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John,
The leak check for unpressurized aircraft involves pulling a vacuum equivalent to 1,000 ft above ground and watching the altimeter for one minute for any loss in altitude. (Pressurized aircraft are a bit different as the values are tied to maximum pressure differential. see FAR 21.1325). If the loss is less than 100 ft, you're good. This test is easy for the owner/builder to perform because one only needs to pull a vacuum on the static side of the system.
During the real pitot-static test, it becomes necessary to also control the pressure to the pitot side to avoid getting too large of a differential. For that you'll need the real equipment used for certification. If you were to pull a vacuum to 10,000' without controlling the pitot side, the differential pressure could damage things - the ASI for one, as it would be pegged.
Chris Zavatson
N91CZ
360std
From: John Barrett <jbarrett@carbinge.com>
To: lml@lancaironline.net
Sent: Wednesday, January 11, 2012 7:13 AM
Subject: [LML] Re: Pitot static checks
Chris,
I actually have one of these pumps already. Is it safe to use on instruments? How do you know max vacuum to apply? Do you simply read it on the aircraft altimeter while you’re doing the test? Can I assume that if I don’t go over 10,000 feet, say, that will be sufficient and at the same time not destructive? How to keep from damage when I take the altimeter out of the system?
I have Tru Trak autopilot, Cheltons and steam gauge backups.
Thanks,
John
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Chris Zavatson
Sent: Wednesday, January 11, 2012 3:16 AM
To: lml@lancaironline.net
Subject: [LML] Re: Pitot static checks
I use a MightyVac hand help vacuum pump to check for leaks. It is inexpensive and available at auto parts stores.
-very useful to have around after breaking into lines and especially to verify system integrity before getting an official check done.
From: John Barrett <jbarrett@carbinge.com>
To: lml@lancaironline.net
Sent: Tuesday, January 10, 2012 9:55 AM
Subject: [LML] Pitot static checks
I am having trouble with leaking Pitot system on my IVP. Attempts to perform IFR cert for first flight indicate that leaks in the standby altimeter and airspeed indicator are producing 750 fpm leaks -- not acceptable.
Have attempted to repair these with clear fingernail polish as advised by Fred Moreno (thanks Fred) and this improved the situation from about 3-4,000 fpm to the existing 750 fpm. Only trouble is I was not present when the test was done this morning and to date my only recourse for testing is to have the folks from Lancair avionics do a test and tell me the results. I do not know now if the problem is isolated in these two instruments or could be elsewhere because I don’t know if the techs from Lancair made any attempts to insure the current leak was in the instruments noted; only that they isolated them previously and felt this was where the leaks were.
To round out my dilemma, I live on the Washington State Olympic Peninsula and the airplane is in Redmond across the field from the old Lancair factory. I have a 130 knot Beech Sierra I use to commute and with the winter weather and my work schedule it’s unpredictable when I can get to Redmond.
My question is does anyone have a testing system for checking out the pitot static system and tracking down leaks so that I can repair them and only invite Gary Lane back from Lancair avionics when I know the system to be leak free? If there is a simple design that allows one to assemble such a device that would be good. If someone has one made up and would loan or rent it to me that would also be good. If I had something like this I could narrow down the source or sources of leaks and fix them systematically.
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