BY TONY BINGELIS, 8509 GREENFLINT LANE. AUSTIN. TEXAS 78759

HOMEBUILT AIRCRAFT INTERIORS Parti Basic Cockpit Accommodations

ITH ALL THE new homebuilt, ultralight and lightplane (ARV) designs crowding into the homebuilt scene I sometimes wonder if there aren't more aircraft designers than there are builders. Among the current crop of favorite homebuilts are some very nice designs. So nice that I wish I could start building 3 or 4 of them at one time. But, I assure you, one homebuilt project at a time is plenty for anyone. All of those nice designs have cockpits but who thinks of cockpit accommodations when selecting a design to build? It is the aircraft's overall appearance that we get hooked on initially. Then, predictably, our interest will switch to the aircraft's touted performance, but seldom does the matter of cockpit size and interior layout command much of our attention until sometime later. Of course, there may be an exception to this process, especially if the airplane design is exceptionally small, or if there just happens to be a prototype before us that we are invited to climb into and try on for size.

At any rate, no matter what selection process you follow in picking a project, don't get completely taken in by the beauty of a particular design without first determining other es-

sentials, like the cockpit's ability to accommodate you comfortably, for example. A good roomy cockpit should be rated on a par with good looks and good aerodynamic performance. If the cockpit compartment is cramped or poorly designed, you will become dis-

enchanted with your pride and joy soon after it is completed. Avoid that dismal prospect by giving early attention to the cockpit features that are really important to you. If you are already building and have never sat in, or flown, a copy of the design, you might well be wonderng how well your cockpit will fit your requirements. The Cockpit Area In General I guess most any builder expects a few surprises to crop up during the construction of his project. But one surprise that nobody expects or wants is to learn that his cockpit is too small for him, that it is difficult to get into and that there is insufficient leg room. Perhaps it is also too narrow for his broad shoulders. Insufficient headroom can become a major irritant, too. But of course there is a penalty to pay for generous headroom and shoulder width accommodations in any cockpit and that is profile drag. You should, therefore, expect that cockpit space will ordinarily be at a minimum consistent with "average" comfort needs because profile drag is usually reduced with a reduction in profile area. Crowded or not, all of your cockpit housing and control functions will have to be made

to fit into the confines of the compartment area set aside for the cockpit or cabin. Seating Accommodations Before you undertake to install any

of the miscellaneous support systems

and equipment, you must decide where to install the seat or seats. The seat must be positioned and installed to assure your comfort and efficiency during the operation of your airplane. This means that you will have to determine the proper horizontal and vertical position best suited to your own physical configuration. A cockpit designed or built especially for your own use need not have an adjustable seat. That would only involve a lot of unnecessary work and extra weight. Just make sure that you position the seat where you want it before you build it into the structure. If you intend to allow other pilots to fly your airplane, or if you are building a two seater, adjustable seats and/or rudder pedals could be worth installing. Any adjustable seat should be of a simple design and must be constructed and proof tested to your satisfaction before installing it in the aircraft. But remember this . . . if is far easier to make the rudder pedals adjustable than it is to engineer and build a sliding seat installation. Besides, a runaway seat on take-off could be disasterous. That sort of thing does happen, you know.

The structural design of the fuselage exerts a big influence over what you can or cannot do in locating the seat. Often it must be bolted directly to the cockpit floor (no legs) in order

to obtain the minimum headroom you can get by with. In most designs other than the low wing type, the horizontal location of

the seat can be changed to a limited SPORT AVIATION 49

extent. The reason you cannot alter the seat location in many low wing aircraft is because the front spar, typically, cuts across the fuselage in the cockpit area. In small aircraft this absolutely restricts the seat location. The usual practice, in the past, has been to plunk a plywood slab down over the spars to serve as a (butt numbing) seat. I'm happy to say that most homebuilders have progressed beyond this primitive solution, or at least they aspire to install something more comfortable. Present practice is to install a dished out base for the seat bottom in the space between the two spars. As I recall, Mr. Pazmany, designer of the PL-1, PL-2 and the popular PL-4, was one of the early leaders in using this technique for installing seats in all his designs. An immovable seat leaves you with one alternative for making leg room adjustments - adjustable rudder pedals. That is you will have to modify your rudder pedal connections so that they can be adjusted to position the pedal further forward or further back. This will help obtain the proper leg angles for both short and tall pilots. The seat back is another important part of the seating accommodation. Its angle of tilt or slope can, in effect, affect the amount of headroom and the degree of comfort or discomfort the pilot will have. Unfortunately, its location, as well as its slope angle, will be limited by the structural bulkhead directly behind the seat. This bulkhead is most often positioned perpendicular to the thrust line or top longeron. In order to increase the seat back tilt angle, the bottom portion of the seat back has to be moved forward several inches. This, of course, will use up at least 6 inches of potential leg room. Some aircraft designs can

