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Thread: Calculating power required

  1. #1

    Calculating power required

    Hello all,

    I am a beginner in FSAE. Just started an FSAE team in college. I have doubts regarding calculating power required (kw). Its a basic conceptual doubt. Please help me understand it

    If a vehicle is travelling at a constant velocity the power delivered is given as F.v, where F is the force required to overcome all the resisting forces of the car. correct?

    Now if a vehicle is accelerating, some posts say, power delivered is (Ma)*Vavg, that is mass of the car * avg acceleration * avg Velocity. correct?
    the same answer comes if calculated as change in kinetic energy per unit time
    like in this example
    https://www.youtube.com/watch?v=r6RTJd_i6xY


    Now in accelerating case ma = F(net) - F(all resistive force)

    so power delivered by the engine should be F(net) * Vavg . Why is this wrong? Since Fnet is required to over come the resistive forces as well as create an extra force to accelerate the vehicle by a.

    Please do clarify in as much detail as possible
    Thanks in Advance
    Last edited by idontcare; 09-20-2018 at 05:14 PM.

  2. #2
    The equations are basically correct I guess, but we need to know what your actual problem is. Also, (assuming I can guess what your problem is) there is a few different ways to tackle it.

    Regardless of how much power you think you need, the competition regulates this in 3 ways for combustion, and at least 1 way for electric.

    The 3 power restrictors with combustion are 1. maximum swept volume ~710cc (not really a restriction as forced induction is allowed). 2. Intake diameter of ~20mm (This is the main restrictor, limits air flow rate) 3. Noise limit, (which indirectly will also limit power as your exhaust outlet may have to be about 25mm.) Going by other teams, you may end up with 89hp at the engine or 75hp at the tyes, something in that range.

    With electric, you can draw 80kw at the battery, and you may have a 10% loss before it gets to the tyres (very wild guess). Not all the electric teams are using their full 80kw as they hit other issues.

    So how much power is required? All of the power you're allowed to have.
    University of Tasmania (UTAS)

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