15 replies to this topic

[Dave_12]

Do dimpled bodies really make any difference?

 

[Dave Crevie]

I snipped this out of a publication I read from time to time. It's from an older issue, from when the whole idea of dimpling aircraft wings came up. It goes into the theory pretty deep, but of course, does not apply it to wing car bodies;

 

https://journals.the...1019_064614.pdf

 

A wing car body is in effect an upside-down airfoil. It's function, however, is limited because the airflow under the body is restricted by the diaplane and the sides of the body which prevent airflow from getting under the body. The dimples need a fast moving boundary layer of air moving over them for them to work. 

 

The research into dimpled airplane wings was to see if the dimples would substantially increase the stall speed of a wing. Actual testing showed that the advantage was minimal, and I lost interest. As for slot car bodies, someone will have to conduct comparison tests using identical bodies and closely controlled conditions.

[Bill Seitz]

I've used the same body style both with and without dimples, and I couldn't tell any difference or improvement in lap times, but I'm not a competitive wing car racer. As Dave Crevie has pointed out, most of this aero stuff is based on much higher speeds than slot cars typically attain except for perhaps with open cars on the straight. For 1:1 cars, the minimum speed for aero effects is usually stated as 80 mph. My suspicion is that any advantage is barely noticeable, but it can't hurt, so run one if you like. It looks cool and so techie!

 

I'm told that dimples on golf balls make a big difference. I'm not a golfer, so how fast does a golf ball fly? I'd guess maybe faster than a slot car. Also, the golf ball being spherical is one of the least aerodynamic shapes, so reducing boundary layer resistance is a big deal.

 

Slot cars gain down force not so much from airfoil effects as simply ramming air onto a confined plane. They're too slow for any reasonable size low-speed airfoil. However, by "damming" a plane (top of the body), the trapped air pushes down on the plane and provides down force. It's how the flat surfaces on dirt track "wings" (like on sprint cars) work. The shape and incline of the plane has some effect on where the highest pressure areas will be.

 

There are some GTP/LMP bodies that have rather prominent, high "front fenders" which push the airflow into a narrower channel over the front of the body. I suppose the idea is to create more down force, but Bernoulli and Venturi indicate that the velocity increases as the area is reduced, and higher velocity creates lower pressure, not higher. The imposing "fenders" also seem like they'd create more drag. Again, at slot car velocities, how much does this really matter? But with competitors separated by thousandths of seconds, maybe. I'm sure someone has anecdotal evidence. Again, I can't say I've noticed any difference with one of these bodies over one without the high fenders. The biggest influence on slot car down force is the area of the body (length, width) and height of the "dams". The more air that's corralled, the more down force. That also makes more drag, so even as in 1:1 cars, there's a compromise between down force and drag in attaining the fastest time on any particular track. Sometimes the most down force doesn't equate to the fastest lap possible.

[Mr. M]

I read the article carefully and with a dimple twice in diameter as the depth has a little less drag. Something less than 10%. So it could make a difference. I always thought intuitively that the dimples needed to be wider and thus deeper. Would be interesting to see.

[Mr. M]

What I am saying here is that I don’t think the current dimples are optimized. Bigger and deeper could make a difference. The ones we have are pretty small.

[Mr. M]

Back in the day of glue zone G27s, I waxed my wing car before qual day. What a mess. Had to wipe it down with glue to bring it back. It was all over with a decided lack of aero.

[Dave_12]

My thinking is if dimples work then Formula 1 cars would have dimpled bodies which they don't.  

[Samiam]

Whack one of these wing dings with a golf club. The result will verify the effectiveness of those dimples. 

[Dave Crevie]

The University of Iowa did extensive testing on the dimple theory. They tried dimples of various sizes and placements. Their results didn't warrant further research. They went, instead, in another direction. They cut tiny slits in the top surface of a wing, then pressurized the wing to create tufts of air shooting out of the slits. The additional airflow did appreciably increase the stall speed of the wing. It filled the voids caused by the turbulence above the wing, creating more lift, at which point the wing began to "fly" again. 

 

As to golf balls:

 

https://youtu.be/fcjaxC-e8oY?si=Za6-9NoW9sr8BCO4 

[Mr. M]

I think F1 has gone in a different direction. If you look at some of the paint finishes, they are definitely not the high glossy finishes. Kind of a satin look. No one is talking, but it’s definately different than in the past.

[Mike Patterson]

If you look at some of the paint finishes, they are definitely not the high glossy finishes. Kind of a satin look. No one is talking, but it’s definitely different than in the past.

I think they're wrapped.

[Phil Hackett]

I think F1 has gone in a different direction. If you look at some of the paint finishes, they are definitely not the high glossy finishes. Kind of a satin look. No one is talking, but it’s definately different than in the past.

Look at the pictures of Jeff Gordon's #24 "paint job" and tell me there wasn't some aero-adjustments made with the paint. Particularly the hood.

[Jim Difalco]

All aerodynamic integrity goes out the window with 1:1 Nascar sheet metal the second they contact another car. 

[Mike Patterson]

All aerodynamic integrity goes out the window with 1:1 Nascar sheet metal the second they contact another car. 

I believe the bodies are now made of a composite material, so they mostly crack, instead of bending/deforming, and they supposedly will take more abuse than metal before doing that.

[Dave Crevie]

The main parts,fenders etc.,are still hand formed from aluminum. The noses and tails are composite.
There was some experimentation with "shark skin" wraps. Sharkskin has tiny scales, like a fish. The theory was that the scales would drag along a boundary layer of air, reducing drag. I haven't followed up on any of that.

[Dave Crevie]

. 

 

The research into dimpled airplane wings was to see if the dimples would substantially increase the stall speed of a wing. 

 

Correction; I should have said "The research into dimpled airplane wings was to see if the dimples would substantially decrease the stall speed of a wing. (Thanks to Nelson for pointing the slip out)

 

I made the same guffaw in post 9. Maybe this article will help straighten this all out;

 

https://pilotinstitu...hat-is-a-stall/