Q25DQ A helicopter has a large main ro... [FREE SOLUTION]

91影视

University Physics with Modern Physics

Hugh D. Young, Roger A. Freedman

Physics

14th edition Edition 路 1596 pages

ISBN: 9780321973610

Chapter 1: Q25DQ (page 328)

A helicopter has a large main rotor that rotates in a horizontal plane and provides lift. There is also a small rotor on the tail that rotates in a vertical plane. What is the purpose of the tail rotor? (Hint: If there were no tail rotor, what would happen when the pilot changed the angular speed of the main rotor?) Some helicopters have no tail rotor, but instead, have two large main rotors that rotate in a horizontal plane. Why is it important that the two main rotors rotate in opposite directions?

Short Answer

Expert verified

A tail rotor is necessary for helicopters to conserve angular momentum.

Two main rotors also rotate in opposite directions to conserve angular momentum.

Step by step solution

Given that

A helicopter has a large main rotor that rotates in a horizontal plane and provides lift. There is also a small rotor on the tail that rotates in a vertical plane.

Explanation

When the helicopter is in air, and is moving with a constant velocity, no external forces or torques act on it thus conserving its angular momentum.

If the main rotor changes speed, then to balance the changing angular momentum, the passenger cabin would have to rotate in the opposite sense as the main rotor.

Some helicopters have two main rotors that rotate in the horizontal plane as the two rotors rotate in the opposite sense, one clockwise and the other anti-clockwise. Thus net angular momentum of these rotors is zero. This prevents the main cabin from rotating, and no tail rotor is necessary.