KiloNewton/Pound foot of thrust into Horsepower units

AI Thread Summary
The discussion focuses on converting engine thrust from Kilo Newtons and pounds-force into horsepower and watts, highlighting the challenges due to the fundamentally different nature of thrust and power. Participants clarify that there is no direct conversion between thrust and horsepower, emphasizing the need for velocity to calculate power from thrust. The conversation also addresses misconceptions about units, specifically that "pound-foot" is not a valid unit of thrust. Additionally, the distinction between jet engines and turboprop/turboshaft engines is made, noting that only the latter have output shafts that can be measured in horsepower. The thread concludes with a discussion on the relevance of horsepower in modern jet engines, particularly concerning internal components like fans and compressors.
Arjun Singh
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Hi,
I am currently studying aviation engine outputs and to make my study linear in comparative analysis with standard Automotive engines I need some expert help.
Can anyone help me drive precise equations to convert:
1. Engine thrust in Kilo Newton into Horse Power and Watts
2. Engine thrust in Pound foot into Horse power and Watts
3. Watts into Horse Power.
Seems very basic conversion yet I am struggling to derive precise equations for these statement queries.
Would be great if someone can help me out in this.
Thanks
Arjun
 
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Thrust and power are different quantities and can't be directly related. You will need to know more about the propulsion system to find the power at a given thrust. Are we talking jets or propellers?

Also, pound-foot is not a unit of thrust...
 
BvU said:
Hello arjun, :welcome:

wattts to horsepower

Did you know you can simply google these things :rolleyes: ?
An obvious observation. Google as an introductory ideation tool is providing extremely complex correlations while I require very basic yet elemental overview. Perhaps I answered your question now can you help solve mine.
 
russ_watters said:
Thrust and power are different quantities and can't be directly related. You will need to know more about the propulsion system to find the power at a given thrust. Are we talking jets or propellers?

Also, pound-foot is not a unit of thrust...

Jets. On wikipedia in design spec of jet engines, the output efficiency is described in pound foot. Is it not the correct denotion? Also aint the horse power and shaft horse power same notions to describe engine output.
 
Arjun Singh said:
Jets. On wikipedia in design spec of jet engines, the output efficiency is described in pound foot. Is it not the correct denotion?
I don't see it, can you link/quote the article you are reading please.
Also aint the horse power and shaft horse power same notions to describe engine output.
They are, but jet engines don't have an output shaft...do you mean turboprop/turboshaft engines?
 
russ_watters said:
I don't see it, can you link/quote the article you are reading please.

They are, but jet engines don't have an output shaft...do you mean turboprop/turboshaft engines?
I was just addressing your jet or propeller question, as propellers would be turboprop/turboshaft engines.
 
russ_watters said:
I don't see it, can you link/quote the article you are reading please.

They are, but jet engines don't have an output shaft...do you mean turboprop/turboshaft engines?
https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-25
See the powerplant spec in Specifications section.
 
  • #10
Maybe it would be instructive to look at an engine like the General Electric CF6/LM2500, which has both thrust and shaft producing versions. They aren't identical, but it might get you in the ballpark.
 
  • #11
russ_watters said:
Maybe it would be instructive to look at an engine like the General Electric CF6/LM2500, which has both thrust and shaft producing versions. They aren't identical, but it might get you in the ballpark.
What is LP? Also can you help me with the equations query posted earliest in this thread.
 
  • #12
Arjun Singh said:
What is LP?
I don't know, where are you seeing that?
Also can you help me with the equations query posted earliest in this thread.
As I said, there is no such equation. These are not comparable units/performance metrics.
 
  • #13
russ_watters said:
I don't know, where are you seeing that?

As I said, there is no such equation. These are not comparable units/performance metrics.
In the GE engine article you shared, turbine and compressor specifications have HP that is horse power and LP... so what is that?
 
