Leak or ADAHRS failing?

[donramm]

I took my RV-12 in for transponder and pitot-static bi-annual check. I only fly VFR. The tech administering the test asked me if I wanted to do an IFR check of the pitot-static system. Not know what that implied I said "Sure". He covered one static port, put a tube on pitot tube, and put a gizmo over the other static port and turned a pump on. He "raised" the altitude to 2000' MSL and hit the button to stop the pump (which is actually sucking vs. blowing, of course). On an IFR check the altitude is supposed to change at no more than 100 feet/minute (or something like that). Mine went very abruptly to field elevation. So, my static system apparently has a leak. I told tech I would check the system and return to retest.

I have looked for leaks in what is very simple plumbing for the static system in an RV-12 and found none. I heard Paul New, one of the hosts of the "Ask the A&Ps" podcast, suggest using a plastic syringe to do some testing on my own. I covered one static port, insert the tip of the plastic syringe I purchased in the other static port (ensuring I have an air-tight fit) and I get same results as when the tech did test with $$$ equipment. I "raise" the altitude up to 2000' by **slowly** pulling the plunger out on the syringe and when I stop, the altitude quickly returns to field elevation.

I disconnected the static system tube from the ADAHRS and hooked up a very low pressure air source, plugged both static ports, and checked for leaks in the 5 junction points in the static system (inside of static ports and the "T" that joins the tubes from the static ports and connects them to the ADAHRS) and found none.

I did this testing in "Test Mode" and not in "Test Mode" of ADAHRS and get same result.

How can I check the ADAHRS unit itself?

It is probably obvious: I did not build my RV-12.

 

[Rhino]

Sounds like it failed the case leak test. That's the only thing that mentions 100 feet. It's 100 feet in total leakage in one minute, about a minute after the altitude has stabilized. Are you saying it drops like this while you're still holding the syringe steady, or after you remove it? If it's the former, it sounds like you have a leak. If the latter, that's normal.

 

[donramm]

I pulled the plunger out slowly to get it up to 2000' (or so) and stopped -- did not remove the syringe from the static port -- and the altitude quickly dropped to field elevation.

I have a friend with an RV-12 and Dynon setup. Did it on his airplane. Pulled the plunger to take it up to about 2000' and stopped -- again, did not remove the syringe -- the altitude dropped some but stabilized above field elevation. I didn't hold it for a minute to see if it would continue to go down. Since it stabilized above field elevation, it was obviously different than mine.

I looked in the Kit Assembly Instructions for details about the plumbing. My ADAHRS does not have the FLF-00007 Push-To-Connect elbows that re depicted. I upload picture of my ADAHRS and what the KAI shows. So, I ordered the elbows from Vans.

 

[Marc_J._Zeitlin]

I looked in the Kit Assembly Instructions for details about the plumbing. My ADAHRS does not have the FLF-00007 Push-To-Connect elbows that re depicted. I upload picture of my ADAHRS and what the KAI shows. So, I ordered the elbows from Vans.

Two possibilities - first, the tubing is not tight in the nylon fittings - you can easily check to see if the nuts are tight and that the "olive" is inside, gripping the tube.

Second, I do not see any sealant on the 1/8" NPT threads into the ADAHRS. It's possible that it's just not visible under the nuts, but it's also possible that whoever installed the nylon fittings into the brass NPT female fittings didn't understand that ALL NPT threads need sealant (do NOT use teflon tape). If there's no sealant, that could easily be the source of a leak (in both the static and pitot lines).

 

[maartenversteeg]

From my own experience, I had a problem with airspeed indication, the pitot hoses in my wings, long time 10 years standing and then wing installation movements caused a number of cracks nearly around the tube which needed replacement (and opening the wing).
But you mention using a plastic syringe and that is also what I did to prove that my repairs had really fixed the issue. I had closed all the drainage holes on the pitot and applied pressure to the pitot and was looking at the airspeed, push the pressure till it read 80 kts and then let go of the syringe as to not disturb the pressure. I kept seeing the pressure disappear. Spend many hours, adding a water manometer and limiting the part of the tubing being tested. Eventually I found that after letting the syringe go it, very slowly moved back due to the pressure, so unless I held the syringe in position the syringe was causing my pressure loss problem.

