Cockpit Design SimplifiedBy Michael C. Myal, EAA 797828763 Cunningham, Warren, Mich.

rpHERE IS an apparent need for a simple solution toJL the problem of cockpit layout. Other methods are pre-

sented elsewhere which unnecessarily complicate the pro-cedure. A design technique, pioneered by General Motorsand developed through the SAE (SAE Standard J 826),is used throughout the automobile industry. It is simple,realistic, and positive.

Structural design of the aircraft should begin onlywhen the cockpit area is dimensionally fixed and its com-fort variables related to the intended purpose of this de-sign. This simplified cockpit design technique should be anencouragement to the homebuilt aircraft designer to be-gin his project with confidence, and will prove to be atime-saving asset to the manufacturer of aircraft.

THE MAN. Human factors specialists agree thatman's needs be completely analyzed before attemptingthe design of any vehicle. These highly skilled peopleseek to provide the vehicle operator with degrees ofroominess, comfort, visibility, and safety consistent withthe function of the vehicle or structure. They alwaysbegin with the human and his requirements, capabilities,or limitations. Our simplified technique follows this prin-ciple; ample cockpit space is guaranteed.

By employing a scale 2 D MANIKIN of a large size,as shown in Fig. 1, people of lesser stature will be fully

accommodated. The standard size of this manikin has beenselected with extreme care. He is 90 percentile in allbody segments, which means 90 percent of the Americanmales are shorter for each body segment. Studies haveconclusively proved man is not perfectly proportioned;he may have short legs and a long torso or vice versa.Thus, this manikin actually determines the space require-ments of better than 95 percent of the American males,since all of its body segments are at the 90 percentilelevel.

The question might now be raised, "Why not use a95 percentile manikin?" Economics of structure weightencourage the use of the 90 percentile size; the cockpitshould never be primarily designed for the extremelylarge person. Persons over the 95 percentile level willpossibly be sitting in a "jack-knifed" position. The prob-lem here is no different than that daily faced by thatsize of man. Doorways, clothing, even tying a shoelace,are generally overcome—if not gracefully. For the sakeof improved aircraft PERFORMANCE space must be con-sidered a premium, not to be lavishly used.

ATTITUDE COMFORT. We agree that the 90 per-centile manikin will provide adequate space, but theproblem now arises as to man's comfort requirements.

(Continued on next page)

^Ef fect ive Head Room

BACKANGLEBAR

BACK

5.0 inches

LOWER LEG -I-

FOOT

J_ ^ 90 THIGH 90° „• i

Fig. 1 Scale layout of the SAE 2 D manikin with degree scale orientationand insert of assembled manikin. The + sign indicates angle increase.

SPORT AVIATION 7

MTT|Kjr, HEIGHT

14*

Fig. 2 Some seating possibilities of the 2 D manikin.Space is allotted by controlling human comfort angles.Very difficult to compare using linear measurements.

COCKPIT DESIGN SIMPLIFIED . . .(Continued from preceding page)

There are two comfort factors: Attitude comfort is thatPHYSIOLOGICAL reaction of the body to position or pos-ture, while seat comfort is usually considered as thatdegree of support given the seated body. People tendto recognize the latter and mistakably judge the over-all comfort of the compartment by the softness of theseat cushions. Seated attitude is a far more serious as-pect of comfort, since little can be done to improve itonce the aircraft is built without resorting to costly re-work.

Let us first consider attitude comfort. The humananatomy (also the 2 D manikin) can be literally doubledup into a "squatting" position so that it occupies only 25inches of horizontal space in the airplane. Although notat all practical, this comparison brings out several sig-nificant features of the human anatomy. First, the bodyis highly adaptable to many posture attitudes and manyof its segments have considerable freedom of movement.Second, the body segments are highly sensitive to angu-lar displacement. We will use these elements to correctlydesign our cockpit with the 2 D manikin.

