X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 30 Jan 2010 14:41:20 -0500 Message-ID: X-Original-Return-Path: Received: from smtp-auth-01.mx.pitdc1.expedient.net ([206.210.66.134] verified) by logan.com (CommuniGate Pro SMTP 5.3.2) with ESMTPS id 4103655 for lml@lancaironline.net; Fri, 29 Jan 2010 13:28:38 -0500 Received-SPF: none receiver=logan.com; client-ip=206.210.66.134; envelope-from=rpastusek@htii.com Received: from HTBOB001 (static-72-66-86-7.washdc.fios.verizon.net [72.66.86.7]) by smtp-auth-01.mx.pitdc1.expedient.net (Postfix) with ESMTPSA id 9F65D847F6 for ; Fri, 29 Jan 2010 13:28:03 -0500 (EST) From: "Robert Pastusek" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: [LML] Re: Airspeed sensing switch: Pressurization X-Original-Date: Fri, 29 Jan 2010 13:28:01 -0500 X-Original-Message-ID: <036e01caa110$cb7d0fc0$62772f40$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_036F_01CAA0E6.E2A707C0" X-Mailer: Microsoft Office Outlook 12.0 Thread-Index: Acqg+DoQ+imQn4xlT36N+pzx9X1gTwAFY9cQ Content-Language: en-us This is a multi-part message in MIME format. ------=_NextPart_000_036F_01CAA0E6.E2A707C0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Colyn, =20 I=92ve 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=94 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 =93back-flow=94 the cabin air through 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 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=92t see any way for the cabin to be = pressurized after landing. Other comments? =20 Bob =20 =20 Paul pointed out the obvious: a door with even 1 psi behind it is dangerous. (1 psi times 600 or so? I don't have the measurements) =20 So I do buy the argument that at low throttle settings, and under normal circumstances, you aren't going to have much residual pressure in the = cabin. But there are lots of possible failure modes here: a) pressure = controller malfunction b) pressure controller set way below landing altitude c) = exhaust valve is not operating correctly - not enough cabin exchange rate. = These may argue for the pressure switch =20 The suggestion I like the best is "check cabin pressure before opening = the door". =20 =20 =20 ------=_NextPart_000_036F_01CAA0E6.E2A707C0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Re: [LML] Re: Airspeed sensing switch: Pressurization

Colyn,

 

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.=

 

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?

 

Bob

 

 

Paul pointed out the obvious:   a door with even 1 psi behind it is dangerous.  (1 psi times 600 or so?   I don't have the measurements)

 

So I do buy the argument that at low throttle settings, and under normal circumstances, you aren't going to have much residual pressure in the cabin.   But there are lots of possible failure modes = here:  a) pressure controller malfunction b) pressure controller set way below = landing altitude c) exhaust valve is not operating correctly - not enough cabin exchange rate.  These may argue for the pressure = switch

 

The suggestion I like the best is "check cabin pressure before opening = the door".

 

 

 

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