Eating the Elephant—Part 3

I love designing and building the cockpit. More than any other part of the ship, the cockpit is where the pilot lives and works—it is home. Sure, there have to be wings, powerplants and a fuselage—but the beauty of those is for the outside observer—the cockpit is what defines the flying experience for the pilot.

To be more specific, what I really enjoy is designing instrument panels and controls—getting everything in just the right place and making it all intuitive to the pilot. Having controls exactly where you think they should be—ah, that’s perfection.

Good panel design is always evolving, of course. The move from steam gauges to glass cockpits brought with it an entirely new idea of how displays should present information and how many functional displays a pilot needs. Modern electronics, computer hardware and software—they allow us to let the ship take care of menial chores while the pilot becomes a decision-maker. Autopilots can steer the ship more accurately and efficiently than a typical human “meat servo,” so why not let it take care of the magenta line while you have a look at that weather up ahead.

The Enemy Is Time

But the problem in designing a new cockpit is that it takes time to build an airplane—and in the passage of time come new ideas, new thoughts—and sometimes new hardware. The panel that you designed early in the process might evolve into something entirely different between the time you start the tail kit and the time you hang the motor. Somewhere in there, you have to commit—have to choose a complement of equipment and how it is going to be laid out. To not do so means putting off myriad things, not the least of which is wiring.

That delay can lead to a lack of progress as you find yourself boxed into a corner. You can’t close out the floor until you run the wires for the antennas—but you can’t mount the antenna until you know if you’re going to have one or two communications radios—and having two com antennas changes where the transponder antenna has to go… Until you start making these decisions and mounting hardware, you are not going to make much progress.

Decision Tree

You make the hard decisions. You decide on a complement of avionics, an EFIS and a lighting scheme. You know how many electrical buses you’re going to run, you’ve decided on an electronic ignition (or maybe you’re sticking with magnetos…it’s your choice, so why not?) and you have started making a list of switches and circuit breakers (or fuses). After a couple of months of playing around with layouts, you’ve decided on a panel, so you start cutting metal, drilling holes for switches and even running wires. And when you finish, everything works—and the smoke stays in!

Wonderful, congratulations. You’ve had an enjoyable few months and come up with a great design. Then the what-ifs appear. Didn’t you intend to have a built-in oxygen system? And how about those heated seats? (I distinctly remember you thinking about heated seats!) Well, it’s not too late to add both. But that also means you’re going to need a place for the controls, an oxygen pressure gauge and a circuit breaker for each seat. Horrors, you now have to add things to your perfect panel!

This is why I personally don’t have panels cut, powder coated and silk-screened for my projects. I know that as the project evolves, there will be things I need to add. If you have a perfectly finished panel from one of my many friends in the panel-building business, it is hard to modify them as you go.

If you don’t want to disturb the effect of a perfectly finished panel (very much like your luxury car), you are stuck with your original ideas. But if you cut your own, paint your own and label it yourself—you always have the tools and skills to make changes that don’t look like changes!

The Rocket Evolves

Let’s take a look at the evolution of our Rocket cockpit. Now that I’ve been around the block a few times, I know what I like. You’d think, therefore, that I’d get it right the first time around. You’d think.

I’ll talk more about the avionics choices in the sidebar “The Avionics Suite,” but for now, let’s just say that the panel complement was fixed early on and I am very happy with the choices. The layout came naturally—I like symmetry and the boxes lent themselves to that. Originally, I had planned to have no switches on the panel—all of them would be relegated to the side panels as we did on our RV-3. I also wanted only two power wires—main and aux buses—running into the panel. That meant that all the circuit protection for the panel-mounted boxes would have to be on the panel. So that introduced some breakers.

Since I wanted to build an annunciator panel to visually balance the Garmin G5 backup EFIS, I had a natural place to add the breakers for the panel-mounted avionics—and I thought everything was simple. But it wasn’t! I also wanted some critical equipment to be powered by both buses, and that meant more breakers. OK—a row of breakers under the right-side avionics boxes would do.

But then my plans to put the magneto switches over on the left-side panel with the engine levers was sunk in a real-estate fight. Sure, I had room for the fuel pump switch there, but not much more. Time to rethink. How about some switches under the EFIS that get used all the time? Mags, start, avionics master and some lights? I could leave the electrical power management over on the right-side panel as originally planned. As such, the cockpit flow was going to be very nice.

I hadn’t even cut any metal yet and things were evolving!

The switches ended up under the EFIS and any breakers related to the panel or critical functions found homes there as well. With this design, I cut metal, painted and labeled. And all was right, good and happy—I liked the layout and the flow was excellent.

A Breath of Fresh…

But along came change. The built-in oxygen system has the bottle ahead of the panel, up against the firewall, and I had the valve/regulator on the port side. But when I got the rig in hand, it was longer than I expected and the bottle had to shift right. That real estate was taken by the GEA 24 (the Garmin engine monitor box). But if I flipped the bottle, there was room for the GEA on the port side (because of the difference between the avionics stacks on each side) and all the components were happy once again.

Now the O2 gauge and controls needed to be on the right instead of the left (to facilitate short high-pressure O2 plumbing—always a good thing!). So, bingo—the electrical panel needed space for those. And since I had decided to add a GAD 27 to control flaps, trim and lighting, I now needed a place for panel dimmers. Oh and there is that pesky ELT control panel, a knob for the FlyONSPEED AoA that I was going to add for further testing and then there was the seat heat switch and a switch to disable the trim and flap switches in the back seat when I have non-pilot passengers.

I could go on and on, of course, but you get the point—things will change as your airplane matures. I am a huge believer in setting the requirements early, then sticking to them. Being the proverbial “kid in the candy store” when new stuff comes along is a great way to never finish. But you also need to remain flexible when you have better ideas of how to lay things out. And you will!

Is That Your Final Answer?

Now of course, at some point, you are going to lock things down—but if you wire and lay things out early in order to work when the fuselage is wide open, you are inevitably going to make some changes along the way. But be smart about them and plan to leave some blank panel space somewhere (probably not on your “work of art” panel, but on sides, center console or overhead (if you have one). And more importantly, when you run wire bundles, include some “spare” conductors for future use. This way, when you add that powered CO detector, you have a power wire already run for it—you didn’t just know that was what it was for! Likewise, include some shielded twisted pairs—you’ll eventually add some avionics box that needs them.

We “scar” spacecraft with extra wires all the time because it beats breaking into wiring bundles later. It’s smart to have space for expansion of a CAN bus or maybe putting some extra aux wires into your audio panel so that you don’t have to break into the connector when adding some new bauble that makes sound when you expand your electronics later. It might be painful to add things like this now when you really want to be done with wiring. But believe me, adding wires into a finished airplane later is far, far worse.

There’s always “just one more thing,” so remain flexible as you build. After all, the average airplane takes three or more years from start to finish and you may change your mind on a few things after looking at many other projects and planes along the way. Allowing space for expansion and using painting and labeling techniques that you can duplicate so that changes don’t look “scabbed in” can produce a stunning aircraft in the end.