D

David-aviator

Well Known Member
I've been in touch with Dynon tech support and we have not yet been able to nail down the cause or solution to what is going on. Here's the issue.

When first installed back in 2003 the D10 was in agreement with the Van's ASI to within 2 or 3 knots. Sometime recently, the spread has gone to about 6 knots on take off and on final, and up to 12 knots at cruise speed. It is indicating slower than the Vans unit and has been confirmed by working a know TAS derived from GPS runs back to calibrated speed.

The still air calibration procedure has been worked twice with no change in the error. The discrepancy has been apparent since installing version 5 but may have been there with previous version 4 software. Yesterday version 5.1.1 was installed with no change.

Has anyone had this problem and if so, how was it resolved?
 
Please confirm there are no leaks in the pitot or static systems, and that both ASIs are using the same pitot and static sources.

I think the first step would be to make a water manometer to confirm which ASI is wrong. You can get the formula to convert between water height and ASI reading from this thread.
 
Kevin Horton said:
Please confirm there are no leaks in the pitot or static systems, and that both ASIs are using the same pitot and static sources.

I think the first step would be to make a water manometer to confirm which ASI is wrong. You can get the formula to convert between water height and ASI reading from this thread.
Click to expand...

Good point on checking the system for leaks. The ASI's have separate pitot tubes but share static pressure.

The D10A is in error, not doubt about it. That was confirmed by determining TAS with GPS and using the Jeppesen CR-3 to find calibrated air speed. Just set OAT over TAS and go to the CAS over PA scale and read it. Vans ASI is in error by a couple knots, Dynon by 10-12.

There is a single silicon tube running from the Dynon pitot to the indicator and one of the end fittings may be leaking. The D10A has always run about 3 knots slower than the Vans unit, something has changed.
 
An interesting check would be to swap the pitot lines, if that is practical, and see if the problem follows the pitot.
 
Just as a note, we've probably had 10 people over the years send back their EFIS units because they were 100% convinced that the airspeed was wrong. Every single one we have checked has been dead on, down to a knot at 200 knots. It's always been a leak somewhere else in the system.

This is not to say that it couldn't be wrong. We'll happily look at it here and recalibrate it or repair it if needed, but history has shown that there is a much higher chance something else is going on in the rest of the system, and we'd rather you not have to spend the time and expense of returning it if nothing is wrong.

The suggestions above to swap pitot systems or to run a water manometer are both excellent ones.
 
altitude varies

I have a related but yet different issue with my D10A. It was recently upgraded from the D10 to D10A. Before, when the barometric pressure was set the same both the steam gauge altimiter and Dynon would read the same altitude and follow each other perfectly. Both instruments are on the same static line. Now, it seems that they can differ by up to 100 feet. If i set them both the same on the ground by going to the altitude calibration page, they both read the same innitially, and continue to do so for a little while, but after flying for perhaps a half hour, they will no longer be in agreement. It seems like the instrument needs a chance to warm up and stabilize.

Steve Ciha
 
DYNON D10A is OK....

Kevin Horton said:
My money is on pitot leak, almost certainly much closer to the D-10A than to the pitot tube.
Click to expand...

You win, Kevin. When the D10A was installed some time ago, the barbed fitting at the unit to receive the silicone tube from the pitot was finger tight only - I can't believe I did not tighten it! No wonder the unit always was 3 knots slow and recently got worse.

A short flight today in rather bumpy conditions revealed Dynon and Vans ASI's are right on - they agree with each other within a knot even with the turbulence. That is most acceptable. :)

Thanks to all for the input.
 
You must log in or register to reply here.