Mounted ELT

July 26th, 2014

While I was contorting myself back into the baggage compartment to work on the autopilot pitch servo, I went ahead and installed the new ELT also.

For those of you keeping track at home, you might be confused because I already mounted the ELT a long time ago. In fact I did it twice. Well, I didn't like either of the two previous arrangements, and also new and improved ELT technology has come along in the meantime. I wanted the benefits of having a 406 MHz ELT, so I bought an ACK E-04. That's the least expensive one on the market, although they are still not what I would call cheap.

Anyway, does this look like a happy face or what?

You're supposed to mount the ELT in a more or less level orientation, as far back in the fuselage as possible, and attach it to something strong enough to resist deforming in a crash. I attached the mounting bracket to the F-729 rib, using structural screws for the top two holes that go through the reinforcing angle. It's plenty strong.

Here's what the ELT looks like popped into its bracket:

I still need to connect the power and GPS inputs, not to mention mount and connect the antenna, but first I have to go to Oshkosh to work…

Autopilot upgrade

July 25th, 2014

I sold my Trutrak autopilot system and changed over to the Garmin G3X autopilot instead. Fortunately the GSA 28 servos fit into the same bolt holes as the old servos, so installing the new pitch servo was straightforward. And it's a bit lighter too.

The electrical connections were surprisingly not that hard to retrofit either. Of course the wiring is very different between the two systems, but the servos use a similar number of wires, so I was able to repurpose existing wiring for new tasks. The old stepper motor drive and torque sense wires became CAN and RS-232 lines – luckily I had the foresight to use shielded wire. The only new wire I had to run was a single conductor for the autopilot disconnect line; in the old system the red button was connected to the control head in the panel, whereas in the new system it connects to both the servos. The power and ground wires stayed the same.

I'll have to come up with something to do with this oddly-shaped hole in the panel, which used to be occupied by the Trutrak autopilot control head. I'll figure it out.

I haven't installed the new roll servo yet, since I need to redo some wing wiring, but the wiring that goes out through the side of the fuselage is now all prepared for the Garmin autopilot.

Audio panel downgrade

June 29th, 2014

Another of those "did a lot of work, made little observable forward progress" updates…

When I started my panel design, Garmin made two audio panels, the GMA 340 and the GMA 347. These had different capabilities – the 340 is all analog and the 347 features digital processing – as well as completely different mounting trays and connector pinouts. I went with the 347 on the basis that it must have 7 more "somethings" than the 340.

Fast forward to now… in the intervening years, they've come out with the GMA 240, an excellent low-cost audio panel targeted at us homebuilders, and the GMA 350, a high-end all-digital number. Both of these new audio panels use the same wiring as the old GMA 340, which makes my 347 sort of an odd man out. Given that the 240/340/350 pinout seems to be the favored arrangement for audio panel connectors these days, as well as the fact that the GMA 240 is also lighter and cheaper than the 347, I decided to remove my existing audio panel and convert to a GMA 240 tray. Might as well do it now while I've still got access to the wiring, as it would be almost impossible to do later.

Old audio panel tray removed:

Redoing wiring in accordance with the new schematic I drew. Fortunately it was mostly a matter of de-pinning wires from the old connectors and re-pinning them in the new ones, with only a few new wires or splices required.

Connectors tested, strain-relieved, and sealed up:

I enlisted Mary's help to reinstall the tray in the radio stack, as there was one stubborn fastener which was impossible for me to reach from both sides simultaneously.

New audio panel tray bolted in place with connectors installed. I'm glad I did this now, because the only way to access these connectors once the top skin is riveted on will be with a crash axe or a stick of dynamite. Maybe both.

Testing… everything works!

So I spent a bunch of hours removing a perfectly good audio panel and replacing it with another one. But at least the new one is lighter by a pound and a half, and its seemingly more common pin arrangement might save me some trouble down the road.

Compressor repair

May 10th, 2014

Ever since I bought my air compressor, a factory-overhauled unit from Campbell Hausfeld, the pressure regulator has been broken in a very specific way. When set to the On position, it would run the compressor automatically as designed, topping up the air pressure whenever it dropped too low. However, it would also do this when the switch was set to the Off position, thus making a mockery of the entire concept of having an On/Off switch. I knew all along what the problem was – a little plastic bit inside the regulator housing wasn't quite long enough to interrupt a set of relay contacts – but the inertia of doing nothing about it made it pretty easy to ignore for a very long period of time.

