> > Just out of interest, what material is this (who wrote/published it)?
> > Does it give a formula, or at least a reason for this? (I'm asking
> > because I suspect that the author got something very wrong here.)
>
> It's from the Canadian Forces Air Command Weather Manual (which is
> quite good, at least for weather). Here's the relevant passage:
>
> The performance of an aircraft depends on several factors, among
> which temperature is important. The efficiency of a jet engine
> depends in part on the difference between the outside air
> temperature and the maximum temperature attainable in the combustion
> chamber. When the air temperature increases above a certain value,
> depending on the altitude, the true airspeed and the aircraft
> efficiency both fall off, the aircraft's operating height is reduced
> and there is an increase in fuel consumption per mile.
Thanks. That doesn't give away much of what the author thought... It
all seems a bit funny -- if the efficiency drops at a given air
temperature, then where does the combustion temperature come in? And
why is the change not continuous and smooth?
Anyway, I suspect the author read about the optimal efficiency of
thermodynamic engines somewhere, and abused the efficiency of the
Carnot cycle here... that efficiency is indeed 1-T1/T2, where T1 and
T2 are the lowest and highest temperatures in the cycle,
respectively. BUT it only applies to closed-cycle processes, which the
jet engine's combustion process definitely isn't. Also, it is only a
theoretical maximum that is technically difficult to get close to.
Andras
===========================================================================
Major Andras
e-mail: [EMAIL PROTECTED]
www: http://andras.webhop.org/
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