Dynon D10a wind and aoa problems

boeing737driver · #1 04-23-2012, 02:08 PM

Hi,

I just finished installing the remote compass, oat and aoa pitot to go with my D10a. I have two problems:

After calibrating the aoa by doing 4 stalls, power on and off, flaps up and down, I find that my RV-6 stalls with only one red bar showing on the aoa display. The manual says the stall should occur near the border between the red and yellow. Dynon says to redo the calibration flight and there is no other way to adjust the display. Which makes me wonder why the manual says if you can't get a good calibration, call tech support. And tech support says do what the manual says. LOL I'm thinking if I do the calibration stalls without going all the way to the break that might move the indication to a more reasonable value.

The other problem is that in flight the calculated wind displayed is different for different directions of flight. For instance when test flying north or south the winds showed light and variable or very low while flying east or west the wind showed 20 to 30 knots from the south. I suspected that my compass calibration was bad so I've redone it and the heading agrees within a degree or two of actual magnetic heading on our various taxiways. But, in flight the wind values are still diferent for different directions of flight. My steam airspeed reads 5 knots higher than the efis. And incorrect indicated/true airspeed would effect the wind calculation, too. Tech support said compass calibration is the main problem they have seen, but I don't know how to make mine better.

Let me know your experiences/suggestions.

Thanks,
Bruce

N282S · #2 04-23-2012, 05:40 PM

Let me know the fix on the winds. I've relocated the magnetometer and recal'ed on a compass rose (two differant ones) about five times. Still bad wind info and of course the heading is also off a bit.

boeing737driver · #3 04-23-2012, 08:57 PM

Hi,

My magnetometer is in the wing tip and turning on the strobe or nav light has no effect on the heading. It's mounted within .3 degrees of the D10A panel unit in pitch, roll and yaw measured with a digital level. And I'm confident that my compass calibration is good to within 2 degrees.

I did another forum search and did get a tip that incorrect OAT, which effects the TAS calculation, could be a factor. So I'll double check my OAT with a good thermometer. And, flying with the ball not centered will create an erroneous heading input which will create wind errors.

So, for my next test flight I will keep an eye on the ball as well as recording TAS, IAS, OAT, altitude, heading, track and ground speed as well as the displayed wind for N, S, E and W bound legs. Maybe that will help narrow down the source of the errors.

Bruce

Ironflight · #4 04-23-2012, 10:55 PM

Have you checked for a static leak by any chance? the fact that you have different ASI readings could mean that you've got something going on in Static, and that affects airspeed, which will definitely mess up the winds. I haven't seen how the error looks in a Dynon, but have had this happen with my GRT panel (not the GRT's fault - it was a plumbing leak elsewhere), and the first symptom is winds that don't make sense.

Paul

boeing737driver · #5 04-24-2012, 07:46 AM

Another good idea. I've had the altimeter out for wiring access since I did the leak check. I'll recheck for leaks.

Thanks,
Bruce

boeing737driver · #6 04-24-2012, 11:34 AM

Hi,

I did a leak check on pitot and static this morning and both are leak free. I double checked the OAT with another thermometer. I recalibrated the compass for the 6th or 7th time and then went for a test flight. The winds aloft forcast was SW at less than 15. On the surface (4454 ft) the wind was less than 4 knots and variable.

I flew N, S, E and W compass headings at 8500 feet with the ball centered. OAT was 16c, IAS was 135 on efis and 139 on the steam gage. Efis showed 158 knots TAS. The results:

Mag N, track 001, ground speed 158, wind 270/5 & Light and Variable
Mag S, track 179, ground speed 156, wind 241/5 & Light and Variable
Mag E, track 082, ground speed 162, wind 190/24 & 183/24
Mag W, track 277, ground speed 154, wind 193/26 & 191/33

My theory is that the winds were light and variable or low from the SW, but the compass in flight is off when flying E or W by about 5-6 degrees. On the ground the compass agrees with the mag heading of our N-S taxiway and E-W taxiway within 1-2 degrees. How can the compass calibration change between taxiing and flying?

The quest continues.

Bruce

Sam Buchanan · #7 04-24-2012, 11:53 AM

Quote:

Originally Posted by boeing737driver

Hi,

I did a leak check on pitot and static this morning and both are leak free. I double checked the OAT with another thermometer. I recalibrated the compass for the 6th or 7th time and then went for a test flight. The winds aloft forcast was SW at less than 15. On the surface (4454 ft) the wind was less than 4 knots and variable.

I flew N, S, E and W compass headings at 8500 feet with the ball centered. OAT was 16c, IAS was 135 on efis and 139 on the steam gage. Efis showed 158 knots TAS. The results:

Mag N, track 001, ground speed 158, wind 270/5 & Light and Variable
Mag S, track 179, ground speed 156, wind 241/5 & Light and Variable
Mag E, track 082, ground speed 162, wind 190/24 & 183/24
Mag W, track 277, ground speed 154, wind 193/26 & 191/33

My theory is that the winds were light and variable or low from the SW, but the compass in flight is off when flying E or W by about 5-6 degrees. On the ground the compass agrees with the mag heading of our N-S taxiway and E-W taxiway within 1-2 degrees. How can the compass calibration change between taxiing and flying?

The quest continues.

Bruce

You haven't told us where the magnetometer is located in your plane or which canopy you have. If the mag is anywhere other than in a wingtip, it will be impacted by a sliding canopy. If you calibrated the mag (and taxi) with the canopy open, you will see different headings when flying with the canopy shut. The canopy frame has enough ferrous material to deflect the magnetic field.

If you have a tip-up......I'm out of ideas.....

boeing737driver · #8 04-24-2012, 12:12 PM

Thanks for the input. The remote compass is in the left wind tip, forward of the spar. It's mounted with aluminum angle, aluminum rivets, aluminum rivnuts and brass screws. The Dynon serial connector came with magnetic hardware, which I used. The wing tip mounting screws are stainless and are very slightly magnetic.

I'm out of ideas, too.

Bruce

boeing737driver · #9 04-25-2012, 09:05 AM

Hi,

The calibration for the remote sensor is on the ground only, so that isn't an issue. I just remembered that the cable was from Stein so the magnetic hardware on the connector may not be what Dynon would like, so I will ditch it and us brass there. Thanks for the suggetions.

The quest continues!

Bruce

boeing737driver · #10 04-25-2012, 07:45 PM

Hi,

A pocket compass showed no deflection anywhere around the remote compass, but I replaced the steel hardware with brass anyway.

When I originally installed the D10A I had no remote compass so I ignored the grounding of the shield on the remote compass wire harness. Today I remembered that so I got the D10A end of the schielding attached to ground.

On test flying, after the umpteenth calibration the winds were much closer at cruise on the cardinal points of the compass. They varied from 220 at 13 knots to 260 at 22 knots. It was an afternoon flight and a bit bumby which kept everything moving around a bit. I'll try it again in the morning when the air is smooth.

Then it will be time to try out a stall series to recheck AOA calibration.

Bruce