Stuff and Fold

Making a hinged instrument panel for ease of maintenance.

February 7, 2022

As the saying goes, a homebuilt airplane is never done! Especially with the nature of constant technology evolution, there’s always another new must-have gadget or useful avionics upgrade. There’s also the issue of flying an older homebuilt whose avionics are either obsolete or failing. Time waits for no man, and especially not for avionics.

From the practical side of things, working backward and upside down underneath and behind the instrument panel has never been one of my favorite activities. So when I first built my plane, I decided up front to hinge the panel at the bottom so it could be swung back to a decent angle, allowing behind-the-panel work to be done from the top.

I’m going to detail the approach I took and its essential elements, but my guess is that the approach would vary depending on your particular panel and airplane configuration and available mechanical structures to work with. (Our instigator-in-chief offers a few of his own observations in the sidebar below.) The main message here is not “do it like this,” but, rather, think about it and see if you can find a way to include hinging in your panel implementation. You’ll find it well worth the effort in the long run.

Figure 1: With the upper supports disconnected, the author’s panel tips backward at the upper surface to make access so much easier.

In my case, the entire panel hinges. You may find it easier to apply to individual panel inserts. The essential elements of this hinged panel implementation are 1) the hinges at the bottom; 2) top screwed-in retention points, one on each side; 3) rubber vibration isolation mounts included in each attachment; and 4) rear support for the radio stack. Figure 1 shows the panel swung back, with easy access to everything behind the panel, including items mounted on the firewall and nose gear housing. Work can be done sitting on either the front seats or on the spar carry-through with the seats removed.

Figure 2. Two views of the hinge line and the rubber vibration isolators.

Vibration Isolation

Rubber vibration isolators are an optional feature. I went with vibration isolation because my plane originally had vacuum-driven steam gauges, and their bearing life expectancy can be compromised by vibration. There is also reason to believe that avionics life expectancy is improved with less vibration. It’s up to you whether to include this. If so, rubber mounts, like those shown, are available in many sizes from McMaster-Carr.

Hinged at the Bottom

The hinges are short pieces of standard aircraft hinge material. Their flat flange area is easy to mount on one side and accommodates the rubber vibration mounts on the other flange and the other side of the rubber mounts attached to a fiberglass flange on the fuselage. See Figure 2. The assembly, in turn, has a cover to keep from scraping body parts that come in contact with the hinges.

Your biggest challenge might be finding the ideal hinge diameter and coming up with a way to remove the hinge pins should you desire to do so. Because this is not strictly speaking a structural piece, you don’t necessarily have to have the hinges run full span.

Figure 3 (left) shows the panel swung out and the distance from the isolators to the fuselage mounting tabs. Figure 4 (right) reveals the center-stack support. Portion A is the fuselage (fixed end) and the tab (B) is part of the stack support structure on the panel itself.

Top Retention Points

The top of the panel, when swung into place, has a pair of rubber mounts on each side that meet a pair of fiberglass flanges and secure the panel with nuts from the back. Figure 3 shows the left and right attach points in the swung position. Of course, especially in an aluminum airplane, these retention points could be made solid as well as bolted directly through the panel rather than from behind.

Figures 5 (top) and 6 (above) show the need to tie all electrical and plumbing along the hinge line so that nothing gets pulled loose when the panel is tilted.

Radio Stack Mounting

Depending on whether you have a significant radio stack, you may wish to include some back-of-the-stack support as well. Figure 4 shows this arrangement with the panel swung back. The radio stack includes a pair of side plates, which at the back engage two aluminum angles, each in turn supported at the top with rubber vibration isolation mounts. The side plates are then retained with Southco winged quarter-turn fasteners. Swinging the panel requires reaching underneath to the back to disengage the stack supports, however.

If your panel is hinged, there will be a few additional constraints to consider up front. Those include accommodating air vent hoses and wiring to work with the swing down of the panel. One simple thing is to route all wiring that leaves the panel at the bottom and out the sides so that as the panel is rotated, it simply slightly twists the wiring bundle a bit on the same axis as the hinging of the panel. See figures 5 and 6. Or, wiring that goes forward may include a sufficient amount of slack to accommodate the additional length required with the panel swung down. This may require providing a panel/harness manufacturer with the appropriate guidance on what you plan to do. Fresh air vent hoses likewise will require some slack to allow panel movement.

Sure, it is a lot easier to just bolt that stock Van’s sheet of panel aluminum or that nice pro-built custom panel into the mating aluminum structure. But I would urge you to think about it and come up with your own way to incorporate a hinge mechanism! Your back will thank you!

Photos: Reinhard Metz, Marc Cook.

The GlaStar Version

Reinhard’s approach to the folding panel is a good one for a lot of airplanes, including his Wheeler Express. I have been the beneficiary of a couple of different approaches to the same idea. The first was my Glasair Aviation Sportsman, which had the more or less standard panel arrangement using a fiberglass primary structure and sheet metal inserts. The outer panel fits the airframe, and you cut the metal inserts to work with whatever avionics you happen to have.

A fold-down panel is easy to fabricate and so helpful down the line.

One benefit of this arrangement is that you can partially remove a segment to work behind the panel, something Reinhard hints at in the accompanying story. If done carefully, you can remove even the large segment on the pilot’s side without too much effort, though the Sportsman having access to the back of the panel from above and below definitely helps. It’s not a quick job, however, and I found myself using this technique only when having to commit to a big project behind the panel. Otherwise, I found ways to work from above and below, getting the occasional bruise from the control stick to show for my efforts. (Come to think of it, an easily removable stick might have been equally valuable.)

A standard inset panel.

Of course, today’s avionics are likely to center on a single large screen in front of the pilot, so some thoughtfulness about what’s mounted to the back of the display and consideration about service loop on the connector could make it possible to remove that display, disconnect it from the front and set it aside as you work behind the panel.

With the aluminum and instruments removed, access to behind the panel is easy.

Another solution was implemented by the builder of my current GlaStar, Charlie Eubanks. Although the panel appears to be a simple, segmented all-aluminum affair, it actually has two fold-down sections, one in front of the pilot and the other in front of the passenger. (The center section is fixed.) Charlie’s tactic was really simple, using aluminum fork-style hinges on the lower edge of the panel to ride on the steel tube that crosses the cockpit. The individual panels themselves are secured with screws to the existing tabs on the cross-tube as well as by screws along the outer edges of the radio stack and by similar plates at the far outboard portions of the panel. When secured by the glareshield, it’s a solid structure overall, despite using only 0.050-inch aluminum for the panel.

All wiring and hoses need to be free to pivot with the folding panel.

Of course, the trick to such panels is to route all wires and hoses in such a way to facilitate the fold-down. In my case, all wires descend from the instruments to join bundles that run left and right, just above the cockpit cross-tube. A bundle of wires that spans the radio rack has a U-shaped diversion toward the firewall so that either or both sides can be dropped and there will be no stress on the wires. Hoses are another matter, but all the pitot/static lines have quick-disconnect fittings and only two disconnections are required to allow the panel to fold down: just the pitot and static at the TruTrak autopilot head. The rest of the lines are carried tight to the instruments, so there’s no need to disturb them when the panel folds down.

Every time I work on the GlaStar’s avionics, I offer a grunt of thanks to Mr. Eubanks for saving my back and my neck.

—Marc Cook

Stuff and Fold

Vibration Isolation

Hinged at the Bottom

Top Retention Points

Radio Stack Mounting

LEAVE A REPLY Cancel reply

In Case You Missed It

No Two Rivets Alike

Engine Theory: Forced induction

Stage Right

Kitfox Celebrates Forty, Too