Jet Engine Thrust Question

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?

"Darkwing" theducksmail"AT"yahoo.com wrote
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?

Think about a Glider.......:-)

Bob Moore

"Darkwing" wrote
How does rated thrust for a jet engine translate to actual power?

I know that this is going to be hard to believe, but...because of the
formula for computing "horsePOWER", when the jet is not moving, there
is no "POWER" being produced, just thrust. At somewhere around 300 KTS,
one pound of thrust will equal one horsepower. Google it!

Bob Moore

"Darkwing" theducksmail"AT"yahoo.com wrote in message
...
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.

"Robert Moore" wrote in message
5.250...
"Darkwing" wrote
How does rated thrust for a jet engine translate to actual power?

I know that this is going to be hard to believe, but...because of the
formula for computing "horsePOWER", when the jet is not moving, there
is no "POWER" being produced, just thrust. At somewhere around 300 KTS,
one pound of thrust will equal one horsepower. Google it!

However, this still doesn't tell us anything because the aircraft engines do
not need to produce max thrust at 300 Kts. Even at normal cruise, the jet
engines of most production aircraft are only producing about 25-30% of max
thrust.

The only time you have to have more thrust than aircraft weight is if you
plan to take off vertically with no takeoff run.

"Darkwing" theducksmail"AT"yahoo.com wrote in message
...
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?

On Oct 2, 10:01*am, Robert Moore wrote:
"Darkwing" theducksmail"AT"yahoo.com wrote

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?

Think about a Glider.......:-)

Bob Moore

To figure out how much thrust is required to keep the airplane in
level flight, divide the weight of the aircraft by the L/D Ratio of
the airplane. For Example my glider weighs 700 lbs and has a L/D ratio
of 38:1 at 50 kts. So at 50 knots it takes 700/38= 18.4 lbs of thrust
to maintain level flight. Since this is the best L/D it will take more
thrust to fly both slower or faster than 50 kts.

Brian
CFIIG/ASEL

"Mike" nospam@ microsoft.com wrote in
:

"Darkwing" theducksmail"AT"yahoo.com wrote in message
...
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.


Bertie

"Bertie the Bunyip" wrote in message
...
"Mike" nospam@ microsoft.com wrote in
:

"Darkwing" theducksmail"AT"yahoo.com wrote in message
...
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.

"Mike" nospam@ microsoft.com wrote in
:

"Bertie the Bunyip" wrote in message
...
"Mike" nospam@ microsoft.com wrote in
:

"Darkwing" theducksmail"AT"yahoo.com wrote in message
...
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....


Bertie