EFIS D100 ASI Indication problem

[rodger1331]

Looking for some help about a problem with the ASI indication on the D100.  The D100 is connected to the same pitot and static lines as a standard calibrated mechanical ASI and there is always a variation of between 2 to 4 knots between the two instruments with the D100 generally indicating less than the mechanical ASI.

The readings of the ASI on the D100 are not steady but oscillate up and down quite quickly by about 1  to 2 knots but the mechanical ASI is rock steady across the speed range. The D100 was purchased last March and the problem has been there since it was installed in the aircraft.

Anyone got any suggestions as to a possible cause or cue for this problem, any help would be very much appreciated.

 

[Dynon]

Our EFISes do have very reactive displays, so what looks rock-steady on an analog indicator can be more active on the EFIS tape. Seeing a video of just how active it is could be instructive. If you have (or can take) one, you can send it to support at dynonavionics dot com with a link to this case. As for the variation, testing usually proves us out, most of the time

If you had leaks in the pitot or static system upstream of the pitot, particularly upstream of your T on the D100 side, you could see a lower indication on the D100. That would be the very first thing to investigate.

What airspeed ranges are we talking about here, by the way? In slow flight, do they still disagree, or do they converge back together?

For what it's worth, figuring out "truth" is a little harder than just comparing to GPS because wind is virtually always non-zero.

Other approaches to testing for truth involve building a water manometer. And we're happy to take a look at it here too if you don't mind the round-trip. You may be able to find a calibrated airspeed test set around a well-equipped airport too.

 

[rodger1331]

The mechanical ASI has been calibrated recently using a water manometer and the variation between the two indications varies slightly depending on the airspeed which rages from 40knts to 110knts. In general at about 90knts the D100 reads approximately 85 / 86knts.

I will try and get a video of the indications next time I fly and then pass it through to support to give you a better feel for the problem.

In the meantime I will check for any leaks upstream of the T piece as you suggest, in fact I can check the integrity of the whole system using a water manometer on the pitot.