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-   -   Low air speed (https://vansairforce.net/community/showthread.php?t=80254)

JohnJacobsen 12-20-2011 06:16 PM

Low air speed
 
I could use a little help on this one. My air speed has been reading low since first flight. I am indicating a stall of 35 knots, the airspeed is consistantly off thru the whole speed range. Rv-7 equiped with Dynon D-180, Dyon pitot, safe air static.
Pitot static tested ok, air damns in front of static no effect, static vented to cabin slight change, new static and pitot lines no effect, drilled out safe air ports and installed rivet (like vans ports) no effect, added washer under static port (rivet) no effect, different pitot tube no effect.
Have not compared to another airspeed indicator as I only have one. Seems to me that the D-180 is off, but Dynon tells me that since it passed the pitot static test that it was probably ok.
If anyone has any suggestions for me I would appreciate it.

N941WR 12-20-2011 06:24 PM

I would go back and check your entire pitot system again.

Mine was reading low, and like you, my stall was at 35 MPH. I replaced the entire pitot and AoA lines, from the D100 back to the Dynon pitot tube. Found a pretty good leak at the connection to the pitot tube. Problem solved.

JohnJacobsen 12-20-2011 06:29 PM

I've already replaced the lines, both pitot and static. As well as passing a pitot static test with a Barfield pitot static tester.

Tom Martin 12-20-2011 06:38 PM

set your altimeter to field elevation and then do a low pass (100) over the runway and note the altimeter setting. You will have to eyeball the 100 feet but if the altimeter is reading something much different then the 100 feet plus field elevation then you have a static error.

lostpilot28 12-20-2011 07:35 PM

Already replaced the lines and checked the static system for leaks? My next guess would be the instrument. Fortunately for you, Dynon has (I think) the ability to calibrate your airspeed and altimeter.

LettersFromFlyoverCountry 12-20-2011 07:46 PM

Any other RVers in the area with a similar Dynon instrument you could swap out for a quick check?

AX-O 12-20-2011 07:48 PM

Did you try the recalibration function on the Dynon?

JohnJacobsen 12-20-2011 07:49 PM

Nobody I know that has a D-180. Looking for a steam gage Airspeed to hook up for comparison.

JohnJacobsen 12-20-2011 07:51 PM

Yeah tried recalibration

NDrv8r 12-20-2011 07:53 PM

Quote:

Originally Posted by JohnJacobsen (Post 607946)
Have not compared to another airspeed indicator as I only have one. Seems to me that the D-180 is off, but Dynon tells me that since it passed the pitot static test that it was probably ok.
If anyone has any suggestions for me I would appreciate it.

airpeed calibration is not part of the static system test, however the Barfield test box is capable of airpeed testing. my skyview and D6 were spot on.

you might consider using a homemade water manometer to check your airpeed and plumbing. search for other threads on airspeed, you'll find more info.


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