X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 26 Sep 2007 08:22:17 -0400 Message-ID: X-Original-Return-Path: Received: from smtp103.sbc.mail.mud.yahoo.com ([68.142.198.202] verified) by logan.com (CommuniGate Pro SMTP 5.1.12) with SMTP id 2352341 for lml@lancaironline.net; Wed, 26 Sep 2007 04:17:24 -0400 Received-SPF: none receiver=logan.com; client-ip=68.142.198.202; envelope-from=gbfitz@swbell.net Received: (qmail 3975 invoked from network); 26 Sep 2007 08:16:45 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=swbell.net; h=Received:X-YMail-OSG:Message-ID:From:To:References:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=VaUg0QvwtaCu2RANBw4XL/715ZScIZgmM4JXxUO/mMBfAnkgB4rZtvwre7Li7Q3IvMim6wxQOvuSQdThccFJB97sIL19QhYsK1EFKouEUdtnHeXBpXhfGniOOuQfjlGGodYEcJCCeaIJPlyF6LScomlC3kyB01yKoC8vgZgyhnU= ; Received: from unknown (HELO eaglenest61) (gbfitz@swbell.net@70.130.163.29 with login) by smtp103.sbc.mail.mud.yahoo.com with SMTP; 26 Sep 2007 08:16:44 -0000 X-YMail-OSG: hpXJ4lQVM1k7HB5UjZKNrHCwerBwQdgzVLmqA8G9OTxbDin_ X-Original-Message-ID: <00c401c80015$3a434720$4001a8c0@eaglenest61> From: "Gary Fitzgerald" X-Original-To: "Lancair Mailing List" , "Douglas W. Johnson, MD" References: Subject: [LML] Re: Airspeed Indicator Consult X-Original-Date: Wed, 26 Sep 2007 03:14:14 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00C1_01C7FFEB.50C69EE0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1807 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1896 This is a multi-part message in MIME format. ------=_NextPart_000_00C1_01C7FFEB.50C69EE0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Doug, This may sound stupid, but did you leave your alternate air switch on? Anyway, it sounds like the static input to your AS came loose, or has a = sizeable leak or something. Keep in mind your airspeed indicator is essentially a differential = pressure gauge, and if it's reading low, it could be due to low ram = pressure OR high static pressure. Now, on the ground, static pressure = is, well, pretty static. With your engine off and plane not moving, the = pressure inside your fuselage will pretty much equal the pressure = outside the fuselage, so even if your static line is leaking, a test = using pressure on the pitot tube (but relying on ambient pressure for = the static port) will not indicate any problems. Now, with the plane = moving, the pressure inside the fuselage and the pressure outside the = fuselage can vary somewhat. Normally, the airflow over the various = openings in the fuselage will cause the pressure inside the fuselage to = be less than that read at a correctly-positioned static port, leading to = higher than normal AS readings, and this is what had me stumped for a = while. The key here is that your plane is pressurized, and from what I = gather from reading other posts on this list, you L-IVP guys "puff up" = your planes at low altitudes. The pressurization system will cause the = pressure inside the fuselage to be higher than it would be externally, = leading to lower airspeed readings if the AS is getting it's static = input from inside the fuselage vice the external static port. Keep in mind I don't have a IV-P, probably never will, and am 10 years = into building an LNC2, so take this FWIW. Gary Fitzgerald LNC2 extra-slow build ~70% engine: TBD St. Charles, MO Subject: [LML] Airspeed Indicator Consult In true medical fashion, I would like to request of you all 2nd and = 3rd opinions about the cause of an Airspeed Indicator (AS) problem I = developed last week. So, we have here a situation in which the AS tested out fine on the = ground, and bad in the air. Any idea why? Doug Johnson ------=_NextPart_000_00C1_01C7FFEB.50C69EE0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Doug,
 
This may sound stupid, but did you = leave your=20 alternate air switch on?
 
Anyway, it sounds like the static = input to=20 your AS came loose, or has a sizeable leak or something.
 
Keep in mind your airspeed indicator is = essentially=20 a differential pressure gauge, and if it's reading low, it could be due = to low=20 ram pressure OR high static pressure.  Now, on the ground, = static=20 pressure is, well, pretty static.  With your engine off and plane = not=20 moving, the pressure inside your fuselage will pretty much equal the = pressure=20 outside the fuselage, so even if your static line is leaking, a test = using=20 pressure on the pitot tube (but relying on ambient pressure for the = static port)=20 will not indicate any problems.  Now, with the plane moving, the = pressure=20 inside the fuselage and the pressure outside the fuselage can vary=20 somewhat.  Normally, the airflow over the various openings in the = fuselage=20 will cause the pressure inside the fuselage to be less than that read at = a=20 correctly-positioned static port, leading to higher than normal AS=20 readings, and this is what had me stumped for a while.  The = key here=20 is that your plane is pressurized, and from what I gather from reading = other=20 posts on this list, you L-IVP guys "puff up" your planes at low = altitudes. =20 The pressurization system will cause the pressure inside the fuselage to = be=20 higher than it would be externally, leading to lower airspeed readings = if the AS=20 is getting it's static input from inside the fuselage vice the external = static=20 port.
 
Keep in mind I don't have a IV-P, = probably never=20 will, and am 10 years into building an LNC2, so take this=20 FWIW.
 
Gary Fitzgerald
LNC2 extra-slow = build=20 ~70%
engine: TBD
St. Charles, MO
 
Subject: [LML] Airspeed = Indicator=20 Consult

In = true medical=20 fashion, I would like to request of you all 2nd and 3rd opinions about = the=20 cause of an Airspeed Indicator (AS) problem I developed last=20 week.
 
 
So, = we have here a=20 situation in which the AS tested out fine on the ground, and bad in = the air.=20 Any idea why?
 
Doug=20 Johnson
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