Everyone knows that the little dimples in a Golf ball reduce drag,so the ball will travel further.Has anyone seen this applied to a car at Bonneville?I'm sure when you get going real fast,the air reacts differently.But for those under,let's say 200 mph,why wouldn't this work?
[ QUOTE ] Thought of that at the Dentist today. [/ QUOTE ] What type of gas were they givin ya? I gotta dentist appt soon and want some too! Rat..
If you watched the Tour de France, the Limar company from Europe outfitted several pro teams using this feature on Aero helmets used in the time trials.
you gotta remember that a golf ball is also spinning alot when it is flying down the fairway. I thought i heard that the dimples were for the air to be "scooped" from the front of the ball around to the back or wherever. Also, that it adds to the stability when this happens
fordiac is right. The dimple design has more to do with spin and the fact that the ball is round. It is more about breaking the wind in front of the round ball. More likely to have use for the VW guys. The straight, slick sides of a lakes or drag car drag less than dimples.
From sciencenetlinks.com [ QUOTE ] Golf Ball Dimples We asked aerospace engineer Bob Thurman. He designs golf balls for Wilson Sporting Goods in Humboldt, Tennessee. Thurman: The dimples are there to reduce the aerodynamic drag, that would be acting on the ball if it were entirely smooth. He explains that when a smooth ball sails through the air, it leaves a big pocket of low-pressure air in its wake. That creates drag, which slows it down. Thurman: So if you can make that wake smaller, then the pressure differential goes down. So the drag force is actually reduced. The dimples do this by creating turbulence in the air around the ball. That forces the air to hug the ball more closely. So instead of flowing past it, the air follows the curvature of the ball around to the back. The result is a smaller wake, and less drag. [/ QUOTE ] Since the boundry layer is moving slower than vehicle speed,I'm thinking that surfsce friction is less important than reducing trailing vortexes. The pictures a couple days ago of the sand coated bowling ball experiment seem to support this.
Actually, the louvers on the back of a roadster, or the little triangle shaped splitters on the trailing edge of the lakesters and streamlines create a low drag turbulance to lower the drag on the car.
Something that Thurman didn't mention, is LIFT. If you look at how an airplane wing works, you have a high and low pressure differential, drag... etc. The air going over the top of the wing creates a lower pressure, as it p***es, and actually lifts the wing. The air under the wing doesn't support it, like a surfboard on water. I think even a small bit of lift on a car at 200-300 mph would be a bad thing. Lift would create instability, by taking weight off the tires, and even the slightest cross wind would move it off it's course. For example... roll a penny across the floor, and blow it from the side. It'll move off of it's path pretty easily. Now try the same with a bowling ball. So, unless you're driving perfectly straight into the wind, you'd be asking for trouble by reducing the weight put to the ground. If you dimpled the whole car, the pressure differential might change from side to side, and pull you off course. I don't know how much would be too much, but I think I'd want a little downforce instead. I'm sure there's alot more to it than this, like the fact that cars are long and thin, as opposed to being round... and blah blah blah, so drag can be reduced by aerodynamics, rather than lift. Maybe I picked a bad day to quit sniffing glue. JOE
[ QUOTE ] Something that Thurman didn't mention, is LIFT. If you look at how an airplane wing works, you have a high and low pressure differential, drag... etc. The air going over the top of the wing creates a lower pressure, as it p***es, and actually lifts the wing. The air under the wing doesn't support it, like a surfboard on water. [/ QUOTE ] Yes it does, if you want to look at it that way. I know it's commonly called LIFT but I prefer to think that if I have a low pressure on one side of a "plane" and high pressure on the other, the high pressure is going to try to overcome the low pressure by pushing the plane toward the low pressure, In the case of an airplane wing, that's usually up. In the case of a F1 race car front and rear inverted wings, it's down. If a low pressure "****ed" things into the air all we would have to do is toss our trash into the air and it would be ****ed into outer space by the vaccuum of space. You have a low pressure on top of the airfoil and a relatively lower pressure on the bottom. look at it as the same as holding a piece of paper in front of your shop air hose and blasting one side of it...the low pressure side didn't "****" the piece of paper across the garage, did it? A venturi in a carburetor is a type of "airfoil" rolled up into a tubular shape. It works by lowering the air pressure inside the venturi relative to the outside air and then the higher air pressure on the surface of the gas in the float bowl pushes the gas to the lower pressure void area in the venturi. If the venturi was "****ing" the gas then it wouldn't be affected by al***ude changes. Al***ude lowers the air pressure on the gas in the float bowl, so it doesn't push the gas with as much pressure, so you run lean. Then there's all the exceptions to all the theories... read some of them here. http://science.howstuffworks.com/airplane2.htm I look at belly tanks and I see what amounts to a wingless lifting body. They have always been hard to push really fast, probably because they loose traction. Maybe if they were just the bottom half of the tank and flat on top they would work like an inverted airfoil and have increased downforce at speed instead of decreased. I'm not much of a golfer (only played twice) but I bet the amount the ball spins depends on which iron is used and a flat #1 driver isn't going to spin it if you hit it square, I wouldn't think anyway.... Was that enough Midnight Rambler?
