FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

NUMBER 10 35
First Tests on Solid Propellants
The first experimental series was conducted in
1927 and 1928 at BPD by my father, with the collaboration
of Dr. Marenco. Then 18 and an engineering
student in my first years at the university, I
was the second collaborator, free of charge. The first
chamber designed to test the above concepts is
shown in Figures 1 and 2. The propellant in C was
ignited by an ignition charge set off via a percussion
cap by a mechanical device p-m. The combustion
products were exhausted at the opposite end
through a nozzle F. The chamber was intended to
contain at most 0.1 kg of propellant. With a total
volume of 600 cc the maximum combustion pressure
was 2000 atm and the thick walls were calculated
for 4000 atm at the elastic limit. As an additional
safety measure the nozzle end was designed
to burst open at 1000 atm. All these safety precautions
were, of course, necessary because the tests
involved a great amount of uncertainty and were
to be conducted on an open test-stand, under our
very eyes. Indeed, more than once during the preliminary
testing the protective action of the safety
features of the nozzle end were called upon. The
chamber was free to move axially on rollers and
the thrust was converted into oil pressure by a
piston P3. Both chamber pressure and thrust were
recorded on a rotating drum by means of a double
channel mechanical manograph of the kind used in
gas engines.
However, the preliminary tests were carried out
without the manograph. The only instrument was
a "crusher" (Cr, Figure 2) intended to provide the
maximum pressure. Numerous attempts were made
to find a reliable binder between the double-base
cylindrical charge and the brass case containing
the charge, so as to inhibit burning on all but the
frontal surface. These attempts failed to attain the
necessary reliability, and once in a while resulted in
strong overpressures, reaching once the burst limit
of the nozzle end, because of the failure of the
binder. As a result, my father decided that the
inhibition of the burning surface was too unreliable
and he decided to concentrate on charges with unrestricted
burning.
The propellant chosen for these initial tests was
cordite, readily available in appropriate sizes at the
Naval Arsenal. The corresponding composition of
it is shown below:
Nitroglycerin
Nitrocellulose
Vaseline
Barium Nitrate
FIGURE 2.—Schematic sketch of first solid propellant test chamber.
Total
25
62
5
8
Too
Tubular charges of approximately 21 mm outside
diameter and 7 mm inside diameter were used. The
charges C were free to move in the brass case B
(Figure 3) but held within it by a charge-holder g.
The ignition charge c was a mixture of 2 g of ballistite
and 1 g of black powder. In order to help the
propagation of ignition, because the ignition charge
was located downstream of the main propellant,
three thin strips of ballistite were inserted into the
propellant hole. After the initial test, further to
improve the regularity of ignition, which still was
not entirely satisfactory, the nozzle was provided
with a burst diaphragm. The diaphragm, visible in
the details of Figure 2, kept the chamber closed
until a preassigned burst pressure was reached. The