Re: Some Turbofan Questions

From:         Dave Martin <dai@innet.lu>
Organization: INnet NV (post doesn't reflect views of INnet NV)
Date:         20 Jul 96 15:56:04 
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JVRusso wrote:
> Regarding thrust generated by turbofan engines, I don't have exact
> figures, but for high byass engines (PW4000, GE90, etc) the majority of
> the thrust comes from the fan. The main purpose of the core (high
> compressor/high turbine) is to generate enough horsepower to turn the fan.
> The lower the bypass ratio, the more excess thrust is available after hp
> is taken out to turn the fan.

Figure as I recall is around 80% from the fan and 20% from the turbine.
i.e. 40, 000 lbs vs 12,000 lbs for the older GE. The fan thrust drops
off at higher altitudes whereas the core drops off but slower. You get a
higher TAS for an airframe efficient CAS at altitude so it's still a
bargain to climb (to the optimum altitude of course - typically mid to
upper 30's for a fan aircraft).

Regards,
Dave.