this all assumes that the mains are stablised at 50Hz!
testing here in south africa reveals that the supply can vary up to 5%!
> -----Original Message-----
> From: Eric Evers [SMTP:evers@mcmail.com]
> Sent: Friday, September 26, 1997 1:09 AM
> To: 'europa@avnet.co.uk'
> Subject: RE: Calibrating Engine RPM
>
> 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
> To: europa@avnet.co.uk
> 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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