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D10A Wind Velocity Arrow Problem

Toobuilder

Well Known Member
Now that I have my remote compass and temp probe up and running, I've come to realize that my wind direction/velocity indicator has some significant errors. The arrow seems to agree with the conditions if I'm headed into a wind, but it almost never shows a tailwind, even if I do a 180. The main problem is the velocity indication. Again, headed into the wind it generally agrees with my TAS and GPS ground speed, but if I'm going crosswind, the number will be way off. Last night for instance I was seeing 80 knots, despite actual conditions being closer to 6 knots.

I understand this thing to simply be a difference engine, and my heading, track, TAS and GPS ground speed are all in agreement enough that I can get a general sense of winds aloft with mental calculations... How come the Dynon can't figger it out?
 
Now that I have my remote compass and temp probe up and running, I've come to realize that my wind direction/velocity indicator has some significant errors. The arrow seems to agree with the conditions if I'm headed into a wind, but it almost never shows a tailwind, even if I do a 180. The main problem is the velocity indication. Again, headed into the wind it generally agrees with my TAS and GPS ground speed, but if I'm going crosswind, the number will be way off. Last night for instance I was seeing 80 knots, despite actual conditions being closer to 6 knots.

I understand this thing to simply be a difference engine, and my heading, track, TAS and GPS ground speed are all in agreement enough that I can get a general sense of winds aloft with mental calculations... How come the Dynon can't figger it out?

I had the same problem so before you do anything drastic, do a True Airspeed (TAS) check using 3 legs with GPS track and groundspeed as indicated at this URL. Once I did this, it turned out I had a static port location problem which threw the TAS number off making the crosswind number wrong. I corrected the problem and now my indications are spot on and extremely accurate. Make sure you stay on a constant Magnetic HEADING not GPS track (don't use a GPS slaved autopilot) for the test. If you use GPS track, everything will be wrong.

:cool:
 
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What he said....same thing happened to me early on. Also verify the compass calibration.
 
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I believe one thing Dynon told me to check when I had a simular problem was the D10A compass calibration. If the compass is off by a small amount it will make a large difference in the wind velocity and direction.
 
I'll recheck all these, but my TAS and compass calibration is pretty close. ...Like within one or two units for each. Does it make sense for the resulting wind velocity to be off by 70+ MPH?
 
I'll recheck all these, but my TAS and compass calibration is pretty close. ...Like within one or two units for each. Does it make sense for the resulting wind velocity to be off by 70+ MPH?

Also keep in mind it takes several (30?) seconds to stabilize once you've changed heading *or* airspeed. I've found mine to be quite close in cruise, and completely inaccurate in maneuvering flight, for example.
 
Good point. I was expecting it to resolve instantly, like the GRT in the -8 seems to.

Thanks for the data points everyone.
 
I'll recheck all these, but my TAS and compass calibration is pretty close. ...Like within one or two units for each. Does it make sense for the resulting wind velocity to be off by 70+ MPH?

Assuming your compass calibration is accurate, which seems to be, you really need to confirm your displayed TAS is accurate as verified by an independent flight system test. How did you confirm your TAS was accurate? The best way to do this is with the GPS method.

:cool:
 
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Yep

My D-100 winds aloft were waaaay off when I bought the airplane, and so were the headings. I went to another airport that had a surveyed compass rose and calibrated the Dynon....perfect after that.

Best,
 
Assuming your compass calibration is accurate, which seems to be, you really need to confirm your displayed TAS is accurate as verified by an independent flight system test. How did you confirm your TAS was accurate? The best way to do this is with the GPS method...

While I have yet to do the full GPS triangle, it's not real hard to calculate the rough wind velocity in your head by looking at the GPS GS as you make a few passes upwind and downwind. If you're going across the ground at 180 into the wind, and 200 going downwind, it's not hard to figure out that the wind is 10 and your TAS is 190. This simple average lines up prety close to my TAS display. Maybe not "dead nuts", but certainly close.
 
Right there with you Michael. Mine does the same thing. I have done the airspeed checks, compass calibrations, etc... If my static system was the culprit you would think something would be off between my GPS, Airspeed Indicator, my own pilotage, something.
I have seen a tailwind in a headwind, complete opposite crosswind, you name it. I am always shocked when it actually agree's with what is really happening.

Anyway, I don't use it and never really cared. My Dynon isn't slaved to anything needing that data anyway....
 
I flew with my compass uncalibrated a couple of times after installing the remote magnetometer and OAT probe. I observed behaviour much like yours, with wildly varying numbers.

After calibrating, the numbers became much more accurate, and that was with a "rough" ground calibration... Based on the taxiways at my home field, with an estimate for North. Then I calibrated using a Compass app on my cell phone, and it got better yet. Some day i'll have to go taxi over to the compass rose on the airport and do it properly... I expect it'll get even better! :)
 
Calibrate with the canopy closed if you have a slider

I had the same issue with my D180 even after calibration. Then I realized, via VAF, that my canopy frame is magnetized. Once I calibrated with the canopy closed, it all worked fine. If you have a slider, keep this in mind.
 
I tried the compass rose thing a few times with mediocre results. The last time was with the laptop plugged in and using my iPhone compass. It seems to be very close now, and getting better (if that's possible).

To Jon's point: I really only use the velocity arrow to decide if one cruising altitude is more favorable than another.
 
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