Anyone have 800 Lbs of clay handy? New mythbusters episode

VIDEO: Mythbusters test golf ball-like dimpling effect on fuel economy (*Spoiler Alert!*) — Autoblog Green

They actually got a 15% increase in fuel economy by "dimpling" the car.

Maybe 1600lbs. I will take some too. I saw that episode too. It was awesome.

Yes, I saw this episode also, and I thought that it was one of their better ones.

I couldn't see anything wrong with their methology for this test. They must have had some real scientists/engineers/statisticians help them design their testing protocols this time.

Sounds plausible, but why does it work? I remember posing this question to my high school physics teacher, and he said it works for golf balls, but not cars. The dimples, he said, actually increase drag, but because of the spin of the ball, more lift is generated, and it flies farther. On things that are only somewhat streamlined, the dimples would help by bringing the airflow closer to the surface. On really smooth surfaces where the boundary layer flow is already laminar, dimples would only cause turbulence. When I asked about pressurising the inside of the body, and letting air out through tiny holes in the base of the dimples, to make little 'ball bearings of air', he said I was making his head hurt.

Maybe I should watch the show, eh?

Does this mean I should get out a ball pein hammer and go to town on my car? :madgrin:

Shouldn't you wait to find out the optimum dimple size? Or would you rather make a bunch of different sized dents to see what works best?

Can you Clay-bar a clay car?

With the latest in computer technology (hardware & software) being used by automotive and aerospace engineers, I would think that this "golf ball dimpled car" experiment could have been perfectly simulated on a computer, with fantastically accurate results. I wouldn't be surprised if many automotive companies have already done this experiment and either yielded unconvincing results, or are keeping their discoveries secret.

Or perhaps the car companies already discovered the slight improvement in MPG, but the increased manufacturing cost of a dimpled body was prohibitive. Or perhaps they did a marketing analysis and discovered that most buyers (except golfers) were turned off by the dimpled appearance.

Start with small dents, then make them bigger to see if it improves mileage. :madgrin:

Complete absurdity...and unfortunate that many of the uniformed take Mythbusters results as fact or anything "scientific" just because they do "tests" of urban myths. This leads to snake oil salesman selling "dimple kits" to add to your car and other illegitimate products along the same line...unfortunately they make their money...and the uniformed lose theirs with nothing to show for it other than an empty wallet.

Why are golf balls and cars different? Because a golf ball is in a constant state of rotation...cars are not. Cars are basically rolling blocks of drag compared to a rotating golf ball that gains its aero advantage due to "turbulant" air flow. Turbulant air flow works for golf balls...not cars. It makes no sense to dimple a car because they already have laminar air flow...in fact car manufacturers spend millions and millions of dollars to reduce turbulent air flow and air separation to make their cars with the lowest coefficient of drag as possible.

If dimples decreased drag on a car do you think you would not have already seen a dimpled car on the salt flats breaking world speed records?

Their methodology is hardly a scientific experiment...far from it.

Buy this and come back in a year with your results...it's not going to help you get better FE...sorry.

MPG-Plus™, Drag Reducing Technology, Improve MPG, Vehicle Wraps, FastSkinz™

Better off taking your money and putting it on the #3 horse in the 4th race. Next they will be telling us that "shark skin" car coverings decrease drag because sharks are "really fast" in the water!

Just imagine how fast sharks would be if they only had dimples!

Golf balls are round. By their very nature, round objects generate a lot of drag. There is no way to get anything close to laminar flow over a round surface. The dimples induce turbulence, which helps reduce flow separation drag. You see something similar with the kammback rear end of the Prius. The flow is going to separate there, so the kammback induces turbulence to fill in the void, thereby reducing drag. As other posters have also noted, golf balls spin at a very high rate. The dimples drag the air around with them, producing lift. It's a twofer: lower drag and increased lift, all for one low price.

As for your idea about pumping air out through little holes, it's not a bad idea but you are doing it backward. The process is called boundary layer control, and involves sucking air through thousands of tiny holes. It works by sucking in the turbulent layer of air adjacent to the skin of the aircraft, allowing for a longer laminar flow. Several full scale jet aircraft have successfully used this technique.

Now we can look at micro dimples, sometimes called shark skin. This is an idea that has been exploited for years by the Navy and the designers of high performance racing yachts. Marine animals beat us to it by a long shot, which is why it is often called shark skin. The idea is to cover a surface with tiny bumps or scales. The tiny bumps or scales induce a micro layer of turbulence which rides along the surface of the object. The turbulent layer is so thin that it doesn't easily perturb the adjacent laminar layer, but instead buffers it. You can think of it as a lubricating layer helping to speed the laminar air on its way.

Tom

Thus the new body suits Olympic swimmers are using.

Thank you for this explanation. Do you think there is any use for this type of stuff for vehicles? That is, are the MythBusters on to something?

I tried to put dimples on a shark once. He didn't like it.

Best wishes.

Stumpy

What about adding shark fins? That would look cool. :madgrin:

Quite possibly. There are a few complicating issues. The first is that most cars are not that aerodynamic in the first place. The special surface is only going to help a streamlined surface. If you are pushing a brick through the air, it isn't going to help much. The two other issues are cost and aesthetics. Consumer products such as automobiles are very sensitive to costs. Likewise, aesthetics play a big part in car sales. If a car looks funny, it's not likely to sell well. Look at all the criticism of the Prius and people thinking it looks dorky. It looks like it does to get good aerodynamics.

I suspect coatings may become used on cars, but only as efficiency begins to take top priority. It will be a while.

Tom

You don't think it will work on my GF's motorhome? :madgrin:


Hey, that gives me a great idea - I will come out with a shark skin kit (shelf liner with contact adhesive) for RVs. I need something to hawk on Ebay if I don't get a job soon.

I think shark fins were tried in the 1950s.

Tom