X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 02 Feb 2010 08:01:37 -0500 Message-ID: X-Original-Return-Path: Received: from elasmtp-dupuy.atl.sa.earthlink.net ([209.86.89.62] verified) by logan.com (CommuniGate Pro SMTP 5.3.2) with ESMTP id 4107996 for lml@lancaironline.net; Tue, 02 Feb 2010 07:34:31 -0500 Received-SPF: none receiver=logan.com; client-ip=209.86.89.62; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=RowXY13M8uOTP2x4OXhvZlI+0v3bsVAdz6QdQA8WlrwjM6eqDAqaaKtJcuSrX+Dt; h=Received:Message-ID:From:To:References:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE:X-ELNK-Trace:X-Originating-IP; Received: from [216.57.118.190] (helo=ccaselt3) by elasmtp-dupuy.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1NcHx5-0000bg-L1 for lml@lancaironline.net; Tue, 02 Feb 2010 07:33:55 -0500 X-Original-Message-ID: <409E19E497FA4E48814F92EC64E4EAE2@nvidia.com> From: "Colyn Case at earthlink" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: Airspeed sensing switch: Pressurization (IV-P) X-Original-Date: Tue, 2 Feb 2010 07:33:54 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0086_01CAA3DA.12E620B0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5843 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da94077f4303eb10e15240aad57d0cc1d457e350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 216.57.118.190 This is a multi-part message in MIME format. ------=_NextPart_000_0086_01CAA3DA.12E620B0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Re: [LML] Re: Airspeed sensing switch: PressurizationOf course I wasn't = suggesting manually blocking the outflow valve. I'm saying you should = consider all failure modes in the analysis. Based on the evidence presented so far, I think I'm convinced that you = can't get the plane stopped and have pressure left in the cabin, even if = the outflow valve were blocked. Based on the evidence presented so far, I'm not convinced it's = impossible to land and have a little differential, given all failure = modes. anyway, thanks for the info. that's interesting about the mvp-50 = pressure sensor. ----- Original Message -----=20 From: Robert Pastusek=20 To: lml@lancaironline.net=20 Sent: Monday, February 01, 2010 7:18 PM Subject: [LML] Re: Airspeed sensing switch: Pressurization (IV-P) Colyn, =20 Yes, to pressurize the cockpit, upper deck pressure must exceed = ambient. I THINK (but have not verified) that the pressurization = controller will close completely to achieve the commanded cabin = altitude. If anyone knows about this, please advise. I know there are = some small leaks in my cabin that provide some air exchange, but they = are not very large. I say this because I had a piece of masking tape = over a =BC" shoulder harness attachment hole that dumped into the = baggage compartment (don't ask!). The tape blew through the hole one = day, and in addition to the whistle (Judy said SHRIEK), the cabin = differential pressure dropped to less than 1 PSI.because of the leak. = Power was at low cruise (60% or so) so I might have done better with = more power, but I was surprised that a =BC" hole effectively kept the = cabin from pressurizing. =20 I don't know about the results of plugging the outflow valve, but it = may be academic? At least theoretically, a pressure differential can be = generated from any ambient (outside) pressure, but not sure how, or why = one would try plugging the Dukes controler outlet to do this? I = actually covered and sealed the whole pressure "bucket" in the rear seat = when I was looking for leaks, but my input was from the vacuum cleaner. = As this effectively blocks the emergency dump valve as well, I'd not = consider doing this with another pressure source, and particularly not = with the engine, nor in-flight. =20 On the "failure condition" you ask about: I have a cabin pressure = sensor hooked to my MVP-50 engine monitoring system. It shows cabin = altitude in feet, and is alarmed to annunciate a cabin altitude below = -500' (overpressure on the ground-but only at sea level) and a cabin = altitude above 10,000'. I've only seen it alarm during intentional = tests, but any discrepancy between the cabin altitude displayed on the = MVP-50 and what's set on the Dukes controller would indicate a = failure/problem, noting that this will occur when the differential gets = to 5.5 and the aircraft continues to climb. BTW, I don't have a separate = cabin altitude gauge.the MVP works well for this, AND can be alarmed.=20 =20 ------=_NextPart_000_0086_01CAA3DA.12E620B0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Re: [LML] Re: Airspeed sensing switch: = Pressurization
Of course I wasn't suggesting manually = blocking the=20 outflow valve.  I'm saying you should consider all failure modes in = the=20 analysis.
Based on the evidence presented so far, = I think I'm=20 convinced that you can't get the plane stopped and have pressure left in = the=20 cabin, even if the outflow valve were blocked.
Based on the evidence presented so far, = I'm not=20 convinced it's impossible to land and have a little differential, given = all=20 failure modes.
 
anyway, thanks for the = info.   that's=20 interesting about the mvp-50 pressure sensor.
----- Original Message -----
From:=20 Robert=20 Pastusek
Sent: Monday, February 01, 2010 = 7:18=20 PM
Subject: [LML] Re: Airspeed = sensing=20 switch: Pressurization (IV-P)

Colyn,

 

Yes,=20 to pressurize the cockpit, upper deck pressure must exceed ambient. I = THINK=20 (but have not verified) that the pressurization controller will close=20 completely to achieve the commanded cabin altitude. If anyone knows = about=20 this, please advise. I know there are some small leaks in my cabin = that=20 provide some air exchange, but they are not very large. I say this = because I=20 had a piece of masking tape over a =BC=94 shoulder harness attachment = hole that=20 dumped into the baggage compartment (don=92t ask!). The tape blew = through the=20 hole one day, and in addition to the whistle (Judy said SHRIEK), the = cabin=20 differential pressure dropped to less than 1 PSI=85because of the = leak. Power=20 was at low cruise (60% or so) so I might have done better with more = power, but=20 I was surprised that a =BC=94 hole effectively kept the cabin from=20 pressurizing=85

 

I=20 don=92t know about the results of plugging the outflow valve, but it = may be=20 academic? At least theoretically, a pressure differential can be = generated=20 from any ambient (outside) pressure, but not sure how, or why one = would try=20 plugging the Dukes controler outlet to do this?  I actually = covered and=20 sealed the whole pressure =93bucket=94 in the rear seat when I was = looking for=20 leaks, but my input was from the vacuum cleaner. As this effectively = blocks=20 the emergency dump valve as well, I=92d not consider doing this with = another=20 pressure source, and particularly not with the engine, nor=20 in-flight=85

 

On=20 the =93failure condition=94 you ask about: I have a cabin pressure = sensor hooked=20 to my MVP-50 engine monitoring system. It shows cabin altitude in = feet, and is=20 alarmed to annunciate a cabin altitude below -500=92 (overpressure on = the=20 ground=97but only at sea level) and a cabin altitude above 10,000=92. = I=92ve only=20 seen it alarm during intentional tests, but any discrepancy between = the cabin=20 altitude displayed on the MVP-50 and what=92s set on the Dukes = controller would=20 indicate a failure/problem, noting that this will occur when the = differential=20 gets to 5.5 and the aircraft continues to climb. BTW, I don=92t have a = separate=20 cabin altitude gauge=85the MVP works well for this, AND can be = alarmed.=20

 

 
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