[simpits-tech] Using real instruments

Sat, 25 Jan 2003 16:30:32 -0500

Hi Brian,

Thanks for the Link Trainer tip.  I'll be looking into it.

I think I understand the theoretical workings of the Altimeter.
http://www.allstar.fiu.edu/aero/PSI.htm

The pressure vs. altitude is found here:
http://www.usatoday.com/weather/wstdatmo.htm

I could use a vacuum pump that pulls a 27 in Hg vacuum controlled by
proportional
vacuum regulator to actuate the altimeter. But, that equipment is expensive
and not found often on eBay. :)

I want to modify the altimeter to operate from pressure using a rig I
already have working.  I have a servo driving a pressure regulator (phidget
style).  I have a little program (not mine) that runs in the background that
accepts data
from Falcon4 that drives the servo position.  I'm using it to output a 0-6
psi pressure to a G-suit for G-force cueing.  It should be fairly easy to
use the elevation data to drive the Altimeter regulator.

I've completed the mods to the Altimeter and it works well.  Details to
follow.

Craig R.

-----Original Message-----
From: simpits-tech-admin@simpits.org
[mailto:simpits-tech-admin@simpits.org]On Behalf Of Brian West.
Sent: Saturday, January 25, 2003 9:52 AM
To: simpits-tech@simpits.org
Subject: Re: [simpits-tech] Using real instruments

Hi Craig,
                The WW11 era Link Trainers had their instruments vacuum
controlled. If you uneathed some old service manuals for these they would
likely tell you what you need.
If you find some old Link technical literature I would be grateful to see
it.

Best regards,  Brian West.

-----Original Message-----
From: Craig Rochester <johncraigroch@msn.com>
To: simpits-tech@simpits.org <simpits-tech@simpits.org>
Date: 25 January 2003 04:13
Subject: RE: [simpits-tech] Using real instruments

>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=310513777
0
>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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