  • #14
That's not horsepower in the wiki article for the CF6 - that's RPM. The specification table shows max LP RPM (maximum rotational speed of the low pressure [LP] shaft and components) and max HP RPM (maximum rotational speed of the high pressure [HP] shaft and components). For horsepower, you need to look at the LM2500.
 
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  • #15
cjl said:
That's not horsepower in the wiki article for the CF6 - that's RPM. The specification table shows max LP RPM (maximum rotational speed of the low pressure [LP] shaft and components) and max HP RPM (maximum rotational speed of the high pressure [HP] shaft and components). For horsepower, you need to look at the LM2500.
Ok. Thanks. Can you help me with this -
I am currently studying aviation engine outputs and to make my study linear in comparative analysis with standard Automotive engines I need some expert help.
Can anyone help me drive precise equations to convert:
1. Engine thrust in Kilo Newton into Horse Power and Watts
2. Engine thrust in Pound foot into Horse power and Watts
3. Watts into Horse Power.
Seems very basic conversion yet I am struggling to derive precise equations for these statement queries.
 
  • #16
As has already been explained to you.

1) There is no direct thrust to horsepower conversion. They're fundamentally different kinds of units.
2) Pound foot isn't a thing. When you see lbf in a specification for a jet engine, that's pounds force.
3) Watts to horsepower is easy. It's 746 (if I remember right) watts per horsepower. You can look this up on google in 10 seconds.
 
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  • #17
cjl said:
As has already been explained to you.

1) There is no direct thrust to horsepower conversion. They're fundamentally different kinds of units.
2) Pound foot isn't a thing. When you see lbf in a specification for a jet engine, that's pounds force.
3) Watts to horsepower is easy. It's 746 (if I remember right) watts per horsepower. You can look this up on google in 10 seconds.
Thanks. I had seen the watts to horsepower conversion. Just wanted to confirm.
 
  • #18
Power = thrust * velocity

So you need to know how fast the engine/aircraft is moving when it makes the specified thrust. If it not moving then technically it's not producing any useful output power, although it is producing a lot of power in the form of waste heat and moving air.
 
  • #19
cjl said:
As has already been explained to you.

1) There is no direct thrust to horsepower conversion. They're fundamentally different kinds of units.
2) Pound foot isn't a thing. When you see lbf in a specification for a jet engine, that's pounds force.
3) Watts to horsepower is easy. It's 746 (if I remember right) watts per horsepower. You can look this up on google in 10 seconds.

One more
CWatters said:
Power = thrust * velocity

So you need to know how fast the engine/aircraft is moving when it makes the specified thrust. If it not moving then technically it's not producing any useful output power, although it is producing a lot of power in the form of waste heat and moving air.

Yes. I was trying to understand various engine output comparisons between various aircrafts in an attempt to understand what factors affect the type of an engine selected for a specific aircraft. Also how an aviation jet engine output is comparable to a scale down piston engine or electric motor simply in terms of generated speed of the vehicle. So my logic was that thrust is basically force and force=weight x acceleration. And power (watts) = force x velocity. So was trying to derive a standard watt equation using thrust but couldn't. Also, some engines do have HP in their engine spec, so was trying to work out a logic for these two different specifications. One observation that I made is that turbo shaft and turbo prop engines in many articles do have HP as their output unit and almost all high output turbojet and turbofan engines have thrust as the unit. Is it because of the high output of the later mentioned engines? Also thrust beyond an output denotion didn't seem to have any relative values for standard unit conversions. My queries may seem elementary level so pardon the indulgence.
 
  • #20
Arjun Singh said:
Also, some engines do have HP in their engine spec, so was trying to work out a logic for these two different specifications. One observation that I made is that turbo shaft and turbo prop engines in many articles do have HP as their output unit and almost all high output turbojet and turbofan engines have thrust as the unit. Is it because of the high output of the later mentioned engines?
No, it's because turboshaft and turboprop engines have output shafts and jet engines just move air.
 