 

[donramm]

I did hold the plunder on the syringe to avoid "creep" and the altimeter very quickly went back to field elevation. I'm going to check what Marc Zeitlin recommended next.

Perplexity (my preferred AI-search tool) tells me: "Dynon's official maintenance documentation specifies the use of Loctite 565 or a similar anaerobic thread sealant for these fittings. Loctite 565 is a liquid thread sealant that cures in the absence of air and does not break off in use, making it ideal for these critical systems."

 

[Stevec]

Loctite 565 should not be used on nylon fittings. I suspect their advice was assumin metal fittings.

 

[donramm]

I assume Marc Zietlin was suggesting the use of sealant between ADAHRS and the metal end of the gizmo to which the tubes are attached.

I have ordered two of the FLF-00007 Push-to-Connect Elbows from Vans Aircraft which have an NPT end that threads into the ADAHRS. The "Push-to-Connect" feature of the tube-end of the elbow is not supposed to need any sealant.

 

[Stevec]

Personally, if it’s a nylon fitting like you are using, I would not use anything as the soft nylon should fill the gaps and provide a seal Unless the threads are damaged. If that fitting is leaking i would be looking at the tube going into the fitting being deformed or the sealing olive being deformed or damaged. These problems can be hard to find and sometimes I have found just getting another fitting and try again works. There Is a white PTFE paste, I think it is, that you can get as a sealer, I have not used it myself.

 

[swatson999]

Personally, if it’s a nylon fitting like you are using, I would not use anything as the soft nylon should fill the gaps and provide a seal Unless the threads are damaged. If that fitting is leaking i would be looking at the tube going into the fitting being deformed or the sealing olive being deformed or damaged. These problems can be hard to find and sometimes I have found just getting another fitting and try again works. There Is a white PTFE paste, I think it is, that you can get as a sealer, I have not used it myself.

Available in the Aircraft aisle at your local Home Depot https://www.homedepot.com/p/Hercules-2-oz-Real-Tuff-PTFE-Thread-Sealant-156052/100184716

 

[swatson999]

I pulled the plunger out slowly to get it up to 2000' (or so) and stopped -- did not remove the syringe from the static port -- and the altitude quickly dropped to field elevation.

I have a friend with an RV-12 and Dynon setup. Did it on his airplane. Pulled the plunger to take it up to about 2000' and stopped -- again, did not remove the syringe -- the altitude dropped some but stabilized above field elevation. I didn't hold it for a minute to see if it would continue to go down. Since it stabilized above field elevation, it was obviously different than mine.

I looked in the Kit Assembly Instructions for details about the plumbing. My ADAHRS does not have the FLF-00007 Push-To-Connect elbows that re depicted. I upload picture of my ADAHRS and what the KAI shows. So, I ordered the elbows from Vans.

It's hard to tell from that angle, put perhaps you violated the minimum bend radius on that tubing and kinked it, causing a stress riser for a crack?

 

[Rhino]

Available in the Aircraft aisle at your local Home Depot...

 

[donramm]

I'm counting on the "Push-to-Connect" feature of the FLF-00007 elbows to take care of the tube to elbow seal. If the end that screws into the ADAHRS is metal (as I think it is), I'll use the Loctite 565 on that.

 

[jsalak]

+1 on changing to Push-to-Connect fittings, the o-ring seal is much better. I use Loctite 567 sealant on my threaded fittings on my RV-12. The test procedure for RV-12 Pitot and Static System Leak Checks is in the Production Acceptance Procedures (PAP), section G5.

PAP RV-12 - Van's Aircraft Total Performance RV Kit Planes

Modified/clarified instructions related to dynamic propeller balance requirements; Garmin Autopilot trim knob adjustment change.

www.vansaircraft.com