X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 01 Feb 2010 11:40:19 -0500 Message-ID: X-Original-Return-Path: Received: from elasmtp-mealy.atl.sa.earthlink.net ([209.86.89.69] verified) by logan.com (CommuniGate Pro SMTP 5.3.2) with ESMTP id 4106714 for lml@lancaironline.net; Mon, 01 Feb 2010 09:56:29 -0500 Received-SPF: none receiver=logan.com; client-ip=209.86.89.69; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=WEVF8AiKvgnusHRLVrfgEsc1YA2/KVQM5iNSTgGRkMNEZhxzoxS1gSTI+r4Xg2R4; 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-mealy.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1Nbxgu-0001MD-Ml for lml@lancaironline.net; Mon, 01 Feb 2010 09:55:53 -0500 X-Original-Message-ID: From: "Colyn Case at earthlink" X-Original-To: References: Subject: Re: [LML] Re: Airspeed sensing switch: Pressurization X-Original-Date: Mon, 1 Feb 2010 09:55:54 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0171_01CAA324.BE8F1A40" 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: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da9406fc91e0afeda5034d513ff125297db46350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 216.57.118.190 This is a multi-part message in MIME format. ------=_NextPart_000_0171_01CAA324.BE8F1A40 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Re: [LML] Re: Airspeed sensing switch: PressurizationBob, ok I get that. =20 I'm trying to understand abnormal operation in a little more detail. So I think concerning normal operation. two things are true: 1) upper deck pressure must exceed ambient 2) there's enough volume per second to overcome the leaks and valve = exhaust in the cabin. You say you can't make any cabin pressure below 24" @16000 My guess is the cabin pressure exhaust valve never closes in normal = operatoin because it has to meet the requirement total air exchange = every n seconds ( I forget the constant). Now if you plug that thing, = you would get pressure at some lower map, right? I wonder what that = is? I also wonder how you would typically notice that failure condition. =20 ----- Original Message -----=20 From: Robert Pastusek=20 To: lml@lancaironline.net=20 Sent: Saturday, January 30, 2010 2:41 PM Subject: [LML] Re: Airspeed sensing switch: Pressurization Colyn, =20 I've not commented on this before, but for the Lancair IV-P using the = TSIO-550/turbo to pressurize the cabin (and this may not apply to other = configurations), it is not possible to maintain cabin pressure when the = engine is not producing power, or is off. The cabin is connected to the = engine intake system by a 1 =BD" duct/controller that can only be turned = off by dumping it to the ambient atmosphere. The result is that the = cabin very quickly goes to engine intake or ambient pressure when power = is reduced sufficiently to spool down the turbos. You can test this for = yourself by pulling power to idle when pressurized and timing how long = it takes to "back-flow" the cabin air through the intake system.there is = not a one-way valve in this system. In my experience, the time required = to reach ambient outside pressure is a few seconds; certainly less than = a minute at the max pressure differential of 5.5 PSI. =20 Again, other aircraft/setups may work differently, but for the IV-P = with a TSIO-550 built to plans, I can't see any way for the cabin to be = pressurized after landing. Other comments? =20 ------=_NextPart_000_0171_01CAA324.BE8F1A40 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Re: = [LML] Re: Airspeed sensing switch: Pressurization
Bob,
 
ok I get that.   =
I'm trying to understand abnormal = operation in a=20 little more detail.
So I think concerning normal operation. = two things=20 are true:
1) upper deck pressure must exceed=20 ambient
2) there's enough volume per second to = overcome the=20 leaks and valve exhaust in the cabin.
 
You say you can't make any cabin = pressure below 24"=20 @16000
My guess is the cabin = pressure exhaust=20 valve never closes in normal operatoin because it has to meet the = requirement=20 total air exchange every n seconds ( I forget the = constant).   =20 Now if you plug that thing, you would get pressure at some lower map,=20 right?    I wonder what that is?
I also wonder how you would typically = notice that=20 failure condition.  
 
----- Original Message -----
From:=20 Robert=20 Pastusek
Sent: Saturday, January 30, = 2010 2:41=20 PM
Subject: [LML] Re: Airspeed = sensing=20 switch: Pressurization

Colyn,

 

I=92ve=20 not commented on this before, but for the Lancair IV-P using the=20 TSIO-550/turbo to pressurize the cabin (and this may not apply to = other=20 configurations), it is not possible to maintain cabin pressure when = the engine=20 is not producing power, or is off. The cabin is connected to the = engine intake=20 system by a 1 =BD=94 duct/controller that can only be turned off by = dumping it to=20 the ambient atmosphere. The result is that the cabin very quickly goes = to=20 engine intake or ambient pressure when power is reduced sufficiently = to spool=20 down the turbos. You can test this for yourself by pulling power to = idle when=20 pressurized and timing how long it takes to =93back-flow=94 the cabin = air through=20 the intake system=85there is not a one-way valve in this system. In my = experience, the time required to reach ambient outside pressure is a = few=20 seconds; certainly less than a minute at the max pressure differential = of 5.5=20 PSI.

 

Again,=20 other aircraft/setups may work differently, but for the IV-P with a = TSIO-550=20 built to plans, I can=92t see any way for the cabin to be pressurized = after=20 landing. Other comments?

 

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