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Chapter 11: Problem 7

Why do helicopters have two rotors?

Short Answer

Expert verified
Helicopters have two rotors to perform two separate tasks: The main rotor provides lift, enabling the helicopter to ascend, descend, and hover. The tail rotor counteracts the torque of the main rotor to keep the body of the helicopter stable and allow controlled turning.

Step by step solution

01

Understanding the Basic Principle of Helicopter Flight

A helicopter achieves lift due to the rotation of its main rotor. The rapid spinning of the main rotor blades forces air downward, which pushes the helicopter upward due to reaction force according to Newton's third law.
02

Identifying the Two Rotors

A conventional helicopter has two rotors: the main rotor on the top, and a smaller one at the tail, known as the tail rotor or anti-torque rotor.
03

Understanding the Role of the Main Rotor

The main rotor provides lift, allowing the helicopter to ascend, descend, and hover. By changing the angle of the rotor blades as they move around the rotor hub (a process known as cyclic pitch), the pilot can control the direction of the helicopter's flight.
04

Understanding the Role of the Tail Rotor

While the main rotor spins, it generates a significant amount of torque which causes the helicopter body to spin in the opposite direction (Newton's third law). To counteract this, the tail rotor generates a sideways thrust to balance out the torque from the main rotor.
05

The Need for Two Rotors

Therefore, a helicopter typically has two rotors to take care of both the lift and the counteracting of torque. The main rotor provides the necessary lift for flight, while the tail rotor prevents the entire body of the aircraft from spinning uncontrollably due to the torque produced by the main rotor.

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