D-100: Horribly Inaccurate Wind Indication

[MrMorden]

I've been having a problem on my D-100 since I have owned it, and I'd like to get some tech support.

The wind indicator in the lower right of the screen has never been anywhere close to accurate.  As an example, here are two pics showing the D-100 and my Garmin 496:

This is on a day with little to no wind -- notice my indicated airspeed and GPS ground speed are within two knots (GPS is in mph 127mph =111kt).

Yet, the D-100 shows a wind speed of FIFTY-THREE KNOTS, about 45° off the nose!  Simply not possible. 

So, how do I fix this??  I have already performed the resistor removal service discussed in this document:

http://www.dynonavionics.com/docs/support_bulletin_110107.html

That did seem to make the OAT more accurate at lower temps.  However, my temp indications have never been off by any appreciable amount that I could discern.  The 60°F indicated on the D-100 in the pics above is probably very close to correct, given the 85°F ground temps (ground ~1000ft MSL) that day.

I would consider changing the OAT sensor, but it seems to be working well.  Is there some calibration or other setting I can tweak to make the wind speed/direction better than useless?

BTW, this installation is on a Flight Design CTSW, and the OAT sensor is in the factory position, in the inspection cover on the underside of the left wing.

Thanks!

 

[dynonsupport]

Your magnetic heading is off. While OAT has a small effect, magnetic heading has a huge one and just a degree or two will cause significantly wrong winds.

On the D180, you can see that your heading is 270 but your ground track is 294 (magenta arrow).

Mathematically, the only way for this to be true is a large crosswind.

It looks like you need to re-do your magnetic calibration.

 

[mmarien]

If the 270 is a compass reading, it looks like your compass is 25 degrees different from the ground track of 295. The flight path indicator doesn't seem to agree with that difference. If there is no crosswind, the compass and GPS directions should be the same.

Also the GS of 127mph is different from the TAS of 127kts = 146mph indicating a 20mph tail wind.

I'd start with calibrating the compass for sure.

 

[MrMorden]

Thanks guys, I will try the mag calibration!

 

[Battson]

I get the same issue with the wind arrow - but with one key difference. When I am at home base, it's perfectly accurate all the time. The issues arises when I fly some 400NM south and the compass calibration appears to be different. Sounds kind of unlikely, I know, but I do this trip regularly. It happens every time.

I arrive down south and there is a considerable difference between the GPS heading and magnetic heading. I duly ignore the wind arrow, and when I arrive back at home base (400NM north), things are back to normal (mag and GPS headings agree perfectly).

I can only assume the variation in magnetic field in the different locations causes the compass calibration to be inaccurate at the southern locale.

 

[dynonsupport]

What GPS are you using?

Magnetic compasses don't need to be corrected for deviation. What does need to be corrected is the magnetic output of your GPS. GPS' read in TRUE and then have a model to move to magnetic. With a bad model, that could be changing.

Alternately, you are flying from an areas with no mag deviation and going east or west from there, and the GPS is just sending 0 mag var all the time.

We have to update the mag model in SkyView every few years to keep it accurate.

 

[Battson]

I am using a Garmin 296, I thought we already checked to make sure it was set correctly - but it's very possible I didn't do it right...