Avionics cooling fan

June 23rd, 2009

It's a good idea to supply cool air to your most power-hungry avionics, so I bought a cooling fan to go with my Garmin radio stack. Well, actually the fan is made by Sandia Aerospace, but Garmin resells it. It appears to be a run-of-the-mill squirrel cage blower with some fancy gold-anodized sheet metal around it to justify the 10x aviation price multiplier.

The fan has mounting flanges along two sides only (not opposing sides either) and one big honking flange sticking out at right angles, which is just weird. It says "Beechcraft A36" on the label, so maybe the Bonanza has some little odd-shaped cranny that it's designed to fit perfectly into. To mount it in my airplane, I decided to build this little mounting bracket/standoff thing out of some Z-channel material:

If I ever need to replace or service the fan I will be laying upside down with the fuel selector valve poking me in the kidneys, so I wanted to make it as easy to remove as possible. Hence, nutplates instead of discrete screws and nuts.

Here it is mounted to the subpanel. Even though it's only attached on two sides, it's plenty rigid and is definitely not going anywhere.

The bracket is blind-riveted to the subpanel from the aft side. Yes, I realize I already used this picture, but since I fitted and installed these two components simultaneously you'll just have to look at it again. Also note that one of the rivets does double duty holding a plastic tie wrap anchor for the wire bundle that runs through here.

In this shot, you're standing on the left side of the fuselage looking to the right across the forward side of the subpanel. You can sort of see how the cooling ports on the fan are semi lined up with the back ends of the avionics trays – this alignment is aided by the standoff/bracket thing, and will make running the air tubing easier. Once I finish wiring the radio stack, I'll run air ducts from the three outlets on the fan to the two GPS units and the transponder, which are the boxes that generate the most heat.

Panel light dimmer

June 23rd, 2009

I bought an LC-50 dimmer to control the brightness of the various lights in and around my instrument panel. Since the dimmer knobs will be towards the passenger side of the instrument panel, I decided to attach the dimmer module to the aft side of the passenger-side subpanel.

Nutplates on the forward side:

Here it's screwed to the subpanel:

I mounted two potentiometers underneath the passenger's display, and topped them off with some nice-looking knurled aluminum knobs.

None of this is wired yet, but at least the components are physically mounted.

Show & Tell

June 9th, 2009

We had a few people over to our house this weekend, so I decided to clean up the garage and install everything in the airplane cockpit that I could get my hands on. It turned out to be a nice conversation starter.

This was the first time I'd seen the full interior installed at the same time the panel was all powered up. Looks nice.

There are a few things visible in these photos that I haven't documented on the site yet, but I'll get to them soon.

Of course a lot of what you see here is still yet to be finished, but it was neat to see so many things looking "done" at once. One might even think, looking at these pictures, that it might someday become "actually done".

So He Wants to Build a Plane

May 30th, 2009

The following is a guest post…

Mary here, talking to all of you who ladies whose husbands have said, "Honey, I want to build a plane in our garage."  You're understandably freaked out right now – I was when I found out that building airplanes is one of Matt's favorite hobbies.  Don't fret!  This is a doable project!  However, you shouldn't go into it blindly.  Here are some things to expect from an airplane-building husband.

This is a huge endeavor. OK, you probably already figured that out.  But let me give you a little perspective.  Matt began building the plane in Spring 2005.   I started pharmacy school the following fall.  I graduated this month, but Matt's plane is still a year away from flying.  This is not for the flighty (no pun intended).  This is like having a baby.   The plane will be a major part of your lives for years, if not the rest of your life.  (Thankfully, there are no 3 AM feedings.)  And much like a baby, a plane will require you to invest a good deal of money and space.  Consider:

  1. You'll need workshop space.  For a lot of you, this means you'll have to give up parking in your garage.  You also might find an airplane canopy on your guest bed, or ailerons in your spare room.
  2. It gets expensive.  Builders need rivets, rivet guns, clecos, pliers, drills, screws, an air compressor, wires, deburring tools, wrenches, countersinks, fiberglass material, hoses…  It adds up, and will continue to add up throughout the project, as he'll need to get more and more stuff. The UPS guy and I are pals.
  3. As I mentioned above, it takes a ton of time.  If you want to be at his side 24/7 either be prepared for him to never finish the plane or go out and help him. Which brings me to my next point…

