Re: Thrust/HP

Date:         17 Aug 97 01:57:23 
From:         Wayne McCandless <SR-71@usa.net>
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In article <airliners.1997.1727@ohare.Chicago.COM> Wally,
gordow@cts.com writes:
>At the expense of sounding stupid, could anyone explain the
>mathematical relationship of thrust(rocket or jet) and horsepower.
>More precisely, how does one convert from one to the other.  I can't
>begin to relate how long and often I've pondered this question. Any
>help would be greatly appreciated.

Not a stupid question at all.  You might want to try a bit of
dimensional analysis to help work through the confusion:

1 HP = 33,000 lb-ft/min = 550 lb-ft/sec; right?

                     -- and --

Thrust is in units of lb-force.

Therefore,

An engine pushing a plane along at a (true) airspeed of 550
ft/sec is delivering one horsepower for each pound of thrust it
produces.

Left as an exercise for the student:  B747 sits at end of runway all
4 engines at full howl, brakes locked.  Each engine is providing
about 44K pounds of push.  Velocity of plane is zero.  How many
horsepower is being delivered?  Where does the ³missing² power go, if
anywhere?