The effect was to swap those letters before and after the main rotor scrambling unit.

It is a development of the Bell 212 with the major difference being the composite four-blade main rotor.

Most research is now directed towards reducing the noise from the main and tail rotors.

The main rotor and transmission system of the R-4 was retained.

This also resulted in the main rotor being mounted very close to the cabin roof.

In theory, with the props cut, they should have slowed his fall the same way the main rotor did on a helicopter.

Helicopters have several different configurations of one or more main rotors.

If before, it could have slowed the main rotor, he said.

As it prepared to land, the main rotor was struck by enemy gunfire.

The French make their main rotors turn clockwise when viewed from above.

Above the battlefield, the helicopter rotors beat the air, like thunder.

They have also been used successfully, though not efficiently, as tip jets on the end of helicopter rotors.

The whirring of the helicopter rotors was loud and clear.

The heavy thup-thup-thup of helicopter rotors could be heard in the background.

Flybar may also refer to an element of the helicopter rotor.

From the distance came the first faint sounds of helicopter rotors.

The sound of helicopter rotors filtered through the trees.

Far off in the distance, Lynch heard the drumming sound of helicopter rotors.

Suddenly, the drone became the distinctive beating of a helicopter rotor.

At a minute to ten the sky came alive with helicopter rotors.