Page 237 - The Jet Engine

Performance

by-pass ratio engine, the weight reduction compared given duty. The use of higher strength light-weight
with a pure jet engine is in the order of 20 per cent materials is also a contributory factor.
for the same air mass flow.
50. For a given mass flow less thrust is produced by
49. With a high by-pass ratio engine of the triple- the by-pass engine due to the lower exit velocity.
spool configuration, a further significant improvement Thus, to obtain the same thrust, the by-pass engine
in specific weight is obtained- This is derived mainly must be scaled to pass a larger total mass airflow
from advanced mechanical and aerodynamic design,
which in addition to permitting a significant reduction than the pure turbo-jet engine. The weight of the
in the total number of parts, enables rotating engine, however, is still less because of the reduced
assemblies to be more effectively matched and to size of the H.P. section of the engine. Therefore, in
work closer to optimum conditions, thus minimizing addition to the reduced specific fuel consumption, an
the number of compressor and turbine stages for a improvement in the power-to-weight ratio is obtained.

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