Dear Europaphiles,
I would like to give my comments on RPM readout based on about 100 hours
experience on my mono XS with a 912S engine. I installed an EIS panel (see
below) which has a digital RPM display and I also installed a Rotax R629M 2 inch
analog tachometer since I believed that I would use the analog as the primary
tacho indication. Before flying the plane, I belonged to the school which
believes that analog indication is the only way for quick understanding.
Interestingly I had spoken to Greg Toman at Grand Rapids Technologies who make
the EIS unit on another matter and he explained that I would stop using the
analog gauge and would rely on the digital. I did not believe him, but he was
right. The EIS refreshes very rapidly, at least as quick as the needle swings,
and it is always extremely accurate. For example, I have a WhirlWind constant
speed prop and in cruise, I can adjust the RPM up or down within 10 rpm by using
about a quarter turn of the prop vernier. I find now that I never refer to the
analog tacho.
I should explain that I have no personal or business relationship with EIS but
for those considering panel design,I can highly recommend the EIS 2000 unit. It
has various pages which can be accessed as necessary and a default favourite
page where I display :-
RPM
Oil temperature
Oil pressure
Fuel pressure
Fuel flow (this is an optional extra item)
CHT
EGT
All the outputs can be set with high and/or low alarms which flash a large red
lamp.
The other engine outputs available on my unit on the other pages are :-
Total fuel remaining. (Reset at every fuel fill)
Endurance time (Calculated by fuel remaining divided by current fuel flow)
Voltage
Coolant temp
Timer for current flight. (This resets automatically)
Total engine time. (Equivalent to Hobbs time)
Finally, analog gauges do have their place. I do use a Manifold Pressure analog
gauge to set my cruise throttle opening.
Cheers, John
N262WF
Fred Fillinger wrote:
> Nigel Charles wrote:
> > ...
> > An rpm gauge is the only engine gauge which I feel needs analogue display.
> > Ironically these are often the ones which need the most setting up. Mine
> > overeads by 200rpm at 5800rpm.
>
> RPM should be the most suspect of all. Convenient to think digital is
> more accurate, but you can't just count pulses - accurate to within
> parts per million, but at even 50RPM resolution, the display update
> rate is unacceptable. Other approaches then become dependent on
> mechanical and other issues in the stator ass'y from whence come the
> pulses, with accuracy attainable with $$, unless the higher price is
> just more profit. Same for analog gauges. Digital RPM checkers which
> read optically are very accurate and affordable. Borrowing or buying
> one of these is arguably a must! Or a freq counter from Radio Shack
> and do the math.
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