Mythbusters "tests" efficiency of dimples vs. smooth, and clean vs. muddy car
 

Admin note: 2 threads were started on this topic. The other one is here: http://ecomodder.com/forum/showthrea...les-10718.html

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I don't watch the show regularly, but this one might be worth tuning in for the entertainment factor.

Also.. don't they have it backward? Isn't the common myth that the clean car gets better mileage?

Hmm, I can imagine having enough mud buildup in the wheelwells to reduce the distance between them and the wheels. Or mud sticking to the rear of the car, drying and hardening, layer on layer, in the shape of a Kammback extension. But by the time either of these would have a noticeable aero effect, the weight penalty would start to be a pain.

I will be watching it. I love mythbusters even tho they seem to be obsesed with explosions.

I love Mythbusters BECAUSE they seem to be obsesed with explosions... hehehee

I think the muddy/clean thing is like the golfball dimple theory. Sometimes rough is better than smooth. I'm actually looking forward to this one...

If it works you could cover your car with rocker guard or ceiling texture and paint over it. Might look kind of cool.

They are supposed to be "dimpling" a car, I think.

I could just see them firing golf balls at a car to get the dimples.

SOunds like a hail storm car to me! :)

Dave

I'm sure it'll be entertaining and worth watching.

I predict their conclusion will be "we can not detect a fuel economy difference between these two cars".

It would take a pretty extreme setup to do aerodynamic testing sensitive enough to detect mud. A wind tunnel would do it, but they wouldn't take a car to a wind tunnel for a simple myth like this. Short of that, you'd need high speed bidirectional coastdown testing on a totally windless day. Even if you accounted for airspeed, small crosswinds would skew your results beyond utility.

As to the effects of mud: It tends to increase the car's frontal area, obviously. Cakes of mud on streamlined surfaces will increase your Cd, while cakes of mud in your eddies will tend to decrease your Cd. A muddy truck with its panel gaps and hood cowl filled with mud will probably get better gas mileage, but unless your aeromodded Metro gets a teardrop-shaped tail made of mud, it's likely to get slightly worse gas mileage when muddy.

New myth - it stems from the golf ball conundrum.

I can't imagine what type of thoughtless people frequent the MB forums to come up with/perpetuate this ****.

Golf Balls
 

It's always been my understanding (and that of my college professors) that dimpling an entire object serves no purpose if that object will not be changing orientation. The reason that it works on a golf ball is because the golf ball spins in the air and is not stabilized. I have seen pictures of bowling balls being dropped into some thick liquid, and they got the same effect by putting a simple wire to trip the boundary layer toward the front of the ball. Before you go dimpling the entire surface of an automobile, consider strategically placing something to trip the boundary layer.

I was going to post this but I figured someone would get to it before me


From what I saw, theyre going to load up some kind of paint gun and spray mud on it
then they stamp it with a "golf ball" pattern

theyll also probably be covering up gaps and making some partial grill block with caked up mud

I just set my TiVo to record it. :D

I predict the same thing - no detectable difference from a clean vehicle to a "plausibly" muddy one.

I also predict that where it will get most interesting and entertaining is when they test the "implausibly" muddy vehicle at the end to force some result to show up.

Maybe they'll just blow it up?

I keep my cars clean and waxed regularly as well as inside the garage.

I always wondered if the rough shark skin type surface would make a difference.

Golf ball dimples are more for predictable flight paths. Hit a smooth golf ball and its flight path is very erratic.

regards
Mech

VW set a 24 hour distance record with a very streamlined diesel car ~20 years ago and after each fuel stop, it gained several MPH due to the crew removing all the bugs from the nose. The speed slowly declined through each segment until the next 'scrub' cycle...

Source?

Welcome to EM

Maybe someone more adept at Googling than I can narrow down the results below the half-million mark, but the reference at the bottom of this article: http://media.gm.com/de/opel/de/downl..._Speedster.doc
is the best I could manage. I think the writeup was in Car & Driver in 1977.

One way I could see bugs (or mud) significantly affecting aerodynamic performance is if the vehicle is designed to preserve laminar flow along its whole length. Think smooth, seamless HPV speed racers, most solar race vehicles, gliders.

Regular road-going cars don't have laminar flow much beyond the nose.

-but then the nose is the only place the bugs would be deposited...

The less surface friction the less overall drag.

That is what I think they will find.

Sadly the more slippery you make the car by reducing all drag factors, the lower the efficiency of the engine on the BSFC map.

Offsetting factors will probably make it close to a wash.

Just my opinion.

regards
Mech

Wash-n-wax it for best fe- it promotes laminar flow!

No! Wait! Put Skinz and vortex generators on it for best fe- they promote "helpful, controlled" turbulence!

I'm so confused. :confused:

What i find laughable is that they stubbornly refuse to test braking distances at higher tire pressures. It would be a really easy test to do for them. Instead i see then going to great lengths to prove/disprove this and that. Yeah the explosions are cool and so are a good few of their experiments. But i still don't see any mythbusters tire pressure testing.

As for dirty vs clean......hardly measurable i'd say. There might be some difference found if they do the exact same test over and over all day long and get a good average. But i bet it'll be tiny, if any at all. Grumble....grumble...moan......

ollie

Their concern with tire pressure testing is the possible long term effects of higher pressures, which they can't prove or disprove. If they were to note that higher tire pressures could even remotely be safer, then something happens to some asshole who takes the advice and runs them all the time, they're in the legal firing range, and up ****'s creek without knee waders.

You have to think about things from a legal standpoint, not what's really true.

I think I have said this, it's entertainment.

not as entertaining since Kari had her baby

she was mine

http://t0.gstatic.com/images?q=tbn:I...SmileyFace.jpg

Oh she had it? I was mad that she got married, and he's ugly too. :(

They already failed so hard, it's only 1 minute in.

True! Not counting, of course, the windshield. :)

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Looking forward to the play by play of the show. It's not airing on the Canadian Discovery Channel ... today anyway.

24 mpg for "dirty" car
26 mpg for "clean" car

They used a Taurus car, but used a really crappy way to measure fuel economy.

They just failed, AGAIN!

Darin -
You'll be able to watch it I think tomorrow on Discovery.com

I don't foresee any explosions in this one.

11% improvement on gas mileage with a dimpled car. :rolleyes:

oh geez, pretty soon we are going to see clay molding golf ball dimple kits on this forum claiming 11% gains "AS SEEN ON MYTHBUSTERS"..... LOL

Oh my. :D

Now I have to see it.

LOL, lets see $3k for hail damage pays for the car and I get 11% better mileage. Guess I have to park it outside in the next hailstorm.

regards
Mech

So what testing technique did they use? I remember for the tailgate up/down one they totally emptied the tanks and put 1gal in each of two brand new identical trucks and just drove on the freeway with cruise control until they ran out of gas...I wonder if "drafting" drag differences caused any problems in that episode (I'd have to go back and watch it again).

So much fail in testing.

Filled can full of gas, weighed it, and put it in the trunk. Ran car up to 65 on car's tank. Flipped switch at starting line that transferred where the engine was getting gas. (from the gas tank to the baby tank in the trunk) and then shut it off after a 1 mile run at 65. Then re-weighed it and did the math from there.