Compass cal / winds aloft error

[lancair360]

Talking with support about this. Putting it out to the group braintrust.

Lancair 360. Dynon Skyview system, dual 7" screens, AP panel, radios, all of it. Engine has dual PMAGs. Using compass internal to ADAHRS.

Winds aloft in gross error, compass cal did nothing to help. Contact Dynon and they can see a split between ground track and mag heading going down the runway, so I do cal again. No luck.

ADAHRS goes back to them for a bank angle thing, ops check good (limitation of the software, ADAHRS totally fine, it's a turbulence thing). Redo compass cal, still no luck.

When sitting in the hangar, booted up, if I turn on the alternator switch (engine off) the compass would swing near 20º. Even if this is a steady state I cannot calibrate it out. Decide to get a remote magnetometer. Install it in a spot where, same test, I get 0º compass movement. With all systems running (except engine) I can only induce a 3º compass swing with nav and recognition lights. Winning spot. Installed per the manual, brass hardware, good to go.

As soon as I start the engine the compass swings, and stablizes. Turn on the alternator and another swing, but stablizes on the "new" heading. Go do compass cal tonight and it's still all completely wrong. Winds aloft is fiction, and there is a 10-20º difference between heading and ground track in flight. It was obvious looking out the window that wasn't the case and there certainly were not 70kt winds aloft where I was. Coming back to land the compass is many over 10º off from runway magnetic heading.

I know there is nothing wrong with the ADAHRS or remote compass. I am running out of ideas. Doesn't seem I can get a good calibration no matter what I do.

Thoughts?

Thanks everyone.

 

[jakej]

"As soon as I start the engine the compass swings, and stablizes. Turn on the alternator and another swing, but stablizes on the "new" heading. "

Hopefully you tested outside of the hangar, all bets are off otherwise.
Did you do a ground calibration with all systems on (those you always use/need to use in flight) including wearing headset & engine running?
What brand of Alternator do you have ?
Is this a new equipment install or something that developed over time?
Where is the O.A.T mounted ?
I also have a composite plane & understand the pain you can have with RF & EMI.

 

[lancair360]

"As soon as I start the engine the compass swings, and stablizes. Turn on the alternator and another swing, but stablizes on the "new" heading. "

Hopefully you tested outside of the hangar, all bets are off otherwise.
Did you do a ground calibration with all systems on (those you always use/need to use in flight) including wearing headset & engine running?
What brand of Alternator do you have ?
Is this a new equipment install or something that developed over time?
Where is the O.A.T mounted ?
I also have a composite plane & understand the pain you can have with RF & EMI.

---Yes, ground cal done with flight conditions, all systems running. No compass interference from boost pump, fuel transfer pumps, strobes (AeroLED), pitot heat, landing lights, transponder (IDENT), comm 1 or 2, flap motor, gear motor, intercom. All lights are LED.
---Alternator is a B&C 60A, P/N BC462-H. Gear driven off the back of the motor. Voltage regulator mounted aft side of firewall above pilot's feet
---Dynon all installed back in 2015. I bought the plane in 2020. ADAHRS was on Dynon's bench months ago, the remote compass is brand new. AP panel overhauled 2021. Pitch servo overhauled 2021. #1 screen got new HDD 2021. GPS250 antenna replaced with GPS2020 antenna in 2021. ADS-B box updated to new in 2020.
---OAT probe mounted starboard side at fresh air NACA duct, so roughly where co-pilot's knees are


All good questions, thank you! Being composite I wonder if there is just no getting away from the noise. If that's the case then so be it. If there is something else going on I'd like to solve it. Given how benign the compass behavior was with the remote in the new spot vs the ADAHRS I really thought I had it!!

 

[Marc_J._Zeitlin]

Being composite I wonder if there is just no getting away from the noise. If that's the case then so be it. If there is something else going on I'd like to solve it. Given how benign the compass behavior was with the remote in the new spot vs the ADAHRS I really thought I had it!!

So you didn't say where the adahrs is or where the magentometer is in your plane. Might be useful to know (or might not...).

I've installed both Dynon and Garmin systems in many composite planes, and there's no reason that the magnetometer can't be accurate to within a few degrees (mine is, for both my HDX and G5 - two different magnetometers) in my COZY MKIV.

If it only happens with the engine running, what ignitions do you have, and if EI's, where are they mounted and where is the wiring for them? Where does the alternator wiring run, in relation to the ADAHRS and magnetometer locations? What type of spark plugs and wires are you using?

 

[lancair360]

ADAHRS is top center behind the panel. Remote is under passenger seat.

Dual PMAGs.NGK plugs. Wires are from EmagAir. No compass change running on one mag

all wiring to/from the battery runs down the keel of the plane.

aircraft was built as a VFR race plane. Might be nothing I can do short of gutting and re-wiring. If that’s the case at least I know. And that’s fine. I won’t do it, but it’s fine.

 

[Marc_J._Zeitlin]

ADAHRS is top center behind the panel. Remote is under passenger seat.

Dual PMAGs.NGK plugs. Wires are from EmagAir. No compass change running on one mag

all wiring to/from the battery runs down the keel of the plane.

aircraft was built as a VFR race plane. Might be nothing I can do short of gutting and re-wiring. If that’s the case at least I know. And that’s fine. I won’t do it, but it’s fine.

