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| MIL-S-8551O(AS)
3.4.7 Standard parts.
MS or AN standard parts shall be used wherever they are
suitable for the purpose.
3.4.8 Restraint construction.
3,4.8.1 Stitch pattern and cord size. Stitch pattern and cord size shall
sustain a minimum of 100 pounds per inch of stitch length, and shall apply with
figure 8.
3.4.8.2 Wrap radius. The wrap radius shall be the radius of the fitting over
which the strap is wrapped at the buckles and anchorages, as shown on figure 9. The
strap wrap radius shall be not less than 0.062 inch.
3.4.8.3 Hardware-to-strap folds. Figure 10 illustrates a recommended method to
reduce the weight and size of attachment fittings by folding the strap at an anchor-
age buckle fitting.
3.4.8.4 Surface roughness of fittings. Fittings in contact with the straps
shall have a maximum surface roughness of RMS-32.
3.5 Weight. The complete seat of each size, including the restraint, shall not
exceed the weights tabulated below:
Size of seat
Weight (lbs)
1
15
2
30
3
45
4
60
3.6 Structural strength and deformation. Longitudinal, lateral and upward seal
structural strenght and deformation requirements are based on the 95th-percentile
clothed occupant weight of 242 pounds (see 6.4.2) plus the weight of the seat and
any equipment attached to or carried in the seat. Downward seat structural strength
and deformation requirements are based on the effective weight of the 50th-percentile
clothed occupant plus the weight of that portion of the seat which must stroke
during vertical crash force attenuation. Table I lists the applicable weights and
load factors. Seat deflections shall be controlled to limit occupant contact with
surrounding structure.
3.6.1 Forward load. The seat shall have a static forward load deflection curve
measured along the longitudinal (roll) axis of the aircraft which rises to the left
and above the base area and extends into the acceptable seat failure area shown on
figure 11.
3.6.2 Aftward load. The seat strength shall be sufficient to withstand a load
factor of not less than 12.0 for aftward loads measured along the longitudinal
(roll) axis of the aircraft.
3.6.3 Lateral load. The seat shall have a static lateral load deflection curve
measured along the lateral (pitch) axis of the aircraft which rises to the left and
above the base curve and extends into the acceptable seat failure area shown on
figure 12.
8
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