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  #1  
Old 09-18-2021, 01:26 PM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 32
Default Airspeed Low

Hey Guy's,
I have a 2011 RV 12. My airspeed is reading 10 knots low at all airspeeds. I have the Dynon D180. I did the airspeed leak down check with the syringe and it passed easily.
I've checked the tubing for defects and checked the connections at the Dynon. My tubing goes from the pitot tube directly to the Dynon (no module).
Any ideas would be appreciated.
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  #2  
Old 09-18-2021, 02:32 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,242
Default

What does the static port look like?

I assume you have a 3 or 4 leg ASI calibration flown at several airspeeds?
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  #3  
Old 09-18-2021, 03:01 PM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 32
Default

I have not flown any "calibration " legs. The airspeed does not come alive until right at rotation. Then it is 10-15 knots low when cross checked against 2 GPS at all airspeeds.
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  #4  
Old 09-18-2021, 03:30 PM
dothetime dothetime is offline
 
Join Date: Jul 2015
Location: Boynton Beach, Florida
Posts: 175
Default Low airspeed

I have a D180, did you do the zero airspeed calibration?
Check the D180 manual.
Dave

Last edited by dothetime : 09-18-2021 at 03:31 PM. Reason: Error
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  #5  
Old 09-18-2021, 06:12 PM
John-G John-G is offline
 
Join Date: Jan 2012
Location: Northeast Ohio
Posts: 759
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Jost a thought. Have you checked to make sure that the dimple drilled into the pitot tube for the screw that secures the pitot tube inside the gear reduction unit has not become breached by the screw?
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  #6  
Old 09-18-2021, 08:15 PM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 32
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Quote:
Originally Posted by John-G View Post
Jost a thought. Have you checked to make sure that the dimple drilled into the pitot tube for the screw that secures the pitot tube inside the gear reduction unit has not become breached by the screw?
I checked the dimple and it was fine. Thanks.
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  #7  
Old 09-18-2021, 08:17 PM
Jcurry Jcurry is offline
 
Join Date: Jul 2021
Location: Cocoa,Fl
Posts: 32
Default

Quote:
Originally Posted by dothetime View Post
I have a D180, did you do the zero airspeed calibration?
Check the D180 manual.
Dave
I did the calibration but no help. Thanks.
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  #8  
Old 09-18-2021, 08:22 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 3,149
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Is there any part of your system that was not part of the pressure boundary during your syringe test?

I have a D180 and D100 combo. I notice that the D100 comes alive about 15 knots, but the D180 doesn’t until about 25 knots. There is also a difference of a few knots between the two nits IAS. Not really applicable to your issue, but thought I would mention it.
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  #9  
Old 09-19-2021, 06:19 PM
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Caveman Caveman is offline
 
Join Date: Nov 2006
Location: Oklahoma
Posts: 685
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Quote:
Originally Posted by Jcurry View Post
I have not flown any "calibration " legs. The airspeed does not come alive until right at rotation. Then it is 10-15 knots low when cross checked against 2 GPS at all airspeeds.
Am I misreading your post? It sounds like you are trying to reconcile gps groundspeed with indicated airspeed while on takeoff roll. If that's the case it won't work unless the wind is dead calm.

As others have hinted at, try flying the test pilot school Excel spreadsheet routine so often referred to here on VAF.

Thanks,

Joe
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  #10  
Old 09-19-2021, 07:00 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,788
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Quote:
Originally Posted by Jcurry View Post
I have not flown any "calibration " legs. The airspeed does not come alive until right at rotation.
This doesn't sound right.
Quote:
Then it is 10-15 knots low when cross checked against 2 GPS at all airspeeds.
At what altitude? At 5000' or so I'd expect IAS to be 10% or so lower than average ground speed.
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