Building an airplane is not just something for him to do.  This can be a family project. You don't have to be out there every second – despite what the pictures on Matt's blog might suggest, I'm not out in the garage every time he is.  It will go a lot smoother if you get involved.  There are certain tasks that are a lot easier to do with a second pair of hands, and everything that gets done puts you a little bit closer to flying.  Even going to the workshop for a few minutes to look at the neat new thing he built can be a big morale boost.  And men, this is a two-way street.  Make a deal that for every, say, 30 minutes, your wife spends on the plane, you spend that much time on something she likes, or do some of the household chores for her, or stay home with the kids while she runs errands.  And speaking of kids, they can help too.  But use your good judgment; letting your toddler handle a rivet gun is probably a bad idea.

You'll meet a lot of new people in this process. Your husband will probably make friends with other builders through VAF, the EAA, and local airports.  Take advantage of this! For one thing, it gives him someone else to talk shop with when you get sick of the airplane stuff.   For another, a lot of these guys are married too, and you and the builder's wives can commiserate.  Airplane people are some of the nicest, most interesting people you'll ever meet.  Far-flung airplane pals can also tip you off to places to visit on your next vacation and maybe even get you a free lunch somewhere.  (Thanks Doug!)

You need to be his #1 cheerleader. I'm not asking you to put on a short skirt and wave pom-poms [aww. -ed.] unless you enjoy that sort of thing, [woohoo! -ed.] but airplane building can be a frustrating process, and your husband probably won't enjoy every part of it.  (See also: Matt and fiberglass)  Help keep him going during the difficult parts.  If you can't help, come down and talk to him while he builds, or let him bounce ideas off of you.

You may also need to keep him on task. Again, not every part of this is enjoyable, and it's easy to get discouraged, especially for someone who has a demanding job.  He may, like Matt, suddenly think it's more important to work on one of his other projects than the plane.  While sometimes that's necessary (the plane can wait if Junior needs help with his science project), too much of that can mean he loses momentum and before he knows it, he hasn't worked on the plane in a month.  Planes that don't get worked on don't get done, and we want these planes to get done.  I once had to threaten Matt with no slushes for the rest of his life if he didn't give up his extra projects and just focus on getting the plane done.

And finally, have a sense of humor. So your friends all think you're crazy, you can't walk into your house without tripping over a just-delivered box of parts, and your guest room looks like an obstacle course.  So what?  You and your spouse have a fun (hopefully) relationship-strengthening project you can do together, and even if you're only minimally involved, you always know what he's up to.

– Mary

Audio input jack

May 18th, 2009

I wish I had one of the new GMA 240 audio panels. The 240 has a stereo input jack right on the front panel, which the much more expensive GMA 347 that I have does not. So to enable my passengers to plug their iPods into the panel and hear the audio in their headphones, I had to track down and wire a separate 3.5 mm audio jack – one of the fancy switching kind that uses a separate set of contacts when the plug is inserted. This will let me use the single set of input pins on my audio panel for both external audio and XM music from the GDU 375 MFD.

I made this little bracket to mount the jack on, since the threaded part of the barrel is way too short to go all the way through my 0.090" thick instrument panel:

The mounting hole is drilled oversize to accommodate the enlarged plastic shoulder on the jack body. This insulates the jack from the metal panel, to prevent the possibility of a ground loop (which is important for quiet audio).

A mylar washer under the nut keeps things insulated there too:

The bracket is attached to the panel with a pair of #4 screws, and the hole in the panel is oversized to keep the nut from shorting to ground. Functional and looks good too.

Six wires are soldered to the five contacts on the jack… two separate pairs of left and right channels, and one common low connection. The two sets of wires also share a common shield.

The little ear on the bracket is for an adel clamp that supports the wires:

Here's what it looks like installed in the panel:

My dad was in town for Mary's graduation, so I enlisted him to help test the audio quality.

Now this is some flying music:

I don't have an XM antenna hooked up yet, but I verified the MFD side of the audio wiring using the 1 kHz factory test tone:

I noticed that this bundle of wires behind the subpanel is starting to get pretty close to a couple of subpanel rib flanges. I will probably put some cat grommet on the flanges, and tie-wrap some plastic conduit around the wire bundle too.