11% More MPG With No Engine/Driveability Change

[StarHalo]

Well I've said it for some time that if you dimpled an entire vehicle like a golf ball, it'd be more efficient - leave it to the Mythbusters to actually pull it off. Last night's episode featured a 26 MPG clay-coated Ford Taurus that when dimped over the entire body returned 29.65 MPG (yes the baseline was the car already covered in clay, yes the clay removed to make the dimples was placed back in the car), an 11% improvement with no change or modification to the engine, and would be no change in driveability in a non-clay/production body panel model.

Just as hot-rodders and ricers are glad to tack on all kinds of unique and bizarre add-ons that scream their intentions, I'm quite sure that serious hypermilers (who already drool over the solar panel roof option on the new Prius) would pay handsomely for this treatment on their cars. So if you're interested in being a millionaire next year, start cranking out dimple body kits for the Prius today..

 

[JakeGMCHD]

So my Line-X Rocker panels that have a dimple pattern could be helping out my mileage??

 

[EngrPaul]

This explains why Photon Fanatic flashlights THROW better.... :naughty:

I guess pretty soon we'll see it used just about anywhere...

http://www.inventors-network.de/en/TLT/TLT_Intro_temp.htm

http://www.lighthouseww.com/index.p...id=184&zenid=ff33815a1f0a0e4e047b13fb691133b7

 

[Patriot]

I watched the show last night and saw the whole meal deal but if this is valid and repeatable why haven't aerodynamic engineers utilized this previously? Why aren't Formula 1 racing teams and Gulf Stream aircraft applying this science if it's a real advantage? Something seems to be missing.

 

[asdalton]

I watched the show last night and saw the whole meal deal but if this is valid and repeatable why haven't aerodynamic engineers utilized this previously? Why aren't Formula 1 racing teams and Gulf Stream aircraft applying this science if it's a real advantage? Something seems to be missing.

There are two types of aerodynamic (or hydrodynamic) drag: boundary layer (viscous) drag and wake (pressure) drag.

A smooth surface minimizes the former, and a tapered rear minimizes the latter. Think about airplanes and submarines.

The trick comes when you have a shape with terrible wake drag, like a sphere. In that case, roughening the surface can reduce the overall drag by keeping the boundary layer from separating from the surface. This change makes the wake drag much less -- and even though the boundary layer drag becomes worse, there is a net improvement. This is why golf balls have dimples.

The outcome of adding dimples to a car is difficult to predict without experiments or detailed computer modeling. Its shape is not as poor as a sphere, but not as good as a fish or a jet plane.

 

[LuxLuthor]

There are two types of aerodynamic (or hydrodynamic) drag: boundary layer (viscous) drag and wake (pressure) drag.

A smooth surface minimizes the former, and a tapered rear minimizes the latter. Think about airplanes and submarines.

The trick comes when you have a shape with terrible wake drag, like a sphere. In that case, roughening the surface can reduce the overall drag by keeping the boundary layer from separating from the surface. This change makes the wake drag much less -- and even though the boundary layer drag becomes worse, there is a net improvement. This is why golf balls have dimples.

The outcome of adding dimples to a car is difficult to predict without experiments or detailed computer modeling. Its shape is not as poor as a sphere, but not as good as a fish or a jet plane.

That was an excellent and well reasoned response.

I stopped watching Mythbusters when I realized they are more interested in having fun and getting ratings than using real science or controlled experiments.

 

[Dawg]

I think I will try to do mine on the cheap........Now where did I leave that ballpeen hammer?

 

[TorchBoy]

That episode of Mythbusters hasn't arrived in NZ yet. Did they mention wind speed at all?

Thanks for that explanation Andrew. I thought golf ball dimples increased the drag which allowed spin to impart further distance to its flight, so golf balls go further in air than in a vacuum. Is that another myth that they should test?

 

[EngrPaul]

Looking forward to the next hailstorm coming my way... or maybe I'll just park at the mall for a week.

 

[Marduke]

I watched the show last night and saw the whole meal deal but if this is valid and repeatable why haven't aerodynamic engineers utilized this previously? Why aren't Formula 1 racing teams and Gulf Stream aircraft applying this science if it's a real advantage? Something seems to be missing.

Aerodynamicists are spending billions researching just these effects. The problem is that boundary layer control is an order of magnitude more difficult to model analytically, predict, and most importantly, control than attached laminar flow.

But these effects are used in more places than you might think. Something most people are familiar with are the new "shark skin" suits Olympic swimmers are wearing, and breaking records with. This fake shark skins create a turbulent boundary layer near the surface which lowers drag. Research on furthering this knowledge is ongoing.
http://aem.eng.ua.edu/people/lang/lang.asp

 

[RocketTomato]

Looks like a car design PhotonFanatic would come up with. Or one of the Ecofont designers.

 

[Kestrel]

There is an electric vehicle around where I live that has body panels done in this manner. The car is white, naturally... :tinfoil:

 

[orbital]

+

Those 'aero dimples are way too big,
I'd like too see the results if they were much smaller.

This concept will trickle into lots of things.

 

[smokelaw1]

SPEED HOLES! Homer Simpson was right all along!

 

[Blindasabat]

... I thought golf ball dimples increased the drag which allowed spin to impart further distance to its flight, so golf balls go further in air than in a vacuum. Is that another myth that they should test?

