Mythbusters discovers that dimples on your car saves fuel

O

Old Fatass

First time out of the vault
I know it's an episode a few months old. But I just watched it and I was baffled. So is chevy and toyota gonna start making these or what? lol

http://www.autoblog.com/2009/10/22/mythbusters-golf-ball-like-dimpling-mpg/


The Mythbusters must be closet car fans, because the hour-long show on the Discovery Channel seems to be producing more and more experiments involving automobiles than ever before. Their latest again involves fuel efficiency, this time testing if a dirty car is more fuel efficient than a clean one because of the golf ball-like dimpling effect of the dirt. Turns out dirt doesn't make a difference, but Adam and Jamie went one step further to test if covering a car in actual golf ball-like dimples would improve its fuel efficiency. According to cable's most crack scientists, yes, it will.

The show's team completely covered a last-gen Ford Taurus with modelers clay and figured out that it would achieve about 26 mpg at a constant 65 mph. They then went about adding over 1,000 dimples to the car's exterior. To keep the experiment consistent, all 1,082 dimples removed from the clay exterior were put in a box and set in the back seat so that the car would weigh exactly the same as before dimpling. The theory is that, like a golf ball, the dimples would reduce the car's drag through the air, thus allowing it to travel the same distance at the same speed using less fuel. The result? Over 29 mpg.

Follow the jump to watch the whole episode for yourself, though if you're only interested in watching the dimpled car do it's thing, skip ahead to about 40 minutes in.
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I know why that happens, and no, they're not. The costs and problems associated with the dimples don't outweigh the speed gain. And it's not really news.

It delays airflow separation by making the air turbulent Separation is a huge problem on non-aerodynamic surfaces such as a car and a golf ball.

If you want to know more details, ask me.
 
It delays airflow separation by making the air turbulent Separation is a huge problem on non-aerodynamic surfaces such as a car and a golf ball.

If you want to know more details, ask me.
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No i don't. I hated aircraft engineering school and i left that for good!

Buuut... woudln't the cost of adding dimples disappear in like, 5-10 years of using the car?
 
Well, I can't really be sure why they don't do it, only assume. So here's me "talking out of my ass", i.e making an educated guess:

For instance, making dimples all over the car probably reduce its crashworthiness. This is a structural engineering/material science problem. Cars are designed to crumple in a certain way when they crash. Making dimples increases the stress in that location, meaning the car will deform differently in a frontal collision. Then again, the shape of the insides is fairly important as well, so if it's negligible I can't tell.

There's the obvious design bit. Few customers would want a dimpled car, it looks kind of stupid. Why do people buy SUVs to get the groceries when they could buy a smaller car and save $$$ on fuel? I think similar principles apply, especially when the fuel gain is so negligible.
 
Maybe the size of the dimples woul matter. Cars tend to get smaller, more and more people care about the fact that fuel is expensive.

I've thought about the car's crash resilience... but maybe the dimples could be made out of paint or some other light layer.
 
The dimples have to be depressions. So you either need to make a second layer, like they did, or punch them into the car.
 
Well, people buy Renaults, so I don't see how there couldn't be a market for cars with dimples on them (if it would be feasible to construct them and sell them with 4. PROFIT!! of course). Slightly more pleasing to the eye in comparison I would say.

Seriously though, isn't it possible at least that it is in part our perception of what a car looks like that makes us think dimples look strange on one. It could just be something that takes a while to get used to seeing.

I for one wouldn't mind, if it didn't effect other properties of the car a lot. But then again, I own a Toyota Aygo.
 
A car could be made a lot more functional than it is today. Just sayin'. Aerodynamics are just the tip of the iceberg.

But even so, there's little interest, because it's a very established industry with specific design traditions that change slowly. Not to mention there's a shitload of other engineering limitations.

But hey, it's a business idea, so launch it: "our car saves 0,005% fuel compared to other makes!"

vw-1-liter-car.jpg
 
Didn't I see this episode quite a while back? Why bring this up now? It's technically feasible but completely ptless and pain in the arse to do. I don't think any savings you can make on the fuel is enough to pay for someone to sculpt your car by hand.
 
Many car bodies are plastic now. Setting aside aesthetic and tradition concerns changing the plastic mould to include dimples doesn't sound technically challenging to me. Altering the underlying body to accommodate the dimples may prove challenging, but hardly insurmountable.

And before we consider this the real question involves taking the dimples to the next level: Consider that varying the size of the dimples may alter the handling and efficiency characteristics further than was demonstrated in the show. A real next test would be to cover the same car with different size, distribution and orientations of dimples to see if the mileage gains can be further modified. I also wonder how dimpling would alter road handling characteristics.

For instance, according to the show, when they ran a model car through a dye tank to simulate airflow over the dimpled model the slipstream (separation?) collapsed more efficiently behind the car, presumably accounting for the increased mileage. Maybe by making larger/smaller/better/faster/cheaper dimples near the back of the car could achieve the same result with less overall dimplage? Maybe the opposite is true? Maybe incorporating a spoiler in the dimple plan would yield unanticipated benefits?

In all I'm intrigued whenever that episode is on, and would be very interested in anything that investigated this phenomenon more completely.
 
Slipstream isn't the same as flow separation.

There's a whole field concerning the aerodynamics of cars. As I said, today's cars aren't optimal from an aerodynamic point of view.
 
If the flow is laminar, you don't have to put anything in the slipstream. It's just there.

I think that spoilers, ailerons and all things like that, actually cause more drag and more fuel consumption, but add to better handling.
 
Blakut said:
I think that spoilers, ailerons and all things like that, actually cause more drag and more fuel consumption, but add to better handling.
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Yes, this is a big concern for designers of F1 chassis, where you need to maximize downforce in corners but minimize drag on the straights. I don't know how much drag you get in proportion to the downforce you gain from a spoiler on a road car though.

Are you in the vehicle engineering program at KTH, Victor, or are you just taking those kinds of courses anyway?
 
You can join in Murdoch, 's cool.

Are you at University of Minnesota, or do you work from an underground lair?
 
I work at a medical device firm in the Twin Cities, doing regulatory affairs stuff. I enjoy it much more than I probably should, I like the paperwork and protocol; does that make me a bad person? :question:
 
Murdoch likes to infect people with gonorrheoea and chlamydia for 'scientific purposes'.

Anyhow, the whole dimpled car shite is getting out of control. Less consumption isn't the only thing it causes. Way to go for onesided nonsense.
 
Paperwork...ugh...protocol....


only if by paperwork you mean lab notes and by protocol you mean some computer thingie...that can be more awesome...
 
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