j. The various terms of which the energy balance is composed are plotted against time in figure 49. Notice that
only a small fraction of the chemical energy made available by the combustion of propellant - (curve A) is transformed
into useful work (curve D). Most of the available energy is either lost through dissipation (curve B) or maintained in a
potential form as gaseous internal energy (curve C) of which a sizable portion is completely lost to the atmosphere at the
end of stroke. The values of the various terms of the energy balance at the end of the stroke and the thermal efficiency
for firings of the M5 catapult with an experimental charge are tabulated in table XV. The thermal efficiency is defined as
the ratio of the mechanical energy of the accelerated mass to the energy of propellant combustion.
Table XV. Values of Energy Balance Terms Upon Completion of Stroke
Propellant:................................................
Propellant-Continued
Composition....................................... T18
Length ......................................................... 1.95 in.
Lot ..................................................... PAE 12951
Impetus ....................................................... 777.5ft-lb/gm
Web................................................... 0.17in.
Ratio of specific heats ................................. 1.24
Number of perforations ...................... -1
Igniter ................................................................ 65 gm A1BP
Outer diameter................................... 0.447 in.
Energy of
Initial
Gaseous
propellant
Internal
internal
Mechanical
Propellant
Firing
Cycle
Thermal
combustion
energy
energy
energy
Energy
(1/2 mv3+mgs)
Propelled weight † (lb)
charge (gm) temp. ( .) time (sec)
F
efficiency
FN
PoVo
PV
loss H(t)
ν-1
ν-1
ν-1
(%)
(ft-lb)
(ft-lb)
(ft-lb)
(ft-lb)
(ft-lb)
310..............................
89.0
70
0.193
8.6
264,410
8420
129,580
22,690
120,560
310..............................
89.0
70
0.193
8.1
278,790
9780
131,560
22,590
123,040
310..............................
89.0
70
0.182
9.0
258,420
6770
129,700
23,360
112,130
310..............................
89.5
-65
0.195
8.2
214,460
9990
105,220
17,550
102,420
310..............................
89.2
-65
0.198
8.3
208,150
6230
99,570
17,220
97,590
310..............................
90.0
-65
0.203
7.2
214,690
8340
92,430
15,500
116,000
310..............................
89.4
160
0.168
10.0
289,620
7120
126,750
28,930
14,300
† Weight propelled vertically upward.
k. All of these energy-time functions, with the exception of the dissipation function (curve B), were derived directly
by feeding experimentally obtained data into the theoretical equations given previously. The energy remaining after all
the other energy forms have been accounted for is the dissipation function.
l. Figure 49 indicates the following approximate energy balance at tube separation in terms of the percentage of
the energy produced by combustion of the propellant charge:
This indicates an overall thermal efficiency of approximately 10 percent for a catapult.
This efficiency is also
representative of removers and thrusters.
54. Thrusters. From an interior ballistic standpoint, the major difference between thrusters and other stroking propellant
actuated devices (catapults and removers) is in the term of importance, i.e., for a thruster which is a closed system, the
main function is the overcoming of a resistive force and the kinetic energy imparted to the mass is incidental.
65
