The Murphy Builders Site

No, I'm just testing starting with the tubing next to the pitot tube... not
the pitot tube itself. My problem is somewhere in the connections down the
line. I try Dick's divide and conquer suggestion. Thanks.



On Fri, Dec 26, 2008 at 4:39 PM, Wayne G. O'Shea <oifa@irishfield.on.ca>wrote:

Dick beat me to it..... heated pitots have a drain hole in them. Is that
your air leak??

Dick beat me to it..... heated pitots have a drain hole in them. Is that
your air leak??

Yes Ron, your leakage appears to be excessive. A good tight system
should hold for minuets not seconds.

Having done a lot of IFR Certs in the past, I developed my own methods
for troubleshooting. The simplest way using your method is to "divide
and conquer". That is to say find the easiest access to a connection in
the middle of the system and test to find which half of the system is
leaking and prove that the other part is not. Then go to a connection
about one forth of the way and continue to isolate the system this way
until you pinpoint the problem. It may be necessary to use another air
speed indicator as a test instrument.

One other thing some pitot heads have a tiny bleed port near the aft
end. I use zinc chromate paste (putty) to cover over those types of
areas to help isolate the source. I also use putty around a tube and
squish it onto a static port to make a sealed attachment to the port for
leak tests, just don't get the stuff into the little hole.

I hope this helps.

Dick Wampach SR-108

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
Ron Shannon
Sent: Friday, December 26, 2008 3:52 PM
To: rebel-builders@dcsol.com
Subject: [rebel-builders] pitot test

I'm on my second pitot test, using a piece of rolled up surgical tubing
to
generate pressure on the end of the pitot tubing at the top of the left
strut, then clamping the surgical tubing with a cleco edge clamp.
Starting
with IAS at about 70 kts., I have an indicated "leak" showing IAS
degrading
at a rate of about 1/2 kt./sec. I can't detect any leaks with soap
bubbles
-- on those joints I can see/get to with everything hooked up --
including
no leaks on either end of the surgical tubing. Unfortunately, even
although
I've carefully tightened everything up as best I can, the behind-panel
space
is so full I can't see all the joints simultaneously when all
instruments
are hooked up. To test all joints, I'd have to pull the EFIS's and plug
those lines, etc., which I'm reluctant to do unless I have to because I
wouldn't be testing all joints simultaneously, not to mention it's a
PITA!
:-)

EAA has an article suggesting the pitot line should be tight enough to
hold
airspeed for a minute. Is that standard appropriate? How tight should
this
really be?

Ron
http://n254mr.com




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