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NUMBER 10 97
FIGURE 9.—ORM-50 engine on the test stand.
Along with development of engine design, methods
of propellant feeding were investigated, and as
early as 1930 it was found that pressure-feeding was
more efficient for small rockets, and pump-feeding
for large rockets.
Proposed and tested in 1931-32 were a number
of piston-pump assemblies, such as the ORM-A engine
with a pump assembly (see Figure 6) capable
of feeding nitrogen tetroxide plus toluene propellant
into the 300-kg thrust engine.
In 1933, the ORM-23 through ORM-52 engines,
burning a nitric acid plus kerosene propellant and
provided with pyrotechnical and chemical ignition
systems, were developed and statically tested. The
ORM-50 experimental engines with a thrust of 150
kg and the ORM-52 engines with a thrust of 300 kg
passed official static tests in 1933 (see Figures 7 and
The experimental short-run ORM-23 engine was
specially developed and manufactured to work out
the method of initial ignition by means of an airgas
flame (gasoline and air mixture). Satisfactory
results were obtained for the single as well as for
the repeated ignition.
The numerous tests of various types of experimental
rocket engines made by that time showed
that uncooled nozzles deteriorated rapidly; therefore,
to increase the permissible rocket-firing duration,
air-cooling of the nozzle was applied in the
ORM-24 and ORM-26 engines. The cooling was
effected by means of shaped adapters attached on
the outside (in the ORM-24) and shaped fins on the
nozzle (in the ORM-26).
The test runs indicated that air cooling was inadequate.
Therefore, the design of the ORM-27
engine provided for a complete fluid-flow system to
cool the combustion chamber and the finned nozzle.
Temperature compensation of the nozzle expansion
was also provided in this engine.
Some other methods, in addition to those mentioned
above, were suggested to protect the nozzle
against failure. For example, in the ORM-28 engine,
use was made of an uncooled thick-walled
nozzle, whereas in the ORM-30 engine, the nozzle
was protected by a fuel curtain produced by additional
injectors. Neither of these produced satisfactory
results.
In later designs (beginning with the ORM-34
engine), the problem of nozzle cooling was solved
more comprehensively: the nozzles began to be
designed with complete flow-cooling.
The most advanced engines developed at the Department
II of GDL were ORM-50 and ORM-52.
The 150-kg-thrust ORM-50 engine burned a
nitric acid plus kerosene propellant ignited chemically;
it was developed at the request of the Moscow
Group for Study of Jet Propulsion (MosGIRD),
and was intended for the 05 rocket. It passed the
static acceptance tests in 1933. The engine could
undergo repeated tests. The steel cylindrical combustion
chamber, with an inside diameter of 120
mm, had a regeneratively acid-cooled cover and a
conical nozzle with spiral fins. The diameter of the
nozzle throat section was 23 mm. The chamber was
furnished with four swirl injectors having nonreturn
valves (see Figure 9).
The 300-kg thrust ORM-52 engine, using nitric
acid plus kerosene propellant with chemical igni-