RV-8 and the AV Mag Installation
6/10/22 - A few months ago, when I was doing my Condition Inspection, I sent my AV-30E back to uAvionix to have the internal magnetometer upgrade done and the newest software installed. When I got it back and installed, the unit didn't seem to recognize the internal magnetometer. After talking with uAvionix, who were very helpful, Rebekah did a great job of putting up with all my questions and changing my mind. In the end, I ended up with an external Av Mag to install for heading reference. I am really looking forward to this as my panel mounted compass is pretty inaccurate. I am also looking forward to a future software update that should allow me to get wind speed and direction in flight, just LIKE the big EFIS's have.
I was a bit nervous about the prospect of installing the Av Mag because I didn't really understand the instructions and I thought I would need to install it in a place that would be very difficult to work in. I was going to send it back, but Carl was able to convince me that I could install it in the rear baggage area and it should work well, or at least well enough to be better than what I have.
I think that the installation instructions leave a lot to be desired, but at the same time I recognize that it may just be me. My background is military and commercial aviation where instructions are usually pretty specific. I installed the Av Mag per Rev. E of the AV-30E installation manual. I think the instructions are probably pretty good for the actual setup in the unit itself, but the physical mounting instructions leave a lot to be desired. For instance, in section 11.3.5, item 1 "Wire and mount the AV-Mag", they start off with the installation menu in the unit. I don't even have it in yet, what is the installation menu going to get me?
Item 2a in the same section says "Identify a potential mounting location in the tail or wings." OK, what criteria do I use to identify such a location? Running wires through the wings is difficult enough to take that out of the equation. I was originally going to put it in the tail on the stab saddle under the vertical stab fairing, but it was pointed out that there are a lot of steel parts back there, and it would be very difficult running the wires through the full length of the fuselage.
Item 2b in in section 11.3.5 says to run wires from the AV-30 to the mounting location. Great, where do the wires go? Can I put them wherever I want? Of course not. I eventually found figure 12 and figure 8, many pages back, that detail where the wires go. It would be nice to have that referenced in the Av-Mag installation section.
I read through the Dynon Skyview installation instructions for their magnetometer and they had some good information on how to choose a mounting location. I used those concepts. One that they suggested was to use a compass moved around in the area you plan to use to see if it picks up any interference. I settled on mounting on the right longeron in the rear baggage compartment.
I know this is not the ideal location, I would prefer to mount it behind the rear baggage bulkhead, about halfway between that bulkhead and the next one aft, but working in there on a completed airplane is not something I really want to deal with.
Using the spare compass trick, it appears that this area is relatively free of interference.
I made an adapter plate to hold the Av-Mag to the longeron. I had forgotten how thick the longerons are. I was planning to fasten the plate with 3 LP4-3 blind rivets and punch out the stem so there would be no steel. It was too difficult to get the proper tools in there to do a good job of drilling straight holes, so it is held on with double-sticky tape. If that location works, I will probably use some Pro-Seal as an adhesive.
Once I got that mounted, I discovered that I didn't have any of the proper shielded wire so I couldn't finish. I chose to put it all back together and go fly instead.
6/17/22 - 6/19/22 - I got the wire from Aircraft Spruce this week. I foolishly thought that it would be a simple matter to run and connect the wires. Silly rabbit...
The double sided tape I used failed earlier than I thought it would, so I mixed up some pro-seal and mounted it for good. While the pro-seal was setting up, I ran the wires. I was using 3 conductor, 20 gauge, shielded wire. I probably could have used 22 gauge, that appears to be what is coming out of the unit, but I went with the 20.
It turned out that physically routing the wire through the fuselage was the easiest part. There were a few other wires that I piggy backed on. Getting the connector off the AV-30 without either dropping the panel or at least pulling out the AV-30 is, in my case doable, but very painful. There is just barely room for me to get my arm up there and it is pressed against a lot of hard, sharp objects in the process.
The hardest part, of course, is the constant climbing in and out of the airplane to get things you forgot, or didn't know you needed, until you needed it. Getting pins on the end of the wires and getting the wires into the connector was pretty straight forward, as one might expect.
Where the difficulty came was in putting the connector back together. Either the instructions changed since I first installed the unit (of course they changed, the install manual is now about twice the size of the one I used initially), or I didn't read it very closely the first time.
I saw that there is supposed to be a bonding strap (no more than 8 inches long) attached to one of the screws holding the connector to the unit and the shield from the shielded wire is supposed to terminate at the other screw on the connector.
I didn't have a bonding strap that met the stated requirements (at least 3/16 wide braided wire, no more than 8 inches long) so I had to hit up the aviation department at O'reilly Auto Parts. That was after striking out at Autozone.
The strap I bought was much too long, certainly more than the 8" maximum, so I had to cut it to length. That was no big deal since I had to cut the terminals off and install new ones anyway. At least I have a bunch left if I ever need another one. The manual called for 3/16' minimum. The closest I could fine was 1/4". I would have preferred the smaller size, but it worked.
Once I got the connector back together and reconnected it was time to call it a day. I'll do the back end at the magnetometer tomorrow.
Saturday I got out and finished the connections. I really hate dealing with small wire. I buggered up a couple of the supplied butt splices and had to use some other ones. In time, I had all the connections made and fired up the unit. When going through the installation pages, I was glad to see that it recognized the Av-Mag.
I ran through the installation steps, made the required measurements as best I could and it was time to roll it out. There is a page to input the local magnetic field strength. One source of that data is a connected GPS. I wanted to use that, figuring it would be more accurate than using either the default or looking at a web site and entering it manually. With the airplane outside and the GPS locked onto the satellites, the correct figure came right over, which is lucky because I don't think I would have come up with that number myself.
Now it was time to go over to the compass rose and calibrate it. That is not a particularly difficult process, but it requires a lot of moving the airplane about by hand. I figured that if the tail wheel and center of the spinner were both in the center of the line, the airplane should be lined up with the particular heading. On some headings I was able to hit that on the first try, but on others I had to reposition the airplane several times.
Once I was done, it appeared that the display was off by about the same amount at each heading, so I adjusted the yaw in the set up menu. Once complete, it still seems to be off by a degree or two here and there, but it is WAY better than the vertical card compass mounted int he panel.
Unfortunately, the weather was still a little to yucky to go try it out in the air. Maybe tomorrow.
I look forward to some of the features that this unit will bring in future software updates. In all fairness to uAvionix, I'm sure that others wouldn't have had the same difficulties I did and in another airplane, one with better access, particularly behind the panel, this would have been as easier process. While I do think the instructions could be improved, after going through them about a dozen times or so, I think I understand them better now.
Epilogue- Friday 6/24/22 - I finally got to try the Av-Mag in the air today. It is a little difficult to tell how well it works as I can't really tell in flight. I figure that on the ground, with the tires preventing drift, the GPS track should be the same as the magnetic heading. In most cases it seems to be off by a few degrees, but I need to spend more time with it to get a better feel for how much.
While taxiing back the hangar this afternoon after my second flight of the day I got an error message on the AV-30 that said "Warning: Config and preferences reset to default. Reconfig required. Press any key".
Of course, the first problem was that I couldn't find the "Any" key. The right button worked just fine though. I sent an email off to uAvionix to find out if this kind of thing happens often. I hadn't changed anything or done anything differently, so it took me by surprise.
I thought that it had dumped everything I put into and became just like it was when it came out of the box, but it seems that only the screen customizations were dumped. The Install and Setup entries that I made seem to be intact. The compass calibration is not something that I would like to have to do again if not really necessary.
For now, it seems to be working well and it didn't dump on me on Saturday's flights which were longer than Friday's.