HUMAN FACTORS: , CONTRdL LOCATION , Ph.D 6020 Ashbukv'' llwater, OK

ELBOW CONTACT

SRL

SEAT CONTACT

I/

A. Fore/Aft Clearance

D,

*UE TO THE limited confinement of the cockpit space, the builder and designer of homebuilt aircraft have a problem with the location of aircraft controls. The control

stick is generally used in homebuilt aircraft because of the simplicity in installation as compared to the wheel. However, there are clearance limitations that must be adhered to in the design for a control stick. Figure 10 illustrates the clearance problems and limits for the control stick. The aft clearance includes both elbow contact with the seat back and stick contact with the seat

edge (Fig. 10-A, C). The lateral clearance between the pilot's legs should be at least 12 inches, at knee height (Fig. 10-B). The knee height depends on seat pan height and seat back inclination. Fore and lateral limitations (Fig. 10-A, C) depend on functional reach (Table I) plus the physical dimensions of elbow-fingertip length (Fig. 2-A) and forearm-forearm breadth (Fig. 3-M). The control stick movement constraints are shown in Figure 11. From the neutral position the stick moves 5 inches fore and 7 inches aft (Fig. 11-A). The lateral limits are 7 inches to either side at the handle level (Fig. 11-B) and 6 inches at the knee level (Fig. 10-B). The height of the stick handle (aft position) should be 8 to 10 inches above the SRL (Fig. 10-A). The elbow rest height (Fig. 1-E) can be used. This height can also be used to locate a right

side mounted elbow rest. Such a rest reduces pilot fatigue. In a neutral position the right forearm should be at approximately a 19 degree angle to the stick. The height of the stick handle when in neutral position should be 13.5 inches above seat reference level (SRL). The throttle should be located 13 to 15 inches to the left of the stick in line with the stick handle. The throttle should located 13.5 inches above SRL. Thus, the mid-point of the throttle handle will be located in alignment with the midpoint of the stick handle when both are in a neutral position. The throttle should move 5 inches fore (open position) and 5 inches aft (close position) with respect to neutral position. Again, a side mounted elbow rest to support the left forearm in line with the throttle serves to reduce pilot fatigue. The shape of the stick handle must be compatible with the anatomical features of the hand and wrist. A round (1 inch diameter) or oval (1 inch by 1.25 inch) handle provides grip security. The handle should taper from thumb to little

finger (Fig. 12-A) since when the wrist is in a neutral position the fingers shorten in the grip position. As the stick moves fore the wrist rotates downward (ulnar deviation) and rotates upward (radial deviation) as the stick 30 JULY 1983

B. Lateral Clearance

C. Reach Limit

FIGURE 10: CLEARANCE FOR CONTROL STICK

moves aft. The wrist range of motion is illustrated in Figure 12-B. The handle should be in a vertical position when the stick is in the aft position (Fig. 12-C). Many homebuilt aircraft use a side mounted control stick. Such location is necessary when cockpit design places the pilot in a semi-reclining position; however, a side mounted control stick reduces the pilot's arm range of motion. Instead of arm motion the pilot becomes more dependent on wrist movement. Fore and aft movement is limited to 30 degrees either side of neutral and lateral

A. Fore/ Art

FIGURE 11: CONTROL STICK MOVEMENT CONSTRAINTS

B. Lateral

FRONT VIEW

SIDE VIEW

A. Anatomical Grip

FORE

AFT

HANDLE VERTICAL

C. Handle Position

B. Wrist Range Of Motion

FIGURE 12: DESIGN OF CONTROL STICK

movement to 45 degrees (Fig. 13-A). An armrest of sufficient thickness to allow grasping the handle with the wrist in a neutral position increases wrist range of motion and reduces pilot fatigue (Fig. 13-B). The control pedal locations are given in Figure 14. The pedals should be 7.5 to 10.5 inches from the center line (Fig. 14-A). The position of the pedals from the seat reference point depends on the leg length segments (Fig. 2-G, H, J) and the angles formed by the joint segments. Optimum angles are given in Figure 14-B. The knee joint

angle should be 135-155 degrees with the ankle joint being

90-100 degrees. The foot should be at a 90 degree angle with the pedal when the pedal is in a neutral position. Pedal width should be 6 inches minimum with length 10 inches. This length is for a rudder-brake pedal combination. A heel rest with both pedal and heel rest giving positive foot position on the pedal is imperative so that

the foot remains in proper position. Loss of directional control during landing is a frequent homebuilt aircraft

accident. The taildragger gear configuration coupled with SPORT AVIATION 31

30°

B. Wrist Position A. Stick Limitations PIVOT FIGURE 13: SIDE MOUNT CONTROL STICK

PEDAL

J

7.5" TO 10.5"

KNEE

13" TO 19"

0

THROTTLE

0

STICK B. Knee And Ankle Joint Angles

A. Pedal Locations TOP VIEW FIGURE 14: LOCATION OF PEDAL CONTROLS

the pilot's foot improperly positioned on the pedals are the primary causative factors. The relationship of the seat to the instrument panel and controls is a major problem in cockpit design for the builder and designer of homebuilt aircraft. A seat with adjustable position appears to be an obvious solution but lack of space, mechanical factors, and crashworthiness make this a complex answer. Although problems still 32 JULY 1983

exist, particularly for the large person, design for the 50th percentle persons is a compromise solution. Human factors in cockpit design is an intricate and technical subject. This series of articles represents the major points to be considered by the designer and builder of homebuilt aircraft. In the interest of safety, human factors are no less important than mechanical factors and construction techniques.