So magnetometers in the cockpit tend to be problematic - I might try moving it to the tailcone, up as high as possible to get it away from control pushrods and cables, as well as the wiring down low. If the PMAG's are putting out EMI/RFI, and feeding that into the main wiring, getting the magnetometer as far away from any other wiring as possible might help. Also, if possible, putting some sort of filtering on the power/ground wiring to the magnetometer may help.

Good luck...

 

[airguy]

You're obviously seeing the effects of magnetic fields induced by currents flowing in wires - and the only way to eliminate that is tto get as far away from the wires as possible. As suggested above the aft tailcone is a preferred location with a minimum of high-amperage draw loads, that or a wingtip will generally be your best locations.

 

[lancair360]

Wingtip and tailcone are no-go’s.

would the induced magnetic fields only effect the magnetometer or could they effect the wiring to the magnetometer and induce error that way?

Dynon support has a calibration hack I’m going to try. If that doesn’t work then it’s EMF/RFI that I cannot escape.

hopefully tomorrow try to recalibrate. Will report back.

 

[jakej]

"all wiring to/from the battery runs down the keel of the plane."
"hopefully tomorrow try to recalibrate". Will report back. --- that may? work however there could be causes that make that difficult.
So does the SV network cable run with the battery cables for any length ?
FYI re O.A.T. - I'd mount it elsewhere as cabin/cabin heat temperatures will give a variance from actual air temp.
P-Mag wiring will not affect it either.
You should not be having these issues with any aircraft composite or otherwise - it's usually an install issue with composites being more difficult for the inexperienced EAB builders.
I have a Glasair, have wired 10 in total as well as Lancair & other types, without any issues at all. Can you email me pictures of the install as it may result in a light bulb moment - much easier to troubleshoot that way rather than spending time guessing ?

I'll message you with my email address.

 

[lancair360]

"all wiring to/from the battery runs down the keel of the plane."
"hopefully tomorrow try to recalibrate". Will report back. --- that may? work however there could be causes that make that difficult.
So does the SV network cable run with the battery cables for any length ?
FYI re O.A.T. - I'd mount it elsewhere as cabin/cabin heat temperatures will give a variance from actual air temp.
P-Mag wiring will not affect it either.
You should not be having these issues with any aircraft composite or otherwise - it's usually an install issue with composites being more difficult for the inexperienced EAB builders.
I have a Glasair, have wired 10 in total as well as Lancair & other types, without any issues at all. Can you email me pictures of the install as it may result in a light bulb moment - much easier to troubleshoot that way rather than spending time guessing ?

I'll message you with my email address.

Network cable runs with battery cable for a couple feet.
Email sent. Thank you.

 

[lancair360]

Per Dynon support I redid the ground cal. When I took the runway for takeoff the heading perfectly matched the charged runway heading.

did the inflight cal and when I landed the heading was over 10° off of the runway heading.

after the inflight cal I did four compass points to grab winds aloft data and it is incorrect as always.

seems ground cal is good and inflight messes it up?

 

[skysailor]

You do not need the flight calibration. Ground calibration is acceptable. Is your Dynon using an GPS 250 antenna? The early ones had a software error that caused an incorrect magnetic variation table to be used after a certain date a few years ago. This affected heading and therefore winds aloft. I had to purchase two new antennas for this reason. Unfortunately, even though the Dynon antennas were defective in this regard no part of the purchase price was assumed by Dynon. Current GPS 250 and all GPS 2020 antennas do not have this problem but there are no markings on the antenna to determine this.

 

[lancair360]

Brand new GPS2020 antenna installed last winter.
Thanks for the input everyone. This is very helpful

You really don’t need the inflight calibration?

 

[jakej]

Yes, do it & mix up the turns while doing so. Follow the on screen instructions & number count needs to be over 100, I prefer to get it around 125 - then you’re good to go

 

[lancair360]

Yes, do it & mix up the turns while doing so. Follow the on screen instructions & number count needs to be over 100, I prefer to get it around 125 - then you’re good to go

Doesn’t work. In flight calibrations both been over 100. Compass not aligned after. It’s worse.

 

[jakej]

That was just general info - your case is very different, I still think it’s to do with the network cable being alongside the battery cables. Is there any way you can move just the network cable and email me a photo of that area ?

 

[lancair360]

That was just general info - your case is very different, I still think it’s to do with the network cable being alongside the battery cables. Is there any way you can move just the network cable and email me a photo of that area ?

Where it runs out is the panel there is no other place to put stuff. It’s this or nothing for real.

Dynon recommends doing just the ground cal, see how that does on its own. And go from there.

 

[henryhallam]

Why do you say wings and tailcone are no-go? I have a similar situation in my Lancair 360 (MkII large tail), though perhaps not quite as bad as you are seeing. I don't yet have a remote magnetometer and was considering putting one either in the tail, wing stub or wingtip - access seems quite possible to any of these on my plane.

 

[lancair360]

Cannot run wires to either wing. Tail would have to build a special spot back there and I can’t get back there, also the fabrication would be a huge problem. Plus cables would still run next to battery cables for a couple feet.

 

[skysailor]

You do not need the inflight calibration. The system did not even have that as an option until a few releases ago. Careful ground calibration can yield excellent results. My Glasair Super IIS RG (fiberglass just like your Lancair) was calibrated on the ground and has never had a problem. The flight calibration is just easier, not better. It would easy enough to try the ground calibration to see if it works for you.