COCKPIT ROOMINESS. The actual size of the cock-pit area can now be easily defined by the 2 D manikinand its COMFORT ANGLES. These four angles, the foot,knee, hip, and the back angle are representative of hu-man body segment angular ranges as determined by de-tailed researches of the subject. We can, by manipulat-ing the angles on the 2 D manikin, individually or incombination, depict a realistic cockpit configuration forany type of aircraft which will provide full room andcomfort for over 95 percent of American males, (Fig. 2).To complete our side view, the height over the occupant'shead is established. Called EFFECTIVE HEADROOM inthe automobile industry, this standard dimension is meas-ured on a reclining 8 degree line from the "H" POINT,the hip joint center of the 2 D manikin for conventionalback angles. The 8 degree line has been determined asbeing the average position of the head for conventionalseat back angles, which due to postural differences inpeople, can vary from approximately —2.0 degrees to+12.0 degrees. In order to maintain a consistency withhuman seated height measurements, this dimension ismeasured from the "H" point to the roof or headliner,and a constant 4.0 inches is added to this figure to com-pensate for the distance to the bottom of the buttocks.I JULY 1963

%

95

90

80

70

60

50

40

30

_2Q ___10

5

A

38.1

37.6

37.1

36.6

36.3

36.0

35.6

34.3

34.9

34.3

33.8

B

33.2

32.7

32.1

31.7

31.3

31.0

30.7

30.3

29.9

29.3

28.8

c25.4

24.9

24.4

24.1

23.7

23.4

23.1

22.8

22.4

21.9

21.5

D

24.2

23.9

23.5

23.2

22.9

22.7

22.4

22.2

21.9

21.4

21.1

F

19.1

18.8

18.5

18.2

18.1

17,?

17.7

17.5

17.2

16,9

16.6

PERCENTILE TABLE VERSUS HUMAN DIMENSIONSFig. 3 Human comfort variabilities. A quick check ofthese variables will determine your percentile size rela-tive to adult American male statistics and will aid yourevaluation of your prototype.

The width of the cockpit must be considered fromthe standpoint of roominess. The prime dimension indi-cated comfort is SHOULDER ROOM, the distance be-tween opposing longerons or the trimmed side walls atthe "belt" or lower window opening. This dimension isclosely related to human shoulder width shown in Fig. 3.A shoulder room dimension of 40 inches is needed toaccommodate two 95 percentile men in the side-by-sideconfiguration, allowing .8 of an inch for light clothing.

Perhaps only one 90 percentile and one 50 percentile malewill occupy the airplane at a given time, which reducesthe shoulder room requirement to 37.5 inches. The PSY-CHOLOGICAL factor here will largely establish cockpitwidth; presumably, the lesser dimension might be ac-ceptable to the occupants of a fast, short-range shipwhile the dimensions over 40 inches would possibly benecessary for slower longer-range aircraft. In any case,the 40 inch dimension (or 20 inches for the single-placeaircraft) should serve as a point of departure, comparingthis figure to existing aircraft cockpit widths to deter-mine the final dimension of shoulder room.

To define our cockpit roominess, only six facts arerequired: the four comfort angles, effective headroom,and shoulder room. Study of aircraft and automobile di-mensioning practices, as found in Fig. 4, before attempt-ing the initial layout will prove beneficial to the de-signer.

LAYOUT AND PERFORMANCE. We have estab-lished a guide for determining the proper shoulder roomand have briefly mentioned the psychological aspect ofthis dimension. Just as we balance the aircraft perform-ance factors of speed, range, and maneuverability to fitthe intended purposes of the airplane, so, also, we mustconsider the size and comfort of the passenger compart-ment in terms of over-all intent of the airplane. It iseconomically desirable to provide the pilot and passengerwith the MINIMUM SPACE consistent with the task as-signed the aircraft.

Aircraft profile drag is a function of frontal area;less frontal area results in less drag for the same shapeof fuselage. The tandem arrangement which offers mini-mum frontal area, is not completely successful in this re-spect because of present engine configurations. Cockpitfrontal area can be said to be the product of the chosenshoulder room and fuselage depth at the cockpit section.The aircraft side views in Fig. 2 best describe fuselagedepth. By reducing effective headroom, we immediatelylower the top fuselage line and decrease the frontal area.We can also reduce the frontal area by raising the heelof the manikin. These reductions in fuselage depth affectthe comfort of the occupants. To what extent this processcan be carried out should be of prime concern to the de-signer.

To begin our design, we should first construct the2 D manikin scaled to the drawing size; Fig. 1 containsthe necessary information for making an accurate card-board, plywood, or plastic tool. Degree quadrants shouldbe incorporated for each of the body segments. On aclean piece of vellum, horizontal and vertical lines areestablished. The intersection of the two is used to locatethe "H" point. Next, by drawing an 8 degree line fromthis point, just as in a heading in map plotting, the ef-fective headroom line is established. The average di-

mension of 90 percentile male erect sitting heights (but-tock to top of head) is 37.6 inches, while the 95 percentilefigure is 38.1 inches from Fig. 3. Normal body posturewill reduce this by approximately 1 inch. Since we shouldaccommodate 95 percentile of the males, the dimensionwe could use is 37.1 inches of effective headroom. How-ever, intimate contact of head and canopy or head liningis not acceptable, so we could increase this figure to 37.6inches. Scaling this dimension onto our layout and mark-ing off an additional one-half inch for a canopy or head-lining thickness will establish the top fuselage line andthe necessary headroom.