I brought up the dimples before. And I think it was on the louver thread. What I remember being said was that it takes different sized dimples to react properly to a given speed or something odd like that. The thought came from something I heard years ago somewhere about major league baseball experimenting with dimpled bats to increase bat speed - but ball sports don't really interest me at all so who cares. After seeing the pictures of the bowling ball with sand glued experiment I thought for moment what a surface like that would do to airflow. Rust and mild pitting may not be such a bad thing.
[ QUOTE ] The air under the wing doesn't support it, like a surfboard on water. [/ QUOTE ] I was going to jump in here, but the good Doctor covered it quite well. Couple of other things you can think about, there are airfoils - the shape of the wing when viewed from the end or put another way, viewing the chord shape - that are symmetrical. Used on aerobatic aircraft although most of those aren't completely symmetrical. The symmetrical airfoils also used on model aircraft that compete in the stunt cl***ification. What makes the symmetrical wing generate lift is the angle of attack. Lift is generated on the bottom part of the wing as well as a percentage of lift is generated on top of the wing. Airfoils are usually chosen for the speed range they will operate in which explains the undercambered wing of the sailplanes and the flat bottomed wing of most other aircraft. You can do a small experiment that will show the validity of the angle of attack theory. Hold your hand out of the window of a car rolling along at highway speed. First, in a neutral position. Then turn it slightly upward so the palm is exposed to the oncoming airflow. The most amount of force you will feel will be on the palm side as that's were the most amount of lift is generated. You can duplicate the stall characteristics of a wing somewhat by turning your hand upward to the point where it no longer cuts through the air generating lift, but the air grabs it and tries to push it back. Not quite the cl***ic example of stall, but you can see that lift per se is no longer generated. For aircraft, the stall point of most wings is right around the 16 degree mark. A sailboats sails are airfoils as well. They generate force vectors on the windward side and lift is generated on the lee side. The trick with the sailboat is to have more force vectors generated in a forward direction than to the rear. ***uming we are beating to windward and not running before the wind. All a sailboat sail is -in most cases - is a severely undercambered low speed wing. Far as golf balls go, I'll go along with the wake minimalization generated by the dimples and add that somewhere along the line I read that a golf ball comes off the club face of a driver - wielded by a player that can knock drives out there about 250 yards or so - at 250 mph. Your distance may vary....
There are quite a few reports about early aerodynamics and some flow interuption experiments, as well as the reports on the original experiments that led to the NACA duct on the National Advisory Committee for Aeronautics (NACA) server. This is what eventually became NASA. http://naca.larc.nasa.gov/
in the early 70's i think, there was some experimentation of using vinyl roofs on nascar cars. don't remember how the theory actually played out, but they apparantly failed to consider how to keep the vinyl stuck on at high speeds.
[ QUOTE ] Why would anyone want a car that would slice to the right? [/ QUOTE ] Then again, if it was a ****** it might be fun.
[ QUOTE ] I look at belly tanks and I see what amounts to a wingless lifting body. They have always been hard to push really fast, probably because they loose traction. Maybe if they were just the bottom half of the tank and flat on top they would work like an inverted airfoil and have increased downforce at speed instead of decreased. [/ QUOTE ] Another part of the problem is the large amount of drag caused by the exposed wheels,and how the wake off the wheels reacts with the air on the body. Small amounts of down force could easily be generated by wrapping the exposed axles in an air foil shape.Varying the angle of attack would adjust the amount of downforce,yet produce less drag than an unfaired(round)axle by reducing the trailing vortexes. If side skirts were added to a typical belly tank,similar to the old F1 cars without touching the ground,that would help control the airflow under the tank and the venturi effect would be stronger than that on the top,creating downforce.It might be possible to vary the angle of attatck of a belly tank to influence downforce without crating excess drag. Maybe we can get Carps to explain to us how ground effects works with a flat bottom F1 car.
I saw this do***enary on 'dambusters' one, during WWII the brits planned on busting all these dams that provided Germany with I dunno how many % of all it's electricity, to do that they developed these giant golfballs full of explosives, I think they used the dimples to give 'em spin, so when they would hit the water they'd bounce on the water 'till they hit the dam, then sank till all the way to the bottom where the pressure would sett 'em off, goodbye dam, and 9 months later, hello baby-boom
The EAA published a huge article on these "Dimples" or "Ribblets" and did dyno tests on various components such as leading edges of props, wings and fuselages with significant results to drag co-efficiencies. The results were significant enough to incorporate some manufacturers to utilize this design on some of their components. I've seen that the World Cup Sail racers use "Ribblets" on their hulls to reduce the parasitic drag of their vessels as well! Who knows..., Dented cars = fast cars...! If each dent equals 5 mph..., my car will do 1,000 mph..., Look out Chuck Yaeger...!! Mark
How would you adjust the airfoil while going down the track to keep the force as desired? Would it need to be computer controlled or could you do it manually? I can imagine a specific rate spring that changes the angle of the wing at a certain downforce. Now how do you make the whole bellytank change its angle of attack? TZ As I understand the dimples on the underside of my knee-board are ther to stabalize it a little
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