Half a croissant, on a plate, with a sign in front of it saying '50c'
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Dimpled car

If it works for golf balls...
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(+6, -1)
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If the dimples on a golf ball reduce drag, why hasn't anyone designed a car with dimples? I know it would look silly at first, but wouldn't it save a significant ammount of fuel?
andrewkorbel, Aug 05 2002

golf ball dimples reduce drag http://van.hep.uiuc.../20020510112102.htm
comments on cars in last paragraph [FarmerJohn, Aug 05 2002, last modified Oct 04 2004]

Another "rough = efficient" car idea. http://www.halfbake...in_20car_20covering
[angel, Aug 05 2002, last modified Oct 04 2004]

Father Teds "dimpled car" http://www.father-t...k/pages/eguide.html
Seris 2 episode 2. [sufc, Oct 04 2004]

Brabham Fan Car of Swedish GP 1978 http://8w.forix.com/fancar.html
It won by 34.6 secs [FloridaManatee, Oct 04 2004]

Brabham Fan Car Photos http://www.amazing4...46_Features_Eng.htm
[FloridaManatee, Oct 04 2004]

(?) Aerodynamic sportswear http://home1.gte.ne...ail/RibletFlow.html
Stuff other than dimpling that makes you go faster [timo, Oct 04 2004]

Speed skiing http://www.speedski.com/
[timo, Oct 04 2004]

Lexus LS430 http://www.familyca...exusLS430/Index.htm
This car has everything...I am talking e v e r y t h i n g ! Including a dimpled undercarriage. [Klaatu, Oct 04 2004]

Good explanation of the dimpled effect of golf balls http://www.aerospac...ynamics/q0215.shtml
[Ling, Jun 23 2008]

...and so it came to pass. http://i.gizmodo.co...s-they-save-you-gas
[2 fries shy of a happy meal, Jan 21 2009]

It has dimples and spins, too Virtually_20Spiraling_20Automobile
a more confusticated approach. [daseva, Jan 22 2009]


       I think that the dimples on a golf ball only reduce drag because the ball is spinning (slowly for a distance shot, more quickly for accuracy). A static dimple would probably increase turbulence.
angel, Aug 05 2002

       It seems increasing turbulent flow in the boundry layer (the slow moving air nearest the ball) with dimples reduces drag. The spinning increases lift giving a total of up to four times longer travel.
FarmerJohn, Aug 05 2002

       Yeah, I was going to offer that service to ak.
DrCurry, Aug 05 2002

       Homer: "Those are speed-holes, Flan-diddly-anders"
Mr Burns, Aug 05 2002

       Dimpled car? Ball peen hammer? Anyone recall the episode of Father Ted where they raffled the car...??
SteveAdams, Aug 06 2002

       Angle is wrong (sorry), the dimples do reduce drag, and this has actually been used on high speed airplanes to reduce heat build up due to friction and drag. The minute dimples were achived through applying a special paint to the planes surface... done about 10 years ago.
Adyonline, Nov 10 2002

       The dimpled effect has also been proven successful for the Japanese women's swim team. The women's suits had tiny "beads" of silicon material (I believe it was silicon) protruding from the surface. Though these were beads and not dimples, it produced the same effect. The result "cut" the waters drag currents over what a regular suit and body creates substantially.
hollajam, Nov 10 2002

       The Youth of America affirms this to be: dope.
Admiral Hackbar, Nov 10 2002

       Post hailstorm
bristolz, Nov 10 2002

       Isn't that what they said about you, too, AH?
yamahito, Nov 10 2002

       The dimples on a golf ball create lift when the ball has a backspin--letting the ball go higher, and therefore farther. Dimples (to some extent--based on the scale of the dimples) break up laminar flow. Laminar flow is the most efficient airflow on a large scale for penetration (though not neccesarily true when generating lift). If you were making a car that flys, then dimples might help. Since most cars are designed to generate a certain amount of downforce (opposite of lift), in order to keep the car on the road, dimples would obviously be a poor idea. Technical explanation: Dimples create vorticies. Vorticies create drag. This is good on the top side of a lifting surface (or on a spinning lifting surface). Many modern aircraft add efficiency by placing vortex generators on top of the leading edge of an airfoil. The bottom surface always stays as smooth as possible to reduce drag and raise air pressure. On a car, you want more air pressure pressing the car down, so the top surface is smooth (notice how auto makers often leave engine, transmission, exhaust, and suspension components exposed under the car to disrupt laminar flow, create drag, and more importantly, downforce).
neverbeaten, May 13 2003

