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<< Lancair Builders' Mail List >>
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Brent, I always appreciate your posts and insights into tough problems.
How did you couple the hose on your compressor to the air mixer box on your
ground testing? One thing to think about is that 7.5psi in the cabin on
the ground is a much smaller pressure differential than flying with a
5psi cabin pressure with an outside density altitude of 29,000'. You
would probably have to pump the cabin pressure up higher than 7.5psi to
really simulate flying in the flight levels. John Wright iv-p Colorado
Springs
-----Original Message-----
From: Brent Regan <brent@regandesigns.com>
To: Lancair List <lancair.list@olsusa.com>
Date: Thursday, April 27, 2000 10:15 AM
Subject: Re: LNC IV-P window blow-out
I have a little advice for IV-P builders/owners out there regarding the
cabin door window. My comments are based on my personal experience and
snip<<<<<
Are you freaking nuts?
FAR 23.1428 calls for proof pressure testing to 1.5 times the normal
operating pressure. This is not a requirement for the builder but I think
it
is a good idea. Perform the pressure test prior to painting the a
Regards
>Brent Regan
John W. comments that "7.5 psi might be more at the flight levels". 7.5 psi is 7.5 psi is 7.5 psi at whatever level.
Having just looked at a number of pressurized planes, I have listed the specifications on two of them below.
A twin Cessna 340 has a 4.2 psi cabin differential. This gives a sea level cabin up to 9,000 ft and an 8,000 ft cabin at 20,000 ft. The cabin altitude is 10,000 ft at 23,000 ft pressure altitude. Although the relationship is not linear you can functionally extrapolate from there. The cabin pressure never goes above 4.2 psi. The 4.2 psi is regulated by the "cabin pressure regulating valve". If cabin pressure ever gets to 4.5 psi, a "cabin pressure dump valve" opens.
A Beech Duke has a 4.7 psi cabin differential. This gives a 10,000 ft cabin at 24,000 ft altitude.
In my searching, I never found a piston driven aircraft pressurized higher than the duke, although I am sure that some piston driven aircraft must have hit the 5 psi mark.
5 psi for the IV-P sounds pretty good when compared to conventional aircraft.
Lorn H. Olsen, President -
lorn@mich.com
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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