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ainut(at)hiwaay.net
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 Posted: Sat Aug 26, 2006 11:10 am Post subject: hp equivalent? |
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Looking for the horsepower equivalent for the l-29 engine. Anyone have
an idea?
Thanks,
David M.
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bcolombo(at)twcny.rr.com
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| Posted: Sat Aug 26, 2006 12:41 pm Post subject: hp equivalent? |
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I believe the formula is for between 1.75-2hp per lb of thrust. I will look
through my turbine books tonight and post the exact numbers
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bcolombo(at)twcny.rr.com
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| Posted: Sat Aug 26, 2006 12:48 pm Post subject: hp equivalent? |
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Convert Thrust to Horsepower
----------------------------------------------------------------------------
----
Is it possible to covert between pounds of thrust and horsepower for an
airplane engine? How is it done?
- David, Michael Hickey, Danny Williamson, Diego Codagnone, John Thomas,
Pashaee, Brad Hornsby
One of the most frequent questions we receive concerns the difference
between thrust and horsepower and how to convert between the two. The
problem is that these quantities are not directly related, so it is not
simple to convert one to the other. The dictionary defines thrust as a force
or pressure exerted on an object, and it is typically measured in units of
pounds (lb) or newtons (N). Power, however, is a measurement of work, which
is defined as the amount of motion a force creates when it is exerted on a
body over a certain amount of time. Power is typically measured in units of
horsepower (hp) or kilowatts (kW). The most common equation used to relate
these quantities is as follows.
where
P = power
F = force
d = distance
t = time
To understand what these definitions mean, let's consider a simple example.
Say you had to move a heavy desk 10 ft (3 m) from one side of the room to
another. You push on the desk with a force of 90 lb (400 N), but the desk
doesn't budge. In this case, a force has been applied, but since the desk
remains in the same place, you didn't perform any work. Now you ask a friend
to help you, and he pushes on the desk with the same force as you. Your
combined force of 180 lb (800 N) allows you to move the desk to its new
location in half a minute (30 seconds).
Based on the above equation, the power you and your friend generated to
perform that work was 60 foot-pounds per second or 80 newton-meters per
second. In the Metric system, the unit of a watt (W) is defined as a
newton-meter per second, so the power it took to move the desk is 80 W or
0.08 kW. The English system equivalent of a watt is horsepower, and 1 hp is
defined as being equal to 550 ft-lb/s. In other words, our 60 ft-lb/s is
equivalent to 0.11 hp. In this case and this case only, we can say that a
force of 180 lb converts to 0.11 hp. As we have seen, however, that
conversion depends on the variables distance and time. If you and your
friend used the same force to move the desk the same distance but it took
only 15 seconds, the power would double to 0.22 hp (0.16 kW).
We can also think of this equation in two slightly different ways. Some
readers may recognize that the force multiplied by distance represents
another quantity called torque (T), so we can say power is equivalent to the
torque a system generates over time.
Others may recognize the term distance over time as the definition of
velocity (v), so we can also say that power is equivalent to the force it
takes to move an object at a constant speed.
It is these two forms of the power equation that are most applicable to
aviation. For example, one of the common types of question we receive asks
how to convert the pounds of thrust generated by the jet engine(s) on a
particular plane into horsepower. The first factor we must consider is that
the thrust figures provided for most planes are in "static" units. Consider
for a moment the Boeing 747-200 with its Pratt & Whitney JT9D turbofans.
These four engines generate a total static force rating of 219,000 lb (973
kN). However, this force is measured by placing the engine on a device
called a test stand.
A simple test stand used for small rocket motors
A simple propulsion test stand is conceptually no different than standing on
a bathroom scale and measuring how much you weigh, or how much force you
exert standing on the surface of the Earth. The stand is fixed to the ground
and an engine is strapped onto it. When turned on, the engine pushes against
a scale (or load cell) that measures how much force the engine produces.
Since the engine doesn't actually move but is rigidly held in place, we say
that the force measured by the stand is in static pounds, or newtons, of
force.
How much power does the 747's Pratt & Whitney engine produce? As we
discussed earlier, a static engine does no work no matter how much thrust it
produces because it results in no motion. We must instead focus our
attention on a plane that is in motion. For example, our 747 typically
cruises around 600 mph (970 km/h). However, we are faced with a new problem
because the plane does not necessarily need every bit of its static thrust
to fly at that speed. In fact, static thrust is really an ideal maximum
amount of thrust that an engine can produce in a test environment. As
discussed in a previous question about thrust ratings, any jet engine will
produce less thrust in actual use than the static value.
