Re: Thrust/Horsepower of modern engines

Date:         27 Aug 99 03:08:02 
From:         Goran Begicevic <goran@tidax.se>
Organization: TIDAX AB
References:   1
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Hmmm...this tends to be a bit complicated calculation.

Energy(Joule)=Force(Newton)*distance(meter)
Power(Watts)=Energy(joule)/time(seconds)

One horsepower(mumbo-jumbo unit) = 746 Watts

Now using simple calculations would mean that jet engine spooling up on
takeof doesn't produce any power, beacuse brakes are applied and airframe
aint going anywhere. In reality, engine is moving air in- and out from
engine heating it up, thus doing the work.

Measuring power on ordinary piston-engines is straightforward procedure of
attaching them to engine-dyno. Jet engine is more complicated.
You could attain approximate HP-figure of jet engine by measuring how many
1000HP piston-engines you need to push same aircraft trough air at same
speed.
Unfortunately, this gets fuzzy beacuse propellers ain't that efficient at
higher speeds.

Your approach of measuring HP/figure as thrust*distance is wrong, beacuse
airframe with less drag will have higher speed with same thrust applyed,
inducing false results.

In my opinion, one of few reliable ways of measuring this is finding out
what's drag-figure for an airliner at speed on full throttle, and
multiplying it with airliners speed, divided with number of engines.

Just my 5 cents, correct me if i'm wrong.