VIDEO: Mythbusters test golf ball-like dimpling effect on fuel economy (*Spoiler Alert!*)
Mythbusters test golf ball-like dimpling on MPG – Click above to watch video after the jump
The Mythbusters must be closet car fans, because the hour-long show on the Discovery Channel seems to be producing more and more experiments involving automobiles than ever before. Their latest again involves fuel efficiency, this time testing if a dirty car is more fuel efficient than a clean one because of the golf ball-like dimpling effect of the dirt. Turns out dirt doesn't make a difference, but Adam and Jamie went one step further to test if covering a car in actual golf ball-like dimples would improve its fuel efficiency. According to cable's most crack scientists, yes, it will.
The show's team completely covered a last-gen Ford Taurus with modelers clay and figured out that it would achieve about 26 mpg at a constant 65 mph. They then went about adding over 1,000 dimples to the car's exterior. To keep the experiment consistent, all 1,082 dimples removed from the clay exterior were put in a box and set in the back seat so that the car would weigh exactly the same as before dimpling. The theory is that, like a golf ball, the dimples would reduce the car's drag through the air, thus allowing it to travel the same distance at the same speed using less fuel. The result? Over 29 mpg.
Follow the jump to watch the whole episode for yourself, though if you're only interested in watching the dimpled car do it's thing, skip ahead to about 40 minutes in.
[Source: Megavideo]
Reader Comments (Page 1 of 5)
pedantic 3:39PM (10/22/2009)
A dirty car will lower your fuel economy. Dirt doesn't make the car suddenly have golf ball dimples. A dimpled car will increase your fuel economy.
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Steven 4:07PM (10/22/2009)
Breaking news: Tyson Gay informed of dimple effect, caught laying on egg cartons before race.
Green Destiny 4:34PM (10/22/2009)
@stephen-
That's pretty funny.
They should have done a top speed test. Relative aerodynamic properties are straightforward to compare that way.
And top speed is definitely sexier television.
James 5:59PM (10/22/2009)
Looks like mobile acne scars (ugh!)....
Aaron 11:04PM (10/23/2009)
Mythbusters needs to take that Taurus (or another car) into a wind tunnel for an accurate measurement of the difference in wind resistance.
Paul P. 3:39PM (10/22/2009)
Hmmm....maybe hail damage isn't a bad thing after all?
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tC 3:43PM (10/22/2009)
+3 mpg? No where near worth it. The only way I would ever do this to a car, is if it yielded gains of 25+ mpg.
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thomas 4:58PM (10/22/2009)
thats over a 10% increase..... with no other modifications.
obviously no one wants to cover their car with clay...
but what if a few panels, or maybe the undercarriage were covered in large, 3" diameter dimples. obviously something a little more designed and a little less improvised than the mytbuster's taurus.
TraderBots 8:05PM (10/23/2009)
Your car would look oh so cool!
http://www.traderbots.com
Benfolio 3:46PM (10/22/2009)
Saw this last night and tried to debunk it in my head as the show went on, but the only variable was the human element: throwing the switch that cut off the car's fuel supply and turned on the auxiliary tank (that was measured to show the amount of fuel used over a measured mile at 65MPH).
I know the dimpled vehicle wrap was busted before for improving mileage, so it appears that its all in the SIZE of the dimples.
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ack154 3:52PM (10/22/2009)
Well if you consider the size of a golf ball and the relative size of its dimples... of course that wrap crap wasn't going to work. This makes a lot more sense technically but soooo impractical and awkward.
matt234 9:19AM (10/23/2009)
Maybe it's related to the speed, not the size of the object covered with dimples. Golf balls travel at about 150 mph. Perhaps at lower speed you need larger dimples.
Venom 3:47PM (10/22/2009)
Like they said on the show, I could see them using this in Nascar and maybe other racing circuits also.
11% fuel reduction is quite significant.
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Steven 4:03PM (10/22/2009)
Interesting. Given that the speeds are so much higher in racing, I wonder what the dimple sizes would be.
Doug 4:16PM (10/22/2009)
It will never be implemented unless cost and complexity of manufacturing can be overcome.... It's doesn't look too hot either.
Farris 5:00PM (10/22/2009)
I can see some type of thin, lightweight polycarbonate dimpled "cladding" being added to 18 wheelers. I think that would be a really cool experiment.
Plus, if it was CLEAR polycarbonate, they could keep the advertisements on the side of the trucks.
Nateb123 5:00PM (10/22/2009)
Speed isn't the issue directly, the size of the boundary layer (where relative velocity
Nateb123 9:51PM (10/22/2009)
So apparently using an equals sign chops off the rest of my post. Anyways, the boundary layer is where the speed of the air is less than the relative speed of the car. Basically, the car's surface is exerting frictional force on air in contact with its surface and dragging air molecules along (thus the name drag). The thicker the boundary layer, the bigger the drag but part of that is inevitably due to size of the vehicle and speed among many other variables. The reason there's a boundary layer instead of a boundary "sheet" of molecules is because air molecules not in contact with the metal surface experience drag (though a bit less) due to being dragged by other air molecules. Outside of the layer, the relative air speed is the speed of the car.
Now dimples act as vortex generators by using turbulence to suck air from outside the boundary layer (with greater relative speed) into the boundary layer. The faster the boundary layer is moving, the less drag. Now because a golf ball is so much smaller than a car, the air it displaces is way less as it moves through the air. This means a smaller boundary layer. For a car, you need dimples big enough to cause turbulence OUTSIDE the boundary layer. That's why dimple wraps don't work. They don't energize the boundary layer with new air. In fact, creating a more turbulent boundary layer with no fresh air to offset those losses will mean MORE drag so wraps REALLY don't work.
For anyone having trouble with the term vortex generator, look at an EVO 9 MR (or 8 I think). Over the back window of the car is one, it's just looks like a sort of diffuser thing with slats. The important thing is their height. They poke just out of the boundary layer. Also some BMWs have these too, just in front of the sunroof so that when the sunroof is open, air prefers to move quickly back onto the roof panel and not into the cabin. Less drag, better fuel economy and less wind in the cabin.
Lemon 2:26AM (10/23/2009)
Nate,
Nice explanation! I thought of the Evo MR right away when I read this.
To all the people talking about how hard it would be to manufacture...how hard is it to stamp sheet metal? Or change the mold for plastic injection molding?
groundZ 3:48PM (10/22/2009)
While I accept the fact that they improved mpg by 3 from a car that already had god knows how many pounds of clay slathered on, I doubt it improve the mpg from a car that didn't have clay slathered on to begin with, clay's really heavy.
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