All About Avionics

Building your own panel is completely doable. We offer some tips on how to get it right the first time.

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Given what I do for a living, I get to see a lot of variety in instrument panels, both professional and homebuilt. My shop produces finished panels for builders to install in their projects, but people may not realize that many of our customers build their own panels. While it may appear to be a daunting task, it is entirely possible for a person of average skill to accomplish. We’ll take a look at some of the tasks and tricks that will help you to build at least some, if not all, of your own instrument panel.

The Layout

First, we start with the blank panel. In many kits this is a bare piece of aluminum that may or may not be cut to shape or have mounting holes. Even in planes that are built with composite, wood or other materials, the core instrument panel is usually constructed of aluminum sheet, though carbon-fiber sheet, fiberglass or wood may also be used.

When cutting out complex shapes, use a pattern or have it cut out for you with a CNC machine. In the above example, the builder did almost all of the cutouts himself, but had the Garmin 796 cutout done on a CNC to ensure accuracy of that odd-shape hole.

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Before you start cutting, prepare a layout of your panel. The easiest way to start this task is the “paper doll” method. Gather your choice of avionics photos, cut them out, and then tape them to the blank panel until you have something that resembles a basic layout. Don’t worry about your cutouts being 100% to scale; just get them as close as you can. If possible, arrange the cutout photos while you’re sitting in the cockpit, pretending you’re flying the plane, to get a better feel for their position.

Though the camera angle doesn’t show it, the stack of trim switches/indicators are aligned vertically with the key-switch hole. Note how the holes for the switches are all aligned and spaced equidistant.

For those less tactile individuals who are more attracted to technology, you can do this same exercise on a computer with a low-cost CAD (computer-aided design) program, a simple paint program, or with pencils, graph paper and a scanner.

It’s worth your time to draw all of the cutout details with pencil or marker before cutting to keep all of your lines straight and even. Remember to cut holes slightly undersize so you can “file to fit” the final openings.

As you build your layout, there are some things to remember.

1. Resist the urge to create a “non-standard” layout when it comes to primary flight instruments and the arrangement of switches. Many flight hours by intelligent people have proven that the standard layout works best, so it’s wise to follow their lead. Deviation will leave your plane both less functional and less attractive.

When mounting rails from adjoining devices that are very close together, you can “stair step cut” the rails to keep them strong within a tight space.

2. Try to keep things lined up as best you can across the panel, both horizontally and vertically. Symmetry not only looks good, it greatly reduces strain in the air and increases the usability of the entire instrument panel. A willy-nilly arrangement creates chaos in the panel and in the wiring behind it.

3. Do not place switches all over the panel; try to keep them in a centralized location. Resist the urge to locate a particular switch next to each specific device. Not only does this require more movement in the cockpit to perform various functions, but it also greatly complicates the wiring behind the panel, reducing reliability. Plus, it’s just a disorganized way to operate the aircraft.

Place switches in one area, grouped by logical function such as main power/alternator/ignition, lighting, avionics and other similar devices. Also, place them in order of importance. For example, you will use the master switch on every flight, but likely only once. The flap switch will probably be used more often, and it’s handy to have it close to the throttle where it can easily be accessed without removing your hands from the flight controls. Also note that circuit breakers or fuses should be located where they are both visible and operable.

4. In both side-by-side and tandem-seat aircraft, place the main avionics radio stack so that it can be operated by the “non-flying” hand. Many tandem drivers claim they can’t turn a knob with their left hand, but it’s easy to do and is much safer than switching hands on the stick or reaching across the panel.

5. The area directly in front of the pilot should be treated as sacred and used only for vital elements such as flight instruments, autopilots, switches and other items that are important for regular flight. Don’t waste that space with items such as ELT remote indicator heads, dimmer knobs, USB ports or other devices that are not critical.

Radio racks are taped together in a mock layout on the bench.

Important consideration to bus bar and breaker layout should be given when large numbers of breakers are used. This allows for simplified and organized wiring, while still allowing multiple busses to be controlled (three in this photo).

Cut and Run

Now that you’ve finished the layout of your panel, it’s time to start cutting, which you can either do yourself or have someone do for you. The first option is not necessarily difficult, but it can be time-consuming. Most pilots are now using EFISes and other digital boxes, so cutting the larger square holes is the easy part; it’s locating and placing various screw holes, switch holes and other smaller items that can be a hassle. That’s where the second option comes in. There are many machine shops and avionics shops around the country with CNC machines dedicated to cutting sheet metal. If you provide them with a good drawing or computer file, most will cut your panel for $90 to $250. Taking into account that you’ll likely spend at least 16 to 20 hours cutting your own panel, it may be more cost-effective to have one cut for you, freeing up your time for other aspects of the build.

