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178 SMITHSONIAN ANNALS OF FLIGHT
perature at the completion of compression to its
initial temperature at the inlet to the engine.
Soon after the publication of B.S. Stechkin's work,
comments on and references to it began to appear
in the technical literature abroad. Soviet Union
priority in this field was unanimously acknowledged.
For example, G. A. Crocco, the famous
Italian scientist on hydrodynamics, recognized in
his fundamentally new work "Hyperaviation and
Superaviation" published in 1931, 4 that the classical
theory of a ramjet engine was first developed by
Professor B.S. Stechkin in the USSR. 5
In autumn 1967, at the first symposium on the
history of astronautics, held in Belgrade, Yugoslavia,
I presented a report (see Paper 16) on "Early
Experiments with Ramjet Engines in Flight,"
which gave the results of experiments with ramjet
models installed in a 3-inch projectile for a field
gun.
Flight tests of supersonic ramjets installed in an
artillery-type projectile proved in practice that
under certain conditions engines of this type could
develop a reaction force, and that, due to this, a
ramjet-type projectile had a greater range than that
of a standard projectile.
Ramjet Test in a Rocket
Having confirmed the performance capability of
the ramjet, the experimental investigations carried
out also showed that these ramjets developed
extra thrust of a comparatively small value. Then
there arose a question of the possible creation of a
ramjet developing thrust much higher than the
drag experienced by the ramjet body within a suitable
streamlined fairing.
To create this, LA. Merkulov, an engineer,
started investigating the thermodynamic cycle of a
ramjet, and his first conclusion was that a ramjet
operating on the proper Brayton cycle, that is, with
combustion at p = constant, where p=velocity of air,
could not develop thrust substantially above the
drag experienced by the ramjet body, and, in fact,
the engine could not thrust even itself, much less
impart a positive acceleration to any vehicle. This
results from the fact that to develop as great a
thrust as possible, the air within the ramjet combustion
chamber must be heated to a high temperature.
But to keep the pressure constant while raising the
gas temperature it is necessary to increase the com­
bustion-chamber cross-section in proportion to the
temperature increase. Thrust augmentation therefore
requires increasing simultaneously the ramjet
dimensions and, hence, the value of its drag.
However, this unfavorable circumstance did not
stop our work. It was proved that if the thermal
efficiency of the cycle was deliberately decreased by
burning the fuel at a decreased pressure; the ramjet
dimensions could then be greatly reduced and,
hence, the drag could be decreased at the expense of
losing some thrust. The question naturally arose as
to what extent the radial dimensions of the ramjet
combustion chamber should be reduced.
It was necessary to choose ramjet dimensions such
that they would allow the greatest free thrust (i.e.,
the difference between the ramjet thrust and the
drag).
Having analyzed the results of the aerojet engine
thermal cycles, Merkulov determined for the engine
the optimal parameters which permitted it to develop
thrust greatly exceeding its drag. Based on
the theoretical investigations carried out by the
Osoaviakhim Central-Council Stratospheric-Committee
Jet Section, some ramjet engine test models
were designed in 1936. All investigations and design
of ramjet engines were performed by space technology
enthusiasts of the Stratospheric Committee
without compensation. These engines were designed
by A.F. Nistratov, O.S. Oganesov, B.R. Pastukhovskiy,
L.E. Bryukker, M.A. Merkulova, B.I. Romanenko,
L.K. Bayev, and others. Many computations
in theoretical investigations of ramjet cycles
were made by A.D. Merkulova.
Then it was necessary to test the efficiency of the
ramjet during flight tests and to show that this ramjet
was able to impart a positive acceleration to the
vehicle on which it was installed. It was decided
that it would be tested first in a rocket.
The rocket equipped with a ramjet naturally
could be tested only as the second stage. As the first
stage, it was desirable to use a rocket with a different
engine (e.g., a liquid-fueled one) or a powder
rocket. For simplicity and reliability in performing
the tests it was decided to use a powder rocket as
the first stage, and a two-stage rocket was designed
that consisted of a powder rocket as the first stage
and a ramjet rocket as the second stage. This project
drew on the experience of GIRD. The second
stage also used solid fuel placed within the combustion
chamber as a grain.