Furthermore, aircraft are equipped with throttles that allow a pilot to
adjust the amount of thrust an engine produces. A good example is the SR-71
Blackbird equipped with Pratt & Whitney J58 turboramjets that produced a
combined static thrust of 65,000 lb (289 kN). Even though the Blackbird
could reach speeds in excess of Mach 3, however, it actually needed very
little of this thrust in cruise flight. Most of the thrust was required to
accelerate through the speed of sound, but once at Mach 3, the SR-71 engines
were throttled back to only 30% or so.
The conclusion of this explanation is that in order to determine the power a
jet creates in flight, we need to know the exact amount of thrust necessary
to fly at a particular speed. We typically know the static thrust rating of
an engine or the airspeed of a plane during flight, but the problem is that
we usually don't know the amount of thrust that corresponds to a particular
speed at a specific point in time. It is because of this disconnect that it
is so difficult to calculate the power generated by the engines on a
particular plane.
Luckily, we do have access to data from a NASA report that does provide all
the data we need to illustrate a sample case. The data is provided for a
Boeing 747-200 cruising at Mach 0.9 at 40,000 ft (12,190 m). In this
example, the aircraft's engines produce 55,145 lb (245,295 N) of thrust,
only a quarter of its rated static thrust, to cruise at a velocity of 871
ft/s (265 m/s). Using the equations provided above, we calculate the power
generated by the 747 to be 87,325 hp (65,100 kW).
The NASA data also includes a few other planes, so let's compare the power
generated by the subsonic 747 airliner to a supersonic fighter like the F-4
Phantom II. In this example, the F-4 cruises at Mach 1.8 at 55,000 ft
(16,765 m). The aircraft's two turbojet engines produce 11,560 lb (51,430 N)
of thrust at its cruise speed of 1,742 ft/s (531 m/s). This combination of
force and speed equates to a power of 36,620 hp (27,310 kW).
These examples illustrate how cumbersome it is to convert between thrust and
power. However, you may be wondering why jet engines or rocket engines are
rated in units of thrust but propeller-driven engines are rated in units of
power. For example, the F119 turbofans used on the F-22 are rated at 35,000
lb (310 kN) of thrust each and one of the main liquid rocket engines of the
Space Shuttle produces 418,000 lb (1,860 kN) at lift off. Meanwhile, a
turboprop engine of a C-130 is rated at 4,508 hp (3,362 kW) and the piston
engine of a Cessna 172 generates 180 hp (135 kW) of power. Why the
distinction?
How a jet engine works
The answer relates to the fundamental way in which each of these engines
works. Turbojet, turbofan, and rocket engines all work by directly
accelerating a fluid to produce a thrust force, so it is most
straightforward to rate these engines in terms of the size of that force. A
piston engine, turboprop, or turboshaft is designed to perform mechanical
work that turns a shaft. In other words, the engine creates a torque, and we
saw earlier that one of the forms of the power equation relates power to the
amount of torque created over time. The shaft that such an engine turns is
connected to a propeller, which is an aerodynamic device that converts that
power into thrust. The engine itself doesn't produce the thrust, but it
turns a propeller that does. Also, two engines that generate the same power
may not necessarily result in the same thrust since one may use a more
efficient propeller than the other. For these reasons, it is more logical to
rate these kinds of engines in terms of the power they create since that is
the most direct quantity they produce.
How a turboprop or turboshaft engine works
Based on what we have seen, you ought to have a better appreciation for why
it is preferable to compare jet engines in terms of thrust rather than power
and propeller-driven engines in terms of power rather than thrust. While the
opposite can be done, the process of converting between power and thrust
requires us to know or assume additional information that is usually
difficult or awkward to estimate.
- answer by Joe Yoon, 26 September 2004
---
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Ernie
Joined: 11 Jan 2006
Posts: 513
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| Posted: Sat Aug 26, 2006 12:56 pm Post subject: hp equivalent? |
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|
In reciprocating engines the simple formula is HP=TORQUE x RPM. In
order to determine the HP of the M701 you would need to measure the
shaft torque of the engine then multiply by 15,400 which is the RPM at
100%. Without knowing the amount of torque (force) the engine can
produce then you cannot determine HP.