  • #21
russ_watters said:
No, it's because turboshaft and turboprop engines have output shafts and jet engines just move air.

OK. Thanks for your help guys. Appreciated.
 
  • #22
Note that you can get to a level of detail on modern jet engines where horspower is useful - specifically if you look at the power required to drive the compressor, front fan, etc, but that's all internal to the engine. Just as a point of comparison though, the power required to drive the front fan on a large modern jet engine can be in the ballpark of 100,000 horsepower.
 
  • #23
cjl said:
Note that you can get to a level of detail on modern jet engines where horspower is useful - specifically if you look at the power required to drive the compressor, front fan, etc, but that's all internal to the engine. Just as a point of comparison though, the power required to drive the front fan on a large modern jet engine can be in the ballpark of 100,000 horsepower.
That's a very ambitious number. I was thinking in the range of 20,000 to 25000 HP. Also is the thrust produced by the entire engine (combination of this fan and the resultant exhaust from the compressor and combustion chamber) has any mathematical relativity to the shaft HP of the fan it is powering.
 
  • #24
I'll admit that I'm just going off memory, but I think that number is about right. That having been said, it doesn't really have any relevance to the performance of the jet engine, it's just part of the internal design. As for your question, no there's not really any direct relation between thrust and fan power. You might be able to construct some relation if you also account for bypass ratio and design cruise speed or something, but it's certainly not just a direct HP to thrust relation.
 
  • #25
If it helps... The RR Trent 60 gas turbine for power generation is around 60MW.
 
  • #26
CWatters said:
If it helps... The RR Trent 60 gas turbine for power generation is around 60MW.
Cool. Will check it out. Let's see what relevant I can find to add to this discussion.
 
  • #27
CWatters said:
If it helps... The RR Trent 60 gas turbine for power generation is around 60MW.

Good - that's sort of in line with my memory, since that's around 80,000 horsepower, and the Trent 60 is a bit smaller than the GE90 engine that I remembered the number above from.
 
  • #28
So another point in the discussion. I was going through an article about a gigantic locomotive used as an ore carrier for mining. Apart from its size and design what was very unique about this machine was that it worked with a electric wheeler system where apart from the gear and clutch system that propels the vehicle there is also an auxiliary electric system drawing its power from an electric motor that is part of the engine power plant, and is coupled with the wheels to facilitate functions like braking, skid protection and the most interesting as an extra power above the gear system for the wheels through AC alternators and four AC traction motors (two in each axle).
https://en.wikipedia.org/wiki/BelAZ_75710
So is such a system applicable to aviation engines, especially high-by-pass turbofans? What I mean is, is the fuel-electric powerplant applicable to aviation or are the conventional mechanical systems most ideal and safest? If I am not mistaken, I don't think Fuel-electric systems make the engine any lighter in weight.
 
  • #29
Arjun Singh said:
So another point in the discussion. I was going through an article about a gigantic locomotive used as an ore carrier for mining. Apart from its size and design what was very unique about this machine was that it worked with a electric wheeler system where apart from the gear and clutch system that propels the vehicle there is also an auxiliary electric system drawing its power from an electric motor that is part of the engine power plant, and is coupled with the wheels to facilitate functions like braking, skid protection and the most interesting as an extra power above the gear system for the wheels through AC alternators and four AC traction motors (two in each axle).
https://en.wikipedia.org/wiki/BelAZ_75710
So is such a system applicable to aviation engines, especially high-by-pass turbofans? What I mean is, is the fuel-electric powerplant applicable to aviation or are the conventional mechanical systems most ideal and safest? If I am not mistaken, I don't think Fuel-electric systems make the engine any lighter in weight.
Your description seems a bit tough to follow, but what is described in the link is a series hybrid, where the diesel engines don't provide any propulsion, they only turn generators, which then power electric drive motors.

