Hexagonal Dimples as a way to improve aerodynamics

[SVOboy]

Search around here for airtabs, Darin (metrompg) did some aba testing and didn't get any of the miraculous results people tend to talk about...

[Palionu]

is there a decent solution for the rear roof? I searched various forums and haven't again found anything conclusive, I'll read that now when i find it.


Later:

Ok, I checked out that forum post with the airtabs, and there is a problem with it. A 2006 Corolla has a CD of .296, my car has the same CD as a new Volkswagen Beetle, .36. Now I have to find an article with either car tested.

[Cd]

How does dimpling help on a golf ball if the ball is spinning constantly ?

As far as dimples on automobiles, I notice that Lexus did a famous job of dimpling the LS430 underside, and to my surprise VW is still using dimpling on the undersides of their cars . There must be something to it, otherwise they wouldn't bother ( Lexus used the dimples as a PR stunt, and this may have been the actual reasoning behing the dimples, but why then is VW using them if they don't really work ? )

[Palionu]

Originally Posted by Cd

How does dimpling help on a golf ball if the ball is spinning constantly ?

As far as dimples on automobiles, I notice that Lexus did a famous job of dimpling the LS430 underside, and to my surprise VW is still using dimpling on the undersides of their cars . There must be something to it, otherwise they wouldn't bother ( Lexus used the dimples as a PR stunt, and this may have been the actual reasoning behing the dimples, but why then is VW using them if they don't really work ? )

The spinning of the ball has some effect but the important thing is that the dimples cause a surface layer of air which directs other air away from the surface, the greater the speed, the greater the effect.

I'll be back in a little bit, going to head out to Home Despot to look at aluminum sheeting to see if any of it is dimpled, I'll be back with the results of my search.


Update: No Aluminum sheeting aside from some dimpled 4" studs that are used as wall supports in buildings that would have to be flattened out to be usable. I considered a rain gutter but with weight = well more weight. Oh well, now to go teach class..

[MetroMPG]

FYI, two of the most knowledgeable people on the subject of aerodynamics on this forum have already posted in this thread regarding dimpling and automotive aerodynamics.

I don't want to discourage anyone from learning through experience something that has already been established by others, but dimples on a car = dead end.

Where did you read that your Civic has the same Cd as a New Beetle?

[Palionu]

On Motortrend it says my cars CD is 0.38 (surprise to me)

and good old untrustworthy Wikipedia says it is 0.36. Type in 2001 Honda Civic when you search the page.

I was wrong in stating that it has the same CD as a beetle, but one guy had put a giant wing on the back of his bug and it reduced it to 0.36 (the article is amiss, sorry). The actual beetle CD is 0.48 according to Wikipedia

[Clev]

Originally Posted by Palionu

I was wrong in stating that it has the same CD as a beetle, but one guy had put a giant wing on the back of his bug and it reduced it to 0.36 (the article is amiss, sorry). The actual beetle CD is 0.48 according to Wikipedia

Ouch. Aren't most trucks and vans 0.45 to 0.49?

[ChrstphrR]

Originally Posted by Cd

As far as dimples on automobiles, I notice that Lexus did a famous job of dimpling the LS430 underside, and to my surprise VW is still using dimpling on the undersides of their cars . There must be something to it, otherwise they wouldn't bother ( Lexus used the dimples as a PR stunt, and this may have been the actual reasoning behing the dimples, but why then is VW using them if they don't really work ? )

Dimpled underpans would have another non-aero reason for being dimpled...
NVH reduction - Noise, Vibration, and Harshness.

Especially for metal parts, dimpling, ribbing, and other forms of bracing or mass-damping would keep an otherwise perfectly flat panel from vibrating at higher frequencies.

High frequency vibration are more likely to bother occupants inside the car, than lower ones. As an overall structure, a more rigid car has better handling, to boot.

That's just my take on that idea. It may be good PR, may possibly have some benefit for delaying flow separation, but my best guess is it's a compromise of all three.

[dichotomous]

Originally Posted by Palionu

Thanks for the idea, I especially like the idea of sticking those on my mirrors instead of a full mirror delete (I like the aesthetic nature of them ok?).

Before applying them, did you do the string test to ensure optimal placement?

nope, I unscientifically stuck them on there. I will be trying to zigzag tape later.

one thing about metrompg's test of the airtabs, I think he used them incorrectly, the air bubble was ONLY in the center of the car, one or two of these tabs could have disrupted that bubble without the drag from a whole back end of them, the string tests show that and I think should have been used to place the airtabs. if you have a drag reduction from the center 2 tabs, but the other 6 tabs are adding drag, well then just keep the center 2. I think its at least worth a shot, so I may be trying with some homebrew airtabs and such on the wifes jetta3. string test first to determine bubble size and shape. then airtab placement

[basslover911]

Dont Get Air Tabs!!

Get "Vortekz" generators; airtabs have a MUCH larger frontal area- remember their made for HUUUGEE trucks and not small metros?!

The large frontal area simply negates any good side effect that they might have on airflow. Vortekz on the other hand add very minimal frontal area... and thats why I have them on now actually