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Small Dynomometer Help

  1. Oct 23, 2011 #1
    Hi everybody, just wondering if you could help me with calculating horsepower & Torque.

    If I have a known "constant load" in ft/lbs & the engine accelerates it from a starting rpm to a peak rpm figure in X time, how can I calculate the Horsepower & Torque.

    Not really sure where to start?

    Can I assume that my "Constant Load" is the same as the moment of inertia of a flywheel & use the appropriate calculations for mine?

    Last edited by a moderator: Oct 23, 2011
  2. jcsd
  3. Oct 23, 2011 #2


    User Avatar

    Staff: Mentor

    Torque is measured in foot * pounds, not foot/pounds. Power is work/time, which is force*distance/time.

    This article may be helpful (the equations are part-way down the article), but if you don't have much background in physics, please ask more questions here so we can help.


  4. Oct 24, 2011 #3
    Thanks very much for the reply, your correct I am not experienced in physics but I will see how I go with the link you have provided as I need to learn more about this for my small dyno.

    Thanks again
  5. Oct 28, 2011 #4
    Not sure if I have this correct.

    Ok, I have a "constant load" of say 5 ft-lb & want to acellerate this from a starting rpm to the final rpm figure, find the Torque of the driving engine.

    T = WK^2 * ΔN / 308 * t

    T= Acelleration torque ft-lb

    WK^2 = Total system inertia includes my (constant load value + the moment of Inertia of the Load Cell shaft, Couplings etc.

    ΔN = The change in speed (rpm)

    t = Time to acellerate total system load (sec)

    As mentioned i'm not sure if this is the correct method & I am not sure yet how to get the Hp figure from this?

    Any help would be greatly appreciated.

  6. Oct 30, 2011 #5
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