and was called an Aeolipile. It consisted essentially of a
the presence of pressurized combustion gases, well
boiler, suspended over a fire, from which two tubes led to
supplied with heat, the gas turbine is capable of
a closed vessel in the shape of a sphere, into which
harnessing probably more mechanical shaft energy than
steam under pressure was introduced. When the steam
any other manmade device of equal size and weight.
escaped from two bent tubes mounted opposite one
another on the surface of the sphere, the tubes became
10-3. Theory of Operation. In order to master the
jet nozzles. A force was created at the nozzles that
theory of operation behind the gas turbine engine, four
caused the sphere to rotate around an axis.
basic principles must be under- stood: mass, pressure,
accelerated mass, and conversion of energy. Each is
b. Branca's Stamping Mill (Fig. 10-1). A further
application of the gas turbine propulsion principle,
utilizing what was probably the first actual impulse
a. Mass. All turboshaft engines attain their high
turbine, was the invention of a stamping mill built in 1629
rotational torque output, or power, from energy
by Giovanni Branca, an Italian engineer. The turbine
transferred to the turbines by the accelerated air mass
was driven by steam generated in a boiler. The jet of
within the engine. Figure 10-2 illustrates this concept.
steam from a nozzle in this boiler impinged on the blades
Within container 1 there are a certain amount of air
of a horizontally mounted turbine wheel which, through
molecules; the exact amount is referred to as mass.
an arrangement of gearing, caused the mill to operate.
This air mass is one of the key components required to
drive the turbine in the mass acceleration principle.
c. Newton's Steam Wagon (Fig. 10-1). In 1687, Sir
Isaac Newton formulated the laws of motion and
b. Pressure. A second component required in the
employed the basic principle used by Hero. The wagon
acceleration principle is pressure, or driving force. To
consisted essentially of a large boiler mounted on four
attain this pressure, container 2 (fig. 10-2) is heated and
wheels. Steam generated by a fire built below the boiler
the molecules contained within expand and exert
was allowed to escape through a nozzle facing rearward.
pressure equally in all directions.
The speed of the vehicle was controlled by a steam cock
located in the nozzle. The steam wagon demonstrates
c. Accelerated Mass. An accelerated mass is
Newton's Third Law of Motion: For every action, there is
obtained by funneling the pressurized gas down a narrow
always an equal and opposite reaction.
passageway (container 3). It is this convergency or
narrowing down of the nozzle area that causes the
Gas turbines are internal
molecules to accelerate and produce the velocity energy
They generate power by
required to perform the rotational mechanical work.
compressing a gas (air) that has been pumped into a
suitable chamber, adding heat energy (by burning fuel),
d. Conversion of Energy. The high-velocity gases
and expanding and expelling the heated gas through a
possess a large amount of kinetic energy. This energy
nozzle using rotating machinery that carries out the
due to motion now must be converted to mechanical
process in a steady flow. The gas that operates the
energy, which can be accomplished by adding a turbine
turbine is the product of the combustion that takes place
wheel to container 4 (fig. 10-2). The first force, as seen
when a suitable fuel is mixed and burned with the air
in the illustration, is the impact or push of the high-
passing through the engine. The gas turbine represents
velocity gases exiting the nozzle and hitting the turbine
one of man's more ingenious means of harnessing
wheel. The second force, which is a reaction force, is
energy. With the use of a few pounds of heat-resistant
generated by the high-velocity gases exiting the turbine
metal, properly shaped, and in
wheel in the opposite direction of rotation.