"Mike" nospam@ microsoft.com wrote in
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"Bertie the Bunyip" wrote in message
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"Mike" nospam@ microsoft.com wrote in
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"Bertie the Bunyip" wrote in message
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"Mike" nospam@ microsoft.com wrote in
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"Darkwing" theducksmail"AT"yahoo.com wrote in message
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How does rated thrust for a jet engine translate to actual power?
I guess my question is, for example, a Cessna Mustang has two
engines that produce 1,460 lbs of thrust each (x 2) so the total
is 2920 lbs of thrust for the two engines. The takeoff weight for
the Mustang is listed as 8,645 lbs. so the engines are only
putting out a 1/4 of the total aircrafts weights. So do they rate
thrust different to the actual weight that the engines can fly?
Is the reason that is does only produce 2920 lbs. of thrust but
the wing is what actually makes the plane fly so the thrust
doesn't need to equal weight?

Max thrust is measured with the engine on a test stand and doesn't
correspond to the aircraft. It doesn't correlate to power,
because the power equation requires work to be performed and an
engine on a test stand doesn't produce work.


Actually, it does. It's moving a lot of air from one end to the
other an also producing quite a bit of heat.

You could say the same about any aircraft engine operating either on
a test stand on the ground or an aircraft in the air, however I
don't think that was the translation of "actual power" the OP was
looking for.



Probably not, but the HP thing is spurious in any case.
All you're looking for at the end of the day is thrust, after all!
It's clearly illustrated by trying to equate HP with performance. A
90 HP OX5 used to fly a Jenny in a semi-satisfactory sort of way. Try
flying one with a Rotax 914 though....

The OP didn't mention HP, but I also assumed that's what he was trying
to equate thrust.



Well, that's kind of the way it was going, OK.

As far as translating the thrust to HP is concernec, you have to look at
a jet engine with a view towards, tractive effort. Simplified, it means
that a given thrust will require less effort when the airplane is moving
(leaving drag out of the equation) An airplane fitted with EPR gauges
will show a reduction in thrust when the airplane accelerates with no
change in throttle setting 9 or , more importantly, fuel flow) The
reason is pretty obvious, the inlet pressure increases with the
advancing airspeed and gives a lower EPR reading as a result. Overlay
this fact on the aforementioned tractive effore notion and you've got
it..



Bertie