Loved the episode but one thing, which may not be pertinent. On a golf ball, I believe the spacing or configuration of the dimples plays a large part in how well it performs. It did not appear that the spacing was uniform on the car.

@ Roger Roger - Who would want a car if it was only partially dimpled?

The spacing determines the efficiency. Ok, the car was not the most efficient.

As far as partially dimpled - I drive ~600 miles per week at around 40 mpg. At 15 gallons, $4 per gallon it costs me $60 a week. A 11% increase in mileage would save me $6.60 per week or almost $350 per year. For that much I might be convinced to drive a dimpled car.

Brian

Not directly relevant to the car experiment, but what is important about how golf ball dimples work is the backspin of the golf ball.
A golf ball spins at maybe 4000rpm (give or take). The backspin interacting with the forward flight of the ball drags air around the back of the ball and directs it downwards. Ball pushing air down equals air pushing up on the ball - the spin generates aerodynamic lift! That is why the dimpled ball hit by the golf pro went about twice as far - the dimples cause more air to be directed downwards than by the smooth ball surface. Even if the dimpled ball had more drag than the smooth ball it could still easily go way further!
Scientific term is the "Magnus effect".

Onmitsu.

quote:

Originally posted by DrDracula:
The test on the hangovers was so clearly flawed that it's embarrassing for the show.

Perhaps they'll try this one again some day under more rigorous conditions.

They also tested the wrong myth. The myth isn't about beer vs. beer and liquor. It's beer before liquor vs. beer after liquor.

quote:

They also tested the wrong myth.

No, they just tested a different version of the myth. That doesn't make it "wrong".

Dimpled car: 11% improvement? Hmm. Here's something Adam didn't mention...What was the difference in wind that day between when they did the runs without and when they did the runs with the dimples?? From the video with the dimples, it appears to be pretty windy on the last runs. I'm not an aero engineer, but doesn't parasite drag increase exponentially relative to airspeed? So...if head or tail wind changed just 4 MPH between the tests, the parasite drag could be at least 11% different. Aero engineers, help me out here... I think we need a re-do!

Yeah. Do it on a treadmill next time. LOL

quote:

davjosmes

Where did YOU come from?

Long time-no see! welcome back! (I used to be Killick123)

Thanks, but....

I posted the dimpled car finish idea to test over a year ago on this site and as with most of the other ideas, people began to jump in with the reasons why it wouldn't work right away.

I have to say it's great to see that they proved it has potential!

So of course I was stunned to see that they had chosen my first suggestion to test, I was surprised that they don't even notify you that they picked your idea - what's up with that?

I always figured they probably brought out the person who gave them the idea to watch them film the episode, but not even an email?

So although it was great to see they used my idea, I guess I feel kind of disappointed that they don't even contact you for any further clarification or a simple thank you for the idea.

I would have thought an all-expenses-paid trip would be in order, but not even a cheesy t-shirt or at least a thank-you email? Wow!

Does anyone else know if that's their normal practice?

Actually, many people have suggested the golf ball car. Your post was probably not original. In any case, its their standard procedure to not notify the poster upon testing of a myth. There are often multiple posters and they can rarely trace the original source.

quote:

I would have thought an all-expenses-paid trip would be in order, but not even a cheesy t-shirt or at least a thank-you email? Wow!

You had unrealistic expectations. Did you honestly think they would spend hundreds to fly you out to their shop, give you the tour, let you on TV, and pay for all of the expenses? Wow, just wow.

quote:

So although it was great to see they used my idea, I guess I feel kind of disappointed that they don't even contact you for any further clarification or a simple thank you for the idea.

Your idea wasn't original. Others have posted the same idea with no knowledge of previous posters. That's the whole reason the FIND button exists.

Here is an idea. Run the test again but instead of adding clay then dimpling it - just add "positive dimples" or stick on bumps. See if the MPG changes from "negitive dimples". I bet some company makes 2 inch 1/2 sphere sick-on bumpers. Reason? Someone could offer dimple kits to reduce gas use, much easier to add - and you can buy them in different colors for "Bling".

