Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Solar Drag Race Model

  1. Oct 16, 2006 #1
    I am working on a model of a solar powered drag race.

    The race: 250 meters, no incline, initial velocity = 0.

    Classical physics gives us the following equations (ignores aero and rolling drag and wheel rotation):

    Velocity as a function of time V = (2Pt/M)^.5
    P = power, M = mass

    Distance as a function of time d = (2/3)((2P/M)^.5)t^(1.5)

    Time to travel x distance t = ((1.5d)^(2/3))(M/2P)^1/3

    But of course we do lose power to aerodynamic drag forces

    Pa = .5rCdAV^3 (r = air density, Cd = aero drag coef., A = frontal area)

    and rolling drag at the wheels

    Pr = CrMV (Cr = rolling drag coef.)

    and wheel rotation

    Pw = FwV^3 (Fw = wheel rotational factor)

    So if our inertial power equals our power in, Pi (from the solar panel) minus our power lost to friction (aero, rolling, wheel rotation), then our velocity equation becomes:

    V = (2((Pi-(.5rCdAV^3)-(CrMV)-(FwV^3))t)/M)^.5

    I need help solving this equation. I have approximated the solution by chopping the race up into small pieces and solving iteratively, but I would rather do it right.
    Last edited: Oct 16, 2006
  2. jcsd
  3. Oct 17, 2006 #2
    There is nothing wrong with solving your problem nummerically!!
  4. Oct 17, 2006 #3
    The primary reason why I was looking for a more elegant solution is that the iterative solution I have created falls apart after only a couple hundred iterations. I have spent several hours looking for the cause of the crash without success.
  5. Oct 17, 2006 #4
    I am surprised that I cannot find the equations I am looking for online. Does anyone have a suggestion as to where to find a comprehensive ground vehicle acceleration model?
  6. Nov 24, 2007 #5
    Soalr Dragster Spreadsheet Calculations

    I put together a spreadsheet that includes the effects of acceleration, air drag and rolling resistance. It can be found at:

    There is no guarantee that it is 100% correct. Let me know if you find any mistakes in it because we are building our solar dragster based on these calculations.
    When I first ran this, I was surprised to find that air drag was the predominant factor, even though the solar powered dragsters were only reaching a top speed of 30 mph or so. I wonder how many top fuel dragster realize this? They may be able to set new world records if they improve the aerodynamics of their dragsters. The air drag at 200 mph may be considerable, even if you've got 2000 HP to work with.
    Jim White
    Last edited by a moderator: Apr 23, 2017
  7. Nov 24, 2007 #6
    air drag has been greatly reduced over the years
    the first ''rail'' cars had all most no bodys or fairing
    but also added to
    by the large wings used to gain traction

    current fuel cars have 6000 hp and go about 330mph
    and both are limited by current rules on engine size and gearing

    many factors are traded off to get to the current balance
    weight traction and drag from wings are some of the major factors
    too little wing will limit traction and lose races
  8. Nov 27, 2007 #7
    Air Drag Exceeds Acceleration Thrust Above 140 mph

    Even with 6000 HP, air drag is an important factor if a dragster wants to reduce their time or increase their top speed in the 1/4 mile.
  9. Nov 27, 2007 #8


    User Avatar
    Science Advisor
    Gold Member

    Believe me, top fuel drag teams are quite aware of aerodynamic drag; but, they are also aware of many other competing problems, including the fact that it takes a LOT of traction (and therefore a lot of downforce) to put 6000hp to the ground.

    Your discovery of air drag problems in drag racing is not particurally ground breaking IMO.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook