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tjs22t(at)verizon.net
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 Posted: Wed Apr 16, 2008 5:12 pm Post subject: tuning the altimeter |
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I've had an altimeter that reads high forever. Anywhere near 3000 or above it's always 180 to 200 higher than GPS or the local approach control. Just compensated by adding 200 but that's not a good long term practice.
I remembered reading in one of Tony Bingelis' books that you could fine tune your airspeed - too high, too low - with a collar or ring on the static pickup if you have one mounted as a tube under the wing. I found the info in his Sportplane Construction Techniques (pages 281, 282) and tried to reference it to the altimeter.
Using a piece of solid core 12 AWG wire, stripped of insulation, I coiled it around a 1/4 drill shaft and with a bit of cutting, fitting, and fidgeting ended up with a C shaped piece that could be made a snug fit on the static tube which is attached to the pitot tube in the standard ACS P/N 15144 part. The stripped wire was .080.
Because I thought what was needed was higher pressure at the static hole, the C piece was mounted about 1/8 inch behind the static hole. First flight this a.m. brought the reading to within 100 feet. A second adjustment brought it on. IAS down slightly, about three MPH in the 120 range.
My pitot static is located just outboard the wing locker on the left wing and behind the spar ever so slightly. I think this rather far rearward location accounted for the lower pressure at the tube inlets. If the reading looks good on next flight a tab of nailpolish will be added to wire.
smallie HDS/3300 325 hours at N94 - always looking for a race
[quote][b]
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rroberts
Joined: 04 Sep 2006
Posts: 50
Location: Birmingham, AL USA
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| Posted: Thu Apr 17, 2008 1:41 am Post subject: Re: tuning the altimeter |
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My Falcon altimeter was off as well but it has a fine tune adjustment just above the knob. Remove that screw and basically pull back a collar then tweek to ensure the pressure window and FE are correct. viola....
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_________________
Low & Slow
Rick
www.n701rr.com
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billmileski
Joined: 07 Aug 2006
Posts: 68
Location: Ledyard, CT
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| Posted: Thu Apr 17, 2008 7:01 am Post subject: Re: tuning the altimeter |
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Rick,
Could you describe what "pulling back a collar" is.. I tried to adjust my altimeter with the screw removed, but couldn't figure out how to get the knob to move only the altitude indication (or Kollsman pressure, not sure which is the one that is disconnected when the screw is out).
Bill
701 912S 120-ish hours
Ledyard, CT
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steerr(at)bellsouth.net
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| Posted: Thu Apr 17, 2008 7:42 am Post subject: tuning the altimeter |
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If you have a Falcon altimeter, you can get detailed instructions,
including diagrams, from their web site - www.falcongauge.com. If the
adjustment is to be done in the plane, the basic steps are:
1. Set the altimeter to the exact field elevation
2. Remove the screw above the know.
3. Separate the gears with a pair of tweezers of small screwdriver
4. Pull out the adjustment knob and set the barometric pressure to the
current pressure
5. Slide the gear back into position and re-install the screw.
Hope this helps.
Bill
billmileski wrote:
| Quote: |
Rick,
Could you describe what "pulling back a collar" is.. I tried to adjust my altimeter with the screw removed, but couldn't figure out how to get the knob to move only the altitude indication (or Kollsman pressure, not sure which is the one that is disconnected when the screw is out).
Bill
701 912S 120-ish hours
Ledyard, CT
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=177423#177423
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billmileski
Joined: 07 Aug 2006
Posts: 68
Location: Ledyard, CT
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| Posted: Thu Apr 17, 2008 8:25 am Post subject: Re: tuning the altimeter |
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Thanks, Bill, will give it a try!
Bill
do not archive
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