merrill@raja.DEC (01/27/86)
Walt Hanstein proposes the following explanation for why piston driven airplanes use odd numbers of cylinders: Rotary engines have essentially a single crank per cylinder bank. If you had seven cylinders in one bank you could also make a two bank 14 cycle engine, 21 cyls., 28 etc. Because these engines are two stroke engines, they require two complete revolutions to fire all seven cylinders once. So a reasonable firing order might be 1 3 5 7 2 4 6 and then 1 again. That would provide reasonable smooth torque. I wouldn't know how to get as smooth a torque using an even number of cylinders. -------------------------------------------------------------------------