COCKPIT WIDTH 24" MINIMUM

FIREWALL FUSELAGE CLEARANCE l" (MIN)

RUDDER CABLE CONTROL STICKNEUTRAL POSITION ( CHECK FOR FULL AILERON DEFLECTION)

MINIMUM ELBOW ROOM 16."

SEAT BACK TILT

AFT BULKHEAD

PLAN VIEW

FIGURE 1 BASIC COCKPIT ACCOMMODATIONS (SINGLE SEAT)

High seats and lots of legroom. That's

the way they used to design airplanes . . .

even

some

homebuilts.

Big

doors

simplify getting in and out of this BD4.

50 JANUARY 1985

RUDDER CONTROL CABLE

EXTENSION STRIPS MAKE OF 4130 STEEL (.050" OR AS NEEDED) EITHER INSTALLATION O.K.

SINGLE STRIP

RUDDER CONTROL CABLE

FIGURE 2 MAKING RUDDER PEDALS ADJUSTABLE

easily give up that amount of space (mostly biplanes) while others simply cannot. Entry and Egress Considerations Now, how about getting in and out? Will your knees fit under the instrument panel? They bend only in one direction you know. If you're lucky, you probably have already had the opportunity of getting into and out of the prototype and are familiar with any shortcomings the cockpit design might have in this regard. If so, you can better anticipate the type of adjustments you may have to make, if any. For example, the bottom of the instrument panel might have to be raised slightly or the panel moved forward (away from you) to correct an entry difficulty unique to your needs.

If you have to move the instrument panel back to make room for gyro instruments between a front fuel tank and the instrument panel, be careful that you do not make it more difficult to get into and out of the cockpit. Anyone building a two seater should also think about his passenger's needs. Passengers are not, ordinarily, familiar with structural limitations and could damage your airplane or themselves if provision

is not provided for a dignified entry

and exit. A built-in handhold is a valuable aid and one that can be fitted easily to most any windshield bow.

The provision for ease of entry or exit under normal and emergency conditions should not be compromised. I

don't think that is asking too much, do you?

Control Stick Dilemma? After you have resolved the seat location problem, you should turn your attention to finding the best position for the control stick. I'm sure that if you are building from plans, the control column mounting mechanism location is already established and you are "stuck" with that particular installation. Most of the

time the location will be just about right. Sometimes, however, it may place the control stick in an awkward position, too far forward or aft for comfort. Of course, slight changes in the stick's neutral position can be

made by lengthening or shortening the control cables (or elevator pushpull tube). However, this causes the control column to be slanted and may SPORT AVIATION 51

The new way, not seats just a reclining floor or cradle on which a cushion is placed. Comfortable? Yes, but your legs have to be poked into the opening under the panel. Before you build you better try these "Star Wars" designs on for size to see if you like the accommodations. Better check your shoe size too.

A center mounted radio and vertical console is no problem in a two seater, but it could be in a single seater where the pilot would, in effect, have to straddle it.

convey a false "neutral" sensation through your hand. A better way to make larger changes in the positioning of the control stick's neutral position is by making and installing a curved control column. A curved control stick will often eliminate or at lease minimize this kind of problem. It may also eliminate the problem of your knees or legs getting in the way and interfering when applying full aileron. It is well to remember that a short control stick will increase control sensitivity and a long one will reduce it. However, don't make your control column so long that it just barely clears the bottom of your instrument panel because your knuckles won't. 52 JANUARY 1985

