Re: 42,000 feet

Date:         30 Mar 97 03:54:27 
From: (BHunnewell)
Organization: AOL
References:   1
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Katie Schwarz wrote>
> got an e-mail from someone suggesting that the engines lose a lot of
>fuel-efficiency above 40,000 feet because "your turbofan engine turns into
>a turbojet engine." Anyone have any comments on how important this might
>be, compared to the issue of weight?

I've always been told that the big advantage to flying higher in jets is
that the engines get more efficient as it gets colder. Above the
tropopause-the air continues to get thinner but the temp remains constant,
so, there is no real increased efficiency to flying above the tropopause.
I could be wrong- I'm just an USAF pilot :-)