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klaus(at)utdallas.edu
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 Posted: Sat May 31, 2008 2:06 pm Post subject: Cabin Pressure Test |
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Hi,
We have carried out some tests of cabin pressure versus ambient pressure
measured by the static system.
Setup: Airplane: 601HDS. Additional altimeter in the cockpit,
set to same altitude as panel altimeter on the ground (792 ft MSL)
before starting the engine.
All measurements at 75 deg F OAT, altitude 2,000 - 3,000 ft MSL.
In each case, the additional altimeter was HIGH relative to the panel
altimeter,
meaning that cockpit pressure was LESS than the pressure in the static
system.
Below, that difference is given in ft. To convert to
inches mercury, divide by 1000, since 1000 ft altitude roughly
corresponds to
1 inch of mercury column. The difference depends on airspeed, as one
might expect. Here are the details. True airspeed is estimate using
GPS for calibration.
Speed (TAS kts) Altitude Difference (ft)
85 100
100 150
112* 200
* This is max level speed for the plane (601 HDS, 912 Rotax engine,
GSC wood propeller)
My friend J. Wybanga, expert pilot/mechanic, counseled that cockpit
temperature can be a big factor when outside temperature
is low. We did a test of this, and found that at max speed, turning
on the heater raised the alt. difference from 200 to 220 ft, which is
not
much. But outside temperature was 75 deg F. I did not want to go through
the long climb to 14,000 ft to repeat the test with low outside
temperature.
Why is this important? In pre-GPS days, sellers of airplanes sometimes
would turn off the static system and turn on the heat to demonstrate
high airspeed to the buyer. According to Wybanga, under extreme
circumstances, this can turn an older 150 mph Mooney into a 180 mph
speedster.
If you buy a plane and speed is of concern, insist that a handheld GPS
unit
is taken aloft for measurements if there is no panel GPS installation.
Happy flying,
Klaus
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jetboy
Joined: 22 Jul 2006
Posts: 233
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| Posted: Sat May 31, 2008 8:48 pm Post subject: Re: Cabin Pressure Test |
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In my CH701 I can go from 63 kts IAS to 70 Kts IAS by pulling the line on my external static port. when a passenger complains it goes too slow thats what I do
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Ralph - CH701 / 2200a |
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kmccune
Joined: 22 Sep 2007
Posts: 577
Location: Wisconsin, USA
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| Posted: Sun Jun 01, 2008 5:08 am Post subject: Re: Cabin Pressure Test |
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Now thats funny, right there!
Kevin
do not archive
| jetboy wrote: | | In my CH701 I can go from 63 kts IAS to 70 Kts IAS by pulling the line on my external static port. when a passenger complains it goes too slow thats what I do |
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_________________
“Always do what you are afraid to do.”
R.W. Emerson (1803-1882)
"Real freedom is the sustained act of being an individual." WW - 2009
"Life is a good deal...it's worth it" Feb 1969
Dorothy McCune |
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ggower_99(at)yahoo.com
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| Posted: Mon Jun 02, 2008 6:24 pm Post subject: Cabin Pressure Test |
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Hey thats having a real inexpensive Turbo!!! Love it 
Saludos
Gary Gower
Do not archive
--- On Sun, 6/1/08, jetboy <sanson.r(at)xtra.co.nz> wrote:
[quote]From: jetboy <sanson.r(at)xtra.co.nz>
Subject: Re: Cabin Pressure Test
To: zenith-list(at)matronics.com
Date: Sunday, June 1, 2008, 12:48 AM
[quote]--> Zenith-List message posted by: "jetboy" <sanson.r(at)xtra.co.nz> In my CH701 I can go from 63 kts IAS to 70 Kts IAS by pulling the line on my external static port. when a passenger complains it goes too slow thats what I do -------- Ralph - CH701 / 2200a Read this topic online here: http://forums.matronics.com/viewtopic.php?p=185686#185686 [quote][b]
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