High in the night sky, he had heard the hum of an airplane motor.

The purr was from high above, like the roar of an airplane motor.

An hour later he heard the first buzz of an airplane motor.

As Stuart hesitated, he heard the roar of an airplane motor.

Then, from far away, came the thrumming of an airplane motor.

He slept until the sound of airplane motors woke him.

Off to the west came the roar of two airplane motors taking off.

It had been employed for the killing of airplane motors at a distance.

Far off, he could hear the roar of an airplane motor.

Then came the thought of the airplane motor that he had heard.