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Making Your Instrument Panel
By Tony Bingelis (originally published in EAA Sport Aviation, July 1996)
You have probably studied photos of numerous instrument panels from time to time during the construction of your homebuilt. And by now, you undoubtedly have toyed with a few ideas of what you would like to work into your panel.
Fortunately, this is one area where you as the builder can exercise considerable latitude in designing and constructing the custom instrument panel you want . . . without affecting the structural integrity or the flight characteristics of the airplane.
Airplanes being built from kits will probably be furnished with an aluminum blank intended to be used as an instrument panel and, possibly, a suggested typical layout for the instrumentation.
However, most builders like to add more instruments and equipment to suit their fancied needs, although, believe it or not, it’s been said that some builders actually want to simplify their instrument panels.
Naturally, the instrumentation you install should be determined by the type of flying you expect to do. That is to say, if you intend to limit your activities to clear weather flying, it would be ill advised to load your airplane down with a vacuum system, gyro instruments, multiple radios, and a complete all-weather instrument flight capability.
In doing so, the added weight will be significant and will have a definite effect on your takeoff and climb . . . however unimportant you might rationalize that to be.
Certainly, the extra instrumentation and radios will have a noticeable effect on your wallet. Unfortunately, a lighter wallet will do nothing to improve your takeoff distance and rate of climb.
Before you start cutting holes in that panel you must decide what kind of instrument panel you want. That is, which instrumentation option do you want? Here are three options:
1. A Basic VFR Panel. This is the simplest panel with the minimum mandatory instruments installed - and perhaps one or two added personal favorites.
2. An IFR Panel. A "full panel" installation with gyro instruments (vacuum or electric), intercom, and all the necessary equipment and avionics suitable for day/night operations under instrument conditions.
3. Something in between (call it a deluxe VFR panel if you wish).
Even though you limit your instrumentation to one of these options, similar panels may vary greatly because of the many optional instruments and manufacturers from which a builder can choose.
Instrument Arrangement Does Matter
After you have decided what instrumentation you will need/want for the type of flying you will be doing, you will have to decide how to arrange your instruments. This is important because a good instrument layout will enable you to spend more time looking out for traffic than looking for randomly located instruments.
A sure way to obtain an effective arrangement is to work out few rough sketches to reflect what you have in mind.
Next, select the one layout sketch you like best and make a full size drawing, on paper, of that panel to check out clearances and instrument spacing. Almost any two-seater, side-by-side configured homebuilt will probably be capable of accommodating all the instruments, radios, lights and buzzers your heart desires.
A single seater or a tandem two-seat aircraft on the other hand does not have the space for expansive instrumentation and avionics without some careful planning. You may even have to locate some instruments on sub panels built into the sides of the aircraft or positioned between your legs on the floor.
Your instrument arrangement, especially for the narrower small panel, must be carefully worked out on paper beforehand lest you forget to include some essential instrument in the limited panel space you have available . . . it does happen.
Be sure you have provided space for each of the mandatory instruments required by the FAA. FAR Part 91 lists these for VFR Day only:
- Airspeed Indicator
- Magnetic Direction Indicator (Compass)
- Oil Pressure Gage (for engines with oil pressure system)
- Oil Temperature Gage (for air-cooled engines)
- Temperature Gage (for liquid cooled engines)
- Fuel Gage for each tank
- Landing Gear Position Indicator (for retractables)
Your instruments, when fitted to the panel, should not result in a random arrangement which might be likened to a shotgun’s scattered pattern. Instead, try to group your instruments in a logical arrangement that will ensure easy scanning. That usually means the most important flight instruments will be in the middle of your viewing area . . . where you would expect them to be.
Naturally, you can expect your instrument panel to be somewhat different than similarly equipped panels in other aircraft of the same type. A lot depends, as I have already pointed out, on the type of flying you expect to do and the instruments selected.
Another factor which may influence and possibly complicate your orderly arrangement might be the instruments and goodies you have previously acquired and would like to use.
Finalizing The Layout
If you regularly fly other aircraft you might consider duplicating your favorite panel. Habits are hard to break and if, for example, you are already used to having the key and ignition switch on the left side of the panel, why locate them somewhere else in your new homebuilt?
After you have settled on the general arrangement of instruments for your panel, check once again to see that you have provided space for all the essential instruments.
Next, be sure there is adequate clearance for all structural parts and between each instrument.
Avoid crowding the instruments. The minimum spacing between instruments should be a last resort. That sort of thing will make the removal and replacement of instruments more difficult later should maintenance be necessary.
