Therefore:

W= 1.4 X 2 X 10-4 X 1,800 X 0.210

The actual web is 0.110 inch.

This equation may be applied to catapults, removers,

and thrusters, remembering that it is only a first order

approximation.

volume is usually estimated in one of two ways,

depending upon the size of the individual propellant

grains. If the grains are "small" and will be oriented

randomly when loaded into the cartridge case, the

loading density is taken to be about 30 in.3/lb of

propellant. For an example, suppose it is estimated that

8 grams of propellant in the configuration of a cylinder

0.25 inch long by 0.10 inch outside diameter are

required for a thruster application. The case volume

required would then be estimated as:

30 in.3/lb X 8 gm x lb/454 gm = 0.53 in.3

Additional volume also must be provided for the case

cap and igniter charge retainer.

This must be

determined after estimation of the igniter charge volume

by a preliminary design of the head cap.

(2) To determine the charge weight for a

loaded iii some definite geometrical armament. The

thruster, calculate the energy expended in

grains are then stacked in the cartridge with their

doing the required work (in inch pounds).

centerlines parallel to the centerline of the case. The

Then find the intersection of that

case volume is then estimated by the size and number

particular abscissa with the curve

of the grains and their geometrical arrangement. This is

representing the propellant to be used,

discussed in section II, chapter 6, in the design example

and the ordinate of that intersection

on the M3 Catapult.

represents the approximate charge (in

grams).

actuated devices developed up to the present time has

been black powder. A rule of thumb that has evolved to

thickness of the grain between any two adjacent

estimate igniter charge weight is the use of about 40

surfaces of the propellant and the initial propellant web

grams of black powder per pound of propellant. This

in inches, w, may be estimated from equation (6):

estimated igniter charge may have to be increased or

(6)

decreased depending upon results of firings between -

where *C'*=pressure coefficient of linear burning rate of

65F. and 200F.

the propellant (of the order of 2 X 10-4 in./sec/psi). As

before, *P *is peak pressure (1,800 psi) and *t*m is stroke

time (0.210 sec), for the M5 catapult.

commonly are used. Critically stressed port ions of

components of propellant actuated devices are designed

applications, minimizing the weight of assemblies is a

so that material is used efficiently.

primary consideration. For this reason, materials which

possess a high strength-to-weight ratio, such as heat-

treated alloy steels and high-strength aluminum,

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