Ernie
On 8/26/06, Brian Colombo <bcolombo(at)twcny.rr.com> wrote:
[quote]
Convert Thrust to Horsepower
----------------------------------------------------------------------------
----
Is it possible to covert between pounds of thrust and horsepower for an
airplane engine? How is it done?
- David, Michael Hickey, Danny Williamson, Diego Codagnone, John Thomas,
Pashaee, Brad Hornsby
One of the most frequent questions we receive concerns the difference
between thrust and horsepower and how to convert between the two. The
problem is that these quantities are not directly related, so it is not
simple to convert one to the other. The dictionary defines thrust as a force
or pressure exerted on an object, and it is typically measured in units of
pounds (lb) or newtons (N). Power, however, is a measurement of work, which
is defined as the amount of motion a force creates when it is exerted on a
body over a certain amount of time. Power is typically measured in units of
horsepower (hp) or kilowatts (kW). The most common equation used to relate
these quantities is as follows.
where
P = power
F = force
d = distance
t = time
To understand what these definitions mean, let's consider a simple example.
Say you had to move a heavy desk 10 ft (3 m) from one side of the room to
another. You push on the desk with a force of 90 lb (400 N), but the desk
doesn't budge. In this case, a force has been applied, but since the desk
remains in the same place, you didn't perform any work. Now you ask a friend
to help you, and he pushes on the desk with the same force as you. Your
combined force of 180 lb (800 N) allows you to move the desk to its new
location in half a minute (30 seconds).
Based on the above equation, the power you and your friend generated to
perform that work was 60 foot-pounds per second or 80 newton-meters per
second. In the Metric system, the unit of a watt (W) is defined as a
newton-meter per second, so the power it took to move the desk is 80 W or
0.08 kW. The English system equivalent of a watt is horsepower, and 1 hp is
defined as being equal to 550 ft-lb/s. In other words, our 60 ft-lb/s is
equivalent to 0.11 hp. In this case and this case only, we can say that a
force of 180 lb converts to 0.11 hp. As we have seen, however, that
conversion depends on the variables distance and time. If you and your
friend used the same force to move the desk the same distance but it took
only 15 seconds, the power would double to 0.22 hp (0.16 kW).
We can also think of this equation in two slightly different ways. Some
readers may recognize that the force multiplied by distance represents
another quantity called torque (T), so we can say power is equivalent to the
torque a system generates over time.
Others may recognize the term distance over time as the definition of
velocity (v), so we can also say that power is equivalent to the force it
takes to move an object at a constant speed.
It is these two forms of the power equation that are most applicable to
aviation. For example, one of the common types of question we receive asks
how to convert the pounds of thrust generated by the jet engine(s) on a
particular plane into horsepower. The first factor we must consider is that
the thrust figures provided for most planes are in "static" units. Consider
for a moment the Boeing 747-200 with its Pratt & Whitney JT9D turbofans.
These four engines generate a total static force rating of 219,000 lb (973
kN). However, this force is measured by placing the engine on a device
called a test stand.
A simple test stand used for small rocket motors
A simple propulsion test stand is conceptually no different than standing on
a bathroom scale and measuring how much you weigh, or how much force you
exert standing on the surface of the Earth. The stand is fixed to the ground
and an engine is strapped onto it. When turned on, the engine pushes against
a scale (or load cell) that measures how much force the engine produces.
Since the engine doesn't actually move but is rigidly held in place, we say
that the force measured by the stand is in static pounds, or newtons, of
force.
How much power does the 747's Pratt & Whitney engine produce? As we
discussed earlier, a static engine does no work no matter how much thrust it
produces because it results in no motion. We must instead focus our
attention on a plane that is in motion. For example, our 747 typically
cruises around 600 mph (970 km/h). However, we are faced with a new problem
because the plane does not necessarily need every bit of its static thrust
to fly at that speed. In fact, static thrust is really an ideal maximum
amount of thrust that an engine can produce in a test environment. As
discussed in a previous question about thrust ratings, any jet engine will
produce less thrust in actual use than the static value.
Furthermore, aircraft are equipped with throttles that allow a pilot to
adjust the amount of thrust an engine produces. A good example is the SR-71
Blackbird equipped with Pratt & Whitney J58 turboramjets that produced a
combined static thrust of 65,000 lb (289 kN). Even though the Blackbird
could reach speeds in excess of Mach 3, however, it actually needed very
little of this thrust in cruise flight. Most of the thrust was required to
accelerate through the speed of sound, but once at Mach 3, the SR-71 engines
were throttled back to only 30% or so.
