What happens to a helicopter after a hard landing in relation to Ground Resonance?

After a hard landing, the helicopter can experience ground resonance, which is a dynamic instability that occurs when the rotor system’s vibrations cause the helicopter to shake. This phenomenon is particularly relevant in helicopters with a fully articulated rotor system.

When the helicopter lands hard, it can create uneven forces throughout the structure, and as the blades begin to move forward, they can induce vibrations in the rotor system. These vibrations may resonate with the natural frequency of the helicopter's landing gear or the ground itself, exacerbating the instability. The forward motion of the blades contributes to this process because it influences the cyclic feathering of the blades and the interaction with the rotor hub, thus initiating a feedback loop of vibrations that can lead to further oscillations if not controlled.

Understanding this behavior emphasizes the importance of managing landings and correcting any imbalances during the approach and landing phases to prevent vibration issues and potential damage to the helicopter.