Next step is to design the attitude comfort of ouraircraft. Refer to Fig. 4. The back angle can normallyvary from 20 degrees to 35 degrees. According to theN.A.A. rules for 190 cubic inch displacement racing air-planes, the back angle cannot exceed 20 degrees; we canassume that stiffer back angles are required in alert situ-ations. On the other hand, the reclining back angles ofover 45 degrees, which are used on the "Foka" and"Zefir," Polish sailplanes, indicate a lesser alert require-ment. It is recommended that a 24 degree back angle beused whenever possible, which provides an attitude withrelaxed, but firm, support compared to the best of today'sautomobiles. Only for crop dusting, racing, or similaralert situations would lesser angles be necessary. Higherback angles, over 24 degrees, are advantageous for thepassenger, in that they place more of the torso weightonto the seat back also increasing the hip area comfort.

The hip angle is the major comfort angle in the pack-aging of the cockpit. A comfort relationship between theabdomen and the thighs, the large hip angle generallyprovides more comfort. However, an extreme angle over105 degrees will usually place the body in an awkwardunbalanced position. A hip angle of 95.0 degrees, plusor minus 2.0 degrees, is recommended as a preliminarydesign starting point. In the rear compartment, varyinghip angles ranging as low as 80 degrees can be utilizedto develop occasional seating.

The knee angle has a high latitude of angular move-ment. Any angle between 80 degrees and 140 degrees canbe considered satisfactory for our design. Angles over140 degrees should be viewed carefully to insure thatthe under thigh tendons at the knee junction are not sub-jected to excessive seat pressures. The foot angle, whichis measured at the barefoot-lower leg intersection, shouldbe held at 90 degrees to establish the zero rudder posi-tion. The ranges of angular movement are 80 degrees to120 degrees. Rudder pedal travel should be such thatunder a full turn condition the manikin foot angle doesnot exceed 115 degrees, preferably 110 degrees, when theheel point position of zero rudder is held.

Assuming that we have chosen 24 degrees, 95 de-grees, 120 degrees, and 90 degrees for the back, hip, knee,

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Piper Colt . . . . . . . . . . . .Piper Cherokee . . . . . . . . . . . .Cessna 140 . . . . . . . . . . . . . . . .Beech Bonanza1963 Corvette Fastback1963 Corvair Monza Coupe1963 Buick Riviera1963 Cadillac Sixty Special

FrontalArea

12.213.211.5

. 14.2

Fuselage Effective ShoulderDepth Headroom Room

44.146.544.547.4

38.439.039.339.337.037.837.640.0

40.041.037.343.048.253.956.358.7

BackAngle

25.0°27.5°20.5°22.5°24.5°22.0°27.0°23.0°

HipAngle

95.0"98.5°91.0"87.0°96.0°90.5°93.0°91.0"

KneeAngle

122.0°118.5°122.5°97.5°

127.0°124.5°116.0°120.0°

Foot Knee Torso to Torso toAngle Clearance Panel Wheel

89.0°106.5°74.0°62.0°72.0°81.0°84.0°82.0°

7.77.36.54.5

21.922.123.619.8

15.515,014.. 59.5

Fig. 4

Fig. 4 Aircraft and automobile dimensions, taken to ac-celerator or rudder pedals. A check of these vehicles and

their comfort will be helpful in establishing your initiallayout. (Seats in rearmost position).

SPORT AVIATION 9

Fig. 5 Photograph of the SAE 3 D manikin. Used by au-tomobile manufacturers to check prototypes and for quali-ty control of production vehicles. Here installed inCessna 140.

COCKPIT DESIGN SIMPLIFIED . . .(Continued from preceding page)

and foot angles, respectively, we set these angles on ourmanikin which is then placed on the vellum with the"H" point superimposed over the intersection point. Themanikin is rotated about the "H" point until the backbar is parallel to vertical and the back contour is at 24degrees. The manikin is outlined on the vellum in thisposition.

