X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao107.cox.net ([68.230.241.39] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTP id 3730031 for flyrotary@lancaironline.net; Tue, 23 Jun 2009 20:40:20 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.39; envelope-from=alventures@cox.net Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao103.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20090623212729.KIXI2915.fed1rmmtao103.cox.net@fed1rmimpo01.cox.net> for ; Tue, 23 Jun 2009 17:27:29 -0400 Received: from BigAl ([72.192.135.181]) by fed1rmimpo01.cox.net with bizsmtp id 7ZTU1c00J3uzsQg03ZTUsv; Tue, 23 Jun 2009 17:27:29 -0400 X-VR-Score: 0.00 X-Authority-Analysis: v=1.0 c=1 a=paBUCOFK8LgA:10 a=Ia-xEzejAAAA:8 a=DL0JBfHQAUeJ9tf66zYA:9 a=mFafVYUyLnaZ7hG6cZ4A:7 a=Zc5fmkr4rXxCS8auO9EaTrGyER8A:4 a=EzXvWhQp4_cA:10 a=Ue7zoshsy6Znc4G1:21 a=ZwwJ04VQ67ak2VSI:21 a=80QGLQXISNn_A1uxLvEA:9 a=qcY-wnbxHGO9g9zAvGAA:7 a=zNck55JdT6aipBS1q4tJ7JlzN5wA:4 a=hYNQYdWbENlBqPAi:21 a=3Uv28IOngDZA2kEz:21 X-CM-Score: 0.00 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: progress report #347c Date: Tue, 23 Jun 2009 14:27:43 -0800 Message-ID: <9E252A43241E45F0A6615674A1F8A43F@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0006_01C9F40E.C5855960" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6838 In-Reply-To: Importance: Normal Thread-Index: Acn0OocuUnmrgNpNT+m5RQ0OMMcz6QAFnXsg X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_0006_01C9F40E.C5855960 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable =20 A perfect Vulcan Mind Meld!=20 Huh? =20 BTW; don't be surprised if your EM2 doesn't read correctly. When I got = mine it was off by about 2". I got a gauge and re-calibrated; but I have = noticed it has drifted off some over the last couple of years. But it doesn't = really matter. Think of it as 'relative' MAP; the important thing is that it changes properly with change in altitude. =20 Al =20 _____ =20 From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen Sent: Tuesday, June 23, 2009 3:48 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: progress report #347c Bill; =20 Yes; at or near sea level the correction factor is 1.000. If your = airport is at 5000 ft, the correction factor is 0.832. So if the ATIS (or the altimeter setting to give you field elevation) is 29.92, then your = engine off MAP should read 24.9". And, yeah; you're right - who needs a chart, = the correction is about 1" per 1K ft. My field elevation is about 1400', = and the correction is 0.95, so my engine off MAP is .95 x altimeter setting; = if 29.92 then my MAP should read 28.4". =20 Al =20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Bradburry Sent: Tuesday, June 23, 2009 10:00 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: progress report #347c =20 Al, Ok, Part of my misunderstanding lies in the fact that my field = elevation is 55 feet. So both will read close to the same here. You are saying = that his readings would have to be corrected for his 5000 foot altitude which = is about 1 inch per 1K feet? =20 Bill =20 _____ =20 From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen Sent: Tuesday, June 23, 2009 2:12 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: progress report #347c Al, Hmmmm, Further explanation would be helpful here. I thought that the altimeter was actually reading the air column weight or pressure at its location. If you set the altimeter to the field elevation, it seems it should read the barometric pressure in the window =20 Gees; I was hoping you wouldn't ask - then I wouldn't have to think = about it:-). =20 Well; it goes something like this; your altimeter setting is the = barometric pressure of the station as if the station were at sea level. So the altimeter setting is barometric pressure with an altitude correction applied. Your MAP is absolute ambient pressure. Absolute pressure is measurement relative to a perfect vacuum, as in = outer space. A zero reading occurs when the pressure is reduced to near = perfect vacuum conditions. The ambient atmospheric pressure at sea level is approximately 29.92 inches of mercury, or 14.7 pounds per square inch, = or 760 mm of mercury. As you go up the ambient atmospheric pressure = decreases and your Absolute pressure gauge (MAP) reading also decreases. =20 I have a chart of the barometric vs ambient pressure, but I don't know = where I got it. Anybody know? I'll check the internet and see if I can find something; or I could scan it and send it. =20 Al G ------=_NextPart_000_0006_01C9F40E.C5855960 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

A perfect Vulcan Mind = Meld! 

Huh?

 

BTW; don’t be surprised if = your EM2 doesn’t read correctly.  When I got mine it was off by = about 2”.  I got a gauge and re-calibrated; but I have noticed it has drifted = off some over the last couple of years. But it doesn’t really matter. = Think of it as ‘relative’ MAP; the important thing is that it changes properly with = change in altitude.

 

Al

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Tuesday, June 23, 2009 3:48 = PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = progress report #347c

Bill;

 

Yes; at or near sea level the correction factor is 1.000.  If your = airport is at 5000 ft, the correction factor is 0.832.  So if the ATIS (or the altimeter setting to give you field elevation) is 29.92, then your = engine off MAP should read 24.9”.  And, yeah; you’re right – = who needs a chart, the correction is about 1” per 1K ft. =   My field elevation is about 1400’, and the correction is 0.95, so my engine = off MAP is .95 x altimeter setting; if 29.92 then my MAP should read = 28.4”.

 

Al

 

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Bradburry
Sent: Tuesday, June 23, 2009 10:00 = AM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = progress report #347c

 

Al,

Ok,   Part of my misunderstanding = lies in the fact that my field elevation is 55 feet.  So both will read = close to the same here.  You are saying that his readings would have to be corrected for his 5000 foot altitude which is about 1 inch per 1K = feet?

 

Bill

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Tuesday, June 23, 2009 2:12 = PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = progress report #347c

Al,

Hmmmm, Further explanation would be helpful here.  I thought that the

altimeter was actually reading the air column = weight or pressure at its

location.  If you set the altimeter to = the field elevation, it seems it

should read the barometric pressure in the = window

 

Gees; I was hoping you wouldn’t ask – then I wouldn’t have = to think about itJ.

 

Well; it goes something like this; your altimeter setting is the barometric = pressure of the station as if the station were at sea level. So the altimeter = setting is barometric pressure with an altitude correction applied.  Your MAP = is absolute ambient pressure.

Absolute pressure is measurement relative to a perfect vacuum, as in = outer space. A zero reading occurs when the pressure is reduced to near = perfect vacuum conditions. The ambient atmospheric pressure at sea level is approximately 29.92 inches of mercury, or 14.7 pounds per square inch, = or 760 mm of mercury. As you go up the ambient atmospheric pressure decreases = and your Absolute pressure gauge (MAP) reading also decreases.

 

I have a chart of the barometric vs ambient pressure, but I don’t = know where I got it. Anybody know?  I’ll check the internet and = see if I can find something; or I could scan it and send it.

 

Al G

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