What term describes self-excited vibration that occurs when the blade lead-lag frequency equals the fuselage's natural frequency?

What term describes self-excited vibration that occurs when the blade lead-lag frequency equals the fuselage's natural frequency?

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

Answer: (B)

Ground resonance is the self-excited vibration that happens when the rotor blade’s lead-lag frequency coincides with the fuselage’s natural frequency. When those two frequencies align, energy from the rotor’s lag motion is fed into the airframe through the landing gear, creating a feedback loop that makes the helicopter oscillate more and more with little to no pilot input. This is a resonance phenomenon tied to the helicopter being on the ground, not just a general vibration or a surface-effect phenomenon. So, while vibration and oscillation are broad terms, ground resonance specifically describes this dangerous coupling between rotor dynamics and the airframe that leads to large, self-sustained oscillations.

Ground resonance is the self-excited vibration that happens when the rotor blade’s lead-lag frequency coincides with the fuselage’s natural frequency. When those two frequencies align, energy from the rotor’s lag motion is fed into the airframe through the landing gear, creating a feedback loop that makes the helicopter oscillate more and more with little to no pilot input. This is a resonance phenomenon tied to the helicopter being on the ground, not just a general vibration or a surface-effect phenomenon. So, while vibration and oscillation are broad terms, ground resonance specifically describes this dangerous coupling between rotor dynamics and the airframe that leads to large, self-sustained oscillations.