Alan B
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| posted on 20/5/11 at 04:52 PM |
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Cool project
But is it just me finds it incredibly pie in the sky?
Eg. 208 mph and 20mpg........with a muliti-ton offroader?.......
I don't think so...
linky
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JoelP
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| posted on 20/5/11 at 04:58 PM |
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dreaming!
funnily enough though, i saw on discovery the other day that those enormous 200 tonne mining trucks do 4mpg, which i dont really believe.
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beagley
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| posted on 20/5/11 at 06:13 PM |
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quote:
Originally posted by Alan B
But is it just me finds it incredibly pie in the sky?
Eg. 208 mph and 20mpg........with a muliti-ton offroader?.......
I don't think so...
linky
This "could" be possible but definitely not at the same time. Look at the Corvette as an example. It can acheive high speeds, but when
babied can return close to 20 mpg. Applying a little physics and a lot of extrapolation:
The drag encountered is exponential to the speed of the vehicle so to go from 200 to 250 requires a HUGE increase in power. To better explain, a
Lamborgini Murcielago tops out around 200 and has 572 hp. The Bugatti Veyron hits 250 but to do that requires an extra 429 hp. Make sense..... nah,
doesn't to me either. 
Drag is a bitch, but I definitely want them to do it just because.
Beags
I'm not scared!!! I'm just marking my territory.
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Kwik
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| posted on 20/5/11 at 06:16 PM |
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drag is exponential, and exponentials are a pain to deal with. that car is dreaming if they want to go 200mph with those tyres... they will just melt
with all the heat...
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sprouts-car
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| posted on 20/5/11 at 06:20 PM |
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Drag is exponential?
Build blog
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Kwik
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| posted on 20/5/11 at 06:37 PM |
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quote:
Originally posted by sprouts-car
Drag is exponential?
i thought it was....
edit: or do you not know what it means?
if so, if you wrote drag in a algebraic formula it would have a square variable in it.
if your still not with me, if you go 2mph, you need 4 of something. if you go 3mph, you need 9 of something. if you go 4mph, you need 16 of
something.
the gap between the "something" increases more and more with every mph you increase.
[Edited on 20/5/11 by Kwik]
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beagley
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| posted on 20/5/11 at 07:06 PM |
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quote:
Originally posted by sprouts-car
Drag is exponential?
It tis [edit] NOT [/edit] exponential .... [edit 2] It is a function of velocity squared [/edit 2]
A quick search turned out the following formula:
Force of Drag = .5 * (Mass Density of Fluid) * (Velocity ^2) * (Coefficient of Drag) * (Reference Area)
Mass Density = Mass per unit volume
Velocity = duh
Coefficient of Drag = .7 for a Caterham which is 2nd on the list so basically we drive bricks
Reference Area = Frontal Area of Object Moving through fluid (yes, air is technically modeled as a fluid)
Now to do some test calculations using the Veyron and Murcielago from the earlier post. We will assume these values some are correct, others were
just made up for the sake of math
Density of Air at 20 C = 1.2041
Velocity = 200 for Lambo and 250 for Bugatti
Coefficient of Drag = .7 since we are using the same value for both iterations we can use whatever we want
Reference Area = .92 m^2 which will be the same for both iterations as well.
Lambo Drag Force = .5 * (1.2041) * (200 * 200) * (.7) * (.92)
Bugatti Drag Force = .5 * (1.2041) * (250 * 250) * (.7) * (.92)
Lambo = 15,508.808 whatever units
Bugatti = 24,232.5125 whatever units
I hate drag
Beags
[Edited on 5/20/2011 by beagley]
[Edited on 5/20/2011 by beagley]
[Edited on 5/20/2011 by beagley]
I'm not scared!!! I'm just marking my territory.
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Miks15
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| posted on 20/5/11 at 07:18 PM |
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it isnt exponential, it is a function of the velocity squared.
Exponential would be e^velocity.
2 different things arent they
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beagley
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| posted on 20/5/11 at 07:28 PM |
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quote:
Originally posted by Miks15
it isnt exponential, it is a function of the velocity squared.
Exponential would be e^velocity.
2 different things arent they
You are correct, I will edit my equasion post. Its been a while since I've had to do algebra.
I'm not scared!!! I'm just marking my territory.
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MikeRJ
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| posted on 20/5/11 at 07:32 PM |
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For a given drag coefficient and frontal area, power requirements rise with the cube of the speed i.e. to double the maximum speed you need around 8
times the power.
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MikeRJ
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| posted on 20/5/11 at 07:33 PM |
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quote:
Originally posted by JoelP
dreaming!
funnily enough though, i saw on discovery the other day that those enormous 200 tonne mining trucks do 4mpg, which i dont really believe.
I find that hard to believe as well, gpm maybe...
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beagley
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| posted on 20/5/11 at 07:43 PM |
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I hope nobody counts on our math skills..... wow.
I'm thinking I need to head back to uni for some refresher classes.
Beags
I'm not scared!!! I'm just marking my territory.
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iank
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| posted on 20/5/11 at 09:14 PM |
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quote:
Originally posted by MikeRJ
For a given drag coefficient and frontal area, power requirements rise with the cube of the speed i.e. to double the maximum speed you need around 8
times the power.
I agree it's cubed not squared if I remember the post from someone who did aerodynamics for a living.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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dilley
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| posted on 20/5/11 at 09:31 PM |
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.................some very clever people here! If I want to go fast I build a bigger, better engine!
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