Rudder Pedal Placement Try locating the rudder pedals so that they permit your knees to be slightly bent so as to form an appoximate 120° angle (no more than 155°) between your upper and lower legs. This will help you obtain full rudder travel and will establish a comfortable position for your legs. At the same time it will also give you the best foot angle for easy brake application. The so-called "standard dimensions" for the spacing between rudder pedals is often impractical to achieve in most homebuilts. For example, in a single seat installation the rudder

pedal location to either side of the centerline of the fuselage is determined more by where the control cables are attached than by anything else. If the rudder cables are routed along the fuselage sides, the rudder pedals cable attachment points will, naturally, be close to the fuselage sides. This may require the rudder pedals to be spaced quite far apart in a wide cockpit or quite close together in a narrow cockpit. In an installation where the cables are routed through the center of the cockpit, the pedals will probably have to be positioned closer together, either side of the centerline. Neither condition, however, should create an uncomfortable situation for you. - , -. .....

SEATBACK ANGLE

HEADROOM 2 INSTRUMENT PANEL CLEARANCE (KNEES/CONTROL STICK/KNUCKLES) ^_

EYE_LEVEL_ __

CLEARANCE

REAR BULKHEAD

FIREWALL

WING SPARS LIMIT SEAT LOCATION I 48"

(minimum) CONVENTIONAL COCKPIT LAYOUT (LOW WING DESIGNS)

30° HEADREST BECOMES

FUEL CAPACITY MAY HAVE TO BE REDUCED

REQUIRES LARGER CANOPY

REDUCED

FRONTAL AREA

LINE OF-c. SIGHT/

CONTOURED ,T REDUCED FOOT ROOM

r

SIDE ^MOUNTED/ CONTROL STICK / -xESSENTIAL

AFT BULKHEAD

FOOT ANGLE CHANGE MAY AFFECT BRAKE APPLICATION INCREASED COCKPIT SFfcCE REQUIREMENT

ADVANCED CONCEPT COCKPIT LAYOUT (TYPICAL) FIGURE 3 FACTORS AFFECTING COCKPIT ACCOMMODATIONS SPORT AVIATION 53

This builder had to use a couple of curved control sticks in order for them to be located more comfortably and to clear the instrument panel.

One feature that could create a poor cockpit condition is a wide center console. So will an extension of the instrument panel all the way to the cockpit floor. This is so because you will have to straddle the thing when you get in the airplane. Furthermore, you will be forced to keep your knees apart during the entire flight. The inability to move your legs around because of this hinderance may create a most uncomfortable condition. In addition, you may no longer be able to clamp the control column between your knees (poor boy wing leveler) while handling your navigation charts on flights into strange territory.

While on the subject of legs and knees, be sure that there are rounded smooth surfaces against which your knees may be rested. Sharp corners

and unyielding structures can be torturous on a cross country flight. Incidentally, a center console is not ordi-

narily a problem in a side-by-side two seater. Engine Controls Should you mount the throttle quadrant on the left side, military 54 JANUARY 1985

style, don't make the mistake of locating it too high or too far aft in the cockpit. If you do, you may find that you won't be able to pull the throttle all the way back because your elbow hits the seat back or aft bulkhead. A throttle positioned too high is tiresome if you, like many a pilot, prefer to keep your hand on it most of the time.

Visual and Visibility Factors Before making that final installation for the instrument panel take a critical look at it. Is it too close to view comfortably? Your eyes can see more of it if the panel is not too close. Are there sufficient areas of windshield and windows to see through? Areas free of large frames and braces that might be cluttering your field of vision? Of course, noth-

ing can be done about moving the wings out of your line of sight, but in

the early cockpit layout stages other potential hinderances can be

minimized. For your own safety, good visibility from the cockpit should never be sacrificed for the sake of esthetics. Supersloped windshields, even if distortion

free, aren't always as practical or as aerodynamically effective as they may appear. Seat Belts and Shoulder Harnesses

Plenty has been written about seat belts and shoulder harnesses and I will only say here that they are extremely important, should be installed and must be anchored to solid structure . . . not the seat.