The conclusion of this explanation is that in order to determine the power a
jet creates in flight, we need to know the exact amount of thrust necessary
to fly at a particular speed. We typically know the static thrust rating of
an engine or the airspeed of a plane during flight, but the problem is that
we usually don't know the amount of thrust that corresponds to a particular
speed at a specific point in time. It is because of this disconnect that it
is so difficult to calculate the power generated by the engines on a
particular plane.
Luckily, we do have access to data from a NASA report that does provide all
the data we need to illustrate a sample case. The data is provided for a
Boeing 747-200 cruising at Mach 0.9 at 40,000 ft (12,190 m). In this
example, the aircraft's engines produce 55,145 lb (245,295 N) of thrust,
only a quarter of its rated static thrust, to cruise at a velocity of 871
ft/s (265 m/s). Using the equations provided above, we calculate the power
generated by the 747 to be 87,325 hp (65,100 kW).
The NASA data also includes a few other planes, so let's compare the power
generated by the subsonic 747 airliner to a supersonic fighter like the F-4
Phantom II. In this example, the F-4 cruises at Mach 1.8 at 55,000 ft
(16,765 m). The aircraft's two turbojet engines produce 11,560 lb (51,430 N)
of thrust at its cruise speed of 1,742 ft/s (531 m/s). This combination of
force and speed equates to a power of 36,620 hp (27,310 kW).
These examples illustrate how cumbersome it is to convert between thrust and
power. However, you may be wondering why jet engines or rocket engines are
rated in units of thrust but propeller-driven engines are rated in units of
power. For example, the F119 turbofans used on the F-22 are rated at 35,000
lb (310 kN) of thrust each and one of the main liquid rocket engines of the
Space Shuttle produces 418,000 lb (1,860 kN) at lift off. Meanwhile, a
turboprop engine of a C-130 is rated at 4,508 hp (3,362 kW) and the piston
engine of a Cessna 172 generates 180 hp (135 kW) of power. Why the
distinction?
How a jet engine works
The answer relates to the fundamental way in which each of these engines
works. Turbojet, turbofan, and rocket engines all work by directly
accelerating a fluid to produce a thrust force, so it is most
straightforward to rate these engines in terms of the size of that force. A
piston engine, turboprop, or turboshaft is designed to perform mechanical
work that turns a shaft. In other words, the engine creates a torque, and we
saw earlier that one of the forms of the power equation relates power to the
amount of torque created over time. The shaft that such an engine turns is
connected to a propeller, which is an aerodynamic device that converts that
power into thrust. The engine itself doesn't produce the thrust, but it
turns a propeller that does. Also, two engines that generate the same power
may not necessarily result in the same thrust since one may use a more
efficient propeller than the other. For these reasons, it is more logical to
rate these kinds of engines in terms of the power they create since that is
the most direct quantity they produce.
How a turboprop or turboshaft engine works
Based on what we have seen, you ought to have a better appreciation for why
it is preferable to compare jet engines in terms of thrust rather than power
and propeller-driven engines in terms of power rather than thrust. While the
opposite can be done, the process of converting between power and thrust
requires us to know or assume additional information that is usually
difficult or awkward to estimate.
- answer by Joe Yoon, 26 September 2004
---
| | - The Matronics L29-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?L29-List |
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Ernie
Joined: 11 Jan 2006
Posts: 513
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| Posted: Sat Aug 26, 2006 1:00 pm Post subject: hp equivalent? |
|
|
One caveat, I was referring to shaft horsepoewer. Another way to get a
rough figure is to determine the amount of Power the engine produces
in KW and convert to HP, I beleive the KW rating is mentioned in the
manuals..
Ernie
On 8/26/06, Ernest Martinez <erniel29(at)gmail.com> wrote:
[quote] In reciprocating engines the simple formula is HP=TORQUE x RPM. In
order to determine the HP of the M701 you would need to measure the
shaft torque of the engine then multiply by 15,400 which is the RPM at
100%. Without knowing the amount of torque (force) the engine can
produce then you cannot determine HP.
Ernie
On 8/26/06, Brian Colombo <bcolombo(at)twcny.rr.com> wrote:
>
>
> Convert Thrust to Horsepower
>
>
> ----------------------------------------------------------------------------
> ----
>
>
> Is it possible to covert between pounds of thrust and horsepower for an
> airplane engine? How is it done?