A half inch of floor thickness is scaled on the draw-ing below the heel establishing the bottom of the fuse-lage. A full scale check of this layout indicates a designfuselage depth of 44.7 inches and a frontal area of 12.4square feet as compared to the production aircraft inFig. 4. If we increase the knee angle from 120 degreesto 130 degrees by raising the heel, fuselage depth be-comes 41.7 inches, a reduction of 3.0 inches in fuselagedepth or a reduction of 120 square inches, almost .9 of asquare foot of frontal area! The function of human com-fort angles in packaging becomes more apparent withuse. Any change from known cockpit roominess is re-ported in terms of changes in human attitude comfort.Linear dimensions expressing the roominess of a cock-pit, on the other hand, never reflect the true comfort con-ditions.

These typical comfort angles illustrate the simplicityof this procedure to lay out a cockpit. It is hoped thatthis example will stimulate the creativity of the readerto seek an INDIVIDUAL solution to his PARTICULARapplication.

The completed cockpit layout vellum can be used asan overlay to check the finished three-view drawing forstructural clearances or can be the beginning of a freshthree-view design.

PROVING THE LAYOUT. An indispensable tool forthe designer is a seating mockup, Fig. 5. Primarily builtto check out the seating developed during the layoutphase, it is valuable also as a temporary fixture. As the

BIBLIOGRAPHY

(covers important facets of dimensioning developments)SAE Paper 267 B (Also see page 16 of 267 B)

construction phase develops, the platform can be usedto build up the canopy installation, controls, the instru-ment panel, etc., without reference to bulky fuselage.A 4 ft. by 8 ft. sheet of 3/4 inch builder's fir plywoodattached to 2 by 4 sub frame should prove to be suffi-cient to support cockpit components for a four-place cock-pit.

Initially, the seating positions should be checked out.Since the manikin establishes the depressed human con-tour, it is necessary before designing the seat frame andlocation to determine the depressed padding thicknessby the "ouch" test.

Using a sample of the intended padding material,place the pad over a plastic web lawn chair. Sit on sameand have someone check the depressed depth of the padcarefully with a needle! This dimension is then addedto the manikin depressed line and establishes the sideview line of the seat frame. The same technique can beadapted to the approximation of the depressed manikinline for an existing seat using the assistance of a friendabout 69 inches tall and weighing about 170 pounds sit-ting in the seat.

Having determined the rearmost location of the seatstructure, the construction phase can be concluded bythe addition of the foot controls per the vellum layout. Ifyou are about 70 inches in height or shorter you shouldfind an excess amount of leg space in your design. Havea friend over 70 inches in height try it for size; heshould find the size of the compartment to be adequate.

SUMMARY. We have covered most briefly the argu-ments for using the manikin and the comfort dimension-ing method in developing aircraft seating. If you are ofthe one percent of the population that matches the scalemanikin, feel perfectly free to design your aircraft bythe cut and try method. However, you can save valuabledesign time by following this simple procedure and youare further guaranteed that any potential buyer willfind sufficient roominess in your ship. It should be re-membered that linear dimensions from production air-craft can frequently be misleading and, of course, donot tell the entire comfort story. A few pointers to saveweight, the seat structure should be designed as part ofthe wing as in the Beech Bonanza, or fuselage as on theCessna 140. Foam rubber is the best available pad ma-terial; a cored, easily compressed pad rates best for com-fort than the denser variations, although it is not as dur-able. Seat springs are not necessary for aircraft applica-tion; a web backing is sufficient. Cloth is more comfort-able than vinyl; some military researchers recommend 4inches of cored foam rubber covered with "Helenca,"a stretch ski pant fabric which has high performance andis porous. Seat depth should not exceed 18 inches forcomfort, (from the manikin back contour forward). Thenose of the seat should not be squared off.

The seat structure should be fixed for safety andweight reasons; foot controls should be designed fullyadjustable and have at least 5 inches of travel towardsthe seat from the design location. Individual verticalseat adjustment, up to 4 inches if you wish to consider theladies, can be easily accomplished by providing forblocking up the seat cushion pad with styrofoam or otherlow weight materials.

The CG of the manikin is at the intersection of a lineparallel and 10 inches forward of the back and a line5 inches above and parallel to the thigh centerline (kneeand hip point line) for most sitting attitudes.

Technical inquiries concerning the manikin toolsand their availability should be directed to the SAE, 485Lexington Ave., New York 17, N.Y.

10 JULY 1963