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....

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

http://www.inventors-network.de/en/T...Intro_temp.htm

http://www.lighthouseww.com/index.ph...7b13fb691133b7

[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...

[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....

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.

[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!

[EngrPaul]

Re: No Engine/Driveability Change

Some folks would beg to differ, I can think of a few people I know who would consider that car undriveable.

[Marduke]

Another example is the new bicyclist uniforms. Key areas are textured to reduce drag. They didn't do the whole uniform though, as drag would have increased.


BTW, I've never seen another thread bring out so many aerodynamicists and aerospace engineers before.

[Casper507]

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.

Myself,
I stopped watching it when I stopped getting cable. The red head Kari Byron definitely kept my scientific interest up regardless of the subject or it's treatment. (I will not put "that" imodicon up, I will not put "that" imodicon up........)

No offense, but I'm not sure the graphic presentation of getting more lumens out of a flashlight would garner enough ratings to continue the show. But perhaps they could label it as a public service and support it with a designation as a non profit organization. Meanwhile charging a fair fee to the people with shows that actually make money and people actually watch. Something fair like the equivalent of their total production costs to stay on the air. After all it is the publics airwaves they should pay to use them for other than for "public service."

[StarHalo]

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

I'm not sure where this comes from; they carefully described wake drag, illustrated it with dimpled vs non-dimpled golf balls, went to a wind tunnel and illustrated large scale non-/dimpled golf balls and a small scale non-/dimpled car model, went to a water tow lab and repeated with the models, assembled the full scale car, did multiple runs with base/clay base/clay dimpled each to generate averages, used a solenoid-controlled separate fuel cell to be weighed, etc..

I'm sure it would be possible to just show all the needed math and computer simulation results then roll credits, the three-minute show is over. But many people wouldn't buy it, they want to see it actually done and to grasp the science. I think the Mythbusters do a fantastic job at that, at least partially evidenced by the fact that no one else has bothered to do an entire dimpled car before..

Re: No Engine/Driveability Change

Some folks would beg to differ, I can think of a few people I know who would consider that car undriveable.

Right, but could you have predicted a decade ago that the hot thing now would be Honda Civics with giant spoilers and comic-book body panels? Again, hypermilers struggle just for single-digit MPG improvements; returning an added 10%+ from thin air would be very desirable to this growing niche group..

[Patriot]

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.

I think there might be too many variables to compare including the fact that one is a high wing design and the other is a low wing design. While a vertical tail may have been ideal for the Mooney, that design may have proven less efficient on a Skyhawk. Also, I think it all depends on what the design specification is meant to accomplish. Maybe a straight tail would have provided more longitudinal control but at the sacrifice of speed and economy. Obviously fighter aircraft and airliners don't have swept surfaces due to aesthetic reasons. It's a conglomeration of design compromises.

Starhalo
I'm not sure where this comes from; they carefully described wake drag, illustrated it with dimpled vs non-dimpled golf balls, went to a wind tunnel and illustrated large scale non-/dimpled golf balls and a small scale non-/dimpled car model, went to a water tow lab and repeated with the models, assembled the full scale car, did multiple runs with base/clay base/clay dimpled each to generate averages, used a solenoid-controlled separate fuel cell to be weighed, etc..

I'm thinking Lux may have just been stating that in general terms, especially in the area of repeatability. Obviously it's just a TV show so they're not going to be able to provide 50 test samples. While I realize that most of their experiments are lacking the full scientific process, it's still entertaining and in most cases close enough for government work, as they say. The dimpled car data variation in this case was large enough that it's conclusively an advantage. Maybe after further tests the percentage could change to 9% or 13% but it's clearly beneficial on a car this size and general shape.

[FlashCrazy]

I think there might be too many variables to compare including the fact that one is a high wing design and the other is a low wing design. While a vertical tail may have been ideal for the Mooney, that design may have proven less efficient on a Skyhawk. Also, I think it all depends on what the design specification is meant to accomplish. Maybe a straight tail would have provided more longitudinal control but at the sacrifice of speed and economy. Obviously fighter aircraft and airliners don't have swept surfaces due to aesthetic reasons. It's a conglomeration of design compromises.

On anything less than a couple hundred miles per hour, the straight tail is more efficient. Basically you can get away with less area for same amount of lift (which is what the vertical does, lifts sideways to give a yawing force). The Mooney's tail, consequently, has less area than it would've had to have if it were swept. Less area.. less profile drag. Induced drag may be similar, but that comes into effect mainly during operation of the rudder. Yes, all of this is simplified... I won't get into lift-to-drag ratios, roll-coupling, etc., but on these "slow" and small airplanes (more correctly, at these low Reynolds numbers), a straight tail is more efficient ... high wing, low wing, or whatever. That does bring up the point of induced drag due to a blunt tip at the end, but I'm only talking about a straight leading edge... the rear of the fin is swept forward to keep the tip area small, to reduce vortices. That also keeps the bulk of the area closer to the fuselage to keep roll coupling to a minimum (lowers the mean aerodynamic center of the tail). Anyway.. yes you're right.. certainly there's a multitude of design factors to consider. I guess that's why I just sell flashlights.

[blasterman]

I've seen some older research on this same principle with aerofoils, except the dimples were much smaller in scale. Same effect I guess.

Wind resistance is the biggest cause of reduced fuel economy with cars at highway speed as I recall. Rather than mess with these type of 'hacks', it would seem simplier to simply reduce the over all size of the car and tire width that would result in a more realistic reduction in the coefficient of drag. That means smaller cars, and hell will freeze over first, at least in the U.S..... until gas hits $10 a gallon.

[Patriot]

On anything less than a couple hundred miles per hour, the straight tail is more efficient. Basically you can get away with less area for same amount of lift (which is what the vertical does, lifts sideways to give a yawing force). The Mooney's tail, consequently, has less area than it would've had to have if it were swept. Less area.. less profile drag. Induced drag may be similar, but that comes into effect mainly during operation of the rudder.

Interesting stuff! Makes sense though since the Mooney was quicker than other designs with comparable power. I think its main rival at the time was the Comanche which had more power but couldn't fly as fast. My dad used to rent a Mooney 231 when I was a teenager and I remember that plane felt like a real hot rod compared to a 182. Back then there was no air traffic to speak of so you can imagine that we had a lot of low level fun.

[R@ndom]

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.

Sorta like Man vs Wild. Great fun to watch but take it with a grain of salt.

[KD5XB]

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

I'm wondering if that's the same as parasitic drag and induced drag...

But what I REALLY want to know, and apparently it wasn't tested, is how the dimples affected the top speed of the car. That information would tell immediately just how the drag changed with the dimples. Unless there's an RPM limiter or governor, or course.