Re: Why a new super-jumbo isn't going to be built anytime soon.

Date:         23 Apr 97 02:58:16 
From:         "P. Wezeman" <pwezeman@blue.weeg.uiowa.edu>
Organization: The University of Iowa
References:   1
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 On 15 Apr 1997, matt weber wrote:

>     Why no new Super-Jumbo?
        ----snip----
> 2). Engine Performance. Larger engines have tended to more efficient. The
> differences in specific fuel consumption between the JT8 class engines that
> flew the 707/727/737 etc. and thegeneration that followed (JT9/CF6/RB211) that
> flew the next generation were enormous.The JT8's were typically around
> .61pounds of fuel/pound hour of thrust. The JT9's are typically about
> .36,  a roughly 40% improvement in Fuel Economy.
           ----snip----
   I believe that your figure of .36 pounds of fuel per pound of thrust
per hour for the JT9 is the static thrust value rather than that at
cruise. High bypass turbofans produce significantly more thrust at
low speeds than at high speeds because the ingested air is going slower
and hence has a greater change in velocity, and momentum, for the same
change in kinetic energy. "Jane's all the World's Aircraft" has both
values.

                        Peter Wezeman, anti-social Darwinist

                             "Carpe Cyprinidae"