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Old 08-22-2010, 04:49 PM
gblwy's Avatar
gblwy gblwy is offline
Join Date: Jun 2007
Location: Perth, Scotland
Posts: 484
Default PAP - ASI and Altimeter

Sorry to be a pain, but I'd appreciate advice on the test for leakage of air to these devices (EFIS and my steam gauges)

Pumping up my ASI to 130 knots leads to a rapid leakage (5 seconds from 120 to 110 knots) until the pressure has reduced to an indication of 100 knots or so at which point the leakage becomes slow, probably an exponential improvement.

Similarly, sucking out air from one static port (with the other blocked) leads to rapid leakage from 1100 to 900 feet, then dramatic improvement in the leakage rate.

Is this normal? Or should I expect essentially no leakage at any pressure?

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Old 08-22-2010, 06:55 PM
Mich48041 Mich48041 is offline
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 2,578
Default Should not be much leakage

There should not be much leakage. It is expected that a higher pressure differential will cause a higher leakage. But exponential improvement sounds suspicious. Chances are that your test apparatus is leaking. Regardless, the bottom line is that the pitot and static systems must pass the test as outlined in the PAP. The Dynon should warm up for a few minutes before the test because it seems a little unstable when first turned on.
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Old 09-02-2010, 04:26 PM
dick seiders dick seiders is offline
Join Date: Jan 2006
Posts: 875

Both leaked on mine until some rework. The pitot now holds pressure indefinitely at any speed up to 130. By indefinite I mean no loss in airspeed for over 5 min then stopped testing at 130 level Other speeds all held at least 2 mins. then stopped testing. Static leaks like a sieve (sp?) someplace behind the baggage bulkhead, but am not yet ready to pull the tank to make that repair.
Point I am making is the systems can be made to hold w/i the PAP limits.
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Old 09-02-2010, 05:09 PM
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Walt Walt is offline
Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 4,547

Typical "acceptable" leak rate for AS is 2 kts per minute at max speed but no FAR rules on limits.

Static system leak rate is 100 ft/min @ 1000 ft agl.
Walt Aronow, Dallas, TX (52F) RV7A, IO360, C/S, 1500+hrs

EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
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Old 09-02-2010, 07:24 PM
elippse elippse is offline
Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938

We had a static leak on my friend's plane that gave 100 fpm on the VSI after it had been zeroed before takeoff. 'Turns out there was a crack in the VSI case!
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Old 10-01-2010, 05:45 PM
RFSchaller RFSchaller is offline
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,183
Default Try this

I posted this to the syring question: You can take a 3' piece of 1/4" clear plastic hose and fill it 1/3 with water. slip one end on the pitot or static port and raise or lower the free end to get a vacuum or slight pressure.
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