Sender: <marvkaye@lancaironline.net> (Marvin Kaye)
To: lml
Date: Sat, 20 Apr 2002 15:33:35 -0400
Message-ID: <redirect-1171857@logan.com>
From: Brent Regan <Brent@regandesigns.com>
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Subject: Re: pressurization IV-P
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When I pressure tested my IV-P prior to first flight I used my 10Hp shop 
compressor which has a 200 gallon tank. The outflow valve was plugged as 
were all the other ports into the cabin except a 1/2 " port for 
connecting the compressor, a 1/4" port for a pressure gage and the door 
seal pressurization line. I connected the airplane to the compressor 
with a 3/8" commercial air hose.

The procedure was to close the door, pressurize the door seal and then 
connect the air line. One person monitors the cabin pressure with an 
ACCURATE low pressure gage (0-10 or 0-15 PSI) while others scramble 
around identifying leaks. IT IS ESSENTIAL that the gage line is NOT 
"T"ed into the supply line. Use a separate pressure penetration. A big 
tank on the air compressor is helpful as it gives you more time to find 
the leaks. Venting the door seal will quickly depressurize the cabin 
(and clean half the hanger).

Have fresh underwear on hand as the airframe will make some startling 
noises when it is first pressurized. It will also change shape as it 
tries to turn into a sphere. 5 PSI is about what is in a basketball, you 
get the picture.

After about a day of work I was able to get the cabin up to 7.5 PSI for 
about a minute before the air compressor tank ran low. Lancair 
recommends 6.5 PSI but I decided that a test to 1.5 times rated was 
required for my personal comfort. I also know of 4 builders who have had 
structural failures of the aft pressure bulkhead during testing. Better 
in the hanger than in flight.

It is important to have a well sealed cabin in order for the outflow 
valve to function properly. If the cabin has a lot of leaks then the 
outflow valve is almost or completely closed in high altitude flight and 
it has little control over the cabin pressure and your ears will suffer. 
If the cabin is well sealed the outflow valve has good authority over 
the cabin pressure and can make smooth, comfortable changes as required.

Under no circumstances should you operate your airplane at a cabin 
pressure higher than it was tested at on the ground. If you don't have a 
big enough compressor then rent one. There is absolutely no reason to 
risk life and limb in a flight test when the same test can be conducted 
on the ground for a modest investment in time and money. This is true 
for all the systems on your airplane.

Regards
Brent Regan