ADAHRS fine on the ground, but goes out in the air

[revgazza]

G'day.
After 2 years of faultless performance, My ADAHRS is doing something weird.

On the ground or while taxiing, my ADAHRS, compass and GPS heading all agree happily.

However, as soon as start scaring the birds, the ADAHRS goes out by around 30 degrees. And this stays happening for climb, cruise AND descent.

When going northish it is +30 degrees. When going south it is -30.
I have recalibrated the ADAHRS numerous times and it will be fine for just one flight. The next time...trouble.

I have the latest update etc.

Any ideas?

 

[N21HV]

When something that had been working and then it isn't any more, the standard practice is to look at what was the last thing that changed before the problem showed up. Did something new get installed in the airplane? Did something get taken out? Did something like power cable move?
Do you have a remote magnetometer? If you do, I'd look at areas around the magnetometer as well.
When you are on the ground, does it make difference if the engine is running on the ground or not?
Watch the directional indication while on take-off run. Does the offset increase as the aircraft gain speed? Or does the directional indication jump suddenly when the aircraft starts moving?

 

[swatson999]

When something that had been working and then it isn't any more, the standard practice is to look at what was the last thing that changed before the problem showed up.  Did something new get installed in the airplane?  Did something get taken out?  Did something like power cable move? 
Do you have a remote magnetometer?  If you do, I'd look at areas around the magnetometer as well.
When you are on the ground, does it make difference if the engine is running on the ground or not?
Watch the directional indication while on take-off run.  Does the offset increase as the aircraft gain speed?  Or does the directional indication jump suddenly when the aircraft starts moving?

You could look in the datalogs for this info, after the flight. Just load it into Excel and examine or plot airspeed vs. heading, etc. Or perhaps plot using Savvy Analysis tools.

Be better than trying to watch that on the takeoff roll, when you should be focused on the flying part.

 

[swatson999]

One more thing...is this happening while taxiing for take-off, with the plane "configured" for flight? That is, you're not comparing taxi data with no baggage, etc., to flight data all loaded up, right?

I mention this only because I thought my ADAHRS was acting up a bit, but it turned out on that flight I had put the towbar into the baggage area. It's steel. Duh.

Threw the ADAHRS off about 10 degrees.

 

[Raymo]

Also check for moving seat belt cables, which run near the AD-AHRS. I keep mine strapped down all the time so the cable remains in the same place.

 

[KRviator]

Those are good suggestions but what would account for the difference in headings as displayed between the Map page and the HSI?.

 

[dynonsupport]

Page 5-10 of user manual:

The current ground track as shown in Figure 98 is displayed in two ways: the digital readout and
the white ground track line. The border around the digital readout is normally magenta when
based on the GPS ground track. When the aircraft is not moving fast enough for SkyView to
reliably determine the ground track direction, magnetic heading is used instead. In this case,
the border around the digital readout will be white.

On the ground, the map is magnetic based. In flight, it's ground track.

 

[revgazza]

Okay.

So I understand the change from magnetic based when moving.

So why is the magnetic heading going out when I take off?
And why is it okay after I re-calibrate the ADAHRS for just 1 flight?

Is is possible there is a fault developed in it perchance? :-/

I sort of wish there was a simple knob calibration like in a steam driven DG for simple inflight realignment.

 

[Dynon]

I think you only have one ADAHRS. Is that right? It's not impossible for there to be a fault, but calibrations can't really change. Are you getting any other caution/warning messages from SkyView. Any "system event" messages? Are you using the ground or in-flight calibration?

 

[revgazza]

Yes. I have only one ADAHRS. I have used both ground and inflight calibration and I get no warnings or system event errors.

Garry

 

[Dynon]

I have to admit, I'm a bit stumped here, especially if nothing else has changed in the aircraft and it used to work okay. Probably time to get in touch with our technical support team directly at 425-402-0433 or at support at dynonavionics dot com.