"Golfball effect" thinktank...
 

Yes, I've seen the other two threads. This is less related to that, and more related to the "whys" of the functionality. For this thread, lets make the following assumptions: Adam and Jamie of Mythbusters didn't screw anything major up in the science and testing and that some of their testing might hold merit. Dimpling has some affect on the aerodynamics. Adam and Jamie scaled a golf ball up to car size. (Use this third item to establish a baseline dimple size)

I am proposing that dimpling the whole vehicle might not work to our advantage. That dimpling starting at the furthest ranges of the Z and Y axis then working back to the rear of the vehicle is all that's actually required, and that any more than that might work against us. I am also proposing that there is an optimal dimple size for said construction, and that simply scaling up a golf ball might not be the optimum solution. However, investigating this phenomenon has many benefits to this community and should be explored. Currently "boat tails" cause a large extension to the rear of the vehicle. With the golf ball dimpling, it might be possible to lessen the distance and cost of the current home brew iterations. Unfortunately, creating something new like this, takes time and resources.

Now, with all that under advisement, how would we test this? Is this something that can even be done small/medium scale first? How does one figure out the "optimal" dimple size? Is there a mathematical representation for this somewhere? Any other stray thoughts?

Thanks for reading and not throwing bottles at the fence!

Schlicting
 

I would respectfully recommend that you take a look at 'Boundary Layer Theory' by Schlichting.There is extremely solid science which disputes the physical possibility of dimples ever improving the airflow over an automobile.

Here's a link to the book, for reference: http://books.google.com/books?id=8Yu...age&q=&f=false

The folks at Myers Motors, maker of the NmG, (an updated/upgraded Corbin Sparrow) might disagree that the dimples have no positive effect on airflow. If you take a close look at the trailing sides of the front fenders and the lower aft sections of the vehicle, you will find them dimpled. When I toured their (MM) factory a couple years ago, I asked what the dimples were for. They told me that they increased the range because they reduced the drag on the body.

proof
 

I would respectfully take them to task to demonstrate,scientifically,how they accomplished something no one else on Earth was able to accomplish,when they had the resources,technology,and motivation to do so.
It's like the old adage,that extraordinary claims require extraordinary evidence.
The dimples may have an effect,but it may reside in an effect which has nothing to do with golf ball dimples.

Hi All,

To fill in some of Aeroheads remarks. The dimples on the new version of the Corbon Sparrow might (probably) be there for sheet-metal vibration reduction / sheet metal stiffening purposes. Dimple sheet metal like that and it gets quite stiff from work hardening, as well as the 3-d nature of the dimple feature.

That said, I think dimples will work on cars that look like golf balls. Right now, the only one is the New VW Beetle.

Dimples work on golf balls because the shape is so abrupt. If you can keep a ball from rotating, all it needs is a thin ring or groove as the air approaches the widest part.

I believe the Corbin Sparrow is fiberglass, and the dimples are placed as boundary layer turbulators where they might do a bit of good to fix the shape. It would be easier than more extensive mold mods.

I can't tell from your post, do you think they are cosmetic or, they help lower the overall drag and they are just easier to add than say, vortex generators?

A Vortex Generator is harder to add to a mold, and is just a better Boundary Layer Turbulator. IMHO, either type is barely functional in those locations, except to show model changes at a glance and give the sales force something to chatter about.

Dimples on a car could work if you kept your car in a constant 180 degree spin like a golf ball:D something which I, for one, make every effort to avoid!

I totally saw that...And it worked...And they also proved that a hundred pounds or so of extra weight does absolutely nothing to the mpg...of a car of that weight and power..

So, the golfball effect works...it improved the mpg of the Taurus? car, by 15%? right, if I remember correctly.....totally spontaneously...and from what I remember, it was very very scientific and controlled..

But why oh why is it not being implemented? does it cost more to simply make dimples? or what?

I love that kind of educational program..

:thumbup:

micondie -

That's what I was thinking. Therefore, I asked if dimples would be good for racing disk covers, but I was told by smarter people than me that it wouldn't work.

