[simpits-tech] Using real instruments

[Craig Rochester]

Thanks Marv,

I'll get some pics and details posted soon.

Before you modify your altimeter, you might want to consider using vacuum.
VVI(VSI) would also use the same vacuum signal.  The VVI measures the rate
of change of the barometric pressure.  I'm pretty sure it's a pneumatic
gauge, most are.  The vacuum pump wouldn't have to be very big as the amount
of air being pumped is tiny.  I would need to pull a pretty deep vacuum;
about 28 in Hg for 80,000'.  Like this HVAC(refrigeration)unit:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3308108396&category=26198

The vacuum regulator would be very similar to the one I'm using for my
G-suit rig, so the servo mod would be the same.  It may even be possible to
modify a pressure regulator to regulate vacuum.  The principles are the
same, but everything is reversed(sort of).

Another advantage with vacuum is that the instrument would be operating
exactly as it was designed with no jury-rigging required.  It sure would be
great to have the real instrument perform identically as in real flight.  So
with one vacuum signal and one pressure signal you could drive the
Altimeter(vac), ASI(vac and press), and AOA Indicator(vac). Where vac =
barometric pressure and pressure = pitot dynamic pressure.

Craig R.

-----Original Message-----
From: simpits-tech-admin@simpits.org
[mailto:simpits-tech-admin@simpits.org]On Behalf Of Marv De Beque
Sent: Saturday, January 25, 2003 6:50 PM
To: simpits-tech@simpits.org
Subject: Re: [simpits-tech] Using real instruments


Great work, Craig.

Once again, you have taken a lead role in this effort and have come up with
an innovative idea.

I have the same type of altimeter and look forward to your final write up so
I can do the same.

Marv
>
> Ok, I bought the Altimeter.  I took it apart(a delicate task).  It could
> definitely be driven by vacuum, but I'm going to try to modify it to be
> driven by pressure.  The ASTEK meter I have works by the expansion of two
> sealed metal bellows expanding as the atmospheric pressure decreases at
> higher altitudes.  I'm going to drill a hole in each bellows, port them,
and
> try pressurizing the bellows.  In theory this will be equivalent to
applying
> a vacuum to the outside.  If it works I'll post pics of the results.
> Otherwise...anyone interested in a ruined Altimeter? :)
>
> Craig R.
>
> -----Original Message-----
> From: simpits-tech-admin@simpits.org
> [mailto:simpits-tech-admin@simpits.org]On Behalf Of Craig Rochester
> Sent: Wednesday, January 08, 2003 8:39 PM
> To: simpits-tech@simpits.org
> Subject: RE: [simpits-tech] Using real instruments
>
>
> I'm thinking driving the real instruments from two(2) electronic
regulators
> would be simpler than modifying each instrument.  Particularly if you were
> doing a dual pit.  I don't know what the leak rate is on the VSI, but the
> rest could be run from a tiny compressor(and vacuum pump if required).
> Barometric pressure varies from 14.7 psia(0 gage pressure) @ sea-level and
> decreases to about 1.1 psia @ 60,000 feet.  If you could modify or adjust
> the Air Speed Indicator and Altimeter to be off-set down by about 15 psi,
> you could use pressure instead of vacuum.
>
> I know the pneumatic altimeters uses a sealed metal bellows that expands
as
> the barometric pressure falls with altitude.  The movement of the bellows
is
> converted to dial rotation with gears and levers. Maybe there is enough
> adjustment in the works to have the instrument read 60,000 feet with no
> applied pressure and then output 1-15 psi from the regulator.  Or maybe a
> fitting could be fashioned to the bellows and connected to the regulator.
>
> I see electronic pressure regulators on eBay pretty often:
>
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=26210&item=3105137770
> They're called an I/P transducer(eye-to-pee) current to pressure or
> V/P(vee-to-pee) voltage to pressure transducer.
>
> Craig R.
>
> -----Original Message-----
> From:    simpits-tech-admin@simpits.org
[mailto:simpits-tech-admin@simpits.org]
> On Behalf Of Matt Bailey
> Sent:    Wednesday, January 08, 2003 5:04 PM
> To:    simpits-tech@simpits.org
> Subject:    Re: [simpits-tech] Using real instruments
>
> I remember talking about using an air compressor to control real gauges
> several months ago. Sounds like a GREAT idea to me, a little more complex
> than just using servos but the extra realism in gauge movement would
> probably
> be worth it. Not to mention the utter coolness of being able to drop a
REAL,
> UNMODIFIED instrument directly into your sim. The instruments themselves
are
> pricey though, unless you found an old junk instrument but that would
defeat
> the purpose of making your sim accept real instruments since the
instrument
> would not work. :)
>
> Driving gyro instruments like the turn coordinator I suppose could be done
> with servos driving the gyro cages (although the ball is just a ball in a
> glass tube, it's not driven by any mechanical device in real life so it
> would
> probably have to be totally reworked) or just removing the gyros
completely
> and hooking a servo directly to the small aircraft representation. Anyone
> done this?
>
> -Matt Bailey
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