Rotorcraft

Question 1

What are the two main issues driving the multi-rotor configurations widely used in the early
rotorcraft development

Answer 1

Torque balance; Rolling moment in forward fligh

Question 2

How does the single-rotor helicopter deal with the torque balance:

Answer 2

Tail rotor

Question 3

How does the single-rotor helicopter deal with the rolling moment in forward flight?

Answer 3

Flapping motion

Question 4

What is the difference between the helicopter and autogiros

Answer 4

A. The rotor powered by the engine in the cruise flight
B. Autogiros cannot take off vertically without the help of pre-rotator
C. Hover capability
D. The helicopter may be larger than the autogiros
E. Autogiros sometimes are not equipped with rotor control inputs

Question 5

Why does not the autogiro need a tail rotor

Answer 5

The rotor of the autogiro does not connect with the engine, and it cannot transmit torque to the
vehicle.

Question 6

What is the fundamental difference between the helicopter and the autogiros

Answer 6

The rotor powered by the engine in the cruise flight

Question 7

The function of the swashplate

Answer 7

Adjust the blade control angle at different azimuth angles.

Question 8

difference between the thrust and lift

Answer 8

thrust is in the rotor axial direction
Lift is normal in the inflow direction

Question 9

The assumptions of the momentum theory:

Answer 9

Existing a steamtube which is an axially symmetric surface passing through the rotor disc perimeter which isolates the flow through the rotor.
 Incompressible flow.
 Velocity imparted to the fluid is constant across the disk.
 Far away from the disk, the air is at rest.

Question 10

definition of the induced velocity

Answer 10

The velocity increment due to the rotor is called Induced Velocity

Question 11

A figure of merit is used t

Answer 11

evaluate rotor performance in hover

Question 12

indicate why the rotor needs the pre-twist angle

Answer 12

allows most of the blade element (especially the blade tip section) to be in the
optimal attack angle

Question 13

Demonstrate the control strategy of the collective pitch during the autorotational landing

Answer 13

Reduce the collective pitch to maintain the rotational speed, and when the vehicle is close to the
ground, increase the collective pitch to add additional vertical acceleration to reduce the vertical
speed.

Question 14

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

Answer 14

Inertia force, aerodynamic force, and centrifugal force

Question 15

What are the two main reasons related to the rotor that limits the helicopter’s maximum flight
speed?

Answer 15

Advancing tip compressibility effect, stall condition in the retreating side