> - David, Michael Hickey, Danny Williamson, Diego Codagnone, John Thomas,
> Pashaee, Brad Hornsby
> One of the most frequent questions we receive concerns the difference
> between thrust and horsepower and how to convert between the two. The
> problem is that these quantities are not directly related, so it is not
> simple to convert one to the other. The dictionary defines thrust as a force
> or pressure exerted on an object, and it is typically measured in units of
> pounds (lb) or newtons (N). Power, however, is a measurement of work, which
> is defined as the amount of motion a force creates when it is exerted on a
> body over a certain amount of time. Power is typically measured in units of
> horsepower (hp) or kilowatts (kW). The most common equation used to relate
> these quantities is as follows.
>
>
> where
>
> P = power
> F = force
> d = distance
> t = time
> To understand what these definitions mean, let's consider a simple example.
> Say you had to move a heavy desk 10 ft (3 m) from one side of the room to
> another. You push on the desk with a force of 90 lb (400 N), but the desk
> doesn't budge. In this case, a force has been applied, but since the desk
> remains in the same place, you didn't perform any work. Now you ask a friend
> to help you, and he pushes on the desk with the same force as you. Your
> combined force of 180 lb (800 N) allows you to move the desk to its new
> location in half a minute (30 seconds).
> Based on the above equation, the power you and your friend generated to
> perform that work was 60 foot-pounds per second or 80 newton-meters per
> second. In the Metric system, the unit of a watt (W) is defined as a
> newton-meter per second, so the power it took to move the desk is 80 W or
> 0.08 kW. The English system equivalent of a watt is horsepower, and 1 hp is
> defined as being equal to 550 ft-lb/s. In other words, our 60 ft-lb/s is
> equivalent to 0.11 hp. In this case and this case only, we can say that a
> force of 180 lb converts to 0.11 hp. As we have seen, however, that
> conversion depends on the variables distance and time. If you and your
> friend used the same force to move the desk the same distance but it took
> only 15 seconds, the power would double to 0.22 hp (0.16 kW).
>
> We can also think of this equation in two slightly different ways. Some
> readers may recognize that the force multiplied by distance represents
> another quantity called torque (T), so we can say power is equivalent to the
> torque a system generates over time.
>
>
>
> Others may recognize the term distance over time as the definition of
> velocity (v), so we can also say that power is equivalent to the force it
> takes to move an object at a constant speed.
>
>
>
> It is these two forms of the power equation that are most applicable to
> aviation. For example, one of the common types of question we receive asks
> how to convert the pounds of thrust generated by the jet engine(s) on a
> particular plane into horsepower. The first factor we must consider is that
> the thrust figures provided for most planes are in "static" units. Consider
> for a moment the Boeing 747-200 with its Pratt & Whitney JT9D turbofans.
> These four engines generate a total static force rating of 219,000 lb (973
> kN). However, this force is measured by placing the engine on a device
> called a test stand.
>
>
>
> A simple test stand used for small rocket motors
> A simple propulsion test stand is conceptually no different than standing on
> a bathroom scale and measuring how much you weigh, or how much force you
> exert standing on the surface of the Earth. The stand is fixed to the ground
> and an engine is strapped onto it. When turned on, the engine pushes against
> a scale (or load cell) that measures how much force the engine produces.
> Since the engine doesn't actually move but is rigidly held in place, we say
> that the force measured by the stand is in static pounds, or newtons, of
> force.
>
> How much power does the 747's Pratt & Whitney engine produce? As we
> discussed earlier, a static engine does no work no matter how much thrust it
> produces because it results in no motion. We must instead focus our
> attention on a plane that is in motion. For example, our 747 typically
> cruises around 600 mph (970 km/h). However, we are faced with a new problem
> because the plane does not necessarily need every bit of its static thrust
> to fly at that speed. In fact, static thrust is really an ideal maximum
> amount of thrust that an engine can produce in a test environment. As
> discussed in a previous question about thrust ratings, any jet engine will
> produce less thrust in actual use than the static value.
>
> Furthermore, aircraft are equipped with throttles that allow a pilot to
> adjust the amount of thrust an engine produces. A good example is the SR-71
> Blackbird equipped with Pratt & Whitney J58 turboramjets that produced a
> combined static thrust of 65,000 lb (289 kN). Even though the Blackbird
> could reach speeds in excess of Mach 3, however, it actually needed very
> little of this thrust in cruise flight. Most of the thrust was required to
> accelerate through the speed of sound, but once at Mach 3, the SR-71 engines
> were throttled back to only 30% or so.
