[simpits-tech] Using real instruments
Marv De Beque
simpits-tech@simpits.org
Sun, 26 Jan 2003 09:03:43 -0500
I had considered a bellows or syringe style vacuum pump. The only problems
I see is generating the force required to activate the bellows and
controlling the force so you can regulate the amount of vacuum.
That and not having the system leak. ;-)
Marv
On 1/26/03 12:14 AM, "Craig Rochester" <johncraigroch@msn.com> wrote:
> 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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