Why do the sound of aircraft engines change pitch as they fly over us?

What causes the change in pitch of aircraft engine sound as they fly over us?

Does the height of the aircraft affect the Doppler effect on the sound of its engines?

The Change in Pitch of Aircraft Engine Sound

The change in pitch of aircraft engine sound as they fly over us is due to the Doppler effect. This phenomenon occurs because the aircraft is moving towards or away from us.

As the aircraft approaches us, the sound waves are compressed, which results in a slightly higher pitch being heard. Conversely, as the aircraft moves away from us, the sound waves are stretched out, causing a slightly lower pitch to be perceived.

The height of the aircraft plays a role in the intensity of the Doppler effect on the sound of its engines. The higher the aircraft is flying over us, the smaller the effect becomes. This is because the angle of approach or departure is less steep, resulting in a lesser change in pitch compared to when the aircraft is flying at a lower altitude.