FIRST STEPS TOWARD SPACE - Smithsonian Institution Libraries

NUMBER 10
to establish the fact of positive performance of a
ramjet engine, but also to determine the amount
of thrust developed. Based on the preliminary calculations,
the values were defined for drag experienced
by the projectile body and for thrust developed by
a ramjet engine. When the flight velocity with
which the shell escaped the cannon barrel was 588
m/sec, the calculated drag was 20 kg and the ramjet
engine thrust equalled 18 kg; i.e., it was somewhat
less than the drag (Figure 7). Therefore, the
engine was able to compensate 90% of the drag, but
was not able to overcome it completely or to impart
positive boost to the projectile. As the projectile
drag exceeded the engine thrust, its velocity should
decrease as the flight proceeded. The decrease of
velocity caused even greater difference between the
drag and the thrust. Thus, as at the moment of
escaping the cannon, at the initial velocity stated,
so in further flight the designed thrust of ramjet
engines was less than the drag. This did not in any
way confuse us, as the results of flight tests, even
with such a thrust-drag ratio, enabled us to establish
the fact of the ramjet engine operation and to determine
the degrees to which the thrust obtained in
practice approximated that designed.
Processing the flight-test data showed that the
actual drag in fact exceeded that calculated and the
actual thrust was somewhat below that designed.
It could be explained by a number of causes, such
as deformation of the metal frame of the phosphorus
grain, inadequate flight stability of projectiles
with ramjet engines, and so on.
Disclosure of the causes for the decrease in thrust,
kg
80
60
HO
20
0
A\
r
V
fc
^ i J
V*
200 WO BOD S00 fOOO v(m/sec)
FIGURE 7.—Air drag versus thrust developed by ramjet
engine.
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173
compared with the designed value, and the increase
in drag was a valuable result of the first set of experiments.
As soon as the causes of the deficiency
in ramjet engine performance were known, it became
possible to look for methods to eliminate
them and to modify the engine.
After the first set of experiments the second set
of flight tests on ramjet engines were carried out in
February 1934 and the third, in 1935. Six additional
models of ramjet engines were designed for these
tests, which were positioned in the body of a 76-mm
projectile. Some versions of ramjet engines comprise
several groups differing in the size of diffuser entry
section or nozzle throat, and some test models of
projectiles with ramjet engines differed in the
amount of propellant used.
The second version of projectiles with ramjet engine
differed from the first one only in the design of
the phosphorus-grain frame. To decrease the distortion
of the longitudinal ribs of the frame it was
decided to make it possible for the grain to rotate
freely in the chamber. With such a design, the rise
of the grain angular velocity occurred not instantly,
but gradually, thus preventing distortion of the
grain ribs. Owing to the modifications of the jet
engine design, the results of the test were appreciably
better.
To prevent fuel loss, the grain framework of the
third version of the engine was made so as to decrease
the ejection of bits of phosphorus, and phosphorus
with lower melting temperature was used.
Due to this modification of the propellant grain, the
value of specific impulse in the engines of the third
version increased to 423 kg sec/kg of propellant.
In these engines the propellant grain framework
was intended to retain phosphorus during the period
of the projectile boost inside the cannon, and
then it was used as a propellant. That is why the
test of this group of projectiles was quite significant.
Up to that time, the interesting concepts of FA.
Tsander and Yu.V. Kondratyuk, of using metal
propellant in jet engines, were developed only
theoretically or by means of experimental testing
under bench conditions. Ramjet engines designed
by the GIRD third team were the first jet engines
in the world operated in flight using metal propellant
not in the form of powder but as an element
of structure.
During these tests the projectiles with ramjet engine
covered a distance of 12 km (Table 2).