# Using golf ball dimples to decrease vaccuum drag on motor vehicles and aircraft.

by Bararontok
Tags: aircraft, ball, decrease, dimples, drag, golf, motor, vaccuum, vehicles
 Sci Advisor PF Gold P: 2,241 On a side note, I've seen at least one production car with vortex generators very similar to ones used on airplanes; the Mitsubishi Lancer Evolution VIII. Whether they're helpful in terms of mileage, no idea.
 P: 298 It is a good start.
P: 4,780
 Quote by Bararontok It is a good start.
I have no idea what this is supposed to mean or imply.
 P: 43 Vortex generators on cars??? :) Cool idea as an aero enthusiast. As to it's usefulness in reducing drag to improve top speed performance and gas mileage? Hmmmm :). Here's a scholarly report from Mitsubishi on the topic: http://www.mitsubishi-motors.com/cor...004/16E_03.pdf They estimated for the Lancer that it reduced CD by .006. Given that car CD that I've seen listed between .30 to .25 a .006 improvement is roughly a 2% improvement. Given the velocities we drive our cars at I doubt that it could amount to much!
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 Quote by Cyrus In the case of a sphere, there is a sudden and dramatic drop in drag with the use of dimples for a certain Reynolds number. For low Re, dimples are worse, for high speed, dimples are better. In the case of an aerodynamic shape such as an aircraft or car, dimples do you no good - hence why they are not employed.
Exactly! And this based not only on the Reynolds number, but also on the shape. For example, the Reynolds number for a bullet is quite low, but we're not dimpling bullets for a reason, and that reason isn't that bullets are supersonic, as nearly all handgun bullets are subsonic.

Golfballs are a fairly special case, falling into that rare regime of both Reynolds number and shape where dimpling actually improves flight performance.

Interestingly, I find it odd why the wings of most birds are covered by turbulent feathers, as opposed to the beatle's fairly smooth sheets...

Hmm... I feel a study coming on...
 P: 93 mugaliens: Insects versus birds: the great divide http://www.citeulike.org/group/918/article/790560
 P: 595 Yes, thanks, John, and you're absolutely correct with respect to the world of micro-UAVs. They simply fly based much more in the Reynolds numbers of the birds and the bees than of anything approaching a meter or beyond. And yes, sharp leading edges and laminar flow combined with capitalizing on turbulent after-effects is the order of the day! I have a dynamically, self-learning and stabilized helo-toy I bought for $100. I occasionally demonstrate it for guests who are leading aerospace designers, and about half of them still bite off on my story that it's the latest model in the USAF arsenal and costs$200 thousand per copy. When I show them the sales ticket and they're agahst, I remind them the iPhone, iPad and iPod Touch have the same or better sensors, for less than \$300, and that the rest is simply programming, at which point they start to realize this technology no longer costs millions. Of course some of the spouses start fingering their jewels, as they become aware their corporate income-funded riches are about to dry up. As for me? Well, heck, I'm making a mint helping corporations figure out ways to do the same job for thousands of dollars these days that they used to pay millions of dollars for in yesteryear. These days we're at the point where we can re-create the flight of a dragonfly, if not hummingbird, though to be honest, my bet on any territorial flight still rests with the hummingbird. Here's another entry. The key is in advancements in inertial sensors and computational (computer programming) control. Aside from these two factors, we could have done this 50 years ago.
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 Quote by Cyrus I just watched the clip they did with the car, wow. Are you kidding me? That is not a valid test by any stretch of the imagination. They have so much crap that the basic aerodynamic shape of the car is altered to a significant degree. All they had to do was make a two models of a car with and without dimples and stick it into a wind tunnel. Bogus test, sorry.
Watch the whole episode. They did test models, both in a wind tunnel and in a water tunnel with die to look at flow. Both tests conducted at NASA JPL so they're definitely reliable. Both with positive results. In addition, they covered the car in smooth clay and tested it first. Then created the dimples and put the carved out pieces inside the car to compensate weight. They did 5 60mph 1mile long runs each, not beginning data collection until 60mph was achieved each time and stopping data collection at exactly 1 mile. Sounds like they covered all the variables to me.
 P: 276 If you scale up from a golf ball to a toyota prius, I'm curious how much the scale of the dimples would be to harness this..........or it doesn't scale.
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 Quote by claytonh4 Watch the whole episode. They did test models, both in a wind tunnel and in a water tunnel with die to look at flow. Both tests conducted at NASA JPL so they're definitely reliable. Both with positive results. In addition, they covered the car in smooth clay and tested it first. Then created the dimples and put the carved out pieces inside the car to compensate weight. They did 5 60mph 1mile long runs each, not beginning data collection until 60mph was achieved each time and stopping data collection at exactly 1 mile. Sounds like they covered all the variables to me.
Are you familiar with Reynolds number and how to properly scale wind tunnel tests. It is more than likely that they didn't properly scale because the Mythbusters almost never properly scale anything.

That driving test they did with and without dimples was not even remotely close to a well controlled experiment. What if the temperature changed a little and effected the air properties, what if the wind was blowing a little faster during one test than the other, what if the driver accelerated differently or spent some of the time driving at 61mph. Are speedometers really that accurate? (I have no idea) The power required to overcome air resistance goes up with velocity cubed! So a small change in velocity from the wind or driving at a different speed can have an impact. So no, they did not cover all of the variables. They never cover all of the variables.
P: 77
 Quote by RandomGuy88 Are you familiar with Reynolds number and how to properly scale wind tunnel tests. It is more than likely that they didn't properly scale because the Mythbusters almost never properly scale anything. That driving test they did with and without dimples was not even remotely close to a well controlled experiment. What if the temperature changed a little and effected the air properties, what if the wind was blowing a little faster during one test than the other, what if the driver accelerated differently or spent some of the time driving at 61mph. Are speedometers really that accurate? (I have no idea) The power required to overcome air resistance goes up with velocity cubed! So a small change in velocity from the wind or driving at a different speed can have an impact. So no, they did not cover all of the variables. They never cover all of the variables.
Well I can see your point about scale issues as well as temp. dif. and wind, etc., however the acceleration time was not included in the test. They accelerated on the reg. gas tank then switched over to their gas tank that was actually being measured when 60mph was achieved. The car was then put on cruise control for testing time. Yes there could be anomalies, but I was impressed in the testing of variable accountability. Again though, scale, wind, temp., humidity could all lead to false data... they should've used an indoor track!
 PF Gold P: 1,491 I have a lot of respect for the Mythbusters guys. They have done more to interest kids in this country in science and engineering than any government program has, that's for sure. That said, nothing they do in the show should be considered scientifically sound. They do sometimes get it right and they sometimes get some good results, but rarely do they take into account all variables or do a full analysis of anything. Take it for what it is: and entertainment program with a science bent.
 P: 298 The best way to compare the performance of a car body with golf ball dimples or vortex generators with a regular car body is to calculate or research the drag coefficients and the force and power produced by the vacuum drag and produce a table that will list all of these values for the three aerodynamic profiles to perform an accurate comparison. Of course other variables such as the cross-sectional area of the body and the weight of the body will have to be standardized for the comparison of performance factors to be accurate.
P: 137
the paper...
http://www.4g63.de/facts/vortexgenerator-evo-mitsu.pdf

 Quote by Mech_Engineer On a side note, I've seen at least one production car with vortex generators very similar to ones used on airplanes; the Mitsubishi Lancer Evolution VIII. Whether they're helpful in terms of mileage, no idea.

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