Re: Some Turbofan Questions

From:         jvrusso@aol.com (JVRusso)
Organization: America Online, Inc. (1-800-827-6364)
Date:         20 Jul 96 15:56:05 
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On 7 July, wohlers@hdz-ima.rwth-aachen.de (Wolfgang Wohlers) wrote:

:I will try, though I am not sure about it: Today turbofans have bypass
:ratios of about 7. If you say that the change in velocity is about the
:same for bypass and core air (this is not exact of course) you get 7/8
:of the thrust through the bypass and 1/8 thruogh the core air. I am
:not sure how much faster the core air is, but I think most the thrust
:is provided by the bypass air.

Actually, bypass ratio is a measure of airflow, not thrust.

For example, on a turbofan with a BPR of 1.0, for every 1# of air that
goes thru the core, 1# bypasses it. A BPR of 2.0 means 2# bypass for every
1# in the core, etc. (a BPR of 0 would mena a turbo jet, but that term
isn't really used in discussion). The big turbofans run with BPRs of 8 or
more, while the military jets generally range from 0.2 to 0.8, depending
on the design.