Electric lights, running on a.c. mains flicker at twice the supply
frequency. i.e. 100 or 120 Hz depending on where you are. (One flash on
each half-cycle. )
There should be very little flicker from incandescent lamps due to their
thermal inertia but any kind of gas discharge lamp will give a usefully
intense flash. I.e. fluorescent lights, mercury and sodium vapour street
lights should give a useful flicker. Even without any measuring instrument
you should (in theory) be able to do some useful checking if you can run
your engine with the prop illuminated only by mains powered gas discharge
lights(they must be all on the same phase of the supply). On the basis of
50Hz supply the flashes occur every 1/100 th of a second. So if the
engine speed can be finely adjusted to produce the appearance of the prop
being stationary: each blade is advancing to the position of the preceding
blade in 0.01 of a second. That is 6000 times per minute. So a three
bladed prop would be rotating at 6000/3 = 2000 r.p.m. If you see what
appears to be a stationary 6 bladed prop it means that each blade is moving
0.5 or 1.5 positions in 1/100 th of a second so the r.p.m. to produce this
effect is 1000 or 3000. If you can achieve the appearance of stationary 9
bladed prop each blade is moving 1/3, 2/3 or 4/3 of a position and the prop
r.p.m. must be that same proportion of 2000. I.e. 667, 1333 or 2667. (If
you are on 60Hz supply multiply all these prop speeds by 1.2)
Is anyone willing to try this out? At least it is getting dark earlier!
(Apologies to N.Z. & Aussie).
Eric Evers
Largs, Ayrshire,
SCOTLAND - UK
-----Original Message-----
From: Carl Pattinson [SMTP:carl@photos.prestel.co.uk]
Sent: 21 September 1997 21:17
Subject: Calibrating Engine RPM
> Klaus wrote:
>
> >During those test flights I have found out that my RPM indicator reads
300
> >rpm too low!
> >Any ideas how I could calibrate it?
snip
>The meter itself can be adjusted and calibrated using the
"standard" 50hz flicker of a mains light bulb (assuming the electricity
company generators run at this speed).
I would consider loaning my meter if anyone has a need to calibrate.
Carl Pattinson.
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