Chapter 5

Question 1

Which components provide the mass, damping, and stiffness terms of the rotor flapping
dynamics equation

Answer 1

Inertia force, aerodynamic force, and centrifugal force, respectively

Question 2

What is the flapping offset influence on the flapping frequency and flapping phase delay angle?

Answer 2

Increase the flapping frequency angle and reduce the flapping phase delay angle

Question 3

Why the flapping phase angle is close to 90 degrees?

Answer 3

The natural frequency of the flapping motion is close to the rotational speed, and the excitation
frequency is equal to the rotational speed. Thus, the system is in the resonance condition, in
which the phase delay is 90 deg.

Question 4

What causes the lead-lag motion and why the rotor must have the lead-lag hinge

Answer 4

The lag (lead-lag) motion is due to the Coriolis forces provided by the flap and the lead-lag hinge
is used to reduce this harmonic load damage on the rotor hub