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Drag Coefficient

10K views 8 replies 7 participants last post by  DaV8or 
#1 · (Edited)
GM is working on ways to improve the Cd of the Volt. There are materials that reduce skin friction, and therefore reduce drag. Has GM thought about using ideas from these materials to improve the Volt's Cd?

http://www.triz-journal.com/archives/2007/04/04/
This article comments on riblets, for instance.
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#2 ·
Thank you for bringing this subject up. It is a thread along the vein of one that I wanted to start so I am piggybacking here. Hope nobody minds.

I have been thinking skin friction may be something to look at, but figured automotive paint was good already. I do think most cars "transitions" could use a little attention (e.g. hood to windshield, windshield to trunk lid, side to wheel well, etc).

1.) Wouldn't a well designed hood to windshield transition with hidden wipers save a lot more than special made low power wipers? Hopefully the wipers will be protected from air flow.

2.) The photoshop folks would need to mock this up to see how it will look, but chamfered entries from the sides to the wheel well may look interesting and lower the Cd. This might "soften" the turbulence at the front of the wheel well and reduce the pressure by directing flow out to the side of the car at the rear of the well. Another idea would be to offer wheel well skirts for the rear wells as an OPTION. Don't buy it if you don't like it. I probably would not opt for skirts, but would need to see visual to say for sure.

3.) Pinch down the hood in the center of the cockpit. Since they have decided on a 4 seater, the headroom in the center is needed. This would not reduce the Cd much but it would be a nice little reduction to the frontal area (note, drag is a function of Cd, frontal area, and velocity). I think this may even add to the desing appeal too, but again would need see a visual on this as well.
 
#7 ·
1.) Wouldn't a well designed hood to windshield transition with hidden wipers save a lot more than special made low power wipers? Hopefully the wipers will be protected from air flow.
That won't work in climates with bad weather. e.g. snow / ice, it would cause problems and potentionally damage your hood.


2.) The photoshop folks would need to mock this up to see how it will look, but chamfered entries from the sides to the wheel well may look interesting and lower the Cd. This might "soften" the turbulence at the front of the wheel well and reduce the pressure by directing flow out to the side of the car at the rear of the well. Another idea would be to offer wheel well skirts for the rear wells as an OPTION. Don't buy it if you don't like it. I probably would not opt for skirts, but would need to see visual to say for sure..
That would likely look terrible. I think the idea is to create a "Normal" looking car that that performs decent, with the bonus of not "requiring" gas for short trips.

Me... Personally... Would be more likely to buy it based on performance, (acceleration / handling)


3.) Pinch down the hood in the center of the cockpit. Since they have decided on a 4 seater, the headroom in the center is needed. This would not reduce the Cd much but it would be a nice little reduction to the frontal area (note, drag is a function of Cd, frontal area, and velocity). I think this may even add to the desing appeal too, but again would need see a visual on this as well.
I'm not sure I understand what you are saying there?
 
#3 ·
I'll get even a little more tangential... The Aptera's tear-drop design is obviously extremely aerodynamic...but they didn't stop with the shape, they actually have the air that was used to cool the battery packs exit at the tip of the tear-drop to further disrupt the drag effect of the eddying air in that area....just brilliant. Maybe it only buys you an extra 0.01 on the Cd, but every little bit matters at that level.
 
#4 ·
1.) Wouldn't a well designed hood to windshield transition with hidden wipers save a lot more than special made low power wipers? Hopefully the wipers will be protected from air flow.
Here a link that solve the problem.
http://technology.askpaddy.com/car-technology/self-cleaning-wiperless-windshield.html

2.) The photoshop folks would need to mock this up to see how it will look, but chamfered entries from the sides to the wheel well may look interesting and lower the Cd. This might "soften" the turbulence at the front of the wheel well and reduce the pressure by directing flow out to the side of the car at the rear of the well. Another idea would be to offer wheel well skirts for the rear wells as an OPTION. Don't buy it if you don't like it. I probably would not opt for skirts, but would need to see visual to say for sure.
I would buy skirts, but I do agree I have to see what it would look like first. It could have aerodynamic hubcaps. I'm sure GM is working on that as well.
 
#5 · (Edited)
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2.) The photoshop folks would need to mock this up to see how it will look, but chamfered entries from the sides to the wheel well may look interesting and lower the Cd. This might "soften" the turbulence at the front of the wheel well and reduce the pressure by directing flow out to the side of the car at the rear of the well. Another idea would be to offer wheel well skirts for the rear wells as an OPTION. Don't buy it if you don't like it. I probably would not opt for skirts, but would need to see visual to say for sure.

Has anyone tried to make wheel well skirts with a transparent material? If we could order skirts with an antireflective transparent material, we would still gain the aerodynamic benefit of skirts, but avoid the change in appearance to the car. We could still show off our custom rims! Thoughts?
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#6 ·
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Has anyone tried to make wheel well skirts with a transparent material? If we could order skirts with an antireflective transparent material, we would still gain the aerodynamic benefit of skirts, but avoid the change in appearance to the car. We could still show off our custom rims! Thoughts?
Interesting idea and certainly doable with today's UV stabalized polycarbonate. The only real issue I can think of is cleaning. This is a very dirty area of thea car an both sides of transparent skirts would need to be cleaned.
 
#8 ·
look at current sports cars

Any discussion of aerodynamics relates to any car. Decreasing drag improves mileage, high speed acceleration, and peak velocity regardless of what's under the hood. And you need only look at the current cadre of sports cars to make an assessment of what works and what the trade offs may be.
 
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