the aerodynamic lift increase near the surface and does not produce this self-sustained vibration. Vibration is a general term and doesn’t specify the specific rotor–fuselage coupling and feedback mechanism. Coupling describes the interaction itself but not the particular self-excited resonant condition.

Ground resonance is a self-excited vibration that arises from the coupling between rotor dynamics and the fuselage/landing gear natural frequencies when the helicopter is on the ground with the rotor turning. A disturbance causes the rotor flapping and the landing gear to interact with the airframe in such a way that the gear and structure vibrate at their natural mode. This vibration feeds back into the rotor forces, reinforcing the motion, so the system continues to oscillate without an external periodic input. The energy sustaining the motion comes from the rotor drive, not from an outside force, which is why it is self-excited. Ground effect is simply the aerodynamic lift increase near the surface and does not produce this self-sustained vibration. Vibration is a general term and doesn’t specify the specific rotor–fuselage coupling and feedback mechanism. Coupling describes the interaction itself but not the particular self-excited resonant condition.