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-   -   Airspeed Low (https://vansairforce.net/community/showthread.php?t=199309)

Jcurry 09-18-2021 02:26 PM

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.

BillL 09-18-2021 03:32 PM

What does the static port look like?

I assume you have a 3 or 4 leg ASI calibration flown at several airspeeds?

Jcurry 09-18-2021 04:01 PM

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.

dothetime 09-18-2021 04:30 PM

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

John-G 09-18-2021 07:12 PM

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?

Jcurry 09-18-2021 09:15 PM

Quote:

Originally Posted by John-G (Post 1556351)
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.

Jcurry 09-18-2021 09:17 PM

Quote:

Originally Posted by dothetime (Post 1556323)
I have a D180, did you do the zero airspeed calibration?
Check the D180 manual.
Dave

I did the calibration but no help. Thanks.

RFSchaller 09-18-2021 09:22 PM

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 doesnít 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.

Caveman 09-19-2021 07:19 PM

Quote:

Originally Posted by Jcurry (Post 1556317)
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

BobTurner 09-19-2021 08:00 PM

Quote:

Originally Posted by Jcurry (Post 1556317)
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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