X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 08 Sep 2011 02:10:27 -0400 Message-ID: X-Original-Return-Path: Received: from elasmtp-banded.atl.sa.earthlink.net ([209.86.89.70] verified) by logan.com (CommuniGate Pro SMTP 5.4.1) with ESMTP id 5117025 for lml@lancaironline.net; Wed, 07 Sep 2011 21:15:24 -0400 Received-SPF: none receiver=logan.com; client-ip=209.86.89.70; envelope-from=liegner@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=SQ1x+Ajb0dWMyBtUhP9YnspQyy5bxxJHtTuFQ1wrwyAclhk+EiZmAtF8lZlk2rb1; h=Message-ID:Date:From:Reply-To:To:Subject:Mime-Version:Content-Transfer-Encoding:X-Mailer:Content-Type:X-ELNK-Trace:X-Originating-IP; Received: from [209.86.224.38] (helo=elwamui-lapwing.atl.sa.earthlink.net) by elasmtp-banded.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1R1TCX-0006BQ-Po for lml@lancaironline.net; Wed, 07 Sep 2011 21:14:46 -0400 Received: from 71.53.5.73 by webmail.earthlink.net with HTTP; Wed, 7 Sep 2011 21:14:45 -0400 X-Original-Message-ID: <4621787.1315444485717.JavaMail.root@elwamui-lapwing.atl.sa.earthlink.net> X-Original-Date: Wed, 7 Sep 2011 21:14:45 -0400 (GMT-04:00) From: liegner@earthlink.net Reply-To: liegner@earthlink.net X-Original-To: lml@lancaironline.net Subject: Re: Figuring out the pressurization system IV-P -- couple of questions Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Mailer: EarthLink Zoo Mail 1.0 Content-Type: text/html; charset=UTF-8 X-ELNK-Trace: edc6c9c2805b57e3d780f4a490ca6956d5d4673fe7faad86c5d11efdffd41f12e3a5d29b716c061c350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 209.86.224.38 Re: Figuring out the pressurization system IV-P -- couple
From: "Jeffrey Liegner, MD"
Sent: Sep 7, 2011 10:54 AM
To: lml@lancaironline.net
Cc: Dico Reijers
Subject: Re: Figuring out the pressurization system IV-P -- couple of questions

A couple answers from my experience (we all have slightly different styles):

The altitude adjustment knob has both cabin altitude and outside (ambient) altitude on the clear dial (inner and outer ring, adjacent to each other, incremental) with a 5.5psi difference in the markings.  Setting the dial to field elevation (outer numbers) is equivalent to a certain ambient altitude (inner numbers) when 5.5psi difference is obtained (ex, FL230 outside ambient, 8000' inside cabin).

Being mostly on the east coast (local field 370' MSL), I set my dial to ~500 ft above my field elevation and never touch it again.  Even if I land at an elevation much higher (example, Smokey Mountains or Rocky Mountains or Cascade Mountains), and even if I hop there with a fuel stop in between, the gauge is not adjusted.  Once you are on final at your higher elevation airport and power has been reduced to something less than 15", the cabin will not maintain any pressure differential with the outside, so the setting on the gauge is no longer controlling (Duke's is fully closed).  Essential, any turbo PSI previously given to the cabin will vent via porous outlets and even back flow into the engine's upper deck when MAP is reduced below a fairly high threshold.

When taking off from a high altitude airport, but the gauge is still on the lower field elevation setting (missed that check list item), the turbo air will pressurize the cabin and the Duke's valve will try to pressurize the cabin to the knob setting, giving you some ear pressurization during your high power take off roll, and your cabin altimeter will descend.  The spouse will not be happy.

The cabin dump switch is (in my opinion) not worth having on the panel; if you have smoke in the cabin, the smoke and heat (and CO) will vent past your nose/face as it moves towards the rear seat.  One only needs to hit the door seal switch, deflating the seal, to effectively vent everything out laterally before it reaches you, probably also improving your visibility by keeping the ventilation low and out of your field of view.  The air driven switch on the door is an excellent example of non-electrically dependent control of a critical system (I worry when some want an electric toggle, not the pneumatic switch).

And the auto-dump squat switch off the gear down position is also not sensible, a point of pressurization failure due to squat malfunction that adds nothing to the functionality of the system, since this cabin is never pressurized above ambient prior to gear down in the pattern.

The rate knob is the smaller unlabled (white dot only) knurled knob adjacent to the larger pressure dial.  Rotated fully counter-clockwise is slowest cabin rate, and rotated fully clockwise is the fastest cabin rate change setting.






Hi Pete,

Thanks for your detailed email. I have a couple questions...

1) which is the rate knob? The only knob with any description on it is the one where I set the altitude. There is another knob beside it, however it doesn't have a label on it (see attached photo).

2) If I am FL200 and my destination airport is still 150nm away... at what point would I turn the pressurization to the field elevation? As soon as I start my decent?

Thanks,

-dr

lml@lancaironline.net
On Tue, Sep 6, 2011 at 1:21 PM, pete@leapfrogventures.com <pete@leapfrogventures.com> wrote:
The rate knob sets how fast the cabin pressure will change after moving the dial. If you are in test mode, turn the rate fully clockwise so the rate will change more noticeably.
The dukes should be set such that it pressurizes the cabin to about 700 feet above the field elevation on the dial, until it reaches 5.5 psi, at which point the cabin altitude will rise in lock step with increasing airplane altitude.
I fly out of a sea level airport. I typically put the dial at 3000 feet airport elevation. This gives me a 3700 foot minimum cabin pressure. I do this so that, when on a precision approach, which typically start at about 3000 feet, my pulling the power to capture glideslope will not pop the ears of the plane occupants due to a loss of residual pressurization. If I am flying to a high altitude airport, about half way through the flight I will reset the dial to the destination altitude plus 3000 feet. If I know for sure I am not going to be doing a precision approach and can descend to pattern altitude with at least 50% power, then I will only add 1000 feet.

I set the rate knob at the 500 feet/minute rate and leave it there unless I am doing testing. You can determine the proper position on your unit during testing by changing the dial and timing how long it takes to change the cabin altitude 500 feet, then loosening and repositioning the know so that, in the 500 foot position, the work RATE is lined up horizontally.
If I am cruising in the flight levels where 5.5 psi will not maintain a 3700 foot cabin, I will set the dial at 2000 feet BELOW the flight level I will be cruising at. This setting gives me a 5.5 psi cabin every time.
I always do my descents at 65-70% power so as to have enough boost to maintain the 5.5 psi differential.
Note these comments assume the brass plunger on the dukes has been adjusted to the correct maximum pressure differential (mine is set to about 5.6-5.8 psi - this can be done while flying high - note it is very sensitive) and your dial and pressure head are properly matched (you can correct this yourself, but it takes a few flights as it can only be changed on the ground), as the connection between the two is not based on actual values but rather pre-set positions.
Pete



--
Regards,

Dico Reijers

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