Homebuilt Aircraft Interiors, Part 3 - Seat Construction Details
Sport Aviation - 03/85
By Tony Bingelis
TAKE
A PEEK inside the hundreds of airplanes on the Oshkosh flight lines and
you will see cockpit interior treatments that seem to be as diverse as
the expanses of the solar system. Look at one airplane and it will
reflect that stark, fast completion, "let's go", appearance just about
as exciting as viewing a still in an abandoned barn. Alongside it may
be one featuring a beautiful custom appointed overstuffed interior
professionally executed at a cost exceeding $5,000. Let me repeat that
. . . 5,000 bucks!
Now that
you have the proper range and perspective, what are your plans for the
interior furbishment of your airplane? Have you given it much thought?
If
maximum aircraft performance is your forte, you will probably strive
for a minimum nice interior. Maybe you want something a little better
than that and will opt for nice upholstery and matching vinyl trimmed
side panels, Of course, you could always go for broke (ouch) and have
the entire interior installed by professional aircraft interior
craftsmen. Fortunately, you don't have to decide immediately as you can
start at the bottom and work your way up.
Seat Design And . . .
A
good many years ago, a Braniff captain wrote, with choked emotion,
about the hard unyielding aluminum slab seats he and his fellow airline
pilots were forced to sit in for hours on end (oops). This guy, Dick
Cavin, a long time loyal EAAer, went further and even proposed an
excellent seat design that homebuilders could adapt (SPORT AVIATION,
July 1967, "A Discourse on Seats", page 15).
Some
years later, I wrote of the numbing qualities of the simple plywood
slab seat (SPORT AVIATION, January 1973, "Sitting Pretty", page 49).
Though these many years have passed, I am sure that both Dick Cavin and
I are still of the same mind and that slab seats, be they of metal or
plywood, should be classified as antiques and be relegated to a place
of honor in the EAA Museum, deep in its archives where they can best be
used as benches by researches who like to ponder over such matters.
Since
those two dated articles, precious little has been written about
aircraft seat construction or about seats in general for that matter.
I
have always considered Ladislao Pazmany, another true blue EAAer
(designer of the PL-1, PL-2 and the PL-4), a pioneer in the design and
construction of comfortable seating for homebuilders. His all-metal
designs, dating back to 1960, incorporated contoured seat pans built
into the structure. This should prove that the art of constructing
comfortable seating in homebuilts has never been kept as a secret, just
ignored by some builders.
Hopefully,
henceforth, no new builders will ever again be lured into building slab
seats simply because of their functional simplicity. Surely, we all
deserve something better.
Among
the most comfortable of homebuilt aircraft seats are the integral body
contour couches in Burt Rutan's VariEze and Long-EZ designs. However,
they are not for the average aircraft design. Here the pilot is forced
to sit in a more upright seat because of structural limitations rather
than for any other. It is here also that seating improvements can be
made by any builder who cares to improve his accommodations.
First,
I believe that seats should be made to be removable. It is a matter of
convenience. Also a removable seat can often be made more comfortable
than one built into the fuselage structure. In addition to that a
removable seat can be taken to the upholstery shop where it may be
endowed with the finest of fabrics and leathers.
A
built-in seat pan design ordinarily has to be fitted with a removable
upholstered seat cushion and a separate back cushion. Both of these are
best upholstered professionally where the back cushion can be fitted
with straps and snaps or some other means of securing it to the seat
back.
Building Seat Frames
In
one of the old T-18 Newsletters, Editor Dick Cavin described a seat
constructed from a lawn chair. I tried to recall and expand on its
basic details, These are shown in Figure 1. Most everyone has a
couple of broken or marginally safe lawn chairs around the house, I'm
sure. Since summer is over, you wouldn't need them anyway, so . . .
