Mythbusters tests "golf ball" dimples

[MetroMPG]

That was pretty darned entertaining!

FYI, you can view the video here: http://www.megavideo.com/?v=PMB935S8

When I saw the first test (dirt vs clean), I was sorely disappointed by their fuel measurement technique: note the fuel level in the sloshing tube by eye and mark with magnetic arrows!

I was relieved to see them ditch that method for the smooth vs. dimpled tests and opt for weighing the fuel cell each run.

Originally Posted by botsapper

The now famous 'dimples' car should be retested w/ ecomodders' test suggestions.... Any other suggestions?...

Mine are mostly about the testing methods, either things I saw and took issue with, or things they didn't show which leave big questions.

1) They need to do A-B-A. Return the car to its original state to see if the observed effect disappears. Admittedly not easy to put the dimple material back in and smooth it again, but they should have tried.

2) It seemed to me they were relying on Jamie to hold the car's speed. That's a no-no! Need to remove the human foot from the most sensitive input in the experiment - the gas pedal. They should have used cruise control or some other speed control.

3) It's fair to assume weather conditions (temp, particularly) would have changed between the two tests - it would have taken some time to carve out those 1082 dimples. They didn't take that into account. (We don't even know for sure if they did it on the same day due to the magic of editing.)

4) We don't know whether the car was equally warmed up for all tests. (Equal engine coolant temp doesn't count.) We're talking full drivetrain temps, including tires.

Their results are also really big (% improvement), which ratchets up the skepticism a bit more. They claimed 26 mpg (US) for smooth vs. 29.65 for dimpled. A 14% improvement! Yikes.

Has anyone double checked their calcs?

smooth clay:

10056 g to 9553 g gasoline
or 503 g burned
26 mpg (US) their figures

dimpled clay:

9450 g to 8972 g gasoline
or 478 g burned
29.65 mpg (US) their figures

Gasoline weighs 6.073 lbs per US gallon (says wikipedia). 1 pound = 453.59237 grams, so 1 gallon = 2754.7 grams.

smooth: 5 mi / 503 grams = 5 mi / 0.182597 gal = 27.38 mpg (US)

dimpled: 5 mi / 478 grams = 5 mi / = 0.173522 gal = 28.81 mpg (US)

That's a 5.2% improvement by my calcs.

So their calcs seem fishy too. Unless I just screwed it up. (Plausible!)

[gone-ot]

...hm-m-m-m, wonder what the temperature of the gasoline was at each test intervals

...cold at the start, cool by pre-noon, warm by noonish, hot by end of day?

...temperature will affect weight by volume readings.

[pgfpro]

smooth clay:

10056 g to 9553 g gasoline
or 503 g burned
26 mpg (US) their figures

dimpled clay:

9450 g to 8972 g gasoline
or 478 g burned
29.65 mpg (US) their figures

Gasoline weighs 6.073 lbs per US gallon (says wikipedia). 1 pound = 453.59237 grams, so 1 gallon = 2754.7 grams.

smooth: 5 mi / 503 grams = 5 mi / 0.182597 gal = 27.38 mpg (US)

dimpled: 5 mi / 478 grams = 5 mi / = 0.173522 gal = 28.81 mpg (US)

So their calcs seem fishy too. Unless I just screwed it up. (Plausible!)

I pick up on this also but didn't want to write anything because I thought I might have heard them wrong.

[MetroMPG]

I'm going to save any further comments of my own for the other thread on the same subject because it seems to have had more people's analysis in it... I didn't check it before I replied here.

Too late to merge the threads now - it'd make a mess.

Other thread:

http://ecomodder.com/forum/showthrea...oct-10658.html

[gone7]

Attached air flow is exactly what one needs to remove.

One can't argue with results, unless they want to replicate the tests.

Using clay is an excellent method because it can be removed. And let us not forget the extra weight the clay added.

The proof is in the pudding. No theoritical laws mean anything if the process works anyway. Observation is the only true sientific method.

By the way, this is not about windows. They cannot be helped and that is why they are removed in fast cars.

MetroMPG has interesting points, but the test should be done with fuel injection and a air-flow sensor to meet the exactness we need to see.

One can also do the test both ways, different times of day, etc.. But I am not convinced that such a large difference is needing any more detailed tweaks. It pretty much stands alone.

[aerohead]

Originally Posted by ACEV

Attached air flow is exactly what one needs to remove.

One can't argue with results, unless they want to replicate the tests.

Using clay is an excellent method because it can be removed. And let us not forget the extra weight the clay added.

The proof is in the pudding. No theoritical laws mean anything if the process works anyway. Observation is the only true sientific method.

By the way, this is not about windows. They cannot be helped and that is why they are removed in fast cars.

MetroMPG has interesting points, but the test should be done with fuel injection and a air-flow sensor to meet the exactness we need to see.

One can also do the test both ways, different times of day, etc.. But I am not convinced that such a large difference is needing any more detailed tweaks. It pretty much stands alone.

Their 'results' violate 'science.' If Jaime is the 'engineer' he should have remembered from Fluid Mechanics about boundary layers and Reynolds number effects as pertaining to the scale of automobiles.
Dimples on golf balls are boundary layer devices used to force a transition to turbulent boundary layer and alter the ball's separation point.
Automobiles are already in full turbulent boundary layer above 20 mph.Dimples would be redundant.
The dimples could act as turbulators,energizing the boundary layer to achieve attached flow in areas of high angle of attack (rear of the Taurus),but a drag reduction cannot be associated with pure Rn.

[gone7]

See response at the dimples thread. But basically, what works is the proof, and theories are not proof of anything and never have been.

[MetroMPG]

If the methodology is questionable, the results are questionable. It's that simple.

[gone7]

The question is not methodology. The question is in duplication of the results. One can never say for sure with theoretical science; only with practical and applied science. One may, however, say for sure so long as they have run the same experiment for themselves.

I do agree that it is too bad that the threads cannot be merged.

[ChazInMT]

Originally Posted by ACEV

See response at the dimples thread. But basically, what works is the proof, and theories are not proof of anything and never have been.

ACEV, I first came to Ecomodder.com 3 years ago wondering how to make dimples on my truck without adding 600lbs of clay. I was wondering why it wasn't done everywhere, then I got edjumacated. Golf ball dimples don't have the desired effect on cars.

But, don't take my word for it.

Here's an article from a few years back written with Gary Eaker, a former GM & Hendrick Motorsports aerodynamicist.

You're looking for:

Aero Stuff That Doesn't Really Matter
In addition to our list of five tricks that almost always work, here are some things A2 customers might want to try that are really a waste of time.


Golf-ball dimples: They do not work on cars, regardless of the scale of the dimples, unless your car is a 1.68-inch-diameter sphere spinning through the air with no ground plane.

Hot Rod Magazine - Car Aerodynamics Wind Camp Tech Theory

Mr. Eaker has a crazy amount of experience with aerodynamics, ACEV, you basically are saying to him that he is completely full of crap. Are you really that small minded? Aerohead as well is saying dimples are crap.

So you're saying because a pop-science TV entertainment program tested it and found an encouraging result, that settles it, dimples work.

ACEV put your money where your mouth is and test it again, you make the claim that dimples work, you prove beyond a doubt that they do. It isn't up to us to prove they don't, that ain't how science works. You say they enhance significantly, it's up to you to show how significant. Mythbusters does not count as your proof.

It's like you come in here and say you've been to the Moon in your VW Beetle, when we say, "Great, show us some pictures or something." You reply, "You show me pictures that prove I wasn't on the Moon." See what I mean? Quit that. You look really silly. Start seeming intelligent please.