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Old 15th Sep 2020, 12:21
  #10 (permalink)  
Join Date: Jun 2007
Location: Wanderlust
Posts: 2,679
For fuel efficiency everything about an engine is being made to operate to the limit e. g. Fan diameter to process more air mass, compression increasing core pressure, N1 and higher EGT. So the tolerances are reduced. Older engines had more margins. Some of them also had to motor to bring residual EGT down for start. In PW the separated fan through gearing so it could operate at it's own efficient speed. It allowed them bigger fan and less stages of compression reducing weight.
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