Logic will tell you to locate your switches and circuit breakers or fuses along the bottom of the panel, or on a separate sub-panel to simplify access to them.
The same logic should caution you against locating switches and electrical components in the area directly over the radios where access from below would be impossible. The exception, of course, might be when there is a flip-up canopy and the space directly above the instrument panel is open affording pretty good access to the upper areas of the back side of the panel.
Your flight instruments, altimeter, airspeed, rate of climb, and gyro instruments should be grouped and centrally located. Likewise grouped, in another easily viewed location, should be your engine instruments. These in many instances are grouped to the right of the radios.
A good installation is one where your flight instruments are mounted on a removable or hinged panel to give you better access to them and other instruments located on either side.
Of course, if you are young for your age and don’t mind lying on your back in a crowded cockpit to work on the stuff behind the panel . . . forget about that easier access bit.
Instruments in two-seaters (side-by-side) located far to the right of the pilot introduce a viewing problem due to parallax.
To overcome this parallax viewing error, and to make them easier to read, these instruments can be installed in a small cocked panel section. However, this complicates the construction of the panel and you might not even like the effect.
Building The Panel
It is a good idea to use nothing but non-magnetic materials for your instrument panel. This will afford you more options for locating your compass.
The majority of instrument panels, and panel sub-sections, are normally cut out of a fairly thick sheet of aluminum. A large, one-piece, basic panel, for example, may be cut from a hunk of .080" 2024 T3, or the less expensive 6061 T6 aluminum. This thickness will provide enough rigidity for even a heavily instrumented installation.
It is a good idea, too, to make the basic support instrument panel completely removable. If you have a fuselage fuel tank in the nose end, a removable instrument panel may be essential should the fuel tank ever have to be pulled out for any reason. This means the panel should perhaps be attached to the basic fuselage structure with nut plates.
A suggested minimum thickness for a large wide panel, however, would appear to be .060" with adequate support where needed. Heavier panels made of .090" or .125", on the other hand, will carry a needless weight penalty and should not be considered.
Some builders like the appearance of a wood panel and make theirs of plywood or overlay the aluminum panel with a veneer or textured synthetic sheet. Usually, a wood panel is cut from 1/4" plywood stock.
Such a thick panel, however, introduces some problems when it comes time to install the instruments. For one thing, longer screws will be necessary. In addition, the faces of the instruments will be recessed by the thickness of the plywood.
You might not like that effect. However, you could bevel the instrument panel holes and paint the beveled portions flat black. Naturally, it all depends on the effect you would like to achieve. You only have yourself to please.
Panels are best cut out on a bandsaw and smooth trimmed with a disc sander or a belt sander. A saber saw also works well although more finishing work will have to be done. In the absence of such luxurious equipment you can do an adequate job with a hacksaw, a large bastard cut file and sandpaper.
NOTE: Automotive gages take 2" holes while aircraft instruments require 2-1/4" holes. The sizes are not interchangeable so know which instruments take which size holes and where.
Those large diameter (2", 2-1/4" and 3-1/8") instrument holes are ordinarily cut out using a heavy duty Circle Cutter. This tool has an infinite range of hole size adjustments within its capacity, and does a fine job.
Careful! It can be dangerous to use if you allow your hands to get in the way of the sweeping bar and cutter. Always clamp your work to the drill press.
Use a rather slow speed. The larger the hole, the slower the drill press speed should be. About 500 rpm is a good average cutter speed for aluminum.
This tool should not be used in a handheld drill as it is difficult to control without jamming . . . besides, it is a risky thing to do.
After you have adjusted the cutter to the size hole you want, make a test cut on some scrap. You want the instrument to slip into the finished hole easily. You realize, of course, a 2" instrument will not go into a 2" hole, nor will a 3-1/8" instrument fit into a 3-1/8" hole. The holes must be cut slightly larger, but without too much play.
Believe me . . . don’t try for a snug fit. You’ll hate yourself later when you find that nicely painted panel won’t allow the instruments to slip in. Your only recourse then will be to file the holes slightly larger . . . as they should have been in the first place.
Of course, you will ruin the paint job in the process of enlarging the holes a little bit.
The hardest part of making an instrument panel, I believe, is the accurate location and drilling of the many small instrument attachment screw holes.
Alas, it is quite common to find that one or more of the attachment holes has to be elongated before you can get all the screws in. Fortunately, the screw heads will hide all but the sloppiest holes.
Oh, Yes . . .
Measure carefully, or use a drilling template to assure yourself that the drilled screw holes will align accurately and the instruments are not tilted. A tilted instrument, unfortunately, is the first thing anyone sees when looking at your instrument panel.