Such systems are common on trains as well because they generate near full torque all the way down to zero RPM. Trains - and this mining truck - need high torque at low RPM.

Ships can also be powered this way.

Aircraft engines tend to need high rpm and low torque, so I wouldn't expect this to be a beneficial performance profile for aircraft.
 
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  • #30
Electric motors in the power range to replace aircraft engines tend to be extremely heavy, so I wouldn't expect them to be usable as a replacement for gas turbine engines (which are very light for their power output) anytime soon. In addition, as Russ said, the benefit of their use in trains, heavy equipment, etc, is that you can run the engine at a high power, high-efficiency setting all the time and then use the electric motor to run at a wide variety of speeds without the need for a large transmission. However, for an aircraft, the engine runs pretty close to one setting the whole time anyways, so you don't need that variability.
 
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  • #31
Arjun Singh said:
So another point in the discussion. I was going through an article about a gigantic locomotive used as an ore carrier for mining. Apart from its size and design what was very unique about this machine was that it worked with a electric wheeler system where apart from the gear and clutch system that propels the vehicle there is also an auxiliary electric system drawing its power from an electric motor that is part of the engine power plant, and is coupled with the wheels to facilitate functions like braking, skid protection and the most interesting as an extra power above the gear system for the wheels through AC alternators and four AC traction motors (two in each axle).
https://en.wikipedia.org/wiki/BelAZ_75710
So is such a system applicable to aviation engines, especially high-by-pass turbofans? What I mean is, is the fuel-electric powerplant applicable to aviation or are the conventional mechanical systems most ideal and safest? If I am not mistaken, I don't think Fuel-electric systems make the engine any lighter in weight.

It's worth noting that for that vehicle, the electric system isn't auxiliary. Rather, there is no gear and clutch system at all. The 2 diesel engines simply power generators, and all vehicle motion comes from the electric motors attached to the axles. This saves a large amount of space, weight, and complexity since clutch and transmission mechanisms for that much power would be extremely large.
 
  • #32
cjl said:
It's worth noting that for that vehicle, the electric system isn't auxiliary. Rather, there is no gear and clutch system at all. The 2 diesel engines simply power generators, and all vehicle motion comes from the electric motors attached to the axles. This saves a large amount of space, weight, and complexity since clutch and transmission mechanisms for that much power would be extremely large.
Perhaps I was a bit creative with my understanding of the spec. Does a hybrid power plant also improve the maintenance requirement of the assembly? I think it does.
 
  • #33
  • #34
You said
force=weight x acceleration

No.
force = MASS * acceleration
 
  • #35
  • #36
wolf1728 said:
You said
force=weight x acceleration

No.
force = MASS * acceleration
So what would be mass of a body represented in let's say 10 kgs?
 
  • #37
Arjun Singh said:
So what would be mass of a body represented in let's say 10 kgs?
10kg
 
  • #38
A.T. said:
10kg
I was going to give this answer a like, but then I decided it was the easiest question ever asked in the history of PhysicsForums.
 
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  • #39
russ_watters said:
I was going to give this answer a like, but then I decided it was the easiest question ever asked in the history of PhysicsForums.
In tribute to this thread may I say that 10 kg is not its mass, that's its weight or an acquired downward force balanced by its center of gravity calculated by a pressure sensitive mechanical device, a resultant effect of Earth's gravitational field, atmospheric pressure and may we also add the effect of unseen matter or cosmic energy that may have variable effects on the interactive potential of a body of mass on different planets based on their precise location in the solar system. But to calculate an applied force on a body of weight 10 kg, weight would play the 'mass' unit. If I may say mass is actually the total volume of matter contained within a defined shape or body not including its planetary signatures. Am I right to some extent?
 
