FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

262 SMITHSONIAN ANNALS OF FLIGHT
N? 10257,
FIGURE 3.—Gas-turbine for which Swedish patent 10,257 was received in 1897.
After having completed the design of the gas
turbine and made a number of tests on this one,
Unge found that the ballistite propellant was difficult
to handle and, most of all, it did not provide as
much gas an gunpowder. The results of the ballistite
experiments forced Unge back to a propellant
composition of 78.3% niter, 8.4% sulphur, and
13.3% carbon. Later on this composition was
changed to 81.3% niter, 5.4% sulphur, and 13.3%
carbon. These compositions made optimum use of
the qualities of the turbine, but they gave Unge yet
another problem to solve. It turned out to be impossible
to store a charged rocket because the propellant
shrank and cracked during drying, and this
resulted in an explosion because of the increase in
the burning area. The first idea tried, in which it
was intended to retain the moisture with gypsum,
turned out to be useless, because even if the gypsum
swelled in absorbing the water, it, too, shrank after
3 or 4 days.
Tests over several years at the turn of the century
finally solved the problem: when mixed with 0.1-
0.6% of a nonvolatile oil, the propellant always
tried to expand after having been pressed into the
rocket-body. To prevent the propellant charge from
expanding along the central axis of the rocket, a
plate with the same geometrical form as the end
surface of the propellant was fastened immediately
after the propellant had been pressed into the
rocket body. This technique was patented in most
countries in 1903.
To simplify manufacturing of the rocket, the
propellant in its final form was shaped in small
cylindrical pieces (cartouches) covered with paper
or felting soaked in oil (Figure 6 and 7). This cover
served three purposes: first to make the charge
elastic when pressed into the body, second to protect
the propellant when transporting and handling
the rocket, and third, to provide a heat insulation
around the charge. Rockets fitted with this propellant
could be stored for years unaffected by temperature
changes between —25°C and -j-30°C
( —15°F and +85°F), and still deliver the same
thrust when fired. Unge heat tested the propellant
from -20°C to +80°C (-5°F to + 175°F) without
any trouble. The use of the gas turbine and the new
storage propellant also brought into use higher
pressures than before, and this forced Unge to give