No, that one is already well tested. Well, maybe not the vacuum one (at least I haven't seen it), but it has been well demonstrated that with proper backspin, golfballs generate lift to stay aloft. The dimples actually create drag there, but it is used creatively to get what the golfer REALLY wants = distance.

asdalton was correct, faster, better shaped planes and F1 cars would not benefit from this as well as a (relatively) slow moving car, and a submarine is highly optimized as well - same as a ship hull. I would also word it that the dimples induce turbulance earlier to change the wake characteristics or turbulant seperation. Just a different way to say the same thing. A similar experiment is done by placing a wire around a sphere just past the widest point respective to airflow to 'trip' (as I always called it) the laminar airflow into turbulent airflow at the proper place to reshape the turbulent wake making it much narrower and therefore causing less drag. There is a smoke trail picture of a sphere with and without in my textbook from college.

Aerodynamicists already did one better than the Mythbusters several years ago by adding low drag NACA duct shaped protrusions (not ducts) at the back edge of the roof of a car which lowered the drag considerably. They 'trip' the flow into mild turbulance at the rear window controlling the wake. I thought at the time to sell adhesive strips to apply above car rear windows, but realized quickly that the reason they didn't put them on cars at the factory was styling - and they would have been hard to sell in the carefree 80's when I saw them. Maybe now is the time?
<edit> Marduke is on top of it too. I hadn't thought about the new swimsuits, but that is a v. good example. In the new age of increasing car mileage requirements and higher gas prices, car designers will try to put styling elements (edges, trim) near the back of the roof to control the wake better.

 

[StarHalo]

Aerodynamicists already did one better than the Mythbusters several years ago by adding low drag NACA duct shaped protrusions (not ducts) at the back edge of the roof of a car which lowered the drag considerably. They 'trip' the flow into mild turbulance at the rear window controlling the wake.

Don't forget the Mitsubishi Evolution's "Shark's Teeth" (Vortex Generator)

 

[FlashCrazy]

This explains why Photon Fanatic flashlights THROW better.... :naughty:

:lolsign:

asdalton was correct, faster, better shaped planes and F1 cars would not benefit from this as well as a (relatively) slow moving car.....

Exactly. Much of aerodynamic design has to do with the size and speed of the design in question. The rules for slow, small designs are quite different than for fast and/or large designs. In some cases, the rules actually reverse. It has to do with the way it "sees" the air (or the way air "sees" the design...lol). The relative viscosity of the air is different in each case. Look up Reynolds numbers for more details.

I thought at the time to sell adhesive strips to apply above car rear windows, but realized quickly that the reason they didn't put them on cars at the factory was styling - and they would have been hard to sell in the carefree 80's when I saw them. Maybe now is the time?.

Yeah, style influences many things, and puts to bed many good design ideas. I've always loved Mooney aircraft because they came out with a straight vertical tail even though the "in" and modern thing was a swept tail. The swept vertical of a Cessna 152/172 is less efficient than a non-swept one, but it looked better. Style sells.
And yes, I know the early Cessnas had non-swept verticals.. so don't get on my case about that. :nana:

 

[Patriot]

There are two types of aerodynamic (or hydrodynamic) drag: boundary layer (viscous) drag and wake (pressure) drag.

A smooth surface minimizes the former, and a tapered rear minimizes the latter. Think about airplanes and submarines.

The trick comes when you have a shape with terrible wake drag, like a sphere. In that case, roughening the surface can reduce the overall drag by keeping the boundary layer from separating from the surface. This change makes the wake drag much less -- and even though the boundary layer drag becomes worse, there is a net improvement. This is why golf balls have dimples.

The outcome of adding dimples to a car is difficult to predict without experiments or detailed computer modeling. Its shape is not as poor as a sphere, but not as good as a fish or a jet plane.

Sounds like a pretty good answer to me, I'll take it.

Still, it seems that nature benefits from micro textures even on long slippery shapes, through media such as air and water...a shark for example. Perhaps technology is finally at a stage to begin realizing the advantages then incorporate these into actual 3D designs. 3D printing is faster and more common now so maybe we'll see a rapid increase in the creation of models for aero and hydrodynamic testing.

 

[Mike Painter]

I watched the show last night and saw the whole meal deal but if this is valid and repeatable why haven't aerodynamic engineers utilized this previously? Why aren't Formula 1 racing teams and Gulf Stream aircraft applying this science if it's a real advantage? Something seems to be missing.

All other things being equal the length to width ratio is most important. That's why fish look like they do.
F1 cars are long and thin and I'd bet a nickel that they are precisely the best length.

Only a wind tunnel test could give valid results for such an experiment. *Very* professional drivers or computer control over a long period would be a distant second.
Tire pressure, time of day, acceleration and deceleration, difference in mass,etc, etc would all have to be accounted for.

 

[Patriot]

All other things being equal the length to width ratio is most important. That's why fish look like they do.
F1 cars are long and thin and I'd bet a nickel that they are precisely the best length.

In F1, designers don't decide the length and width, the F1 governing body does. Team Aerodynamicists are sometimes thrown a curve ball by the regulations and have to work with what they've been given. So it's not as if they're designed ideally since the regulations are usually designed to slow the cars down, leaving engineers the task of overcoming the set backs of established parameters. Still, the teams are looking for every advantage and I wonder if micro surface textures are in their future or if that's already been explored and overcome through other types of aerodynamic tweaks.

It seems that even long, high ballistic coefficient shapes can benefit from micro textures as Marduke pointed out when he mentioned shark skin and Olympic swim suits. Sometimes I think it's been an overlooked area but perhaps the technology which allows implementation of micro textures just hasn't existed. How do you cover an entire F22 fighter or an Ohio Class SSBN with viscous drag reducing texture for example? Maybe we're at the dawn of of realizing breakthroughs in these areas.

It's all very fascinating!