This was a great episode. With all the various suggestions of the golf ball affect with negative dimples, dimples only on the Apex, under the car, hexagonal dimples and dimples of smaller sizes I saw nothing was mentioned of dimple on say aircraft. Now these are traveling at 8 and 10 times faster than a car wouldn't this warrant an exponentially improvement in efficiency?

I really hope you can revisit this myth and who knows discover a design that can benefit every travel industry.

Car was too dirty.

Test needs to test if small amount of dirt and dust will be enough to create the golfball effect, which was clearly proven.

On that note, I wonder if any top speed record breakers will use the dimples..though I cant imagine this is as new a discovery as it seems.

Test the dusty car...though the difference will probably be marginal one way or another.

I don't understand why they thought the dimples
should be scaled. This applies to the bowling
bowl, model car, and actual car.

In fact, I was surprised, not that there was
a dimple effect, but that it worked with giant
dimples.

Given some of the other comments in this thread,
why don't we see production cars with dimples
of optimum size, shape, and location?
(I read that changing the pattern on golf balls
has a significant effect compared to other already designs that were the results of many
experiments.)

I think i am going to try vortex generators instead. - I bet they have the same effect if not better than the dimples. There is a reason why the airplane industry has used them for years!

quote:

Originally posted by aintnosin:

quote:

Originally posted by DrDracula:
The test on the hangovers was so clearly flawed that it's embarrassing for the show.

Perhaps they'll try this one again some day under more rigorous conditions.

They also tested the wrong myth. The myth isn't about beer vs. beer and liquor. It's beer before liquor vs. beer after liquor.

Yeah, that's how I'd heard the myth, too ("Beer on liquor, never sicker; liquor on beer, in the clear"). I've unscientifically tested that one: vodka shots with a friend, then handed him a Kahlua mudslide. He swallowed it down, turned green, and ran to the toilet. Ahhhhh the good old days of having a 20 year old liver.

Anyway, if Kari ever wants to torture the boys again, I'd love to see that one given a shot.

(And, "Wake up, it's time for science!" = Great t-shirt)

This is one of the most surprising results I have seen from a Mythbusters segment in a long time. The physics of dimpled golf balls were known for many years.

One thing I have to say about the prior posts here that the car did not get much lighter because water evaporated from the clay to improve its gas mileage. At least it would not given it a 11% difference. It was the dimples themselves that did that.

However I think in order to show a big improvement, they need to find someone to make a car panels with dimples surfaces in the steel. Make them about the equivalent weight as a normal panel. That would put the naysayers argument to rest here.

This does give automotive engineers and manufacturers something to think about in this day and age of more fuel efficient vehicles. Maybe someone is already applying to the next generation of automobiles.

quote:

Maybe someone is already applying to the next generation of automobiles.

Yup, in the ultra-efficient electric Myers NMG. It's really an enclosed trike, but highway legal. They only put the dimples where needed: where the wind detaches from the car at the back. This also avoids the problem of having dirt and water collect inside the dimples. See a photo at this link:

http://www.blogcdn.com/green.a...0/pev2009-nmg-08.jpg

I am very skeptical of the result for the following reasons:

1. They were attempting only to change the aerodynamic drag properties of the car, yet they did not seek out a wind tunnel to compare the Cd of the original car to the Cd of the dimpled clay.

2. The fuel measurement was sketchy at best. At 26 mpg, for 5 miles, only 0.19 gallons are used or 24.3 ounces, at 29 mpg, 0.17 gallons or 21.76 ounces is used. Adam flipping a switch while crossing a line does not constitute a controlled experiment capable of controlling the flow of 2.5 ounces of gasoline.

3. 2.5 ounces of fuel can be saved from a slight breeze. Atmospheric and present conditions were ignored.

I burns me to hear people say that automakers are the dumb ones for not doing this because actors on a TV show told you that is saved 11% in mpg. In other words 2.5 ounces of fuel.

Things of interest with clean car dirty car, Golf ball man said hitting the smooth ball was like hitting a brick! more impact area, = disappated energy, dimpled balls have a lower imapact area so more energy is directed forward (Waht if you use a pegged club? then how do you dimple a car, you paint it with hammer finish paint, does that make it have less drag?