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I KiloNewton/Pound foot of thrust into Horsepower units

  1. Aug 23, 2018 #1
    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
     
  2. jcsd
  3. Aug 23, 2018 #2

    BvU

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  4. Aug 23, 2018 #3

    russ_watters

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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...
     
  5. Aug 23, 2018 #4
    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.
     
  6. Aug 23, 2018 #5
    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.
     
  7. Aug 23, 2018 #6

    russ_watters

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    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?
     
  8. Aug 23, 2018 #7
    I was just addressing your jet or propeller question, as propellers would be turboprop/turboshaft engines.
     
  9. Aug 23, 2018 #8
    https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-25
    See the powerplant spec in Specifications section.
     
  10. Aug 23, 2018 #9

    russ_watters

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  11. Aug 23, 2018 #10

    russ_watters

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    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.
     
  12. Aug 23, 2018 #11
    What is LP? Also can you help me with the equations query posted earliest in this thread.
     
  13. Aug 23, 2018 #12

    russ_watters

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    I don't know, where are you seeing that?
    As I said, there is no such equation. These are not comparable units/performance metrics.
     
  14. Aug 23, 2018 #13
    In the GE engine article you shared, turbine and compressor specifications have HP that is horse power and LP... so what is that?
     
  15. Aug 23, 2018 #14

    cjl

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    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.
     
  16. Aug 23, 2018 #15
    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.
     
  17. Aug 23, 2018 #16

    cjl

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    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.
     
  18. Aug 23, 2018 #17
    Thanks. I had seen the watts to horsepower conversion. Just wanted to confirm.
     
  19. Aug 23, 2018 #18

    CWatters

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    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.
     
  20. Aug 23, 2018 #19
    One more
    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.
     
  21. Aug 23, 2018 #20

    russ_watters

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    No, it's because turboshaft and turboprop engines have output shafts and jet engines just move air.
     
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