The
one-inch tubing they are made of is an ideal lightweight material from
which a comfortable seat frame may be assembled. Since the seat
dimensions of a typical aircraft seat are smaller than a lawn chair, a
bit of surgery will have to be performed, No problem here. Simply cut
the tubing sections as shown with a tubing cutter or fine tooth hacksaw
blade and reassemble the frame to the dimensions you need. Insert short
pieces of scrap tubing inside each splice joint area and pop rivet the
assembly together. You can use the same size tubing for the insert
pieces if you slit them with a hacksaw and squeeze them together to fit
inside the tubular frame.
Construct your seat back in the same manner as the seat bottom frame.
Installation
of the seat bottom and back frame will depend, of course, on your
aircraft structure in the area where the seat is to be installed.
Essentially, you will have to design, make and rivet aluminum brackets
to the seat frame. These can, in turn, be bolted to the aircraft
structure providing an easy installation and removal capability. When
making the brackets, keep in mind the need for the seat to be tilted
somewhat to provide the most comfortable seat bottom angle. The closer
the seat is mounted to the cockpit floor, the steeper this angle should
be because with your knees elevated, a greater load is imposed on your
derriere. A steeper seat cushion angle would allow the back of your
upper leg area to take some of the body load. I'm sure that there have
been occasions where you have had to sit in a seat with no tilt angle.
Didn't you feel like you were on the verge of sliding forward out of
the seat? A most uncomfortable hard feeling, wasn't it?
There
is another way to get a good seat frame and that is to buy a salvage
seat out of a Cessna, Grumman American or almost any other lightplane.
As a matter of fact, used seats can often be found at airports that
perform maintenance and repair functions.
All
you really need is the framework but often you can get the fully
upholstered seat for the same price. If its upholstery is in good
condition, fine. Use it. If it is bad you can always redesign the seat,
if you like, and have it reupholstered. If the seat is too wide for
your airplane you can change that, too. I did.
I
located and bought a couple of beautifully upholstered Cessna 172 seats
for my Falco. When I tried them in the cockpit they looked like a
million bucks, thanks to their soft leather-like upholstery but, alas,
they were too wide for the airplane and would have interfered with the
landing gear emergency crank. That problem didn't deter me for long as
I was determined to use them.
I
simply removed that magnificent upholstery and stripped the seats to
their bare aluminum frames. Then I cut a 1/2" section out of the front
and rear frame and spliced it back together. The two seats, now
narrower, fit the airplane perfectly. Incidentally, I also had to cut
off the chair legs and build in a provision for the sliding mechanism
(see SPORT AVIATION, July 1983, "Sliding Seat Mechanisms", page 56).
Here
is another, alas. When I tried to reinstall that beautiful upholstery
it looked lousy because the seat coverings had to be pulled down on the
sides of the narrower seats, ruining the design balance of the
covering. A trip to the upholstery shop took care of that matter and
now I have a couple of sharp looking custom-built seats designed
specifically for my Falco. In retrospect, I could have saved money by
buying almost any kind of salvage seat frames since I had to discard
the upholstery anyway.
Some
builders are installing fiberglass shell seats made for boaters and
sold in sporting good shops. These are quite light and make reasonably
good seats if properly mounted and upholstered. They are difficult to
upholster attractively and equally difficult to mount correctly.
The
correct way to mount these seats is not by screwing short legs to the
bottoms as the load will be very localized. A hard landing could cause
the seat legs to retract through the seat bottom and into your body
with painful results. The seat mount loads should be distributed by
attaching contoured blocks epoxied and/or screwed to the seat bottom.
The attachment hardware could then be bolted to the newly installed
base blocks.
More About Seat Bottoms
Once
you have a seat frame built, you are ready to install its cushioning
support base for the foam padding and upholstery cover. Perhaps the
best support for the seat cushion would be zigzag springs. If your seat
doesn't already have them you can purchase some at an upholstery shop.
These spring steel zigzag springs must be slightly compressed so that
they arc upward in the center about ¾" (See Figure 3 & Figure 4).
