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  #1  
Old 03-03-2021, 12:33 PM
JCSmith's Avatar
JCSmith JCSmith is offline
 
Join Date: Apr 2013
Location: Kenosha, WI
Posts: 42
Default Static leak question

After leak testing my static system, I find a loss of 400 ft in one minute. Ok, Ive been searching for the leak. I just read a good article by Vic Syracuse, and I thought I was on board right up till the end where he described an aircraft autopilot causing a climb when the heater vent was opened. What Vic described makes good sense, but in my case, when I open my fresh air vents with the autopilot on alt hold, it creates a dive instead of a climb. This sounds backwards.
Could this indicate a leak somewhere else in the system? Driving me crazy!
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  #2  
Old 03-03-2021, 01:57 PM
Norman CYYJ Norman CYYJ is offline
 
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You definitely have a leak in your system.
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  #3  
Old 03-03-2021, 02:03 PM
FinnFlyer FinnFlyer is offline
 
Join Date: Aug 2018
Location: Bell, FL
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When I finally found the static leak in my RV-3B it was the plastic multi-size Tee back in the fuselage the builder had used to connect the two static ports to the line running forward.

(By multi-size I mean that each of the legs has progressively bigger barbs as you move away from the ends.)

Can't trust those Tees

Finn
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  #4  
Old 03-03-2021, 03:03 PM
vic syracuse vic syracuse is offline
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So you mentioned the heater vent. Try it with the fresh air vents. That's when a leak for sure will show a decrease on the altimeter.

But with the 400' leak you mentioned, you do have a leak. The easiest way is to split the aircraft in 2, from front to back if you have static lines running up front. Tape off the static ports, and perhaps on the pitot tube IF you have a static port there.

Hate to ask this, but I'm assuming the autopilot is working correctly? I have flown a couple of airplanes that had the servos reversed.

Vic
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  #5  
Old 03-03-2021, 03:15 PM
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JCSmith JCSmith is offline
 
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Thanks Vic, Ill try splitting it in half and checking it that way. Yes, the autopilot has always worked fine. Great article by the way!
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  #6  
Old 03-10-2021, 08:48 PM
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avrojockey avrojockey is offline
 
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I got a Harbor Freight hand pump with all the various fitting sizes...

https://www.harborfreight.com/dual-vacuumpressure-hand-pump-kit-56803.html

...then I worked my way front to back to find my leak. Unfortunately in my case the leak was all the way back at the static port. The aluminum tape I was using to cover the static ports leaked enough to cause a 100 fpm decent. I should have started at the static port first to confirm there was a leak.

It only takes about half a pump on this hand pump to climb 1000' so you have to be careful.
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Last edited by avrojockey : 03-10-2021 at 08:50 PM.
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  #7  
Old 03-11-2021, 07:59 AM
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JCSmith JCSmith is offline
 
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Quote:
Originally Posted by avrojockey View Post
I got a Harbor Freight hand pump with all the various fitting sizes...

https://www.harborfreight.com/dual-vacuumpressure-hand-pump-kit-56803.html

...then I worked my way front to back to find my leak. Unfortunately in my case the leak was all the way back at the static port. The aluminum tape I was using to cover the static ports leaked enough to cause a 100 fpm decent. I should have started at the static port first to confirm there was a leak.

It only takes about half a pump on this hand pump to climb 1000' so you have to be careful.
Thanks Tim, the hand pump sounds like it would be easier to use than the syringe setup I have. I was finally able to get under the panel and after sealing the loose connections on the backs of all 3 instruments the loss is now down to 250 ft/min using a spare altimeter at the T-fitting on the line running back to the static ports. Into the tail-cone next. Im not sure how Im going to be able check the static ports themselves though. Any suggestions?
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  #8  
Old 03-11-2021, 09:44 AM
Ralph Inkster Ralph Inkster is offline
 
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Looking for leaks, I usually start at the instrument and work outwards toward the static port, checking at every connection.
Sometimes the leak might be the static port its self, where the vacuum suction cup can't seal the port (leak through mounting rivets or however the port is attached to the fuselage), in this case we apply aluminum tape over the port and surrounding skin, punch a hole and mount the suction cup over that.
Caution- don't abruptly break the suction as instruments may be damaged.
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  #9  
Old 03-12-2021, 08:47 AM
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JCSmith JCSmith is offline
 
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Quote:
Originally Posted by Ralph Inkster View Post
Looking for leaks, I usually start at the instrument and work outwards toward the static port, checking at every connection.
Sometimes the leak might be the static port its self, where the vacuum suction cup can't seal the port (leak through mounting rivets or however the port is attached to the fuselage), in this case we apply aluminum tape over the port and surrounding skin, punch a hole and mount the suction cup over that.
Caution- don't abruptly break the suction as instruments may be damaged.
Thanks Ralph. I did find all 3 connections a bit loose at the instruments. I also checked the line running back to the static ports and had a 250 ft/min loss there. The two connections at the T where the 1/8 line connected to the 1/4 line were both somewhat loose. Im hoping Ive got it all sealed up now. Thanks for the response!
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  #10  
Old 03-12-2021, 11:05 AM
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Walt Walt is online now
 
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Just an FYI, all pipe thread fitting must have some type of sealant installed on the threads, I use teflon tape on P-S fittings. Lots of folks apparently think the Nylon fittings will self seal, wrong.
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