Interiors: The Inside Story – Part VII

I know I just spent a lot of time last month on the design and upholstery of seats, as well as the importance of seat support and comfort. However, of all the areas of an aircraft’s interior that presents the greatest opportunity for aesthetic and function improvement, it’s the side panels. Think of all the side panel issues that, if properly addressed, can significantly improve comfort, airframe maintainability, durability, cabin amenities, and aesthetic appeal. Since many of the installation, repair, upholstery and inspection techniques are common to or similar for both headliners and side panels, I’m going to include headliners in this discussion.

Remember that notebook you’ve been carrying in your airplane, taking notes about your ideal interior? Well, here’s where it really pays off, enabling you to incorporate all of those details you want in your new interior. Following is a list of various areas that should be addressed before we modify, repair and upholster those dated and dingy side panels.

Airframe Corrosion

With the interior removed, now is the time to undertake a major clean up of corrosion, insulation and old glue, possibly saving your aging airplane from an early date with the salvage yard. This subject was covered in detail in our corrosion series (May – July 2003).


As light airplanes go, Bonanzas and Barons are quieter than most. As insulated by the factory, most of them register at between 90 and 93 decibels at the pilot’s ear, and that’s horribly loud. With the right materials and proper installation techniques, the noise level in your airplane can be reduced by 4 to 8 decibels. What controls sound levels also positively affects thermal properties of the cabin, an obvious benefit. More on this in a future article.

Removal of Abandoned Wiring & Systems

It’s surprising to see how much of this old stuff is still flying around with us in our airplanes. Now is your chance to really clean things up.

Water Leak Detection

The source of a nagging water leak can best be found by taking a garden hose to an airplane with a stripped-out cabin. Start low and work up – you will find it! Often the water wasn’t coming in where the wet spot was.

Systems Evaluation

Now that you can see it all, check out the condition of heat and fresh air ducting, cables, pulleys, and fuel and hydraulic hoses. Carefully inspect old antenna co-ax leads and static lines. You’ll be surprised how much deterioration can occur in a mere 40 years.


Don’t forget to remove the floorboards as part of your inspection and cleanup process. It’s not uncommon to find things under there that belong in a natural history museum. Also, critter droppings are very corrosive. Later in this series we will discuss repair and/or replacement of floorboards.

So much for those issues; now it’s time to put on our designer’s caps and brainstorm the many design options that can be included in your new side panels. If you need some inspiration, spend a little time and see what is being done in new cars. With proper planning you can have all of that neat stuff (and more) in your airplane.

There are basically three levels of side panel renovation:

  1. Retain the original design  By keeping original armrests and reconditioning and upgrading such things as the mounting hardware and mounting brackets, you can make improvements without the more costly option of a total re-design. Dividing large, one-piece panels into smaller sections can make them easier to install and remove. Using modern fasteners and re-trimming headliner and side panel components can prevent damage and save time and money at annual. Discuss the side panel design and installation with your mechanic; he will know what you should consider changing. Remember, many things are possible at this stage.
    I like keeping vintage airplanes original in their design character. But vintage doesn’t have to mean spartan. We can carefully incorporate modern amenities such as reading lights, more efficient ventilation, cup holders, and ergonomic armrests without giving up the elegance of a true classic.
  2. Moderate upgrade  This level of side panel upgrade is done on older airplanes and mostly involves incorporating a later style armrest. This not only looks more contemporary but, due to the molded shape of the armrest, also accesses unused space hidden behind a flat side panel. This upgrade requires the installation of new armrest supporting brackets, cabin door pull mounting hardware, and the forming of a relief in the previously all-flat side panel, but the trouble is well worth it. The advantages of this level of upgrade are first, a major aesthetic change can be made for very little weight gain and cost. Second, by in-setting the contoured armrests, we can get the effect of a cabin that is two or three inches wider without doing the impossible task of actually making the fuselage wider. Third, all the maintenance saving features mentioned earlier can be incorporated in this design.
  3. Total re-design  Finally, there is the all-out effort of total re-design of the interior hard-shell,  meaning the entire original side panel & armrest system is re-designed and newly fabricated prior to upholstery. Since this is a clean sheet of paper, we can take full advantage of almost 50 years of Bonanza flying to rethink this space. Function, safety, and aesthetics can be developed to a whole new level. Add to that modern lighter materials and wonderful things can happen.

