Started panel for real

September 20th, 2008

A month after I submitted the initial set of drawing files, I got the finished panel back from the machine shop. The total bill was… well, I don't even want to write down what I had to pay, but suffice to say it was about quadruple what I was expecting. It turned out pretty nice, but there's no way I would use that same shop again. I would have been better off sending the design to one of the several places that specialize in CNC cutting of airplane panels. Anyway, let's forget that ugliness and keep moving forward.

I fit the various switches, breakers, etc. to the pilot's side panel. Everything fit very well after a little bit of work with a file.

A view of the other side:

Closeup of the alternator circuit breakers… you can see where the machine shop guy made a booboo. The CNC machine was programmed to drag the cutting tool across the surface of the panel, making a nice little trench. Luckily this is not a big deal, since I was already planning to put an engraved placard over the top of this area. If it had been anywhere else, I'd have been pissed.

I used a 1/8" drill to make some little divots on the back side of the panel, for the circuit breaker keyway washers to catch on.

Passenger-side panel installed in the fuselage:

Zero hours on the Hobbs!

Pilot-side panel installed, and looking pretty sweet if I do say so myself. By the way, my plan is to get everything wired up, drill holes for miscellaneous other stuff like parking brake and heat valve cables, and then take it all apart for painting or powder coating (haven't yet decided which).

Same thing from the other side. The canopy deck intrudes a bit on the available behind-panel space, forcing you to think three-dimensionally when locating your panel components. Luckily I got it right, and nothing runs into anything else.

I temporarily installed the radios, and cut some 0.090" filler plates to cover the unused area at the top and bottom of the radio stack.

This is the money shot:

At Oshkosh I good a good deal on this fancy flap switch. It has a little flap-shaped piece of aluminum for a handle, which is a cool touch.

In order to get the switch body to clear the panel frame, I had to make (I hesitate to say "machine" since my tools are fairly primitive) this spacer out of 3/16" stock. Right now it's just captured by the switch, but I may end up riveting it to the panel just because.

I never finished wiring the two buses together at the bus tie diode, so I finished that tonight. This is a power diode with a hefty heatsink, which provides an alternate power path from bus 1 to bus 2, but not the other way. The heatshrink over the terminal ends is just to prevent a short circuit if I drop a wrench across the two terminals while power is applied. Although they are protected by fusible links, I don't want these big power wires flopping around, so I used an adel clamp here. Probably overkill but it makes me feel better.

Here's a view from the other side of the subpanel. All the wires are cinched down tight with tie wraps.

Here's a cool trick… Avery sells these tie wrap bases that have a hole in the middle that's just the right size for an LP4-3 blind rivet. Need to secure a loose wire but don't have anything nearby that you can put a tie wrap around? No problem, just use one of these little guys. I have a feeling I'll be using these by the truckload, all over the airplane.

Engine ground straps

September 16th, 2008

I installed a braided ground strap between the back of the engine and the firewall ground block. This is the heavy-duty conductor that carries the hundreds of amps of starting current back to the negative terminal of the battery. It's fastened at both ends by adel clamps, so there's no strain on the actual terminal ends.

Closeup of the attachment to the engine… it's secured to one of the auxiliary alternator mounting studs with a nut and lockwasher, and is clamped to a neighboring stud.

Then, because I have equal love for both belt and suspenders, I installed a second one. If the first one were to somehow come off, the full current of the starter would flow back to the negative battery terminal through all the various sensor wires, control cables, etc… quickly turning them into smoke. Thus, a backup ground strap. This one goes between a sump bolt on the left side of the engine, over to a nutplate on the lower firewall. I couldn't find a way to provide strain relief for the ends, but it's only a backup.

There's so much stuff back there that it's hard to get a good picture, but you can sort of see where I put some heatshrink tubing over the second strap. There's no danger of a ground wire shorting to ground, obviously, but I wanted to guard against it accidentally rubbing against the engine mount. It doesn't touch it currently, but it's possible that it might flop around and tear up the powder coat.

Propeller arrived

September 14th, 2008

Eight and a half weeks after placing the order, the propeller arrived. It is a thing of beauty. Heavy, expensive beauty.

The box is like eight feet long and weighs ninety pounds. With it sitting like this, there's barely any room to walk. Or store empty beer bottles.

I dragged it over by the wings, and raised it up on some boards so the cardboard doesn't soak up moisture from the concrete garage floor.

For reference, here's the current status of the fuselage:

And the rest of the garage… what a mess.

More panel mockup

September 8th, 2008

I got the plastic mockup of the other half of the panel…

The Hobbs meter and ELT control thingy fit fine:

I put the finishing touches on the CAD drawing and sent it to the machine shop.

Panel mockup

September 7th, 2008

I got the pilot's side half of my plastic panel mockup back from the machine shop. Here it's being clamped to the actual aluminum panel blank to check the accuracy of my CAD outline:

One area down by the air vent needs to move out by an eighth of an inch:

The right side is a bit off as well. These edges are based on measurements that I made while the panel was in the airplane, so I'm not surprised that they're a bit off. Everything else matches up just fine, including the complex curve along the top.

The standby instruments (ADI and airspeed shown here) fit perfectly. I had to pack them pretty close together, but there is still plenty of space to install and remove them.

The starter key switch snaps right into its funny-shaped hole (scroll up to see photo).

The annunciator lights fit in their holes, but I think I ought to be able to space them 1/32" closer together in the final version.

The Cessna master switches fit in their holes, and the Honeywell rocker switches fit as well. The latter is missing its plastic cap, since I plan to order those separately from a place that can engrave legends on them for me.

View from behind the panel… the master switch terminals are pretty close to each other and to the body of the ADI, but judicious use of heatshrink and tie wraps should keep that from being a worry.

Plastic panel mockup clamped to the panel frame in the fuselage:

The fuel pump switch is placed so I can reach it when I have my hand on the throttle:

The corner of the airspeed indicator clears the panel frame with room to spare. This photo also illustrates why I had the mockup made from clear plastic – easier to see where instruments/switches interfere with behind-panel structure.

Another shot of the ADI… also you can see that the cluster of ignition switches and master switches can't easily move outboard without either hitting the panel frame or being rearranged. That would mess up the symmetry; I hate messed-up symmetry.

One surprising discovery: The ADI extends further behind the panel than I thought, so it actually comes within a couple inches of the fuse blocks. No big deal, I'll just have to use right-angle connectors.

I thought about just moving the ADI to the top of the stack of standby instruments, but it would hit the panel frame there.

Not pictured is a bunch of CAD work I did to get ready for the real panel production run, including completely redoing my CAD model of the glass cockpit displays. My panel drawing is dimensioned in inches, and the display outline I keyed in from the manufacturer's drawings is metric – normally this would be child's play for a CAD program to handle, but DeltaCad only seems to store object scale factors to three significant digits. That means that the conversion factor from millimeters to inches is represented as 0.039 instead of 0.03937008… that's an error of about a sixteenth of an inch per six inches, which is why none of the holes in my display screens lined up. Since almost everything else in the panel mockup turned out perfect, it took a lot of head scratching before I figured out what had happened. I converted the metric dimensions to inches by hand when laying out the new model, which should remedy that problem.

Mary was in town this weekend, so we were out doing non-airplane things most of the time.