Re: Some Turbofan Questions

From: (H Andrew Chuang)
Organization: Concentric Internet Services
Date:         07 Jul 96 14:09:01 
References:   1 2
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In article <airliners.1996.1129@ohare.Chicago.COM>,
Robert & Linda Wilson  <> wrote:
>If the engine has separate hot and cold nozzles  like on the P&W JT9D or
>ROLLS RB211-524 you will have zero mixing.

The older RB211-524C/D found on the B747-200/300 has zero mixing, but the
newer RB211-524G/H found on the B747-400 and the B767-300 does mix the
bypass and core flows before exhaustion.

>On engines with mixers, i.e.
>the fan and core streams are mixed and ejected through a common final
>nozzle like ROLLS RB211-535E4 mixing numbers can be of the order of 70%
>with a well designed mixer. This gives a worthwhile reduction in noise
>and specific fuel consumption

However, the engine becomes heavier, and there is more drag.