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| Mythbusters - Golf ball dimpled car MPG | |
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| Tweet Topic Started: Nov 3 2009, 08:55 AM (6,621 Views) | |
| billy508 | Nov 18 2009, 08:43 PM Post #16 |
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billy508
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Let make a Tesla turbine!!! http://www.instructables.com/id/Build-a-15,000-rpm-Tesla-Turbine-using-hard-drive-/
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| nerys | Nov 19 2009, 12:43 AM Post #17 |
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Grr
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Seemed accurate enough to me to warrant some experimentation. When I get around to making a kamback or partial boat tail I plan to make 2 one dimpled and see if I can read a difference. The logic and math are sound the question is will it equate into measurable gains. there test method was solid. even if they went 3 or 4 mph variations during each test that would not come close to account for a nearly 5mpg improvement. Thats just too big a jump to be "minor" driving variation (note while they only show it once on the show for sensible reasons they actually DO those things sometimes many many times to average out the results etc..) |
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| rmcelwee | Nov 19 2009, 06:57 AM Post #18 |
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I would think the dimples help correct a problem if you don't have a kamback. If you have one there would be no reason for the dimples. IMO, if you have crappy aero, dimples would help. If you have good aero then they will hurt. The car they were testing had bad aero. I would think that a smooth boat tail would have given much better results than a trunk lid with dimples. I'm still trying to figure out how to dimple my trunk. Wonder if just slapping some speed bumps on it would give any results? |
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| nerys | Nov 19 2009, 09:30 AM Post #19 |
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Grr
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I think I already typed this on the forum maybe another but here goes. there are more than one "FORM" of aerodynamic drag at play on your car. Dimples will ALWAYS worsen drag on a car. They are NEVER better for aero drag ie Parasitic or SURFACE drag. Now you have ANOTHER form of drag. this is called "base drag" its the "suck" behind your car. in 99% of cars out their (including the prius and most EV's) this "base drag" has a far larger impact on fuel economy than Parasitic drag. so while your increasing parasitic drag with the dimples your REDUCING base drag and the reduction in base drag FAR out shadows in impact the increase in parasitic drag IE net increase in fuel economy. a kamback REDUCES base drag it does not eliminate it. a kamback is an intentional COMPROMISE. a full boat tail designed properly WOULD NOT need any dimples as you are already reducing base drag as much as possible. a kamback does not. dimples would make a kamback CLOSER to the impact of a boat tail (but not quite) ie you should see a benifit. ahh but BUMPS would increase your frontal area and your base drag "negating" the turbulent benefits of the dimples with an equal increase to counter any gains. thats why they are dimpled and not "bumped" thats why I suggest they did not get as big an FE gain as they COULD have. the front half of the roof the entire hood both front quarters and both front doors and back doors should not have been dimpled as these portions have ZERO base drag issues. ie they are adding parasitic drag without any gains. they only needed the dimples on the last half of the roof the trunk and the rear quarter panels. that would have been idea. they would have gotten a slight frontal area penalty (since they added a SKIN to the car is it was thicker their) which might be why they did the whole car though more likely just because it "looked cool" Edited by nerys, Nov 19 2009, 09:32 AM.
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