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  #11  
Old 09-20-2021, 05:45 PM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 31
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Hi All,
Sorry for the confusion. I am not trying to resolve an airspeed vs. GPS disagreement. My airspeed is without a doubt reading 10 to 15 knots low. I believe
I have narrowed it down to a leak in the LH static port. I'm going update my D180 and see if anything changes. If not, I will be gaining access to the tailcone. Unfortunately, I do not have the split bulkhead...
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Jack
Cocoa, Fl
Proud new non-builder owner of RV12 N214LA
ASEL, A&P
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  #12  
Old 09-20-2021, 06:03 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,769
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Easier to do the following test. Disconnect (or plug) the static vents. Open the static line somewhere inside the cabin. Go fly. Problem fixed? (Try with air vents open, and closed.) Cabin pressure is usually different than true static, but not enough to decrease airspeed 15 knots.
An easier, alternative test is to set your altimeter to field elevation, then carefully do a high speed low pass 50’ over the runway. Does the altimeter read field elevation plus 50’? If so your static system is okay.
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  #13  
Old 09-20-2021, 06:28 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,218
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Group - -does the 12 use the same rivet crown shape for the static ports? Historically (here on VAF), it is some issue with the static port that has caused drastic AS errors.
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RV-7
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  #14  
Old 09-20-2021, 06:50 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,769
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Quote:
Originally Posted by BillL View Post
Group - -does the 12 use the same rivet crown shape for the static ports? Historically (here on VAF), it is some issue with the static port that has caused drastic AS errors.
I believe this is true. But the vans’ rivet heads always work, It’s the other, fancier designs, that give trouble!
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  #15  
Old 09-20-2021, 06:55 PM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 31
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Quote:
Originally Posted by BobTurner View Post
Easier to do the following test. Disconnect (or plug) the static vents. Open the static line somewhere inside the cabin. Go fly. Problem fixed? (Try with air vents open, and closed.) Cabin pressure is usually different than true static, but not enough to decrease airspeed 15 knots.
An easier, alternative test is to set your altimeter to field elevation, then carefully do a high speed low pass 50’ over the runway. Does the altimeter read field elevation plus 50’? If so your static system is okay.
Hi Bob,
Great info, I'm going to give that a try.
Thanks
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Jack
Cocoa, Fl
Proud new non-builder owner of RV12 N214LA
ASEL, A&P
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  #16  
Old 09-20-2021, 07:01 PM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 31
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Quote:
Originally Posted by BillL View Post
Group - -does the 12 use the same rivet crown shape for the static ports? Historically (here on VAF), it is some issue with the static port that has caused drastic AS errors.
Hi Bill,
Thank you. It was your first reply that got me looking at the static system. I believe that's what may be causing the issue.
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Jack
Cocoa, Fl
Proud new non-builder owner of RV12 N214LA
ASEL, A&P
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  #17  
Old 09-21-2021, 03:48 AM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 31
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Quote:
Originally Posted by BobTurner View Post
Easier to do the following test. Disconnect (or plug) the static vents. Open the static line somewhere inside the cabin. Go fly. Problem fixed? (Try with air vents open, and closed.) Cabin pressure is usually different than true static, but not enough to decrease airspeed 15 knots.
An easier, alternative test is to set your altimeter to field elevation, then carefully do a high speed low pass 50’ over the runway. Does the altimeter read field elevation plus 50’? If so your static system is okay.
Bob,
Would disconnecting the static line at the back of the D180 accomplish the same thing or is it imperative that I open the static line in the cabin?
Thanks
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Jack
Cocoa, Fl
Proud new non-builder owner of RV12 N214LA
ASEL, A&P
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  #18  
Old 09-21-2021, 06:05 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,219
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The instrument bay has cooling fans that will change the pressure.
Disconnect the static line from the back of the D-180. In its place, attach a spare tube and run it into the cabin.
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Joe Gores
RV-12 Flying
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  #19  
Old 09-21-2021, 06:12 AM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 31
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Quote:
Originally Posted by Mich48041 View Post
The instrument bay has cooling fans that will change the pressure.
Disconnect the static line from the back of the D-180. In its place, attach a spare tube and run it into the cabin.

Good idea. Thanks
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Jack
Cocoa, Fl
Proud new non-builder owner of RV12 N214LA
ASEL, A&P
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  #20  
Old 09-21-2021, 09:56 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 3,146
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When I had a pitot system issue on an Aventura HP I ran a temporary pitot tube and hooked it to a spare airspeed indicator vented to my cockpit for comparison. A little tough to do on an RV-12, but not impossible with a little duct tape and ingenuity.
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