Jet Engine Thrust Question

[Darkwing]

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?

[Robert Moore]

"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

[Robert 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

[Mike]

"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.

[Mike]

"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.

[Panic]

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?
>

[Brian[_1_]]

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

[Bertie the Bunyip[_24_]]

"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

[Mike]

"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.

[Bertie the Bunyip[_24_]]

"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

[Mike]

"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.

[a[_3_]]

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.

[Tman]

Bertie the Bunyip wrote:

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

Guess by that definition Bertie is actually employed!

[Mike]

"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.

[[email protected]]

On Oct 2, 7:39*pm, Tman <x@x> wrote:
> Bertie the Bunyip wrote:
>
> > Actually, it does. It's moving a lot of air from one end to the other an
> > also producing quite a bit of heat.
>
> Guess by that definition Bertie is actually employed!

....and Congress works, QED?

Please reconsider.

[Bertie the Bunyip[_24_]]

"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

[Bertie the Bunyip[_24_]]

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

[Bertie the Bunyip[_24_]]

Tman <x@x> wrote in :

> Bertie the Bunyip wrote:
>
>>
>> Actually, it does. It's moving a lot of air from one end to the other
>> an also producing quite a bit of heat.
>
> Guess by that definition Bertie is actually employed!


Mmm, not a million miles form the truth,I suppose..

No more so than for anyone else in my trade, though...

Fly somewhere, whine and bitch. fly somewhere else, whine and bitch. ..

Bertie