Where:

This form of the burning rate-pressure relationship will be found in other portions of this bulletin.

(1) *General.*

given a required terminal velocity, *v*, and when limitations are set on the rate of change of

acceleration, , and on the maximum acceleration *a*m.

tolerance limits of acceleration, *a*m,, and rate of change of acceleration, , in any specified ejection

direction. The physiological limitations are presented in Table 1, and in military specifications. The

initial slope of the acceleration-time curve is * *and the level portion is *a*m. If a three-tube catapult is

assumed, the corresponding pressure-time curve would be as shown in figure 42. The point marked

tube of the catapult when the telescoping tube stops. If the acceleration is to remain constant, the

applied force must also remain constant. Since the inner tube presents a smaller area to the gas

pressure than the telescoping tube (see fig. 2), the pressure must increase correspondingly to

provide a constant force.

usually are based on a pressure time curve (fig. 43) from which all acceleration-time curve (fig. 44)

can be derived. The solid lines ill both figures show the desired operating conditions.

(*d) *Inasmuch as acceleration is proportional to the pressure acting on the catapult piston and the

velocity and travel are, at least ideally, tile first and second integrals of this acceleration, it is possible

to discuss the performance of a catapult in terms of its pressure characteristics. Curve 0-1-2 of

figure 45 illustrates the ideal pressure characteristics determined from limits of acceleration and rate

of change of acceleration currently used for human ejection in an upward direction. Conventional

catapults are designed to approach this ideal characteristic through the selection of interior ballistic

parameters and propellants. Catapults usually are designed so that the maximum design limitations

are met only at the high-temperature operating condition (curve A of fig. 45) performance is

appreciably lower when operating at 70F. and -65F. (curves

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