Jet Engine Thrust Question

"Mike" nospam@ microsoft.com wrote in
:

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

"Bertie the Bunyip" wrote in message
...
"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....

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

On Oct 2, 6:57*pm, "Mike" nospam@ microsoft.com wrote:
"Bertie the Bunyip" wrote in .18...



"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....

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

You actually can get to the required power needed, if you use the
gllider data given above. I for every 38 feet forward that 700
pounds of glider drops a foot. He told us the speed, so it's easy
enough to compute how many foot pounds of energy is lost every minute.
That will tell you the needed horsepower to maintain level flight.
1
Be really careful about confusing static thrust with power. You can
develop 1000 pound of static horizontal thrust by tying the scale to
a rope, threading the rope over a pulley, and hanging a thousand
pounds on the otther end of the rope. Lost so thrust, but no work is
being done.

"a" wrote in message
...
On Oct 2, 6:57 pm, "Mike" nospam@ microsoft.com wrote:
"Bertie the Bunyip" wrote in
.18...



"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....

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

You actually can get to the required power needed, if you use the
gllider data given above. I for every 38 feet forward that 700
pounds of glider drops a foot. He told us the speed, so it's easy
enough to compute how many foot pounds of energy is lost every minute.
That will tell you the needed horsepower to maintain level flight.
1

The OP never mentioned speed.

Be really careful about confusing static thrust with power. You can
develop 1000 pound of static horizontal thrust by tying the scale to
a rope, threading the rope over a pulley, and hanging a thousand
pounds on the otther end of the rope. Lost so thrust, but no work is
being done.

Which is exactly the situation you have with static thrust which I already
pointed out.

a wrote in
:

On Oct 2, 6:57*pm, "Mike" nospam@ microsoft.com wrote:
"Bertie the Bunyip" wrote in
messagenews:Xns9B2BEC6008C8pis
...



"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, becaus
e
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.

You actually can get to the required power needed, if you use the
gllider data given above. I for every 38 feet forward that 700
pounds of glider drops a foot. He told us the speed, so it's easy
enough to compute how many foot pounds of energy is lost every minute.
That will tell you the needed horsepower to maintain level flight.
1
Be really careful about confusing static thrust with power. You can
develop 1000 pound of static horizontal thrust by tying the scale to
a rope, threading the rope over a pulley, and hanging a thousand
pounds on the otther end of the rope. Lost so thrust, but no work is
being done.

Yeah, it is. you're shifting tons of air from one place to another. It
might not be the kind of work you want, but it's being done. Not to
mention you can run anything off the turbine you like...


Bertie

"Mike" nospam@ microsoft.com wrote in
:

"Bertie the Bunyip" wrote in message
...
"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....

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