Therefore:
W= 1.4 X 2 X 10-4 X 1,800 X 0.210
W=0.11 inch
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.
25. Cartridge Case Volume. a. The cartridge case
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
Figure 22. Curve for approximating propellant
determined after estimation of the igniter charge volume
charge for thrusters.
by a preliminary design of the head cap.
b. If "large"' grains are to be used, they may be
(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
24. Propellant Web. The web is the minimum
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
w=1.4 C'Ptm
(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 tm is stroke
time (0.210 sec), for the M5 catapult.
Section III. DESIGN STRENGTH CALCULATIONS
commonly are used. Critically stressed port ions of
27. General. a. In most propellant actuated device
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-
b. Resulphurized steels are never used, since
treated alloy steels and high-strength aluminum,
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