Compass Calibration: Looking for Alternate Method

[N941WR]

I am (OK, used to be) an active backpacker, so I used my compass (see image, below).
I turned the prop vertical so I could line it up with vertical stabilizer (VS). I then turned the plane in each of the cardinal directions, using the compass to line it up, while sitting on the ramp, away from any metal buildings. If your airplane has tricycle gear, you might need a stepladder to sight along the VS and prop.

 

[jnmeade]

Reinforcing rod in concrete, buried power cables, underground pipes and similar factors can be a factor in selecting a spot for compass calibration.

 

[N941WR]

Reinforcing rod in concrete, buried power cables, underground pipes and similar factors can be a factor in selecting a spot for compass calibration.

Absolutely correct. If you use the compass method I described above, walk around with the compass and see if it is disturbed by any burred metal.

 

[Lon]

I am (OK, used to be) an active backpacker, so I used my compass (see image, below).
I turned the prop vertical so I could line it up with vertical stabilizer (VS). I then turned the plane in each of the cardinal directions, using the compass to line it up, while sitting on the ramp, away from any metal buildings. If your airplane has tricycle gear, you might need a stepladder to sight along the VS and prop.

This sounds like a great method for doing a calibration in a confined space too small for taxiing. But the Dynon instructions say calibration should be done with the plane in its flying configuration, i.e., engine running etc. Did you find that doing the configuration with the engine off worked well enough?

 

[N941WR]

This sounds like a great method for doing a calibration in a confined space too small for taxiing. But the Dynon instructions say calibration should be done with the plane in its flying configuration, i.e., engine running etc. Did you find that doing the configuration with the engine off worked well enough?

I did not have the engine running but had all the electronics turned on.

 

[sunfish]

I’ve done a rough ground calibration and taxi tests indicate I’m out by ten to twenty degrees according to the gps track, will an in flight calibration fix it?

 

[jakej]

Fly it & find out - do you really need an excuse to fly ?

 

[dbwindom]

I just performed another in-flight calibration, because my wind arrow seemed inaccurate. It's interesting to note, that the procedure in the manual casually mentions that varying the rate and pitch with INCREASE your calibration's accuracy. Until then, I was circling in a constant rate, maintaining altitude, and my "calibration index"? ( IDK if this is the actual term used in the manual) was stuck at about 120...totally acceptable, per Dynon, but still less than what I already had. I re-read the procedure...started flying climbing and descending circles, and the "index" started ticking higher!!

 

[sunfish]

126. Is that OK?

 

[dbwindom]

126. Is that OK?

If the number is green...it's within acceptable limits, per the manual.

 

[mrbizi]

Anyone know why the magnometer goes out of whack? It was working fine. Now it’s not. So I did a couple of inflight calibrations and got into green but it was still off by 20 degrees!!!! What the heck. My IFD was correct and in sych with my whiskey compass. What gives?

 

[Albee]

I don't know the answer to your question, but have you considered taxiing N, S, E, & W, using a GPS? On the ground, track = heading, and even a handheld GPS (or tablet/phone) would be a whole lot more accurate than a tablet/phone compass. Google Earth shows a pretty good sized ramp on the SE corner of the airport, and you might be able to establish reliable, accurate tracks on the cardinals while taxiing in that area.

This is what I did, and it worked okay: I did the airborne calibration and got okay metrics, but they got much better when I repeated the airborne calibration.

 

[chriscalandro]

Anyone know why the magnometer goes out of whack? It was working fine. Now it’s not. So I did a couple of inflight calibrations and got into green but it was still off by 20 degrees!!!! What the heck. My IFD was correct and in sych with my whiskey compass. What gives?

Where is your magnetometer located? How specifically did you calibrate it?

 

[BalsaBat]

To clear this up: Anytime you see the words Ground Grack - it's ALWAYS provided by GPS (in SkyView and all GA avionics at least. Airliners and equipment with "true inertial" positioning can do it via those platforms). So the map's GPS ground track is indeed provided by the GPS. The heading on the HSI is magnetometer/ADAHRS.

A technical aside: GPS only ever knows instantaneous position natively, so any GPS-based calculation, whether it's direction (ground track), speed, etc, are all derivations that use recent history (ie, a series of very recent position indications) to derive those values.

Trying to summarize what I've read in this string: after finding a spot free of significant magnetic interference, the initial ground compass calibration is best and easiest performed using ground track (always provided by GPS), but providing you move far enough for a decent gps heading and stay aligned in a particular cardinal heading all the way to a stop. The alternate method of a compass rose (assuming you can find one) takes a lot more work to align the aircraft to, i.e. either two people (pilot and outside spotter) or getting out of the aircraft, starting and stopping the engine, etc.

But when the more accurate in-air calibration is performed, is all the ground information totally over-written anyway, including cardinal points? I'd like to see that answered authoritatively.

IF so, then a highly accurate ground calibration isn't really worth all the fuss; it just has to be accurate enough for the in-air calibration to have a "good enough" starting point. The ground calibration would also give some confidence that the magnetometer is mounted in a good enough location to give it a "chance" at passing the in-air calibration process.

 

[jakej]

“IF so, then a highly accurate ground calibration isn't really worth all the fuss; it just has to be accurate enough for the in-air calibration to have a "good enough" starting point. The ground calibration would also give some confidence that the magnetometer is mounted in a good enough location to give it a "chance" at passing the in-air calibration process.”

The above says it all - that’s the method I’ve been using on many aircraft - a good ‘in-air calibration’ ( I aim for at least 125 on the counter) is what’s really needed - too easy .

 

[PaulSS]

Yep, a rough ground calibration (just the four cardinal points and it really doesn't matter that a truck past by within 400m). Get in the air, fly a bunch of figure of eights and at different bank angles. Get it into the green and keep going for a bit longer to see if it'll got to 110 or whatever and then save. It works brilliantly

 

[airguy]

Yup, that's pretty much the accurate picture.