Believe me, there is a tremendous

amount of difference in the safety, size and arrangement of cockpits among the many designs being offered to potential builders so, if you can possibly arrange it, fly it or at least try it on for size before you start

to build it. Need more information about cockpits and cockpit design? See the following back issues of SPORT AVIATION; • Sliding Seat Mechanisms - July 1983, page 56 • Cockpit Standardizing For Homebuilts? - September 1979, page 35 • The Cockpit Mock-Up and How To Use It - May 1976, page 60 • Crashworthiness and the Shoul-

der Harness - January 1974, page 59

PORTPLANE BUILDER HOMEBUILT AIRCRAFT INTERIORS

Cockpit Conveniences and Refinements Part 2 fA STRIPPED-DOWN austere interior, of course, enables you to have a lighter, more agile airplane. It does not, however, assure you of having the most comfortable or the safest airplane. In an attempt to keep weight down, you might be tempted to deprive yourself of some small creature comforts that could add greater enjoyment to your flying, often with little or no weight penalty being incurred. Don't automatically rule out all cockpit refinements, not without good reason. Here are a few examples of what I have in mind. Each of these can be easily installed and are guaranteed to make your time aloft more enjoyable; a map pocket or map case, glove compartment, arm rests, headrest, heel scuff plates, sun shade or visor, bubble canopy screen or curtain, radio stack vent and handholds to name a few of the more popular items with most builders. Of course, you may not want or be able to incorporate all of these, let's call them, refinements. However, do not rule any of them out until you have read a bit more about each. Let's start with Handholds.

Handholds It depends on your airplane design, naturally, but there can be no argument that almost any airplane should have some sort of an aid to help you get in and out of it. A handhold mounted on the windshield bow (frame) or a hand grip built into the glareshield, particularly in a side-by-side two seater, meets that need and is a genuine cockpit convenience. Your handhold could take any of several simple forms depending primarily upon the type of structure to which it will be attached. Figure 1 illustrates a couple of options. The January 1985 issue of SPORT AVIATION, illustrates two more. The dandiest convenience you can have in any biplane has to be one of those classic handholds built into the top wing cut-out. Without it, pulling yourself out of the cockpit invites the risk of damage to plane and pilot. The weight penalty? A few ounces. Shall we go on? . . . . . . . . 26 FEBRUARY 1985

Select a plain, light colored, semisheer curtain material. It will effectively screen out the hot rays of the sun without creating that closed-in feeling. What makes this installation, or a variation thereof, extra functional is that you will be able to push the curtain back to any intermediate position at will. The weight penalty for this one should be less than a pound unless you have a very large canopy.

It's Curtains For Bubble Canopies A large bubble canopy, particularly on a two seater, must certainly be the airborne equivalent of a sweat shop. The amount of solar heat it lets in must be intensified by the curvature of the large plastic bubble acting like a huge magnifying glass. Although that conclusion may not be scientifically accurate, I am willing to believe it. Boy, does it get hot in there! Do you want quick relief? Mask and paint an opaque band approximately 12 inches wide down the center of your canopy bubble. Do this on the inside of the Plexiglas using white paint. White is the color to use to obtain the coolest cabin temperatures, however miniscule that difference might be. Painting the canopy glass on the inside creates a better effect and also affords protection for the paint from external abuse and chipping. A quick-drying enamel is my choice for the job. Remember, lacquer thinners and other volatile liquids can, in time, cause Plexiglas to craze. Another way to make shade in the cockpit is by installing curtains. Figure 2 should put you on the right track if you want to fabricate a simple installation for your airplane. If your canopy frame tubing is less than %" in diameter, you might feel that drilling those 3/ie" mounting holes for the curtain rod installation will weaken the canopy frame too much. I don't think they would but, if you prefer, you can instead, epoxy small rectangular wood blocks butted up to the canopy frame. With the small holes drilled into the blocks instead of the canopy frame you can still obtain the needed support for the lightweight aluminum curtain rods (W 2024 T3 aluminum tubing).

Radio Stack Cooling Vents A single radio installed in your panel does not require any particular ventilation provision. It is a different matter, though, when you have two or three units installed one directly over the other in what pilots refer to as their "radio stack". Although aircraft radios are now transistorized they still do generate heat and do require some form of cooling to minimize long term deterioration of dielectrics and other component parts. It is unlikely that many of us will have a large stack of radios so we need not concern ourselves with electric fans and similar cooling devices. For the most part, all the cooling we need is what we can obtain from the flow of air through a vent or port located directly over the radio stack. A vent acts very much like a chimney allowing the hot air to rise and leave the radio compartment area. The incoming air is cooler so the cooling cycle continues.

This builder really believes in handholds . . . would you believe, 3 of them? They do make it easier to get in and out from either side.