>
> The conclusion of this explanation is that in order to determine the power a
> jet creates in flight, we need to know the exact amount of thrust necessary
> to fly at a particular speed. We typically know the static thrust rating of
> an engine or the airspeed of a plane during flight, but the problem is that
> we usually don't know the amount of thrust that corresponds to a particular
> speed at a specific point in time. It is because of this disconnect that it
> is so difficult to calculate the power generated by the engines on a
> particular plane.
>
> Luckily, we do have access to data from a NASA report that does provide all
> the data we need to illustrate a sample case. The data is provided for a
> Boeing 747-200 cruising at Mach 0.9 at 40,000 ft (12,190 m). In this
> example, the aircraft's engines produce 55,145 lb (245,295 N) of thrust,
> only a quarter of its rated static thrust, to cruise at a velocity of 871
> ft/s (265 m/s). Using the equations provided above, we calculate the power
> generated by the 747 to be 87,325 hp (65,100 kW).
>
> The NASA data also includes a few other planes, so let's compare the power
> generated by the subsonic 747 airliner to a supersonic fighter like the F-4
> Phantom II. In this example, the F-4 cruises at Mach 1.8 at 55,000 ft
> (16,765 m). The aircraft's two turbojet engines produce 11,560 lb (51,430 N)
> of thrust at its cruise speed of 1,742 ft/s (531 m/s). This combination of
> force and speed equates to a power of 36,620 hp (27,310 kW).
>
> These examples illustrate how cumbersome it is to convert between thrust and
> power. However, you may be wondering why jet engines or rocket engines are
> rated in units of thrust but propeller-driven engines are rated in units of
> power. For example, the F119 turbofans used on the F-22 are rated at 35,000
> lb (310 kN) of thrust each and one of the main liquid rocket engines of the
> Space Shuttle produces 418,000 lb (1,860 kN) at lift off. Meanwhile, a
> turboprop engine of a C-130 is rated at 4,508 hp (3,362 kW) and the piston
> engine of a Cessna 172 generates 180 hp (135 kW) of power. Why the
> distinction?
>
>
>
> How a jet engine works
> The answer relates to the fundamental way in which each of these engines
> works. Turbojet, turbofan, and rocket engines all work by directly
> accelerating a fluid to produce a thrust force, so it is most
> straightforward to rate these engines in terms of the size of that force. A
> piston engine, turboprop, or turboshaft is designed to perform mechanical
> work that turns a shaft. In other words, the engine creates a torque, and we
> saw earlier that one of the forms of the power equation relates power to the
> amount of torque created over time. The shaft that such an engine turns is
> connected to a propeller, which is an aerodynamic device that converts that
> power into thrust. The engine itself doesn't produce the thrust, but it
> turns a propeller that does. Also, two engines that generate the same power
> may not necessarily result in the same thrust since one may use a more
> efficient propeller than the other. For these reasons, it is more logical to
> rate these kinds of engines in terms of the power they create since that is
> the most direct quantity they produce.
>
>
>
> How a turboprop or turboshaft engine works
> Based on what we have seen, you ought to have a better appreciation for why
> it is preferable to compare jet engines in terms of thrust rather than power
> and propeller-driven engines in terms of power rather than thrust. While the
> opposite can be done, the process of converting between power and thrust
> requires us to know or assume additional information that is usually
> difficult or awkward to estimate.
> - answer by Joe Yoon, 26 September 2004
>
> ---
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jorgen.nielsen(at)mweb.co
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| Posted: Sat Aug 26, 2006 2:25 pm Post subject: hp equivalent? |
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I am not an engineer but the explanation below just does not work for me-
what am I missing here? The example of the 747 and F4 use the NASA given
thrust rating and the speed of the aircraft to determine thrust - what about
the air density at 40000ft and 55000ft? That same 747 at say 5000ft at the
same power setting would going at 1/4 of the speed, certainly nowhere near
M0.9?
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taylor(at)snowcrest.net
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| Posted: Sat Aug 26, 2006 4:11 pm Post subject: hp equivalent? |
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The formula is one pound of thrust equals one horsepower(at)375 mph inlet speed
Pete taylor
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ainut(at)hiwaay.net
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| Posted: Sat Aug 26, 2006 5:42 pm Post subject: hp equivalent? |
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Brian, I understand all that. That's why I asked for "equivalent." 