  • #40
Arjun Singh said:
In tribute to this thread may I say that 10 kg is not its mass, that's its weight or an acquired downward force balanced by its center of gravity calculated by a pressure sensitive mechanical device, a resultant effect of Earth's gravitational field, atmospheric pressure and may we also add the effect of unseen matter or cosmic energy that may have variable effects on the interactive potential of a body of mass on different planets based on their precise location in the solar system. But to calculate an applied force on a body of weight 10 kg, weight would play the 'mass' unit. If I may say mass is actually the total volume of matter contained within a defined shape or body not including its planetary signatures. Am I right to some extent?
No. The kilogram is a unit of mass, not weight.
https://en.wikipedia.org/wiki/Kilogram
 
  • #41
  • #43
Arjun Singh said:
I was trying to understand various engine output comparisons between various aircrafts in an attempt to understand what factors affect the type of an engine selected for a specific aircraft.
I assume you're talking about the power or thrust maximum ratings. Since the engine supplier doesn't know which propeller is going to be used, or other relevant variables, it's simpler in the case of propeller-driven aircraft to specify maximum rated power. The designer multiplies power by estimated propulsive efficiency to arrive at thrust available.

In addition to the max ratings there is also thrust and power output under operating conditions, which varies with throttle setting, airspeed, and other factors. Aircraft engine horsepower is not directly comparable with automobile engines. Cars use a different measurement protocol.
russ_watters said:
Aircraft engines tend to need high rpm and low torque,
True with jet engines. Piston engines and direct drive electric motors are often designed to provide lots of torque at low speed. A slow-turning propeller can produce thrust more efficiently.
Arjun Singh said:
So what would be mass of a body represented in let's say 10 kgs?
Confusingly, engineers often say mass when they mean weight. If a body is said to "weigh" 10 kg, it is understood colloquially to mean the amount of gravitational force the body would experience near the Earth's surface.
 
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  • #44
I recently came across an article about a car prototype with standard on road 4-wheel car design boasting of an engine to the scale of 50000 HP which sounded unreal. I am not able to find that article now, so perhaps it was a hoax. Still would such a machine have any practicality as the enough torque required to achieve maximum rpm possible for rubber tyre, on-road mobility at top possible speed can be achieved in let's say within 10,000 HP. So if I have to design a fast production worthy supercar, then I perhaps wouldn't use an engine powerplant beyond 8-10 thousand HP. Any comments?
 
  • #45
Short answer no. Not in a road legal car.

Just for info.. Googke says Top fuel drag racers are running 11,000HP or just over 8MW. They burn 11 gallons a second so even the fuel pump is wicked.
 
  • #46
CWatters said:
Short answer no. Not in a road legal car.

Just for info.. Googke says Top fuel drag racers are running 11,000HP or just over 8MW. They burn 11 gallons a second so even the fuel pump is wicked.
So what is the road legal HP?
 
  • #47
  • #48
Most of the top supercars are in the range 750-1400bhp or in new money around 500kw to 1MW. What I meant above is that there isn't really much if any opportunity to reach those power levels on public roads, only on track days.
 
  • #49
There's no real legal limit, other than that it becomes increasingly difficult to meet any kind of emissions standards and reliability. That having been said, I bet you're thinking of the (claimed) 5000 horsepower Devel Sixteen. I'll be surprised if it ever actually happens though...
 
  • #50
A.T. said:
Among road legal sports cars this one has a lot HP:

https://de.wikipedia.org/wiki/Bugatti_Chiron

I don't know about other types of vehicles though.
cjl said:
There's no real legal limit, other than that it becomes increasingly difficult to meet any kind of emissions standards and reliability. That having been said, I bet you're thinking of the (claimed) 5000 horsepower Devel Sixteen. I'll be surprised if it ever actually happens though...
That's a cool car. Saying the obvious, a lot to depend on development of road networking suitable for high speed cars, for them to become production staples. Let's see how the progress happens. Currently the present public commute systems likes buse networks, need a serious upgrade in India for super cars to really get proper torquing opportunity :) Will do some research on cool public commute engines and share for comments.
 

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