What phenomenon is caused by the synchronization of the main and tail rotor?

The phenomenon caused by the synchronization of the main and tail rotor is known as sympathetic resonance. This occurs when the frequencies of the vibrations produced by both the main rotor and the tail rotor align, leading to an amplification of oscillations. In helicopters, particularly those with a rigid rotor system, this can cause more pronounced vibrations and disturbances in the aircraft's structure and controls.

Understanding sympathetic resonance is crucial for pilots and engineers as it can influence flight characteristics and potentially lead to discomfort or even a safety risk if not properly managed. Recognizing the signs of this phenomenon allows for preventative measures to be taken during operation, ensuring smooth and safe flight.

In contrast, ground resonance refers to a different issue concerning the helicopter’s legs and landing gear interacting with rotor vibrations while on the ground. Blade coning deals with the upward bending of rotor blades under load and is unrelated to the synchronization aspect. Free-tail oscillation involves the tail rotor flapping and is influenced by different dynamics, primarily relating to the tail rotor's operation and its effects on directional control. Understanding these distinctions emphasizes the unique properties and behaviors of helicopters that pilots must know for safe operation.