Time for Tailoring

After the panel is cut, the next step is to “dry fit” all of the components, starting with the radio stack. There are many ways to do this, but the easiest is to start with the empty avionics trays, which can be purchased at a reasonable price in advance of the main avionics units. Align them so that the front faces are close to being flush with each other, using strong tape to secure the entire stack. The stack can now be located in the panel where you will be able to mount the angles used to secure it.

Zip ties are used as disposable holding devices while the circuit breakers and bus bars are being fabricated. At a cost of around two cents each, they make great temporary fixtures while you are wiring.

Your cutout for the radios will be 6¼ inches wide with slight modifications for various protrusions on some pieces of equipment. With the panel secured, you can position the stack in between the two rails to which the radios will be attached. To locate things correctly, the tray fronts should be flush with the face of the instrument panel (taking into account any overlays or other things that may increase the thickness of the panel). Once everything is held in place, you can simply drill from the mounting holes in the panel and into or through the rails, and then use a Cleco or bolt to hold the trays in place. Some builders like to use nut plates to secure the trays, but this is not mandatory.

A typical radio stack mounted in an instrument panel with its associated wiring and antennas attached. Note how the bundles are nicely secured and regularly tied.

Continue mounting other trays for EFISes, GPSes or instruments before moving on to switches and circuit breakers. This allows you to create any initial bus bars that will gang various switches and breakers together along with headset jacks and other miscellaneous items.

Extra slack (service loop) left in wires attached to screens allows you to remove components from the panel without having to disconnect them first.

As an intermediate step, put all of the items back into the panel semi-permanently; this is where the wiring process begins. Don’t start painting yet, because the panel will get dinged up and scratched before you’re finished wiring. Place the panel with all of the components either upside down on a bench or secured on top, allowing you to access the backside. Start the wiring process with the circuit breakers, fuses, vertical power and switches. Run the wires between these items first. If you run one wire at a time and use either zip ties or clamps to group them, the harness will turn out well. This is the time to fabricate any bus bars for attachment to rows of circuit breakers or switches.

A stack of avionics shown with professionally “prewired” harnesses ready to ship to a builder. Installation errors are greatly reduced when the stack is already wired and tested for you.

Wiring It

Next, focus on any airframe grounds that need to be attached to your central grounding point, and run those wires. Once most of the switches and circuit breakers are connected, you can move on to the avionics. I strongly encourage people to use colored wires to identify various components. I use red wires for power, black for ground, blue for GPS signals, yellow for lights, green for shield grounds, and white for standard avionics wiring. Shielded wiring is preferred for almost all audio connections.

An example of a radio stack mounted to its rails along with added straps in the back that serve to better strengthen and secure the racks together.

I’m biased, but I’d recommend that you have the core avionics stack wired by a professional. It’s not that expensive in the overall scheme of things ($500 to $2500), and it’s cheap insurance when we’re talking about $10,000 to $20,000 worth of avionics, or more. It’ll also save you countless hours. Avionics wiring is not magic, but it is tedious and takes careful concentration to get things right. If you do your own harnesses, at least start with a good drawing of all interconnects, and then take it one wire at a time. When you are stringing wires, make sure you leave a bit extra on removable items such as EFISes or GPSes. I leave anywhere from 6 to 12 inches of extra wire, called a service loop, to easily remove those devices from the panel and then disconnect the wires rather than trying to disconnect them first.

Simple nut plates on the instruments are often best for mounting various screens, but using them on the rails isn’t advisable because you may need the future flexibility to add other devices.

Initial Testing

Once you’re finished with all of the avionics wiring (remember, the switch/fuse/circuit breaker wiring is already done), you can proceed with testing your panel. Before you power anything up, there are a number of things to consider:

1. Find a device to power the panel. A 14 VDC power supply is preferred, but a good battery and charger will also work.

2. Check, double-check and triple-check that you have the + hooked to power and the – hooked to ground. More than one customer has called with a sad story of the power and ground being reversed; this typically lets smoke out of the wires and blows up costly items.

3. Have every switch in the OFF position, and have all circuit breakers pulled to OFF (or fuses removed from fuse blocks).

