FAA Questions/Private Pilot Helicopter/Question #15
helicopterFAA-published sample question (PRH, Aug 2021)

Ground resonance is most likely to develop when

A

on the ground and harmonic vibrations develop between the main and tail rotors.

B

a series of shocks causes the rotor system to become unbalanced.✓ Correct Answer

C

there is a combination of a decrease in the angle of attack on the advancing blade and an increase in the angle of attack on the retreating blade.

Explanation

The Helicopter Flying Handbook explains that ground resonance occurs on the ground when a series of shocks (for example a hard landing on one skid or gear) unbalances the rotor system and the oscillation builds through the landing gear. It is not a main/tail rotor harmonic, and the change in angle of attack between advancing and retreating blades describes dissymmetry of lift.

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