MIL-DTL-9479E (USAF)
materials. The +Gz limits are defined for a probability of spinal injury of 5 percent. The limits
specified for other acceleration directions are not nominal limits for a non-injury situation but are
maximum limits beyond which disabling injury can be expected (see 4.5.1, 4.5.8).
3.4.3.1 Ejection acceleration. The acceleration imposed on the seat occupant in the +Gz
direction (parallel to the spinal column) by the ejection catapult shall be limited in terms of
dynamic response index (DRI) values calculated according to the method described (see 6.4.1). If
the acceleration vector is not parallel (within 5°) to the z axis, the acceleration limitations
specified (see 3.4.3.2) shall be used. The limits for specific catapult pre-ignition temperature and
ejected weight representing the ejection seat, personal equipment, and 50th percentile human
body weight are as follows (see 4.5.1, 4.5.8):
a. The mean acceleration time history generated at a pre-ignition temperature of 70°F shall
not yield a DRI value in excess of 18.0 with an allowable standard deviation of 1.0.
b. The mean acceleration time history generated at a pre-ignition temperature of 165°F shall
not yield a DRI value in excess of 22.0 with an allowable standard deviation of 1.0.
3.4.3.2 Acceleration after aircraft separation. The seat acceleration due to catapult/rocket thrust
and aerodynamic deceleration shall be limited to satisfy equation (1) (see 4.5.1, 4.5.8):
2
Gy
2
2
DRI Gx
+
≤ 1.0
DRI + G
(1)
Gy
L
xL
L
where: DRIL is the limit value of the DRI. The value of DRIL shall be 18 unless the resultant
acceleration vector is more than 5 conical degrees off the z axis and aft of the plane of the
seat back, in which case the value of DRIL shall be 16.
GX and GY are the acceleration magnitudes of the x and y axis components of the acceleration
time history that are determined using the technique described (see 6.4.2).
G X L is the limit value for the x axis (fore and aft) of figures 4, 5, and 6.
GYL is the limit value for the y axis (sideways) of figure 7.
NOTE: In cases where there are acceleration components acting in the -GZ direction, the
equation
- GZ
DRI
shall be solved using
in place of
-GZ L
DRI L
where: -GZ is the -z direction
- GZ L is the limit value for the -z direction of figures 8 and 9.
10
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