WORKSPACE EVALUATION AND DESIGN: USAF DRAWING BOARD MANIKINS AND THE DEVELOPMENT OF COCKPIT GEOMETRY DESIGN GUIDES
Kenneth W. Kennedy, Ph.D.
Anthropometry and Biomechanics: Theory and Application
Easterby, R.K., K.H.E. Kroemer, and D.B. Chaffin (Eds.)
pp. 205 - 213
NATO Conference: Series III, Human Factors
Plenum Press, New York, USA
1. USAF DRAWING BOARD MANIKINS
"One of the more recent design tools developed from anthropometric data is the series of USAF Two-Dimensional Drawing Board Manikins - USAF Patent 4,026,041, May 31, 1977. They were designed by the author primarily for use in the design and evaluation of seated work and crew stations, although with the use of appropriate limb parts they are of essentially equal usefulness in standing workstation design. Fifth, 50th, and 95th percentile male manikins were designed in accordance with the anthropometry of the USAF rated pilots projected to the 1980-90 time period. The procedures used in making these projections are included in Churchill and McConville (1976). A plan for the 5th percentile male manikin is illustrated in Figure 1. A 5th percentile female manikin was designed primarily after the current USAF anthropometric data on women from Clauser, et al (1972). An abbreviated list of body-size data after which the manikins were designed is found in Table 1.
Figure 1. Parts layout and assembly view of the 5th percentile USAF male manikin. Scale line, when increased to 16 inches will yield full scale, 8 inches for half scale, and 4 inches for quarter scale.
[NOTE: As indicated above, this is an abbreviated list. These manikins are classified according to their percentiles for Sitting Height, that is, the combined length of the torso, neck and head. Equivalent total arm (upper arm, forearm and hand) lengths to produce those same percentiles for Thumb-Tip Reach are provided as are alternative total arm lengths to reflect 95 percent of the predicted ranges for Thumb-Tip Reach that are compatible with the designated percentile for Sitting Height. Similarly with total leg length, i.e., combined Buttock-Knee Length and Knee Height.]
"Considerable additional anthropometric data were used to establish the overall sizes and mobility of the manikins. Several dimensions, derived from Snyder, et al (1972), were used to establish the relationships between and the mobility limits of the major segments of the torso. The centers of rotation of the head, neck, and torso correspond to the atlanto-occipital joint, the interspaces between the 7th cervical and 1st thoracic vertebrae, 8th and 9th thoracic vertebrae, 3rd and 4th lumbar vertebrae, and the hip joints. Joint range data for the limbs were taken from Barter, et al (1957).
"Information regarding the position of the base of the heart (aortic) valves was taken from Eycleshymer and Schoemaker (1911). Tracking the position of the base of the heart is accounted for by using overlapping arcuate slots and engraved indices on the overlapping parts of the upper torso. The position of the valves can, therefore, be estimated as the torso flexes and extends. By tracking the positions of the eye and aortic valves, changes in tolerance to +Gx and +Gz accelerations can be appreciated.
"Located close to the center of rotation of the manikin segments are adjustment holes and indices indicating ranges of motion. Near the centers of rotation within the head, neck and torso, the letters "E" (Erect) and "S" (Slumped) are engraved. Adjacent segments may be aligned such that the adjustment holes will overlay indices so lettered. When all are overlaying "E", the head, neck, torso, and thigh are in the erect, seated (or standing) position - when overlaying "S", a typical slumped orientation of the torso is achieved.
"Additional upper and lower limbs were designed to allow the user to consider variability in body proportions as well as in body size. Using regression equations based on Eye Height, Sitting, and Weight, and an appropriate factor of the Standard Error of the Estimate, the ranges of limb lengths that can be expected to be associated with the various percentile torso sizes, i.e., 5th, 50th, and 95th percentiles, were determined. The ranges necessary to include the central 90 percent were calculated and alternate limbs were designed accordingly. In practice, the small limbs associated with the 5th percentile torso usually see more use than the others. As will be seen later, however, special design situations require the use of other body/limb combinations to represent the extremes of capability and, therefore, accommodation. To facilitate the use of the manikins for standing work stations, a lower limb of appropriate length was designed.
2. COCKPIT GEOMETRY DESIGN GUIDES
"Cockpit geometry design guides have the general appearance of the familiar U.S. Department of Defense Military Standards 33574, -5, and -6, which specify the basic cockpit geometries of stick and wheel controlled, fixed wing aircraft and helicopters, and the USAF Design Handbook 2-2, "Crew Stations and Passenger Accommodations." They differ from these documents, however, in that they permit a great deal more flexibility in design. These military standards specify single values for the seat back angle, seat angle, vertical seat adjustability and the location and movement envelopes of the throttle, control stick, and rudder pedals. They strongly imply, thy their lack of any alternative guidance, that aircraft of the same generic type must all meet the same standard geometric requirements. The design guides, however, have been developed specifically to portray ranges of acceptable dimensions and relationships. They also will make available more extensive anthropometric and geometric data not found in military standards and handbooks. It is hoped that they will provide the much needed anthropometric data base to permit flexibility in cockpit design.
