A) What is dissymmetry of lift?

The rotor disc on the helicopter is split into advancing and retreating sides. The advancing side has a higher relative wind than the retreating and this causes the left side of the disc to move up and the right to move down, causing the disc to tilt to the left. This problem was solved by Juan de la Cierva in the early 1920's with the addition of flapping hinges which allows the lift to be equalized over the disc.

B) At what height is the helicopter in ground effect?

The height above ground that a helicopter would be in ground effect will vary from machine to machine. As a roungh guide take 2/3rd of your rotor diameter. For example; the R22 has a rotor diameter of 25 ft 2 inches. Two thirds of that is roughly 17 ft. So when the rotor disc is 17 ft above the ground the R22 would be in ground effect.

C) What is translating tendency?

Translating tendency is the tendency of the helicopter to drift to the right (N. American helicopters). Helicopters need a way to counter the torque of the main rotor and the most common way is with a tail rotor. The torque of the main rotor tries to turn the body of the helicopter to the right, to counter this the tail rotor pushes the nose of the helicopter round to the left which means the thrust of the tail rotor is to the right and this is what causes the helicopter to drift right.


D) Name the three parameters needed to get into Vortex Ring State?

1. Descent rate of 500 – 1500 fpm
2. Speed below translation
3. Some power in use