Page 281 - The Jet Engine

Overhaul

replaces and must be produced and maintained so
that their own contribution to the measured
unbalance is minimal. In order to obtain the correct
dynamic reactions when balancing a compressor
and/or turbine rotor assembly on its own, with the
intention of making it an independent module, a
simulated engine rotor must be used to replace the
mating assembly, ref. fig. 25-7. The compressor
and/or turbine rotor assembly having then been inde-
pendently balanced with the appropriate dummy
rotor is thus corrected both for its own unbalance and
influence due to geometric errors on any other
mating assembly.

Moment weighing of blades Fig. 25-9 Integrated blade moment
51. With the introduction of the large fan blade, weighing.
moment weighing of blades has assumed a greater
significance, ref. fig. 25-8. This operation takes into
account the mass of each blade and also the position distributed around the disc in order that these
of its centre of gravity relative to the centre line of the unbalances are cancelled.
disc into which the blade is assembled. The
mechanical system of blade moment weighing may Assembling
be integrated with a computer, ref. fig, 25-9, which 52. The engine can be built in the vertical or
will automatically optimise the blade distribution. The horizontal position, using the ram or stand illustrated
moment weight of a blade in units i.e. g.mm. or oz.in., in fig. 25-TO and 25-11 respectively. Assembling of
is identical to the unbalance effect of the blade when the engine sub-assemblies or modules is done in
installed into a disc. The recorded measurement of separate areas, thus minimizing the build time on the
blade moment weights enables each blade to be build rams or stands.

Fig. 25-8 Principle of blade moment weighing.

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