Purpose of Winglets

[IRstuff]

So, I'm stuck in some traffic on the freeway, going slow, or I wouldn't have noticed this. The car in front of me appeared to have little black winglets glued to the bottom of their rear bumper. Is that a "thing?" It's obviously after-market, otherwise, it would be color matched to the rest of the car, or the owner wanted to make sure they would be noticed.

so, do they actually serve some aerodynamic purpose? or was the owner simply a gullible ninny? I've looked on Google, but nothing I've seen looks like those.

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[MintJulep]

On an F1 car:

http://www.caranddriver.com/features/the-physics-of-diffusers-how-to-make-a-car-really-suck-feature

As an aftermarket stick-on part to a Honda Civic: Makes it look like an F1 car.

 

[IRstuff]

But that looks like something that a) might be actually useful, assuming the car could go fast enough to warrant a diffuser, and b) it looks professionally made.

Neither appear to be true of my winglets; they were THIN, possibly less than 1/16 inch, and were TINY, about 4" square

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[SwinnyGG]

When you say 'winglets' do you mean vertical members?

They absolutely are an important part of a 'real' diffuser, which some cars do have.

 

[IRstuff]

Did I forget to post the picture? duh...

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[MacGyverS2000]

They provide a more laminar flow off of the back of the car. If (and that's a huge if) they track the car, the winglets can make a measurable difference, particularly at 100mph+. If they don't track the car, it's simply for looks.

Impossible to tell from the blurry pic, but if they were black, they were most likely carbon fiber.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

sorry, driving and taking pictures, yech!

it's just that these winglets are TINY; now that I've got the picture up, I can see that these things are barely 2" square, if even that much

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[GregLocock]

I have seen them on a production car, a row of 6 from memory. They were smaller than you describe, and may have even been on the roof line.

Ah, or they may have been on a styling exercise. This sort of thing, but less ugly

Cheers

Greg Locock


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[IRstuff]

Those indeed look like something that presumably belongs. The ones in the picture are more like a black version of the temporary lane markers that the DOT use after re-paving, but prior to doing the permanent lane markers. So think of vertical blind material in a 2-in x 5 in rectangle folded in half, and one half is scabbed onto the underside of the bumper. They could be black-painted aluminum, possibly, since they would need to be stiff to do anything interesting, unless it's fluttering that they're after.

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https://www.youtube.com/watch?v=BKorP55Aqvg

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[SwinnyGG]

I have seen them on a production car, a row of 6 from memory. They were smaller than you describe, and may have even been on the roof line.

Ah, or they may have been on a styling exercise. This sort of thing, but less ugly

Didn't quote your photo to keep the thread clean.. but that's called a vortex generator, and they actually do (at least a well-designed OEM implementation) make a measureable difference in drag, even on a street car.

 

[MintJulep]

The new Lamborghini Centenario will have them, so perhaps that Nissan Sentra? in IRStuff's picture is faster than it looks.

 

[IRstuff]

I wouldn't have an issue buying into those as possibly useful, but the ones I saw were about the size of those red reflectors between those vanes.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[MacGyverS2000]

It doesn't take much to significantly affect the airflow. When you consider the CAD guys are tweaking their models of the body panels a millimeter at a time before running it through the virtual wind tunnels...

Heck, even ridges on an antenna keep it from whistling at 45mph.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[140Airpower]

Right, it doesn't take much to make a "difference" but it can take a whole lot of CFD and wind tunnel testing to know what the difference is from a tiny feature and whether it's helpful or not and under what circumstances. The average car has a pretty poor aero shape compared to what is known about good aero. However, it's very easy to tell what looks good or "hi-tech" or sporty.

Remember when skirts were the rage? Did they "work"? Who cared?

 

[SomptingGuy]

In real-world use, minor aero tweaks are likely to have an effect on whether dirt accumulates on your rear window or not.

Steve

 

[140Airpower]

IMHO, modern tweaks that work tend to show up on almost all cars. For example, if you compare the cowl/windshield treatment of cars from 20 years ago with those of today you will notice a deeper windshield recess today with the recess extending up just about to the roof.
I've read research showing a lessening of wind noise with this. Also, fewer cars have mirrors that blend, instead most are on stalks and they tend to be placed farther behind the edge of the windshield. Again, wind noise is being considered, but the improvement also helps aerodynamics. IMHO, the straight aero benefit is not as compelling to the designers as is wind noise.

 

[TugboatEng]

Moto GP banned them, I think. Manufacturers were using them to spoil the air behind the bike rather than give any aerodynamic advantage.