"There are several critical elements basic to any aircraft cockpit geometry design guide. They are: (1) back angle, (2) seat angle, (3) in the ejection cockpit, the angle of the path along which vertical seat adjustability is achieved, and (4) also in the ejection cockpit, the angle of ejection - the ejection clearance line. The range of body size accommodation is always 5th to 95th percentile for Eye Height, Sitting, although 1st to 99th for this dimension is easily achieved. The ranges of accommodation for all other body dimensions is 1st to 99th percentile, minimum. To achieve these ranges of accommodation, the USAF 5th and 95th percentile male drawing board manikins were used, along with their alternate limbs. Since hard mock-ups and live subjects were not used to verify accommodation, the recommended values must be perceived, as their name implies, to be Guides.
"In the brief space of this paper, only selected guides for an ejection type cockpit can be presented. The first portrays geometric information for cockpits with a 15º seat-back and 10º seat combination and in which vertical seat adjustability and ejection are parallel to the back. Adequate adjustability for 5th to 95th percentile accommodation to Eye Height, Sitting can be obtained with 4.6 cm movement parallel to the back, above and below NSRP: 6.6 cm above and below NSRP [Neutral Seat Reference Point] will accommodate 1st to 99th percentile for this body dimension.
"To help guide the placement of hand operated controllers in the forward direction, the guide contains information showing the relationship between minimum reach capability and the minimum space needed for fore and aft ejection clearance. Obviously, in an ejection-seat cockpit, it is necessary that hand operated controls in front of the pilot be located beyond the ejection clearance line. This requirement is crucial in attempting to achieve accommodation to large ranges of hand reach and Buttock-Knee Length. Back angle and direction of seat adjustment play critical roles in achieving useful, reachable space forward of the ejection clearance line.
"Another important consideration is the range of lower leg (shank) lengths. These values, expressed as arcs originating from expected knee centers, determine the maximum thrust of the foot in the forward direction. It is in this manner that the position of full forward throw of the rudder from its full forward (99th percentile leg) and full aft (1st percentile leg) adjustments. The throw and adjustability dimensions can be developed from these data. For the purpose of comparison, all examples of possible rudder location, throw, and travel in this short paper, are along a horizontal line at NSRP level. This should not be taken as a recommendation. A wide variety of approaches to provide rudder travel and throw can be derived.
"Several other useful data points are included. They include range of eye positions, catapult/ejection eye position, position of the base of the heart, the highest expected knee position during full rudder thrust with the opposite leg, position of the knee of the large pilot and clearance needed for safe ejection, minimum head clearance under the canopy, and others. Although not illustrated in this paper, dimensional information has been developed to provide the designer with several alternatives for locating the maximum full pitch down - full left aileron control stick position: ranges of reference points for the throttle, sidearm control, and forearm rests: a selection of fixed side-stick orientations so as to be centered in the range of forearm pronation/supination: and reach contours in front of the pilot.
"Although not presented here, similar information is also presented regarding another 15º back angle - 10º seat geometry in which, to achieve vertical seat adjustment, the seat is moved forward and upward along an angle established so as to achieve equivalent reach capability for the 1st to 99th percentile range. Using this procedure to obtain vertical adjustability, the smaller pilot is moved upward and forward. This is entirely logical from a human factors standpoint since the smaller pilot should be located higher and farther forward in the cockpit to achieve equivalent general accommodation as the larger pilot.
"The up and forward seat adjustment introduces an interesting and instructive set of design considerations. In the conventional case of vertical seat adjustability upward and aft parallel to the seat back, the pilot with a short torso and with arms shorter than usual - less than 1st percentile - as expected, will represent the minimal reach capability that must be accommodated. With up-and-forward seat adjustability, a pilot with different body and limb proportions produces minimal reach capability. The seat adjustability angle and length are such that the pilot with a long torso and relatively short arms - 45th percentile minimum - will have the least reach forward. This body proportion, then, unexpectedly produces the minimum reach capability from the recommended seat position. Although this direction of seat adjustment appears to result in a slight enlargement of the accessible space forward of the ejection clearance line, another problem is created, that of assuring adequate knee clearance during ejection.
"If there could be certainty that all pilots would adjust to the horizontal vision line, no problems related to safe knee clearance during ejection would be anticipated. However, since pilots often adjust themselves as high as possible, the probability of a clearance problem must be considered. This probability is increased if and when the pilot with a large torso and large Buttock-Knee Length raises the seat up and forward. In an attempt to control the maximum to which the larger pilots can raise the seat upward and forward, a minimal canopy clearance is indicated - 4 cm., approximately the thickness of the hand. It is unlikely that other, better procedures to control knee protrusion can be developed for this method of raising the seat.
"In another variant of the up-and-forward seat adjustment approach, the seat is moved along a 71º angle for the purpose of achieving equivalent positioning of essentially all pilots' eyes. An adjustment of 5.2 cm. along this angle above and below NSRP will accommodate from 5th to 95th percentile Eye Height, Sitting - 7.6 cm. above and below NSRP will accommodate 1st to 99th. The seat adjustment angle and length are such that the body proportions that produce minimum reach capability are the small torso/short reach pilots. The up-and-forward seat travel angle at which the changeover from small torso/short reach to large torso/short reach is between 43º and 71º. The point to which the pilot with 95th percentile torso and 45th percentile reach can be expected to reach, is further forward than that with a 55th percentile torso and 1st percentile reach. It appears that a small amount of additional space for manual control location is made available forward of the ejection line when using a 71º seat travel line. Again, to limit the upward travel of the seat, for the primary purpose of controlling forward knee protrusion, a minimal head/canopy clearance might be required."
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