X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 31 Jan 2010 08:09:25 -0500 Message-ID: X-Original-Return-Path: Received: from smtp-auth-04.mx.pitdc1.expedient.net ([206.210.66.137] verified) by logan.com (CommuniGate Pro SMTP 5.3.2) with ESMTPS id 4105179 for lml@lancaironline.net; Sat, 30 Jan 2010 18:06:37 -0500 Received-SPF: none receiver=logan.com; client-ip=206.210.66.137; envelope-from=rpastusek@htii.com Received: from HTBOB001 (static-72-66-86-7.washdc.fios.verizon.net [72.66.86.7]) by smtp-auth-04.mx.pitdc1.expedient.net (Postfix) with ESMTPSA id 0C92DE4604 for ; Sat, 30 Jan 2010 18:06:03 -0500 (EST) From: "Robert Pastusek" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: Pressurization X-Original-Date: Sat, 30 Jan 2010 18:06:02 -0500 X-Original-Message-ID: <04a201caa200$cb80dc40$628294c0$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_04A3_01CAA1D6.E2AAD440" X-Mailer: Microsoft Office Outlook 12.0 Thread-Index: Acqh5FJefaFoAB5vRXWPaLhpAr3qqwAGAyuQ Content-Language: en-us This is a multi-part message in MIME format. ------=_NextPart_000_04A3_01CAA1D6.E2AAD440 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Craig, I tested my ability to open the door of my IV-P with the seal inflated, just to see if I could do it in an emergency (yes-definitely), but it risks blowing out the seal, so I wouldn't recommend doing it, at least on a regular basis. As you would expect, the door is difficult to open, as you're working the latches against the pressure seal.hard on the latches and other equipment as well. You may have noticed that a large amount of air passes the door seal when it's not inflated. I actually leave it un-inflated for drawing cooling air from the tail NACA duct through the cabin when I'm not running the air conditioner. Therefore, it's not possible to achieve any pressure differential within the cabin with the seal deflated. One issue I have is operating at low altitude (e.g the pattern) with the seal inflated and the engine at low power. The air collected at the NACA inlet on the vertical stab pushes the cabin flapper valve open (as designed) and temporarily pressurizes the cabin a small amount. It then closes and the pressure dissipates, allowing it to open again. The result is a surging that's uncomfortable on your ears. There are a couple of ways to prevent this in my airplane, but it's a bother nonetheless. My best solution so far is to turn on the air conditioner, which diverts the tail scoop air away from the cabin and across the a/c condenser coil and then out the back. (Note that my a/c installation/configuration is a personal design, probably unique in the fleet, so this won't work for others. Bob Do you guys have much luck opening the door before you deflate the door seal? I tried to pressurize the cabin with the door seal deflated...didn't have much success with 32 InHg manifold pressure. I suspect with the engine at idle, it wouldn't be much better. Craig Berland IV-P N7VG 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". ------=_NextPart_000_04A3_01CAA1D6.E2AAD440 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Re: [LML] Re: Airspeed sensing switch: Pressurization

Craig,<= /o:p>

 <= /o:p>

I tested my ability to open the door of my IV-P with the seal inflated, = just to see if I could do it in an emergency (yes-definitely), but it risks = blowing out the seal, so I wouldn’t recommend doing it, at least on a regular = basis. As you would expect, the door is difficult to open, as you’re = working the latches against the pressure seal…hard on the latches and other = equipment as well.

 <= /o:p>

You may have noticed that a large amount of air passes the door seal when it’s not inflated. I actually leave it un-inflated for drawing = cooling air from the tail NACA duct through the cabin when I’m not running = the air conditioner. Therefore, it’s not possible to achieve any = pressure differential within the cabin with the seal deflated. =

 <= /o:p>

One issue I have is operating at low altitude (e.g the pattern) with the = seal inflated and the engine at low power. The air collected at the NACA = inlet on the vertical stab pushes the cabin flapper valve open (as designed) and temporarily pressurizes the cabin a small amount. It then closes and the pressure dissipates, allowing it to open again. The result is a surging that’s uncomfortable on your ears. There are a couple of ways to = prevent this in my airplane, but it’s a bother nonetheless. My best = solution so far is to turn on the air conditioner, which diverts the tail scoop air = away from the cabin and across the a/c condenser coil and then out the = back.  (Note that my a/c installation/configuration is a personal design, = probably unique in the fleet, so this won’t work for = others.

 <= /o:p>

Bob

 

Do you guys have much luck opening the door before you = deflate the door seal?  I tried to pressurize the cabin with the door seal deflated…..didn’t have much success with 32 InHg manifold pressure.  I suspect with the engine at idle, it wouldn’t be = much better.

 

Craig Berland

IV-P    N7VG

 

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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