takumi
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| posted on 30/3/07 at 02:51 PM |
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max speed (drag) vs. power .xls
Might be of interest, gives you a graph of power required to maintain speed X against aero drag, based on Cd and Frontal Area..
Doesn't take into account rolling drag..still good fun tho (and free..lol), and reasonably accurate ~15% maybe..
http://community.rhocar.org/downloads/power%20drag.xls
tak
[Edited on 30/3/07 by takumi]
[Edited on 30/3/07 by takumi]
RobinHood 2B 2.0i pinto, Keihin 38mm Carbs, lightened flywheel, O'Mori remote filter kit, 10 row oil cooler. Modified head, 10.2cr, special
valves FR22 cam, 4- 1 header.
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Johnmor
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| posted on 30/3/07 at 08:17 PM |
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Does that mean we need around 125 HP to achieve 100mph!!!!
seems a bit high, given the weight of the vehicles.
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takumi
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| posted on 30/3/07 at 09:22 PM |
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if you read, it says it does not take into account for rolling drag..
Works very well for all the vehicles I've tried so far..at most 10% out..
Don't get that 100mph in reality will be showing 105-110 on a mech speedo..
[Edited on 30/3/07 by takumi]
RobinHood 2B 2.0i pinto, Keihin 38mm Carbs, lightened flywheel, O'Mori remote filter kit, 10 row oil cooler. Modified head, 10.2cr, special
valves FR22 cam, 4- 1 header.
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MikeRJ
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| posted on 30/3/07 at 10:20 PM |
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quote:
Originally posted by Johnmor
seems a bit high, given the weight of the vehicles.
Weight blunts acceleration, but doesn't have anything like as much impact on top speed. Aerodynamics (or lack of) play a far more important
role in a Locosts top speed.
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Rob Palin
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| posted on 31/3/07 at 10:31 AM |
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The formula for power required is incorrect. The 'p' he refers to is density, not pressure, and shouldn't be included in the cubic
term.
It should be:
P= Fv, so P= drag x speed
Drag @ speed v = 0.5 x density x speed ^2 x CD x A
So Power required purely to overcome drag:
P = 0.5 x density x speed^3 x CD x A
Adding in rolling resistance@
Ptotal = ((0.5xdensityxspeed^2xCDxA)+(rolling resistance factor x mass of car x acceleration due to gravity)) x speed
air density is roughly 1.2kg/m^3
rolling resistance factor ~0.01-0.03, despite what the Bosch Blue Book says. 0.03 seems to give decent correlation with actual Vmaxs.
acceleration due to gravity ~9.8m/sec^2
Units are all S.I. so the power is in Watts. Divide by the 1000 for kW, then multiply by 1.341 for hp. This is power required at the wheels, though,
remember.
To go from mph to m/sec for speed, multiply by 0.44704
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scotty g
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| posted on 2/4/07 at 04:59 PM |
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SMART ARSE 
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Rob Palin
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| posted on 2/4/07 at 09:35 PM |
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:p
Doing this is actually my day job. Plus, no more than 24 hours previous, i'd done a near-identical spreadsheet for someone else on here so all
i did was copy it out. Bizarrely it seems drag spreadsheets are like buses...you wait for ages then several come along at once!
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procomp
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| posted on 3/4/07 at 07:56 AM |
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Hi quote (Doing this is actually my day job.) What typing away on locost builders .
And a big thankyou for the spreadsheet.
cheers matt
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