Why do radial engines have uneven number of cylinders?

Answer 1

It was so the engine would fire after every other cylinder so it would run more smoothly.This is in four stroke engines.
In two strokes it does not matter.Small aircraft engines have any number of cylinders.
Some bigger radial engines had up to 28 cylinders. I can't remember the make.
My friend has a bi-plane with an 8 cylinder radial - fuel injected and it runs pretty smooth at operating RPM.
On the ground, well it is a little rough.

Answer 2

Lycombing did build a even numbered radial engine but it did not perform well enough to be put into production. Balance and harmonics are the main reasons.

Radial engines with 14,18,28,or 36 cylinders are in theory 7 or 9 cylinder engines connected to one another although they have only one crankcase.

the Le Rhone radial engines of WW-I fame had stationary crankshafts and the cylinders rotated with the prop.

Answer 3

I don't know. I do know that alot of people are only used to cars having 4,6,8 or 10 cylinders, but there are cars with 3,5, and 7 cylinders. It was just easy for the initial builders to stay with 4 and 8 cylinders for the four stroke motors, but there is not other reason. A radial engine could have 2-20 cylinders and any number in the middle would work.

Answer 4

They run smoother than even numbers of cylinders. Also true of rotary engines (old aircraft piston rotaries, not the Wankel/Mazda kind!).

Someone mentioned a 28-cylinder radial (Pratt & Whitney made some) . There were also some Wright radial engines of 14-cylinder engines. Those contained multiple banks of 7-cylinders each.

Answer 5

Harmonics and vibration, the odd number cylinders prevent the vibrations from shaking everything apart at low speed.

Answer 6

BALANCE