X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 01 Feb 2010 19:18:49 -0500 Message-ID: X-Original-Return-Path: Received: from smtp-auth-05.mx.pitdc1.expedient.net ([206.210.66.138] verified) by logan.com (CommuniGate Pro SMTP 5.3.2) with ESMTPS id 4107350 for lml@lancaironline.net; Mon, 01 Feb 2010 17:49:35 -0500 Received-SPF: none receiver=logan.com; client-ip=206.210.66.138; envelope-from=rpastusek@htii.com Received: from HTBOB001 (static-72-66-86-7.washdc.fios.verizon.net [72.66.86.7]) by smtp-auth-05.mx.pitdc1.expedient.net (Postfix) with ESMTPSA id BE9DCE4586 for ; Mon, 1 Feb 2010 17:48:59 -0500 (EST) From: "Robert Pastusek" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: Re: Airspeed sensing switch: Pressurization (IV-P) X-Original-Date: Mon, 1 Feb 2010 17:48:59 -0500 X-Original-Message-ID: <069201caa390$be6293f0$3b27bbd0$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0693_01CAA366.D58C8BF0" X-Mailer: Microsoft Office Outlook 12.0 Thread-Index: AcqjXVEEDrr+lgo1QSm4j1lxn7MogQALyZig Content-Language: en-us This is a multi-part message in MIME format. ------=_NextPart_000_0693_01CAA366.D58C8BF0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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=94 shoulder harness attachment = hole that dumped into the baggage compartment (don=92t 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=85because 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=94 hole effectively kept the cabin from pressurizing=85 =20 I don=92t 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 =93bucket=94 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=92d not consider doing this with = another pressure source, and particularly not with the engine, nor in-flight=85 =20 On the =93failure condition=94 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=92 (overpressure on the ground=97but only at sea level) and a cabin = altitude above 10,000=92. I=92ve only seen it alarm during intentional tests, but = any discrepancy between the cabin altitude displayed on the MVP-50 and = what=92s 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=92t have a separate cabin altitude gauge=85the MVP = works well for this, AND can be alarmed.=20 =20 Bob, =20 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. =20 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 =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 =20 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 ------=_NextPart_000_0693_01CAA366.D58C8BF0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Re: [LML] Re: Airspeed sensing switch: Pressurization

Colyn,

 

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…

 

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? =A0I = 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…

 

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. =

 

Bob,

 

ok I get that.  

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.  

 

----- Original Message -----

Sent:<= /b> Saturday, = January 30, 2010 2:41 PM

Subject: [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?

 

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