When we went on trips I would turn it off by flipping the breaker at the fuse panel, which is a well-intentioned idea (avoid burning the house down if the compressor springs a leak) but not particularly a well-executed one (using a breaker as a switch is generally considered bad form). This generally led to simply leaving the compressor in a "live" state overnight, which sometimes caused it to cycle in the wee hours of the morning when the falling temperature caused the pressure to drop below the set point. Although you can't hear the compressor outside our house when the garage door is closed, it is unfortunately sited more or less directly below our bedroom, and is quite audible from in there. It always would wake me up, but I'm a light sleeper so everything wakes me up (here's looking at you, annoying loud neighbor). However, once or twice the sound was even of sufficient intensity to wake Mary from her customary log-like slumber, thus making her quite grumpy indeed. So that was more or less the last straw.

Anyway, I finally got around to replacing the regulator with a $37 part from Pacific Air Compressors:

I'm happy to report that it was a quick and easy job, and now the compressor works as designed in all modalities. Most importantly, I no longer wake up to discover that I'm in the doghouse before I've even found my trousers.

ADS-B equipped

May 10th, 2014

One of the unexpected consequences of being a very slow builder – although I prefer the term methodical, thanks – is that whole new technologies that barely existed when you started can advance to the point of being practically de rigueur before you're finish. One example is ADS-B, which everybody is now required by law to have by 2020… at least if you plan to fly anywhere useful. I'm already ADS-B Out equipped by virtue of having the proper kind of 1090ES transponder and a pair of compliant TSO C146 WAAS GPS navigators, but to benefit from the free traffic and weather data my tax dollars are already providing I need to install a separate ADS-B In receiver. Of course the obvious choice for my G3X system is the GDL 39R:

I'm seriously running out room to install stuff in the airplane, especially something the size of the thousand-page biography of Winston Churchill I've been meaning to read all year. I picked out a place on the F-7107R subpanel rib, where there was still some mounting structure left over from when I was plannig to put a Lightspeed ignition module there.

I used a piece of 0.050" aluminum to make a mounting plate, and bent flanges on two sides to give it some stiffness:

GDL mounted and wired. It's quite simple, just power, data, and an antenna. It will be possible to remove this unit for servicing later, but only if I press forward with my plan to cut access holes in the forward fuselage skin.

Close-up detail of antenna coax routing – an adel clamp keeps the cable from chafing on the sharp edge of the mounting plate:

For the antenna itself, I bought a 978 MHz blade antenna from Delta Pop. Relatively inexpensive for an airplane component, and gets good reviews.

According to the boffins at work whom I leaned on for specific installation guidance, the ADS-B antenna should be mounted at least six feet or so from the transponder antenna, and at least three feet from the comm antennas. It probably also wouldn't like being right next to the hot exhaust pipes. The only places on the bottom of the airplane that satisfy all these criteria are the very tip of the tail, and a spot in the middle of the forward fuselage floor about midway between the spar and firewall. I chose the forward location to making the antenna routing easier.

Of course the fuel pump and its associate plumbing are already located there, so things are a bit tight. I temporarily installed the pump assembly so I could mark the location for the antenna. The coax connector sticks up a bit, so it needs to be far enough aft to be underneath the fuel pump cover, but far enough forward that it doesn't run into the bottom of the fuel pump mounting plate.

Luckily there is a loop of fuel line in a convenient spot to run the coax straight up and through, shown marked by a dot here prior to drilling:

To mount the antenna to the floor I made a small doubler out of a piece of scrap 0.063. I forgot to take pictures of the process, but you should know what one looks like by now because my airplane is positively bristling with antennas.

For corrosion resistance and maximum electrical conductivity I treated the doubler with alodine:

As well as the floor, after removing an area of paint:

I enlisted the help of the lovely Dr. Mary to rivet the doubler to the floor. She did a great job even though I haven't given her much rivet practice for quite some time.

Antenna doubler installed, complete with antenna:

The coax runs along the floor and then does a loop to duck down through the fuel plumbing and connect to the antenna:

Side view:

View of the underside of the airplane sporting a brand-new antenna:

I'm now equipped to both transmit and receive ADS-B. Here's hoping I get this thing finished before 2020 rolls around.