I don't know the thrust rating for the normal L-29 engine nor can I
remember the formula for the conversion. One makes lots of standard
assumptions during the conversion process. I just was hoping someone
knew the values off the top of their head.
Thanks,
David M.
Brian Colombo wrote:
[quote]
Convert Thrust to Horsepower
----------------------------------------------------------------------------
----
Is it possible to covert between pounds of thrust and horsepower for an
airplane engine? How is it done?
- David, Michael Hickey, Danny Williamson, Diego Codagnone, John Thomas,
Pashaee, Brad Hornsby
One of the most frequent questions we receive concerns the difference
between thrust and horsepower and how to convert between the two. The
problem is that these quantities are not directly related, so it is not
simple to convert one to the other. The dictionary defines thrust as a force
or pressure exerted on an object, and it is typically measured in units of
pounds (lb) or newtons (N). Power, however, is a measurement of work, which
is defined as the amount of motion a force creates when it is exerted on a
body over a certain amount of time. Power is typically measured in units of
horsepower (hp) or kilowatts (kW). The most common equation used to relate
these quantities is as follows.
where
P = power
F = force
d = distance
t = time
To understand what these definitions mean, let's consider a simple example.
Say you had to move a heavy desk 10 ft (3 m) from one side of the room to
another. You push on the desk with a force of 90 lb (400 N), but the desk
doesn't budge. In this case, a force has been applied, but since the desk
remains in the same place, you didn't perform any work. Now you ask a friend
to help you, and he pushes on the desk with the same force as you. Your
combined force of 180 lb (800 N) allows you to move the desk to its new
location in half a minute (30 seconds).
Based on the above equation, the power you and your friend generated to
perform that work was 60 foot-pounds per second or 80 newton-meters per
second. In the Metric system, the unit of a watt (W) is defined as a
newton-meter per second, so the power it took to move the desk is 80 W or
0.08 kW. The English system equivalent of a watt is horsepower, and 1 hp is
defined as being equal to 550 ft-lb/s. In other words, our 60 ft-lb/s is
equivalent to 0.11 hp. In this case and this case only, we can say that a
force of 180 lb converts to 0.11 hp. As we have seen, however, that
conversion depends on the variables distance and time. If you and your
friend used the same force to move the desk the same distance but it took
only 15 seconds, the power would double to 0.22 hp (0.16 kW).
We can also think of this equation in two slightly different ways. Some
readers may recognize that the force multiplied by distance represents
another quantity called torque (T), so we can say power is equivalent to the
torque a system generates over time.
Others may recognize the term distance over time as the definition of
velocity (v), so we can also say that power is equivalent to the force it
takes to move an object at a constant speed.
It is these two forms of the power equation that are most applicable to
aviation. For example, one of the common types of question we receive asks
how to convert the pounds of thrust generated by the jet engine(s) on a
particular plane into horsepower. The first factor we must consider is that
the thrust figures provided for most planes are in "static" units. Consider
for a moment the Boeing 747-200 with its Pratt & Whitney JT9D turbofans.
These four engines generate a total static force rating of 219,000 lb (973
kN). However, this force is measured by placing the engine on a device
called a test stand.
A simple test stand used for small rocket motors
A simple propulsion test stand is conceptually no different than standing on
a bathroom scale and measuring how much you weigh, or how much force you
exert standing on the surface of the Earth. The stand is fixed to the ground
and an engine is strapped onto it. When turned on, the engine pushes against
a scale (or load cell) that measures how much force the engine produces.
Since the engine doesn't actually move but is rigidly held in place, we say
that the force measured by the stand is in static pounds, or newtons, of
force.
How much power does the 747's Pratt & Whitney engine produce? As we
discussed earlier, a static engine does no work no matter how much thrust it
produces because it results in no motion. We must instead focus our
attention on a plane that is in motion. For example, our 747 typically
cruises around 600 mph (970 km/h). However, we are faced with a new problem
because the plane does not necessarily need every bit of its static thrust
to fly at that speed. In fact, static thrust is really an ideal maximum
amount of thrust that an engine can produce in a test environment. As
discussed in a previous question about thrust ratings, any jet engine will
produce less thrust in actual use than the static value.
