Re: 777 Engine RPM

Date:         01 Oct 97 19:57:50 
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In article <airliners.1997.2222@ohare.Chicago.COM>, (Alan
Andersen) writes:

>Rotor speed at 100% for the PW4077/4084
>N1	2,900 rpm
>N2	10,800 rpm
>At cruise speed, at altitude, these speeds are not much different
>although the EPR is lower.  The higher the altitude, the faster the
>speeds for the same EPR.  (less air density)

Very simply EPR is a function of actual rotor speed divided by the square
root of the inlet total temperature. This would make the rotor speed some
5%-10% lower at altitude to achieve the same EPR. On the other hand you need
a higher EPR to achieve the same thrust due to reduced air density.

Gerald Wilson