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

diggy

Incidentally the study by Popular Mechanics looks at dimples that are ~5mm, while the Myth Busters looked at dimples ~75mm (just guessing, estimating 3 inches as approximately the the size of the tennis ball they used). I googled a picture of what the Fastskin's dimples look like and found this. http://www.google.com/imgres?imgurl=...1t:429,r:2,s:0

I'm not saying the MythBusters got it right, although it looked reasonably convincing, but its not clear to me that the Popular Mechanics example disproves MythBusters results.

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.

Bararontok

It is a good start.

Cyrus

I have no idea what this is supposed to mean or imply.

dtango

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!

mugaliens

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...

john.phillip

mugaliens:

Insects versus birds: the great divide

http://www.citeulike.org/group/918/article/790560

mugaliens

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.

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.

HowlerMonkey

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.

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.

claytonh4

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!

boneh3ad

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.