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Flywheel design. Inertia dyno for 745 KW engine.

  1. Dec 5, 2012 #1
    Hello again,

    I am currently designing a flywheel for a 745 KW engine inertia dyno.

    Basically my design requirements are so:

    Max RPM: 530 RPM (=55.5 rad/s)
    Flywheel Diameter: 1.7 meters
    Time needed to accelerate: 60 second (to max rpm)

    I need help determining the mass of the flywheel.

    My calculations and way:

    Power=745 KW

    ΔE=P*t=745*60=44700 KJ

    Inertia for a solid disc (flywheel) = 0.5*m*r^2

    Energy in flywheel = 0.5* (0.5*m*r^2)*ω^2

    Isolate the mass:

    m= (4*Energy) / (r^2* ω^2)= (4*44700) / (0.85^2*55.5^2) = 80 tons.

    80 tons seems way off, I've gone over my calcs a few times and haven't found my problem.

    I appreciate any assistance!
  2. jcsd
  3. Dec 5, 2012 #2


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    2017 Award

    Staff: Mentor

    45MJ is a lot, and 530 RPM is slow.

    Cross-check: 1/4*m*v^2 = E where v is the velocity at 1.7m/2 radius:

    Your result looks correct.

    Do you want 745kW over one minute, or maybe a lower charging power and 745kW over less than a minute to discharge?
  4. Dec 5, 2012 #3

    Thank you for your reply, i guess that these are the facts and i'll have to face them and consider "bending" some requirements.
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