CarloSW2

No. They only proved that 100 lb of extra weight has minimal effect on a car already in motion. They deliberately (and rightly, for the experiment) ignored the fuel used to accelerate the extra mass.

golf ball
 

Remember,the golf ball is quite small in comparison to an automobile.Even coming of the tee in a good wood shot at 110-mph,without the dimples,the ball would have a laminar boundary layer and flow would separate before it got to the back side of the ball.
The dimples guarantee an early transition to a turbulent boundary layer,which moves the separation point back behind the ball,reducing it's wake and also the base pressure of the wake for lower drag and a longer drive on the fairway.
An automobile transitions to a turbulent boundary layer at about 20-mph do to it's size in relation to velocity ( the definition of Reynolds Number ).Adding extra roughness can only degrade performance.
I think Bicycle Bob has probably hit on what's going on,that the dimples are behaving like turbulators to feed kinetic energy into a boundary layer on the verge of stalling,allowing the flow to remain attached across a body section which wasn't properly proportioned.
Typically,turbulators cost a drag penalty all the time,but if they reduce form drag more than they aggravate skin friction,there can be a net drag reduction.Proper placement would require rigorous testing.

Just a quick note,the belly pan on the new Ford GT is dimpled.

That was an 11% improvement in mileage from the dimples.

Just as a point of interest i have experimented a wee bit with dimpling on the intake manifold port surfaces on a carbureted V8 engine ,and found a reduction in emissions of about 10%.This was years ago and wasn't worth writing home about.But there was an effect.

Zipp has done extensive wind tunnel research over the years. The fastest bicycle wheels on the planet are dimpled, does this advantage transfer to cars highway speeds? I was told years ago that a tennis ball will go faster with the fuzz on it than without it, seems like you want a "fuzzy" (or dimpled) surface for optimum drag reduction at speeds most of us encounter on the road.http://i934.photobucket.com/albums/a...L_Zipp_808.jpg

[QUOTE=Major Puffer;168373]Zipp has done extensive wind tunnel research over the years. The fastest bicycle wheels on the planet are dimpled, does this advantage transfer to cars highway speeds? I was told years ago that a tennis ball will go faster with the fuzz on it than without it, seems like you want a "fuzzy" (or dimpled) surface for optimum drag reduction at speeds most of us encounter on the road.http://i934.photobucket.com/albums/a...L_Zipp_808.jpg[ /QUOTE] How about i take a tennis ball , flow test it on my cylinder head flow bench,then give it a shave and flow it again .Should give us an indication as to what is going on.

I don't know if you're being serious and I have no idea what a flow test involves. I have an engine that I spent way too much money on, and when I asked the mechanic if he was going to polish the ports till they were mirror-like he said, "not quite that shiny, you want a little swirl as the mixture flows" or something like that. This is the theory behind the various rip-off devices you used to be able to put in your intake somewhere to "boost milage by XX %". 10 percent seems significant to me, wouldn't it increase milage a bit?

How about those cycling helmets that have the dimples, anyone have any first hand knowledge on how they work?

Brian

http://autobus.cyclingnews.com/photo...perleggera.jpg

The dimples on golf balls were discovered almost by accident about 200 years ago. Smooth golf balls fly erratically, something you will see on the driving range when they get worn down.

The first golf balls were like little baseballs and very time consuming to produce ( called featheries) they were very similar in construction to tiny baseballs but packed with feathers, with a leather cover stitched together.

Then they started casting them out of gutta percha, a primitive type of plastic. At first they were smooth, but it was soon discovered that when the surface got scratched up they were more controllable, so they eventually became dimpled as the were cast.

The spin imparted to a golf ball and the dimples create pressure areas below in front and behind at the top of the ball. When the axis of that spin is truly horizontal the flight of the golf ball is perfectly straight on a windless day. When the axes is tilted relative to the ground the ball will turn, in flight, in the direction of the lower side of the axis. This is a slice or a hook depending on the angle of the axis.

I wonder if anyone here has measured the fuel economy of their car after it was nailed in a hail storm, which would (under certain circumstances) create a consistent dimpling of the surface of the sheet metal, at least on the top of the vehicle.

The turbulent wake behind smooth round or tubular object oscillates behind the object and creates more drag than the same wake when it is disturbed by dimpling.

I remember the skin of most sharks is so rough it will literally shred your flesh if you rub up against them.

Another thing to consider is the steps in a planing hull that reduce the surface friction in high speed watercraft.

Not my specialty (aerodynamics) so don't be too hard on my statements if they contain significant flaws.

regards
Mech

New VW Golf and Polo have underbody panel with "golfball efect" ...

Got pics? I've had no luck on Google.

How big dimples? How far apart?

In other words, ~3" wide X ~1/2" deep dimples like on Mythbusters car, or tiny ones like on a regular golf ball?

Dimples probably need to be as uniform as possible, perhaps made out of bamboo?

...actually if one has those particular resources...could prolly DIY-it, into something functional..

