It doesn't matter how many blades the propeller has. It is dependent on
the frequency of your electrical power system. In the United States, 60
Hz is the standard. In other parts of the world, 50 Hz is used. The
United States standard is pretty tight, allowing very small deviation.
Hence multiples of 60 will strobe a moving part, making it appear
stationary

Don't forget those of us with three bladed props. Or four; whatever.
Your point illuminates elegance in thinking.

"EDR" wrote in message
...
Oh, come on folks!
Poor man's tach check...
go out at night
fire up airplane
taxi to place on airport with mercury vapor/fluorescent light
park with light behind you
adjust engine rpm for 600/1200/1800/2400 rpm
if prop blade is not "standing still", adjust until the blad does not
move (strobe effect)