Beats Between Airplane Propellers

Most recent answer: 04/12/2014

Q:
Why does the sound volume (intensity) from a distant propeller-driven aircraft seem to oscillate?
- Andrew (age 27)
Asheville, NC
A:

I'm guessing that you're asking about planes with at least two engines. Then if the propellers are turning at slightly different rates the sound waves from them will oscillate between being in-phase and out-of-phase. They'll be louder when they're in-phase.

Checking if this guess was right, I found an article describing how some planes allow the pilots to keep the propellers synchronized to avoid hearing those beats in the plane. 

Mike W.


(published on 04/12/2014)