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Old 05-17-2011, 03:30 PM   #41 (permalink)
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Now how about winglets?

Obviously a flat spoiler needs side support, but many variations include vertical fins above the surface. Are these integral to the flat spoiler, or do they have additional aerodynamic functions?

Added picture for reference (hope it's ok):



Ernie Roger's version looks fairly extreme, like butterfly wings, but I wonder if that much vertical has any useful purpose. Reading through his postings, he implies there is. Perhaps they are just for stability, but most modern aircraft are using them more on the main wings.

Quote:
Winglets lower drag and improve aerodynamic efficiency, thus reducing fuel burn. Depending on the missions you fly, blended winglets can improve cruise fuel mileage up to 6 percent, especially important during a time of rising fuel prices.
Boeing 737 Advanced Blended Winglets

I wonder if thre is a similar application for cars...

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Old 05-17-2011, 04:14 PM   #42 (permalink)
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Ernie never comments on the specifics of his design choice...perhaps you could email him and ask.

As far as winglets go, they reduce drag both by reducing wing tip vortices and increasing the effective aspect ratio of the wing which increases lift and tends to further reduce drag. A number of airlines have retrofitted winglets to Boeing 737-300s, among others, to save fuel.

Obviously, the height of the end plate on the VW is partly determined by the placement of the wing element and also by the extent to which one wants to remove the inevitable vortices at the tip of the end plate from the wing element. The end plate also functions as a fence to some degree, influencing the airflow from other areas of the body depending upon it's size and placement. (There is an old joke about the fences on the wings of Soviet Migs that the fences were "to keep the air from defecting to the wing tip.")

I believe that Ernie commented somewhere that the increase lateral surface of the wing,s end plate improved the Bug's (lateral) stability in cross winds.

Of course there are practical considerations in the mounting of wings. There are wings mounted on the trunk lids of cars which have the support/end plate angle out so that the wing can be wider than the trunk lid and yet maintain the ability to open it.
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Old 05-17-2011, 04:27 PM   #43 (permalink)
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There is someone on the forums who has some CFD capability. It would be interesting if he would comment on the height of end plates in this application.
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Old 05-19-2011, 12:22 AM   #44 (permalink)
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Quote:
Originally Posted by cfg83 View Post


CarloSW2
A spoiler extending the trunk that much could become home to a rather large solar panel.
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Old 05-19-2011, 12:42 PM   #45 (permalink)
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Speaking of the Blowfish, check out this pic of the belly pan:


Doesn't get much smoother than that...

Although, I notice in later pictures that he added a small air dam and side skirt. I'm sure this was done to reduce drag considering how the car is used and his access to wind tunnel testing.
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Old 05-19-2011, 03:44 PM   #46 (permalink)
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Probably more for stability/ downforce than drag reduction, it is a race car after all.
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Old 05-19-2011, 04:29 PM   #47 (permalink)
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Quote:
Originally Posted by robertwb70 View Post
Probably more for stability/ downforce than drag reduction, it is a race car after all.
Absolutely. You get a significant flow underneath the body at the speeds it goes and you are air-born.
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Old 05-19-2011, 07:16 PM   #48 (permalink)
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Quote:
Originally Posted by UFO View Post
Maybe these "fins" are so large in order to deal with air flow from the side of the car, over the fender, reducing vortices and the wake? A little bit Kamm, a little less "spoiler." The Bonneville spoiler seems to do this job differently. Its spoiler's fins don't follow the line of the rear view window. Instead they emerge from the side fenders. But he doesn't care about trunk access. Maybe that difference in placement (along window vs along fender) goes part way toward explaining their differences in shape and size?
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Old 05-19-2011, 07:58 PM   #49 (permalink)
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I am sure that everyone has seen the little "flip" at the end of the roof line of the Prius and the shade style spoilers at the top of the rear window on a Mazda 3'and a variety of cars.

It would be interesting to see what extending the flip on a Prius and adding some fences would do either in the computer or in some coast down tests on the car.

About the Bonneville car, I would say that it is a fair guess that the front air dam settled the car at speed and reduced the air getting under the car. The side plates, I am sure, did much the same thing...they have been used on a variety of race cars until their use was banned.

Honda has a pretty clean looking belly pan on the Civic Hybrid.
I can not help but wonder if it would mount up on the regular Civic. I may just have to post a Q over on some of the Honda forums.
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Old 05-20-2011, 12:27 AM   #50 (permalink)
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Quote:
Originally Posted by Pendragon View Post
I am sure that everyone has seen the little "flip" at the end of the roof line of the Prius and the shade style spoilers at the top of the rear window on a Mazda 3'and a variety of cars.
I have photographs. I'm finding myself a little obsessed with this idea now. I "built" this ugly thing (below attached) by simply taping down a 2' by 4' piece of black coroplast. I chose that size only because it is close to what I imagine, and I already had a sheet that did not want to cut. The goal is actually to create something larger, something that might provide a surface at least 40 x 32 inches. The larger surface would extend eight inches aft from where this board is. The larger surface is part of an imaginary concept accommodating a 100w 2.5mm solar panel. Over the weekend I might make side wings. I cut some one inch styrafoam blocks to lift the surface and flatten it a little. I want to do a coast down with it.

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