FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

36 SMITHSONIAN ANNALS OF FLIGHT
C \ff
nozzles used in these tests had throat diameters of
either 7 or 8 mm.
Samples of three types of pressure records observed
are shown in Figure 4: some were quite
"normal" (4a); others were rather irregular (4&);
and some definitely "abnormal" (4c). The cause of
the abnormalities was attributed to poor effectiveness
of the charge holder, and indeed a better
design of this essential detail resulted in complete
suppression of such anomalous tests. However, from
the numerous tests it was clearly evident that the
equilibrium pressure was not very well defined and
could vary substantially from test to test, much
more than the small amount shown by Figure 4a, as
a result of irregularities in the burst pressure, the
nozzle and throat area, and the grain dimensions.
P
(atm)
zoo
100
0
FIGURE 3.—Propellant charge container.
Irregularities in the apparent duration of burning
even at equal pressures, such as shown in Figure 4a,
were caused by irregularities of the drum revolving
speed. This defect was inherent in the instrument
and actually prevented accurate determination
from individual tests of the burning rate and of the
specific impulse. The value of this last quantity
oscillated between 150 and 170 seconds.
Based on these results the small rocket stabilized
by tail fins (Figure 5) was designed and launched.
The corresponding charge was tested in a chamber,
as shown in Figure 5, where only the pressure
could be recorded. Larger test rockets, also with
aerodynamic stabilization, are shown in Figure 6.
The corresponding charge was divided into three
tubular grains of 300 g total weight and was tested
^ -- --—- — ---
a
« T(.01 sec)
FIGURE 4.—Pressure records (in atm vs. time in sec): a, Normal tests; b, irregular tests; c, abnormal tests.