Why do aircraft radial engines always use an odd number of cylinders?
A. Radials are built with an odd number of cylinders to give a better firing order and corresponding smoothness with lack of vibration.
www.radialengines.com/frequently-asked-questions/
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Wiki’s visuals nail it:
Reported. This is the 2nd time today (that I’ve noticed) that a newbie has come in and posted the same question as another poster did just a short while earlier.