internal versus remote magnetometer

[13brv3]

Greetings,

I'm still trying to decide if I should try the unit on the panel, before attempting to install the EDC. I noticed yesterday, that while my panel location is fairly clear of powered instruments, radios, etc, I do have the master contactor, and main battery cable just below the spot where the unit will be. I'm thinking this will be a bad thing, but I guess I won't know until I try it.

Is the remote magnetometer more sensitive interference than the sensors in the main unit? If you had to follow the same installation conditions required for the remote magnetometer, I don't see how anyone could ever make the main unit work on any panel.

I guess I'll find out soon enough.

Rusty

 

[dynonsupport]

Rusty,
The sensor in the EDC is exactly the same as the one in the EFIS. It will react the same to interference as the internal sensors do.

We give strict rules about the EDC because if you are going to bother to install it, you might as well locate it as best you can. The EFIS would work great if you could locate it where you put an EDC, but obviously putting the EFIS behind your baggage compartment is't really helpful.

When calibrating, we do our best to remove any interference. This is how the compass works for some people in the panel, since their interference is constant, so we can remove it in software. The biggest issues we have are things that change constantly, which is things like spinning gyros, and wires. The more power the wire carries, the worse it is.

In general, the EDC does end up working much better. If you need/want accuracy within a few degrees, we really suggest the EDC. It also has the added benefit of being calibrated on the ground instead of in the air. Of course, you can always try out the internal compass first and add the EDC later if you aren't happy with the performance of the internal sensor.

 

[13brv3]

Thanks for the info. It's not a matter of buying the EDC, just installing it. UPS is already bringing it today. I would just have to find the least painful location to install it.

One thing that I worry about with the baggage compartment installation is the effect from baggage. If you put a bag with anything ferrous in it, then it would mess up the remote sensor, unless the sensor is far enough behind the baggage compartment to be unaffected. How far is far enough becomes the question.

I might still try to mount the EDC between the firewall, and panel, just under the top skin. This would give it about a foot in all directions from anything ferrous, or powered. I'll have a better idea how to mount it when it shows up, and I can see what I have to work with.

Thanks,
Rusty

 

[dynonsupport]

Rusty,
The biggest reason to stay away from the firewall with the EDC is the engine. That's an awfully big, rotating, shaking, moving, ferrous mass.

Behind the baggage compartment has worked well for most of our customers. You're absolutley right that something metal in the compatment could cause a problem, but if you put it a foot or so behind the baggage compartment wall, you'd need a really big metal object in there to have much of an effect, and your W&B would probably be off with that item in the plane. I think you will find the distortion from a random metal object in the baggage compartment will be less than the distortion you always have from the engine.

 

[13brv3]

I guess if I'm going to install the EDC, I should give it the best chance of success, by mounting it somewhere more ideal. When I go out there today, I'm taking a small compass to put in the EFIS location, for a test. I'll turn on that main contactor, and add some electrical load, and see if I can make it react. Good chance it will, and I'll just forget about the internal sensors.

Thanks,
Rusty

 

[13brv3]

Rusty,
 The sensor in the EDC is exactly the same as the one in the EFIS. It will react the same to interference as the internal sensors do.


If you need/want accuracy within a few degrees, we really suggest the EDC. It also has the added benefit of being calibrated on the ground instead of in the air.

There's something I still don't understand about this. If the EDC is the same as the sensors in the EFIS, then why does the EFIS need such a comprehensive calibration, and the EDC just gets four headings on the ground? Is it because you expect the EDC installation environment to be so clean, and also expect that the unit will be leveled to that tenth of a degree?

I've been helping a friend with an EDC in an RV-8, and he's mounted it twice now. The current installation is close to ideal, behind the baggage compartement, and as close to that tenth of a degree as we could get it. I think he said his West direction is still about 20 degrees off, though the rest are pretty close. I just wonder if the more comprehensive calibration that is used for the internal sensors would help with the EDC as well (if you applied it to the EDC that is).

Cheers,
Rusty

 

[13brv3]

I finished the install, and did the ground and flight call of the internal sensors. It was almost dark, and i don't have lights, so I didn't really get to play with the EFIS much. From what I can see, it's way cool though

Once on the ground, I tested N,S,E,W vs the GPS while taxiing. N,S, and E were all within 5 degrees. Unfortunately, W was 30 degrees off. While taxiing back to the hanger, I started shutting off extra fuel pumps and such, and when I pulled up to my hanger (heading West), it was reading about 260, rather than 240 like before. Yep, turning on and off pumps makes a big difference, since the main battery cable is right below the unit.

Now I could make a compass correction card relative to how many amps I'm pulling, but it would probably be better to just install the EDC. I guess I'll do that tomorrow.

Rusty

 

[BobbyHargrave]

Rusty:
Hello. You must install the EDC iot be like me .