       I'm done with this chewing gum. Any takers?
Cedar Park, May 14 2003

       The dimples do reduce drag. But let's put it in context. A gold ball is the size of a golf ball and is rotating and a car isn't. Also, sharks and Japanese swimmers operate in water where viscous and surface effects are magnified.   

       That is to say, the aerodynamic considerations for a golf ball or a swimsuit will differ from that of a car. True, you might be able to reduce surface drag by breaking laminar flow, but you would also trade off parasitic drag and handling.   

       An important part of the design of cars is to ensure sufficient downforce to improve traction without an inertial penalty.   

       Nevertheless, modern cars designed with increasingly low drag coefficients. There is still much efficiency to be wrung out of the overall form of the car before fine-tuning with complex skins (form sculpting is not a luxury golf balls and athletes have).   

       Also remember that airflow patterns change at differing velocities, and in different conditions of humidity, rain, cross wind, etc., so you may have a hard job tuning your dimple pattern. No doubt the pattern would need to differ over different sections of the car's body too. Imagine the associated incremental production and energy costs.   

       If we are to work on laminar flow, rather than producing a dimpled skin which is difficult to clean, maintain and repair, you might consider leading edge turbulets, etc. Active tuning of positions or these tabs might prove effective under different conditions.   

       Personally, If I were a designer tasked with improving fuel efficiency, I'd redesign the car's form, making it lower and narrower (smaller frontal cross section and more stable), and use high speed low inertia fans to develop a vacuum between the car and the road's surface instead of using large spoilers, which have high associated drag. Formula 1 cars used this briefly before it was banned (AFAIK it was too effective at creating down force).   

       Another aerodynamic improvement that would likely be more effective than dimpling would be a variable-geometry skirt. The skirt would rise at the front, rear and between the wheels at low speeds, so as to clear speedbumps, ramps and bumps, but lower close to the the ground at high speed to maximise downforce.
FloridaManatee, May 14 2003

       This idea (whether sound or no) was baked by Red Green a couple years ago. He dimpled a car on The Handyman's Corner to make it go faster.
k_sra, May 14 2003

       The explanations of dimples on golf balls has been descriptive, if somewhat inaccurate. Golf ball dimples do not create lift, nor do they create vortices. The dimples DO create turbulence. While laminar flow does have the lowest boundary layer losses, it is also extremely easy to disrupt by unfavorable pressure changes. On a smooth sphere, the boundary layer will often separate slightly ahead of the center of the ball, leaving a wide wake. By putting dimples on a golf ball, turbulence is added to the boundary layer. This turbulence allows the remainder of the flowfield to follow the surface of the ball for a greater distance, i.e. it stays attached until farther back on the ball, leaving a narrower wake. So, while skin friction drag is increased by the dimples, the form drag is decreased more, so the overall drag decreases.   

       The lift comes from the spinning of the ball.Even a smooth ball will show this effect to a small degree. Since the dimples do increase skin friction drag, they enhance the effect that spinning has on the airflow. A ball with backspin will have lift, while a ball with topspin will have negative lift, i.e. it will drop faster. A ball with sidespin will have a lift vector pointed somewhere other than vertical, as in a slice or hook.   

       Dimples may help reduce drag on a car if very carefully placed, but golf balls are only dimpled like they are to keep the pattern fairly uniform regardless of orientation. On an aerodynamic body that has a fixed orientation to the airstream, a well-placed trip strip or vortex generator would likely yield even more benefit.
Freefall, Dec 12 2003

       I seem to remember dimpled suits for speed skiers, the ones that go really fast in a straight line (yep, found link).   

