The 2-Part Aero-Body Concept

[merc1980]

You should watch the Top Gear episode of when the Stig crashes the Koenigsegg. They do a before the wing crash and an after the stig asked them to engineer one to put on the car. Very interesting.

[kach22i]

Originally Posted by merc1980

You should watch the Top Gear episode of when the Stig crashes the Koenigsegg. They do a before the wing crash and an after the stig asked them to engineer one to put on the car. Very interesting.

The comment about needing a wing is pretty close to the front of the video, the crash when they push it too far is at the end.

http://www.youtube.com/watch?v=svxRpqeqFRY

<iframe width="560" height="315" src="http://www.youtube.com/embed/svxRpqeqFRY" frameborder="0" allowfullscreen></iframe>

If I have a 25 hp electric pancake motor at each wheel and lead-acid batteries, this should not be an issue, might even have to get out and push it once in a while. However Lithium-Ion batteries and a 100 hp electric motor at each wheel and I will want all the splitters and wings I can fit on there.

[ERTW]

Yo G! I done a CFD...and my computer doesn't want to leave sleep mode just as it converges on an answer It did it twice, so I'll take it as a sign that the automotive gods don't want you to have a certain knowledge...

This model is 2 m wide (racing limit) by 4.2 m long, S = 1.594 m². 335 section rear tires, wheel wells, no mirrors or suface details. By thickness I mean the height of the body - as if you were looking at a wing from the side view. I put a 2" radius on this body 'cause it was quick.

fwiw, it was at Cx 0.357 at 250 IT, and Cz 0.101 (about 100 lb of lift total). A 'tunnel' between the rear wheels will kill some lift, and 11° is too much for the rear taper - although a small spoiler will help.

I think small spoilers on production cars are mostly for style. the 5 part racecar body is to provide as much clean air to the rear wing as possible...although I can't say what it does for drag (minus the wing).

I hope you enjoy the pretty picture...it will now be my avatar

[kach22i]

Originally Posted by ERTW

Yo G! I done a CFD...

This is for the short-tail Porsche 962, right?

Thank you for clarifying the edge radius, when I scale my model the sides are about 30" high, so that would be a 3" radius for me.

I'm very curious as to what the Cd sans wing on that form will be.

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The Top Gear video said the Koenigsegg has a very low Cd, but failed to provide an actual number - the *******s.

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I bet you are right about the 5-Part race car, but letting all that air pass cannot be a bad thing, can it?

I bet it has to do more with turns and cross winds than anything else.
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FYI: Michigan Book & Supply is going out of business, just picked up some foamcore board and corroplast (50% off) for constructing a Mooncraft knock-off (model) with my own twist.

[ERTW]

It's a generic Can Am type car...unless you have exact dimensions I can model I wanted a sense of what the air is doing. The front wheels generate a huge nasty wake...I don't think enough air is attached to the sides to make a plan taper effective.

The 5 part body is Jaray's composite body to perfection. air speed is lower over most of the body - higher pressure means less lift. With the under body shape, it's more like one giant wing with four wheels. Racecars derive up to ~70% of their download from aero. It's also easier to streamline wheel arches, rather than an entire body. I'm sure it helps Cd too.

from koenigsegg's site:
Aerodynamics CCX

Cd. 0,32 Frontal area 1.867 m2
Total Downforce at 250 km/h: 100 kg
Flat underside of chassis. Venturi tunnels at rear of chassis/body.

drag index: 6.63 ft² not even a 1990 oldsmobile cutlass supreme...never mind a fish

the CCR (the most aerodynamic) is: Cd. 0.297. Frontal area 1.825 m2 - almost prius worthy

[kach22i]

Originally Posted by ERTW

drag index: 6.63 ft² not even a 1990 oldsmobile cutlass supreme...never mind a fish

I don't understand this part, is Cd very different from "drag index"?

Granddaddy of the 5-Part body:
Mercedes T80 from 1939 - a photo on Flickriver

The world record car T80 was built in1939 by Ferdinand Porsche. It was equipped with the plane motor DB 603 with 3,000 HP. The T80 should be the worlds fastet vehicle on 4 wheels. It was planned to race in 1940 with up to 600 km/h over the Autobahn. The start of WWII halted this project, so the T80 was never used.

Another image here:
T80 | Flickr - Photo Sharing!

..................another one of that type...
http://foas.us/forum/viewtopic.php?f=1&t=1279


http://www.fourtitude.com/news/publi...ter_3691.shtml




http://www.racingmodels.com/auto-uni...143-3406-p.asp


http://www.tamsoldracecarsite.net/AutoUnion.html

The streamliner recreated. After an autobahn run of 279 mph, Bernd Rosemeyer lost his life when this special Auto Union went out of control. The replica displayed here at Laguna Seca features exquisite craftsmanship.

http://www.motorauthority.com/news/1...ry-celebration

[aerohead]

The drag index,or drag factor,is the coefficient of aerodynamic drag multiplied by the vehicles frontal area,and is expressed as a measure of square area (square feet/square meters).

[kach22i]

Originally Posted by aerohead

The drag index,or drag factor,is the coefficient of aerodynamic drag multiplied by the vehicles frontal area,and is expressed as a measure of square area (square feet/square meters).

Thanks.

I think Porsche in the mid 1980's did a bunch of magazine advertising based on this.

[kach22i]

Introducing the 4-Part Body.

1. Canopy for three people.
2. Single front (with some articulation).
3. Left rear wheel fairing.
4. Right rear wheel faring.

These studies are just that, studies. At first I did look at the Mooncraft car, but I ventured off trying to find my own way.

Like I said before, I considered the 2-Part Body a starting point, one which I could carve into like a block of clay.

Industrial Design - Transportation pictures by kach22i - Photobucket








Comments are welcomed, and I'll try to keep in mind that the area I'm entering is all completely subjective from this point on.

[aerohead]

*Looking at the 3rd group of images from top,the dashed line,from cowl to nose,in between fender blisters is basically straight.This can cause the air to overshoot the corner leading over the top,creating separation right there.If there was camber behind there,a favorable pressure gradient would help hold the boundary layer in place,but we don't have that. Some radius at the top would fix it,allowing the two tributary streamline filaments to merge as one.
*Secondly,in Hoerner's section on canopies and blisters he discusses interference drag where the bump integrates to its attaching wall (your car body).According to his presented data,the canopy will have a drag minimum when its height is about 11.5% of canopy length.
*Also,to minimize interference drag where the canopy and body actually join,a fillet which is 4-8% of canopy length (chord ) is best.If you overdo it,it will create supervelocity,leading to higher local flow speed,which will create shear between adjoining streamlines and likelihood of turbulence.
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I like the leading edge plan view radii and plan taper at rear.Her heartbeat is strengthening!