WINDSHIELD

SPACERS- . [ALUMINUM 1/2 DIA.I

0

FIGURE I. HANDHOLD LOCATIONS (TYPICAL)

All that is needed for ventilating a couple of radios is a small vent located in the top of the glareshield (windshield deck) directly over the radios. Small individual louvers will also work as well.

Note: The ventilating louvers depicted in Figure 3 were purchased at a

NOTENYLON PULLEYS AMD SUCWS 00 NOT TURN NEED NOT TUftN

paint supply store. A set of 9 of these plastic ventilating louvers cost less than

$1.50. They are approximately one inch long but the length can be cut to suit

your installation. Simply drill or cut a one inch hole and press the louver in.

That's all there is to it. These can also be used to serve as air outlet vents for

cabin ventilation. (Source: Many paint stores or the manufacturer, Shur-Lone Manufacturing Co., Inc., 80 W. Drullard Ave., Lancaster, NY 14086 - Ventilating Louvers SV-9.)

The time to install a radio cooling

vent or ventilating louvers is after you

have overlaid your glareshield but before the windshield is permanently installed. Otherwise, access will be difficult because the windshield will interfere with your hole drilling and vent installation efforts. Whatever the type of opening you provide for the ventilation air, the opening should be protected to keep foreign

objects from falling into the radios below. If, because of the number of radios

stacked or because of an exceptionally hot climate, you need more cooling air consider installing ram air cooling. It is easy enough to do. Install a short length of tubing clamp-

ing it vertically to one side of the radio

installation. This will serve as a distributor for the ram air after you plug one end and connect the other with ducting to a ram air source. The ram air will then be ducted to the distributor

MINIMIZING EFFECT OF SOLAR HEAT INSIDE A BUBBLE CANOPY

SPORT AVIATION 27

Any homebuilt to be endowed with a stack of radios should also be fitted with a vent directly above to provide cool air circulation thru the sets. Install your vent before you permanently install the windshield.

PLYWOOD OR IMINUM TRIM

tube and from there spewed out over the radios through strategically drilled holes. If you find this hard to visualize take a look at Figure 3 for instant clarification. If more cooling is required, you could also install a similar distributor on the opposite side of the radio stack. A good source for the ram air would be an opening on the back engine baffle to which you could attach the ducting. It need not be larger than %" or so in diameter.

Map Pocket? Map Case? Call it what you will, every airplane should have at least one. A place to stow your navigation charts, log book and pencil if nothing else. However, map pockets being what they are, seem to attract all kinds of stuff ranging from magazines to sandwiches and used drink cans. Yes sir, every airplane needs someplace to stow things where they are easily accessible to the pilot. Your cockpit will be a safer place, a PERFORATED -1/4" HOLES

ALUMINUM OR PLASTIC TUBE (5/8"WA.)

RADIO STACK—

RAM AIR SOURCE

DUCTING COOLING AIR

FIGURE 3. RADIO STACK COOLING OPTIONS

more attractive and comfortable place, if that sort of clutter is hidden from view

and secured. If you want to see what a messy cockpit looks like take a look in any cockpit that has maps and papers wedged in behind tubular structure or

poked under the seat. A map pocket eliminates that eyesore because its gathered elastic opening does an excellent job of containing anything poked into it. Anyone who is tempted to do an impromptu acrobatic ma-

neuver will be delighted with a map

pocket's capacity and ability to keep everything inside where it belongs. 28 FEBRUARY 1985

The open glove compartment door shows simple installation of the piano hinge and the Hartwell latch. Compartment could, of course, be provided without a door.

Map pockets take many forms and crop up in many locations. This homebuilt has one conveniently located on the door and another behind the seats. The gathered elastic openings help secure and contain the contents during exuberant maneu-

You could, of course, build a regular map case from metal or thin plywood complete with a lid and fastener. That's how they used to be. One of this type would be all right in a biplane or in any airplane with a welded steel tube or metal fuselage where it could be secured to the diagonals or uprights. Somehow a map case, per se, might look a bit out of place in a well furbished interior. Besides, it is difficult to retrieve small objects from the bottom of a hard walled map case unless you have small hands. One of the photos shows how effectively map pockets can be located. Note that one is on the door (actually each door) and the other behind the seat in this BD-4. These locations seem to be made to order to map pockets.