4. Have a coax cable with an antenna hooked into both the transponder and radios. Do not test your radio transmitter or transponder ident without having an antenna hooked up; it may cause a lot of damage.

5. Ensure any loose wires with exposed ends are protected with tape or a suitable device so they don’t touch each other or anything else that could cause a short circuit.

6. Do not power up devices such as autopilots, trim systems, flaps, alternators or other units until they are completely wired, and all of their subcomponents are hooked up and plugged in. This usually means you cannot test those items until the panel is in the airplane.

Labels on wires will make installation much easier no matter which method you choose. They also assist in future maintenance and identification of various wires.

Once you ensure that you’re safe and ready to power up, you can move forward by attaching the power to the panel. If there are no sparks or smoke, start turning on devices one at a time, beginning with items of least importance (or lowest cost). If at any point a breaker pops or a fuse blows, stop and turn off all power until you can figure out what the problem is. Once you have successfully powered up the entire panel, you can start programming the various components and their interfaces such as inputting engine limitations, airspeed reference speeds and GPS interfaces. The more of this you can do ahead of time, the better.

Putting labels or reminders on the back of the panel will help you remember which item is which when you are wiring it up.

Finish Work

Now that you’ve wired and tested your entire panel, you can remove all of the equipment and do the finish work. Typically, professional shops and most builders choose to paint their panels. Use a good quality paint, such as urethane, that will not fade or damage easily, and choose a color such as black or cool shades of white, tan, brown or gray. Bright colors can be distracting. Wood overlays can look good if done properly, but other overlays available in thin sheets such as carbon fiber are easy to work with and can be less tedious. By far the most popular and easiest approach is a painted metal panel with labels on it. You’ll find numerous options for labels.

Sheets of custom-made decals can be printed on demand from your files in any color, size or style you create.

1. Decals. This is what virtually all professional shops use. They are thin, mylar decals printed on a dye-sub printer that can be output in white and metallic. Place the decals on the panel and cover them with a layer of clearcoat. They will look great. Pages of these decals can be custom ordered for $20 to $50 per sheet.

2. Rub-on decals, also known as Letraset. These may also be custom ordered but are very expensive. The end result can look nice, but rub-ons are very difficult to apply with accuracy over large areas, or when applying multiple words or shapes such as arrows and lines. Pre-made sheets that you can purchase online are a good option for the occasional label or word, but they may not be the best choice for an entire panel.

3. Various online DIY decals. There are a number of kits available that work with varying success, but I would advise against going this route. They do the job, but the end result is rarely great, and it takes a lot of time to create a mediocre result. Go with pre-made or custom-ordered decals instead.

4. Silkscreening. This is another DIY option you can do by ordering a custom silkscreen and applying the labels onto the panel. It yields a professional-looking result, but it is tedious and somewhat expensive. Many shops used to do this but have since moved to decals due to the time and expense of the process. The difficulty is that the panel must be perfectly flat in order to apply the silkscreen, which is not always possible to achieve.

5. Laser-etched, laser-engraved. A few shops online will laser-engrave your panel. The end result can look good with a thorough initial preparation. This process usually entails etching through a layer of paint into a contrasting layer below. It can be difficult with small fonts, but it’s high quality.

6. Overlays and placards. You can choose to have overlays made for placement around the switches or circuit breakers and other places on the panel from reverse-engraved or front-engraved materials. Results are usually very good, and costs range from $75 to $500 for an entire panel. A number of trophy shops can do this, but we’ve found the best results come from Aircraft Engravers (www.engravers.net).

7. Other DIY solutions. We’ve seen some very good applications of office-type labels on panels, but we’ve also seen labels written on masking tape. Some of the more creative solutions can be hit or miss.

Note the simple layout of switches and circuit breakers. The valuable space in front of the pilot is used for flight instruments and the autopilot, then radios and finally the map box on the far right.

Installation

When the painting and labeling are finished, reassemble your panel and install it in your plane. The next step is to hook up the airframe items such as lights, flaps, ignitions, probes/sensors and fuel pumps. This is another task best performed one wire at a time, making sure not to string any wire too tightly. Once everything is hooked up, repeat the bench-test process all over again before powering up and testing it in the airplane. Be sure to test the com radio and transponder to ensure they are working well before your first flight.

There is a reason professionally built panels look good. But even if you’re building your own, attention to detail and high standards will create an attractive and functional panel. Stick with the basics, and you can’t go wrong.

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