Wind vectors differ with heading

[Eric_Greenwell]

I've had the plane with SV for about 10 months, and the wind vectors have always varied significantly with direction. Recently, I used the v12 in-flight compass calibration, achieving a green 100. The next flight, I checked the wind reading by flying N, W, S, E at the same altitude, IAS, and location (essentially flew a 2 mile square). Here are the readings (degrees/knots):

N  290/6
W 284/6 
S  26/9 
E  23/9

I also tried a slow ~10 degree banked turn, during which the wind indication barely changed.

The plane is the Phoenix U15, an SLSA manufactured in Europe, so the pitot location is standard, and the IAS readings seem correct in cruise (corresponding RPM) and at stall (correct stall speed).

What's going on?

 

[Dynon]

So in all cases, you're getting a wind from the north(ish), at similar magnitude.

The improved calibration can definitely improve things and deal with more types of interference, but won't make every imperfect magnetometer location perfect. You may be up against the physical magnetic environment of the ADAHRS here.

 

[kurtfly]

I see the same thing in my Glasair. I also performed the in-flight compass calibration with >108 numbers on both ADHARS. I was thinking I had an error in my static system which was causing a slight decrease in altitude and airspeed so I performed a airspeed check by using an excel program called GPS PEC.xls. This works by entering your heading and groundspeed from GPS from 4 headings. Aircraft must be at same power and altitude. It then calculates your TAS and Winds aloft for each heading. In my case the TAS that Dynon SkyView reported is less than 1 knot difference from what GPS PEC calculated.

So I just contributed it to flying in mountainous terrain winds (Las Vegas area).

 

[Eric_Greenwell]

So in all cases, you're getting a wind from the north(ish), at similar magnitude.

The improved calibration can definitely improve things and deal with more types of interference, but won't make every imperfect magnetometer location perfect. You may be up against the physical magnetic environment of the ADAHRS here.

The readings are over 90 degrees apart. That seems extreme. How much compass error would it take to cause that much error in the wind calculation? I could compare the compass reading to the airport compass rose for a calibration check, but I need to know what's a big error: 5 degrees, 10 degrees, 20?

I'll look carefully at the ADAHRS installation again. It's surrounded by a carbon fiber fuselage, but no nearby metal; possibly, the BRS activation cable was disturbed and moved closer to the ADAHRS when luggage shifted on a previous trip.

Why is the reading so steady during a slow 360 turn? Isn't it updating the wind calculation?

 

[Dynon]

Indeed, the wind calculation doesn't update during a turn.

If the mag environment of the ADAHRS has changed, you might try doing the full calibration routine, starting with the ground-based calibration, then the in-air version (the order matters, and it's documented that way).

 

[Eric_Greenwell]

I checked SkyView against the airport compass rose, and NSEW were within 1 or 2 degrees of the rose. Later, I did another in-air calibration long enough to raise the "rating" to 118 in the green.

Since then, the wind readings have been reasonable and adequately consistent; they also match the other electronic compass within +/- 3 kts and 10-15 degrees, at least most of the time. So, probably plenty good enough for my purposes.

 

[Topgunul]

Hello, i´ve had nearly the same problem on my BRM. The solution was a new static port. Since that, the Windindicator, speed and all the other values are in a range with nearly 1 or 2 % difference. Thanks Dynon for your support in this case!!!
Torsten