Re: Thrust/HP

Date:         27 Aug 97 03:57:55 
From:         ergos <ergos@pacbell.net>
Organization: Pacific Bell Internet Services
References:   1 2
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Andrew Goldfinger wrote:
>
> In article <airliners.1997.1769@ohare.Chicago.COM> Mark Drela,
> drela@mit.edu writes:
> >  propulsive_power / fuel_heating_rate
>
> Yes -- and here is a paradox.  Since propulsive_power is proportional
> to velocity, and velocity is basically unlimited (i.e. I can define a
> reference frame in which the aircraft is moving near the speed of
> light),
> the efficiency can be greater than 100%!   It took me a long time to
> figure out the solution to this paradox.  I will wait a bit before
> posting it, so the readers can have the fun of figuring it out.

A guy did it before you. His name is Einstein. He determined that it
would take more energy - an infinity - to move near the speed of light;
that's if your mass is not zero, of course... In other terms you cannot
simply apply Newtonian mechanism in a Gallilean referential moving at
the speed of light...
There is a much better rationale at a much lower speed... Propulsive
power is proportional to velocity as long as the force (thrust) does not
change. I am afraid that would hardly be the case close or at Mach
speeds...

Ergos