       <On a car, you want more air pressure pressing the car down, so the top surface is smooth (notice how auto makers often leave engine, transmission, exhaust, and suspension components exposed under the car to disrupt laminar flow, create drag, and more importantly, downforce).>-neverbeaten   

       Hmm, I think very few cars actually create downforce, most aerodynamic aids just reduce the lift. And slowing down the air under the car surely doesn't create downforce? Look at F1 cars, and now some road cars (Ferraris, Nissan Skyline)- smooth as a baby's behind underneath, all in the name of downforce?
timo, Jan 20 2004

       It seems Lexus has been reading ideas on the HB. Read about the Lexus LS430 <link>
Klaatu, Jan 21 2004

       Forget about the outside surface of the car, put the dimples on the inside of the intake manifold! This is where laminar flow has a most deleterious effect.
ronk, May 12 2004

       HJS was on to this one way before any of us.   

       Homer: "Hey, what are all these holes?" (points at bullet holes in car hood) Car salesmen: "These are speed holes. They make the car go faster." Homer (impressed): "Oh yeah, speed holes."
Giblet, Jan 08 2005

       Up at the top of the page, [Mr Burns] was onto that way before you, too...
david_scothern, Jan 10 2005

       A project! Same chassis with interchangable "car". I envision the chassis to use skateboard wheels.   

       This was originally going to be an anno for the above linked idea, but it is redundant with this preceding one. So, anyway, my anno.   

       The "car" is a shape. Different shapes can be mounted. They all weigh the same amount (1 kg?) The mounting device extends laterally and the "car" can be spun in place with an electric drill. The cars is then rolled down the track, pinewood derby style, and the speed clocked.   

       Do different shapes confer different speeds? Does spin matter? More for some shapes or others? And what about those dimples?
bungston, Jun 20 2008

       //Do different shapes confer different speeds? Does spin matter? More for some shapes or others? And what about those dimples?//   

       1. Different shapes matter in the same way that different engines matter.   

       2. More for some shapes... yes F1 vs Black Cab.   

       3. Dimples create a "wing". This gives lift. Nothing to do with drag. Dimples on the underside rush towards the airflow creating the same effect as a faster airflow under the ball. Dimples on the top side have a relatively slower pace against the "wind". Same surface area. Equals lift. Same as a wing. You can either change the surface area exposed to a common "wind" or you can change the "wind" to a common shape. Same thing, only different. Magnus just got the kudos, because he was the first to notice it.
4whom, Jun 20 2008

       /Dimples create a "wing". This gives lift. Nothing to do with drag/   

       Dimples on a golf ball decrease drag at high Reynolds numbers by inducing turbulence in the boundary layer, which delays flow separation and therefore makes for a smaller wake. This smaller wake gives a reduction in pressure drag, albeit at the expense of an increase in skin friction (due to the dimples vs. smooth surface). At high Reynolds numbers, the decrease in pressure drag is a bigger saving than the increase in skin friction.   

       The golf ball needn't spin in order to take advantage of this. In fact, spinning, and the resultant Magnus effect, is probably detrimental to distance as the lift force must have a corresponing induced drag. The free lunch principle applies.   

       What's more, dimples are not required to take advantage of the Magnus effect. It works on smooth balls too, as air is somewhat viscous.   

       That dimples on a golf ball are there for reasons of spinning and lift is a common misconception, akin to gyroscopics being required to balance a bicycle, and water down a plughole spinning because of the Coriolis effect.
Texticle, Jun 24 2008

       To accomodate the necessity of spin, make your car like this <linky>.
daseva, Jan 22 2009

       /the necessity of spin/   

       There is no necessity. What [Texticle] said.
Texticle, Jan 22 2009

       Mythbusters put this to the test recently and it works!
xaviergisz, Oct 25 2009


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