Furthermore, aircraft are equipped with throttles that allow a pilot to
adjust the amount of thrust an engine produces. A good example is the SR-71
Blackbird equipped with Pratt & Whitney J58 turboramjets that produced a
combined static thrust of 65,000 lb (289 kN). Even though the Blackbird
could reach speeds in excess of Mach 3, however, it actually needed very
little of this thrust in cruise flight. Most of the thrust was required to
accelerate through the speed of sound, but once at Mach 3, the SR-71 engines
were throttled back to only 30% or so.
The conclusion of this explanation is that in order to determine the power a
jet creates in flight, we need to know the exact amount of thrust necessary
to fly at a particular speed. We typically know the static thrust rating of
an engine or the airspeed of a plane during flight, but the problem is that
we usually don't know the amount of thrust that corresponds to a particular
speed at a specific point in time. It is because of this disconnect that it
is so difficult to calculate the power generated by the engines on a
particular plane.
Luckily, we do have access to data from a NASA report that does provide all
the data we need to illustrate a sample case. The data is provided for a
Boeing 747-200 cruising at Mach 0.9 at 40,000 ft (12,190 m). In this
example, the aircraft's engines produce 55,145 lb (245,295 N) of thrust,
only a quarter of its rated static thrust, to cruise at a velocity of 871
ft/s (265 m/s). Using the equations provided above, we calculate the power
generated by the 747 to be 87,325 hp (65,100 kW).
The NASA data also includes a few other planes, so let's compare the power
generated by the subsonic 747 airliner to a supersonic fighter like the F-4
Phantom II. In this example, the F-4 cruises at Mach 1.8 at 55,000 ft
(16,765 m). The aircraft's two turbojet engines produce 11,560 lb (51,430 N)
of thrust at its cruise speed of 1,742 ft/s (531 m/s). This combination of
force and speed equates to a power of 36,620 hp (27,310 kW).
These examples illustrate how cumbersome it is to convert between thrust and
power. However, you may be wondering why jet engines or rocket engines are
rated in units of thrust but propeller-driven engines are rated in units of
power. For example, the F119 turbofans used on the F-22 are rated at 35,000
lb (310 kN) of thrust each and one of the main liquid rocket engines of the
Space Shuttle produces 418,000 lb (1,860 kN) at lift off. Meanwhile, a
turboprop engine of a C-130 is rated at 4,508 hp (3,362 kW) and the piston
engine of a Cessna 172 generates 180 hp (135 kW) of power. Why the
distinction?
How a jet engine works
The answer relates to the fundamental way in which each of these engines
works. Turbojet, turbofan, and rocket engines all work by directly
accelerating a fluid to produce a thrust force, so it is most
straightforward to rate these engines in terms of the size of that force. A
piston engine, turboprop, or turboshaft is designed to perform mechanical
work that turns a shaft. In other words, the engine creates a torque, and we
saw earlier that one of the forms of the power equation relates power to the
amount of torque created over time. The shaft that such an engine turns is
connected to a propeller, which is an aerodynamic device that converts that
power into thrust. The engine itself doesn't produce the thrust, but it
turns a propeller that does. Also, two engines that generate the same power
may not necessarily result in the same thrust since one may use a more
efficient propeller than the other. For these reasons, it is more logical to
rate these kinds of engines in terms of the power they create since that is
the most direct quantity they produce.
How a turboprop or turboshaft engine works
Based on what we have seen, you ought to have a better appreciation for why
it is preferable to compare jet engines in terms of thrust rather than power
and propeller-driven engines in terms of power rather than thrust. While the
opposite can be done, the process of converting between power and thrust
requires us to know or assume additional information that is usually
difficult or awkward to estimate.
- answer by Joe Yoon, 26 September 2004
---
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Bcolombo(at)twcny.rr.com
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| Posted: Sat Aug 26, 2006 6:01 pm Post subject: hp equivalent? |
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david, the normal thrust of a l-29 engine at sea leval normal temp is around
1960. I converted a 1400hp t58 turboshaft engine into a 840lb of thrust
turbo jet by removing the power turbine section, making some mods and
building a tail cone. That being said a jfs 100 is a small 100hp turboshaft
that can be converted into a 90lb of thrust turbo jet. I Dont believe there
is one formula.... Many factors come into play. I have a m701 l-29 engine
on a test stand I built and just ran it for the first time the other day,
was really cool, I was trying to figure out a way to turn it into a
turboshaft myself. I do have some books that better explain it, I will look
it up and try to find a better ans for you.
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