Poor man's prop tach gauge

[Mike Kimball]

I'm resending this with a more appropriate subject line for the archives...

Poor man's way to check the tach: Put a little piece of duct tape on the
back of a prop blade, wait for the sun to do down, then position the
airplane with one of the airport flood lights behind the plane. In the USA
we have 60 cycles per second AC power (plus or minus no more than ~2%
usually). The light will flicker at that rate even if you can't see it. (I
don't know if Canada might be 50 Hz.) Set the rpm at factors of the power
cycle rate. For instance, set 1800 rpm for 60 Hz power. At 1800 rpm the
prop with the tape on it should appear to stop. If it stops at something
other than 1800 rpm, that is how far off your tach is. If it stops at 1700
rpm, it is reading 100 rpm low. (You need the tape because most props are
painted black on the back and would be harder to see.) The prop should
appear to stop at all factors of 60, such as 1200 and 2400 rpm as well as
1800 rpm.

Mike Kimball
SR#044






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