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

[wyatt]

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.

[alohaspirit]

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

[srortega]

I just set my TiVo to record it.

[MetroMPG]

Originally Posted by RobertSmalls

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 ...

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.

[Piwoslaw]

Originally Posted by MetroMPG

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?

[user removed]

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

[MadBill]

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...

[Christ]

Originally Posted by MadBill

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

[MadBill]

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.

[MetroMPG]

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.