 

[BobbyHargrave]

West is not best for me either.  N, E, S all w/i reason as compared to wet and GPS tracks.  W is 22 degrees off (248 vice 270) in my installation.  I have cal'd both on the gnd and inflt and that's as good as I can get it.  My EDC is located aft of the rear baggage bulkhead in RV-8.  Temp probe works nicely now that it is out of the exhaust plume.  Who told me to put it there?

 

[13brv3]

I installed the EDC yesterday. The choice was to put it under the front of the empennage fairing, or behind the baggage compartment of the RV-3.

Under the empennage fairing is clear of all current carrying wires, but the EDC would be within a couple inches of several AN-3 bolts, an ELT antenna, and a trim cable with a steel housing. There's also no way to get a level on the EDC to check it.

Behind the baggage compartment mounting allowed me to make an adjustable shelf, so I could dial in the pitch with good accuracy. The best compromise location is about 9 inches from the closest steel (rudder cables), and about 15 inches behind the battery, which is in the rear of the baggage compartment. This is where I put it yesterday.

It didn't take long to figure out that current in the battery cable is still a problem, since I can watch the heading change with every electrical item I turn on. It's not nearly as bad as when I was trying to use the internal sensors, and it may not really be as bad as it seems. The current in the battery cable will be nearly zero after the engine has run for a few minutes, and the battery has charged back from starting the engine, so this may still be a better option than the empennage fairing, with all it's surrounding steel.

It was too dark to taxi, much less fly (no lights on the plane), but I couldn't resist pulling the plane out on the ramp for a quick test. Without anything on but the EFIS, I did a crude cal of the EDC, guessing at the exact headings. After that, I checked the cardinal headings with power off, then with all the electrical load I could add. In both cases, the max error was about 10 degrees, with the norm being closer to 5-7. I'll have to give it a real cal, and a better test, but this might just work fine.

Since I've got the empennage fairing open, and didn't cut the cables, there is certainly a temptation to try that location as well. Which is worse, being within 15 inches of the battery, or a few inches from bolts and other steel items?

The OAT is an issue for a new thread.

Thanks,
Rusty

 

[dynonsupport]

Rusty,
We have more of a calibration problem with changing magnetic fields (like a battery cable) than with fixed things like steel bolts. You may have good luck in the emp. housing. We can calibrate out stuff that is always there, but we can't calibrate for things that are not constant.

As for the EDC vs. Internal calibrations: We pre-cal the EDC in 3 dimensions at the factory. We can do this because we assume an EDC install will be clean enough that this will work. We can't pre-calibrate the internal sensors in 3D here because we assume there will be so much noise in the panel that it would never work. So we need you to do 3D manuvers on the internal compass, while we do them on the EDC here.

 

[13brv3]

I'm cautiously optimistic about the current location of the EDC. I did some tests again yesterday, but don't know when I'll get to flight test it. Just too many tropical storms and hurricanes passing through the area.

As I mentioned, the current in the battery lead should be nearly zero once the battery is charged following the engine start. I rolled the plane out yesterday, and with nothing running, did a cal of the EDC while aligning the plane carefully to N,S,E, and W. I then checked the wet compass, and EFIS with the power off, then with all the electrical load I could add without cranking the engine. Results were quite fine with me.

True direction / wet compass / EFIS no power / EFIS with elect load
000 / 358 / 357 / 001
90 / 80 / 92 / 93
180 / 182 / 177 / 172
270 / 275 / 273 / 273

If the flight tests are as good as the ground tests, I could easily be happy with these numbers. Just have to wait and see.

Thanks,
Rusty

 

[13brv3]

As a final note, I ended up installing the EDC under the empennage fairing, and it worked even better than it did behind the baggage compartment. It was much easier to install as well, and that would be my recommendation to any RV builder, FWIW.

Rusty

 

[Paul Lee(Guest)]

With all this complexity - not saying it can't be done - wish they would give the option of simulating a standard DG - no magnetic interference problems. I don't mind setting the direction each time, I have to set the baro anyway. Why not give us that option Dynon? The gyros are already in there anyway. It should be simple in software and more accurate.

How about some of you other D10 owners pestering Dynon for the option?

Otherwise I am happy with my old D10 - 75hrs on it now.

 

[dynonsupport]

Paul,
The magnetometer is sensitive to interference just like a normal compass is. We'll be no more or less accurate than a compass placed in the same location. We have the advantage of placing the compass somewhere else in the aircraft instead of in the panel, whereas a wet compass has to just deal with whatever innaccuracy is there with a compass correction card.

If you wish to not deal with the "complexity" of the external compass, you can always use the internal compass. This will be subject to the same interference that your wet compass is, but our software will attempt to correct for this.

Response to your other post:

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1123798877/0#1

 

[Paul Lee(Guest)]

See my reply to other post.
http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1123798877/0#2