> This has probably been discussed a million times before. Typically when I
> am involved in a certain section of the build I become focused and tend not
> to assimilate some of the other stuff coming over the web. I need to
> install a switch for the Hobbs meter. The first thought is to put a T
> where the oil pressure transducer is and plug in the switch upstream of the
> transducer. Are there any other pressure ports on the 914 that I'm not
> aware of? What have others done to ensure accurate recording of engine
> hours with the Hobbs?
>
> Thanks,
>
> Steve A143
> Mesa, AZ
Why do you really need to know accurate Hobbs time? As an amateur-built aircraft
in the U.S., you're not bound in the slightest degree by any run time of any
component anywhere. Admittedly, were you to sell the aircraft, airframe/engine
time will be of interest to a buyer and thus how determined, but big deal.
So, my "Hobbs" time is from that which a Taskem digital RPM display actually
records
in nonvolatile memory. Good 'enuf!
The only place to tap into oil pressure is at the pressure transducer on all
Rotax
91X, or the feed line to the 914 turbocharger. But the grizzled old aircraft
mechanic in me says you do that you introduce a point of failure in a critical
airworthiness system. It's not like there's a Service Bulletin on my other
airplane specifically on this, which on failure causes oil to be spilled inside
the aircraft cabin, until there ain't nuthin' in the sump!
Thus preferable would be to simply read voltage at the Rotax transducer, and
glomp
a transistor to fire a stock Hobbs meter. It's a simple circuit, but if a
builder can't do that, I think it best to at least shop for something that will
record elapsed hours when fed a voltage, like when master is on -- even a stock
Hobbs does that. It won't be exact engine hours, but so what.
Regards,
Fred F.
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