I have this medical helicopter that flys by my house every once and awhile. You can hear the chopper when he’s miles away, and eventually when he passes. However, as soon as he flys over, you hear the exhaust and then nothing. No deep, rotor sounds. Why is that?
Why do you only hear helicopters when they are approaching?
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Printed from: http://arezeez.com/2009/11/30/why-do-you-only-hear-helicopters-when-they-are-approaching/ .
© 2010.
© 2010.
it depends on the chopper…I worked in Army Aviation for 6 yrs and you really cant hear choppers coming in(excluding the Chinook..they tend to have a distinct "whopping"souind).. by the time you hear them they are either right over you or just flew by….I would hate to be the enemy!
because they’re getting closer.
Because the sound waves created by the main rotter blades are projected forward.
This is due to the sound waves being compressed into a more frequent pattern and lessens as the chopper goes by. The same is true for a speeding car, train, any moving object. This is due to the Doppler Effect.
This is called the Doppler effect. As the helicopter is approaching it compresses the sound waves making it louder. As it passes you hear the effect of the decompressed sound waves. A good example of the is a car going by you on a highway. You would notice it sounds different when its coming towards you as opposed to traveling away from you.