I dunno, about the size...i would bet, bigger...b/c of the size of the object...not sure either..

I don't think they proved anything of the sort. Please read this thread to understand why you should be skeptical of the results of that particular experiment: http://ecomodder.com/forum/showthrea...oct-10658.html

+1

I do not even understand where the concept comes from. It makes no sense what so ever. As smooth as our eyes can see...it is still a golf ball micronically. Dispersing frictions, needs the golf ball...but as smooth as we can get it...right down to micronic bumps...increasing every bit of surface to have a function evenly...this equals tight boundaries, less friction..so very simple.

get it?

it was also about the "hail damaged" car gets better gas mileage...

I have not read, anywhere that turbulent waves cannot be on a vehicle w/dimples...if you understand what I am saying....worded weird..

I cannot question, scientific process... when i saw it take place....w/positive results...there is no other explanation...if there is...then they would be required to apologize on national television...B/c they have millions of viewers.....and since auto-makers are implementing this, already...And I know they aren't just doing it for the novelty..

___Mythbusters themselves, were like, it's kinda' ugly...that was the only question, left open..

Ok, MetroMPG, thanks for the link...i'm collecting phrasings

Quote:

Originally Posted by wyatt it works on a golf ball is because the golf ball spins in the air and is not stabilized.

its just a different shape...a car is not any more stabilized..."not stabilized"---what is 'stabilized' object?... the greater portion of a car is above ground level...so is suspended in air, by 4 tires...still, the body travels via air...so the car, is in the same realm of unstabilized object.....

the Great Pyramids of Egypt...are stable, then?....or the Statue of Liberty, or Gateway Arch, is stablized....

The dimples make (at least round like) objects, traveling through air, more stable..

If it counts, the '98 Taurus, was my first car.:p

K

Here are a couple of interesting golfball effect links for your enjoyment. :)

MYTHBUSTERS prove golf ball dimple theory on cars works!!!

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

Brian

Nope, sorry.

Another car with golfball effect is VW Passat 1.6 TDi BlueMotion.

Search is your friend:

http://ecomodder.com/forum/showthrea...aims-8321.html

So, obviously, it needs bigger dimples... Those look like negligible dimples.....lol..After reading the link
Fastskinz Dimpled Golf Ball Fuel Economy - 430-mile 2009 Ford Flex vs Ford Flex Aero Test - Popular Mechanics

From the link: Mythbuster's dimples were made into a thick layer of clay and were much more to scale with a golf ball dimple, and in fact, the dimples in this vinyl wrap are so small and not a gradual shape anyway, so not sure why anyone would think this would work.

So the vinyl wrap thing...only works over land-speed record speeds..and only works to improve mph, not mpg...at top speeds..

cool thanks

top speeds
 

If they worked,they would work at any speed from 20-mph,up to 250 mph after which for us it doesn't matter what they do.

Hey guys,

In 2,004 I read the Popular Science article about Somender Singh grinding grooves in engines. The picture showed him and the exterior of one of his cars. The caption explained that it had golfball dimples. It seems like everyone focused on the engines. On another site someone suggested that the dimples worked like vortex generators. Aerohead, I know that you hate those. I believe that you say that they are band-aids for sloppy aero, although dimples would be far better in a crosswind, right?

Great comments! Dimples are for spinning Beetles!

I do remember a picture in Popular Science around the same time of a new tin can design. It had a dimpled design that made it stronger, allowing thinner metal.

There are sound reasons for dimples on golf balls. The same conditions very rarely occur on cars, and usually only over a small area in a specific crosswind. There is no panacea, or even a two-day course for a master's in streamlining.

I remember seeing informercials for "The Tornado," reading it, and coming to the conclusion that a water bottle was a poor model for an engine. I imagine that golfballs are also poor models for cars. What do you think about Major Puffer's post?

Those rims make some sense. With the tire in front, the dimples make no difference, since any tread, and the tire-rim interface are boundary-layer turbulators. At the back of the wheel, with the rim leading, the thicker boundary layer may close easier behind the rounded tire shape. Maybe. There is still turbulence from other leading parts to do that job much of the time in the real world. And dimples can work to confuse both customers and competition, if not the producer as well. Bicyle riders are also notorious for riding faster if they only think that new parts are helping.

Dimples on a car would work great if cars were spherical. :D

They may well work on rounded areas on the rear of a car though, to help the air make the corner and reduce the wake, as they do on golf balls.

A separation-ridge is probably less awkward though ;)