Here at Air Mod, we have two basic ways of fabricating these new side panel/armrest installations. The first method is to build the new panels using .020″ 2024 T-3 aluminum and mounting them on extruded divider or “T” rail. This system affords us the option of fabricating a continuous armrest that runs from the instrument panel back to the baggage compartment. It looks great and allows for an obstruction-free space inside the new armrest to run electrical wiring and other systems without having to drill holes in cabin bulkheads. An ergonomically dimensioned recession is built in above each armrest, increasing elbow room by an inch or so. The entire interior is mounted on extruded rails, making installation and removal a snap and adding a very appealing visual trim feature.

In pre-1963 airplanes we will also fabricate a new headliner mounted on these extruded aluminum rails. It looks great and is easy to install and remove. Many types of ventilation and lighting upgrades can be incorporated into the new installation.

Since the new side panels described above are aluminum and can only be formed on one axis, we are limited to the shapes that can be generated. Another system we can install employs the use of molded structural fiberglass for the upper side panels. It is very strong, durable, lightweight, and with proper tooling, easily molded into any compound shape. We can now take advantage of previously inaccessible space behind the side panels. Accessing this space allows us to build ergonomically positioned armrests with exotic wood inlayed panels for such things as switches, lights, intercom jacks, or oxygen outlets. Think of the possibilities. Thanks to the characteristics of composite materials, a total aesthetic enhancement is possible. Soft flowing curves of a seat can be fully emulated in the side panels. It’s a win-win deal when the old concept of form and function comes together so well.

Here’s the best part: both of these total re-do systems add very little weight and are much easier to install and remove than old components, meaning less damage at annual inspection and radio repair time – I love it!

We all know there’s no free lunch, so I thought I should give you some ideas of what all of this adds to a standard interior redo. Certainly, the most cost effective side panel upgrade is to install late-style recessed fiberglass armrests. At approximately $650 for a 4-place airplane, they completely change the character and comfort of older Bonanza, Travel Air and Baron side panels. The weight increase is only two or three pounds.

You should expect to pay approximately $3500 for the all-aluminum extruded rail-mounted side panel armrest installation in a 4-place airplane. Realize that this system is an entire replacement of the side panels, armrests, and armrest supporting structures. There is a weight increase of three to five pounds. This modification alone takes about 55 skilled man hours, so you should allow at least an extra week of down time for an upgrade of this complexity.

The most elaborate side panel upgrade is the molded fiberglass side panel system that includes exotic wood inlays and angle-mounted contoured cabin accessory panels; these can contain rheostat-controlled gooseneck reading lights for each cabin seat. The cost for this modification in a 4-place Bonanza is about $5000, due to all of the wood and electrical work, as well as the side panel and armrest fabrication. This modification takes an additional 70 man hours, so factor an additional 1½ weeks to the down time.

Whether you choose to keep your side panels as originally designed, or have a major upgrade installed, many options can be incorporated into the new interior. Here’s a wish list:

  •             Inertia reel shoulder harnesses
  •             Gooseneck reading lights
  •             Cup holders
  •             Wood grain inlays
  •             Overhead reading lights
  •             More efficient vents and vent systems
  •             Additional heat outlets
  •             Super soundproofing
  •             Storage cases
  •             Accessory plugs (14 or 28 volt)
  •             Special storage pouches
  •             Flush-mounted intercom jacks
  •             Better sun visors
  •             Improved oxygen outlet mountings
  •             Discrete storage solutions
  •             Tables

The point is, if you have a need or an idea for something, discuss it with the renovator who is going to do your interior. No idea is a bad idea and, as I’ve stated before, many deficiencies can be improved upon and problems can be solved.

So much for modified side panels and armrests. Most of our customers, and probably those of other shops as well, choose to reuse their original side panels when doing a renovation, so from this point on I will discuss the work required to get those original side panels into better than new condition. There are four different generations of Beech side panels we need to deal with. Next month we’ll get into all the interesting details. Until then, fly safe (and keep taking notes)!

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