Question about engine sound

[Thorlifter]

Ok, I know this may be a silly question, but it's something that bugs me....

When your at an airshow or watching video's of flyby's, why is it when the planes approach, the engine has this incredible, powerful roar, but when it passes, it sounds like the chitty chitty bang bang car.

RROOOOOAAARRRRR....putt putt putt putt.

If I listen to a race car, it sounds just as powerful leaving as it does approaching.

 

[pbfoot]

Exhaust and prop and the engine does not rev as high . FlyboyJ would have 6the definitive answer

 

[tyrodtom]

It's called the doppler effect, and the race cars do it too. The difference maybe isn't enough for you to notice, but it's there. The faster the object is the more the difference.

I'll let somebody else explain the why.

 

[evangilder]

In some cases, they are putting the power to it for the pass, then throttle down as the pass is ending. Kind of like a sports car that pops and coughs when you let off the gas. B-25s are notorious for popping and coughing at taxi speeds and when it's throttled down.