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

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

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

The whirring of the helicopter rotors was loud and clear.

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

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

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

Helicopter rotors are designed to operate in a narrow range of rpm.

She started to run, the whirring of the helicopter rotor blades overhead.

The sound of helicopter rotors filtered through the trees.

Helicopter rotors are designed to operate at a specific rotational speed.

An example of a safe-life component is the helicopter rotor blade.

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

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

Heard birds singing and the faraway flap of helicopter rotors.

He keeps Lucille close, hearing helicopter rotors above as they run along the premises.

The din in his head took on a sickening rhythm, like the sound of helicopter rotors.

They were quiet, and during a gap in the explosions the faint sounds of helicopter rotors could be heard.

He toggled the "remote" and eased in the sound of helicopter rotors.

This system, in its various modified forms, is the basis of most multi-bladed helicopter rotor systems.

A slightly different approach to vertical landing is to use an autogyro or helicopter rotor.

The first thing they heard was a distant mutter of twin-bladed helicopter rotors.

But as long as the helicopter rotor is turning, it won't be deadweight!

Jenybeny looked down to temporary buildings and a great steel box with helicopter rotors on it.

The noise was almost a subliminal thunder over the beating of the helicopter rotors.