Another
type of base support would be a simple canvas insert fitted with
eyelets and laced in position around the seat frame with nylon cord or
rawhide lacing. All fabric shops stock easily installed eyelet
reinforcements.
A third way is
by weaving strips of aluminum 1" or wider (about .032" 2024T3 would be
fine) across the seat bottom and riveting the ends together after
looping the strips around the frame. These various methods are shown in Figure 2.
Foam and Padding
As
for the seat cushioning material, 4 inches of polyfoam is a good
starting point. A four-inch thick block of foam might sound like a lot
but it is really deceiving. What really counts is the resilience of the
compressed foam and the amount of headroom you can afford. When your
full weight is imposed on the foam pad it will compress to about ¼ of
its original thickness, so it is really best to use high-density foam
for a harder support. You could, for example use a 3" thick block of
regular polyfoam and overlay that with of higher density foam.
Polyfoam
is recommended as all-purpose filler because Latex foam rubber is much
heavier and more expensive. So, why us it. The trouble with ordinary
polyfoam is that it bottoms out, leaving very little reserve cushioning
capability. It is possible, therefore, to hurt your spine in a hard
landing, or even in a turbulent flight if the padding is then and lacks
support. The zigzag springs previously mentioned can aid greatly in
supporting your weight. The best cushioning and shock protection you
can install is, however, Temperfoam.
Temperfoam
has the capability of absorbing a tremendous amount of impact shock
compared to common polyfoam and it is flame resistant. It is amazing
stuff but costs considerable more than the ordinary polyurethane foam
used by furniture upholsterers. Still, if you want the best, here is
another aerospace spin-off that you can take advantage of.
Cutting
foam can be frustrating if you try to do it with a razor blade or with
a pair of scissors if the material is very thick. A band saw does a
beautiful job as will an electric carving knife.
You
can make your own electric carving knife by sharpening a length of a
hacksaw blade to a knife edge and grinding one end of the blade down so
it can be chucked in your saber saw (Figure 5).
Adhesives
Adhesives
and fasteners play a very important role in upholstery and trim work so
a few advance comments might be helpful. I find that some of the
well-known upholstery and trim adhesives work well someplace some of
the time, but not always. All in all, I must confess that I've had the
poorest results with the overrated, overpriced, spray adhesives. (Yes,
I did read the instructions.) They seem to work great on large areas
and on initial installation but, invariably, when I go back a week
later I find that some areas of the glued fabric have pulled loose or
have bridged across curved areas. Even though I am aware that trim
adhesives all work best in shear and I don't unnecessarily stretch my
material because of this factor, the bond is often unreliable.
About
once a year I have to go over my aircraft and reattach the trim and
weather-stripping. I guess Texas climate makes a tough proving ground.
At any rate, always follow the instructions for the particular product
you are using and your success rate will be better than it would be
otherwise. One sure way to reduce your adhesive problems is to avoid,
as much as possible, stretching the fabric being attached with
adhesive. This is particularly true of Naugahyde. Don't stretch it if
adhesive is all that will be holding it in place.
Contact
cement is about as good as most of the trim adhesives on the market and
it is much cheaper (by the can) than the other adhesives sold in tubes.
In my estimation the best all-purpose adhesive for upholstery and trim work is PLIOBOND (homebuilt suppliers stock it).
A
good adhesive for fabric-to-fabric gluing is plain ol' white carpenters
glue (Borden, Weldwood, etc.). Surprised? It grabs fairly quickly and
dries clear and doesn't stain the fabric.
Since
my trim is in black synthetic leather I was delighted to discover a
black liquid neoprene rubber that gives truly magical results when
working with black Naugahyde. I use the liquid rubber to fiar-in
difficult corners and around raw cut edges that would otherwise show.
It is a tenacious material that can also fill voids and it will blend
in wherever I need a little cosmetic help with that black synthetic
leather trim.
Clear Silicone adhesives also have their place in trim work as they will adhere to most anything.
More next month.