Another kind of map case is shown here. It takes advantage of a natural recess on each side of the baggage area. It is easily reached by the pilot and provides a convenient stowage place for the maps, charts and log book. However, inverted antics will allow the contents to be spewed all over the cockpit.

A Glove Compartment For Me?

What? No gloves? Well, wouldn't it be a handy place to stow your aircraft log book and papers, extra glasses (for sun or seeing), note pad and pencils and even navigational sectionals? The location on the instrument panel is always easily accessible.

The instrument panel in a two sealer (side-by-side) is made to order for the installation of a glove compartment. Unless your airplane is to be highly instrumented and loaded with radios there will always be a lot of unused blank panel areas. Besides, you won't have to spread out the instruments in order to fill out the panel. Tailor the size of the glove compartment opening to the space available. It should be at least 6 inches wide and about 12 inches deep. A sectional chart is smaller than that so any number of them could also be accommodated. You don't need to fabricate a heavy structure for a glove compartment. A thin plywood base and a cloth sleeve closed on one end would serve just as well. Here again the form that the interior takes will depend on the structure you have to work with. Usually a glove compartment door will be hinged on the bottom with a piano hinge and secured with a Hartwell fastener or latch. This results in a nice flush installation. You can take this basic arrangement one step further and limit the door opening to 90° so as to provide you with a small table to use in flight. A place to put your coffee mug or SPORT AVIATION 29

An armrest for each side and another being developed for the center console

to provide a restful support for the throttle arm. Luxurious but important cockpit

conveniences.

soft drink while you attend to your other pilot duties. Arm Rests Arm rests are welcome accessories in most any cockpit. An arm rest located between the seats can reduce the effort required to hold your arm extended to reach a center mounted throttle. This arm rest could be equally useful to the co-pilot. Add an arm rest on either side

of the cockpit and you will really have it all. During a long flight it is very nice to

be able to sort of raise yourself up on the elbows and shift your weight around to remove the numbing load from your

you-know-what. Even a brief exercise such as that will help rest and refresh your body.

Although making and installing an arm rest is easy, it is a bit more difficult to locate one properly. To be sure you

elegance and are a very practical addition to any homebuilt regardless of whether or not a carpet is installed. The plates are intended to eliminate the wear and tear your heels impose on the floor.

Make the scuff plates of aluminum sheet about .040" thick and measuring about 4 inches by 6 inches. Locate them at the rudder pedals so that when your feet are positioned normally your heels will center on the aluminum heel scuff plates. Of course, you can make the plates larger or smaller to suit your

Heel Scuff Plates These metal plates add a touch of

out some sort of support. Fortunately, fabricating and installing

a headrest is no more difficult than an

arm rest, particularly in this type of aircraft. More difficult is the installation of a headrest in an airplane fitted with conventional seats. Most of these seats

are not very tall and the headrest has to project well above the seat back in order to be functional. This type of headrest is hardly worth the effort and you could well do without one.

personal requirements. Secure them

Sunshades and Visors

of the question, you may be able to

not in your airplane? A variety of shaded plastic visors are stocked by many automotive shops and discount stores. Look for a lightweight design

through the carpet to the floor with small sheet metal screws, one in each corner. However, be sure that there are no wires, hydraulic lines or fuel lines in the area beneath. If the use of screws is out immobilize the plates on the carpeting with Silicone adhesive or Pliobond.

get yours in the best position, you

should wait until your seats are installed so you can try various arrangements.

signs can give you one sore neck with-

Headrests Headrests are almost mandatory in many of the current crop of low profile plastic planes. The reclining seats in

these "star wars" advanced concept de-

You have them in your auto so why

without a frame. Figuring out how to

mount it may be difficult without restricting its. degree of adjustment. Be sure to locate it where you can obtain the best windshield coverage and still be able to flip it up out of your way. Satisfied with the installation? Now

you can flip it down and fly off into the setting sun without squinting . . . just like in the movies.

If you wish to contact the author for additional information, please write to Tony Bingelis, 8509 Greenflint Lane, Austin, TX 78759.

You "star wars builders" of advanced concept aircraft might as well go ahead and install headrests for your reclining cockpit couches. They are relatively easy to make and are essential for your comfort.

30 FEBRUARY 1985