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Old 11-15-2010, 02:08 PM   #1 (permalink)
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Aero shapes and their application?

I've been noticing some of the styling on newer cars and been seeing some of the CD's going down slightly while the styling has gotten sharper in many cases. I'm refering to the front of a vehicle, we'll leave the rear for another thread.
My question, hope this this is understandable:
Does it matter aerodynamically(keeping stability out of the equation) which way you "split" the air?
For example lets a take a 6'x4' rectangular frontal area, on one example the top and bottom taper to the nose while the sides are straight and flat.
On a second example all 4 sides taper to a point. Will one have any advantage over the other?

In addition, when you look at "aerodynamic" cars, whats with the bulges around the wheels? Wouldn't it be more aerodynamic to have the sides flat and smooth with the wheels as flush to the panel as possible?

Guesses..references..theory...gut feelings welcome

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Old 11-15-2010, 03:19 PM   #2 (permalink)
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This is the right way to do wheel arches.
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Old 11-15-2010, 03:34 PM   #3 (permalink)
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Car manufacturers are pragmatic & more dependent on the immediate emotional response for selling their products. Purely engineered shapes might not elicit a positive effect on our lizard brains. Mechanical engineers do not create for an 'impulsive' visual response. That is why they are very dependent on the success of their designers & studios for evocative concepts. The marketing (successful) need for an artist's fine 'visual' balance of proportion, shape, & surfaces of a vehicle. They still have to work alongside solid engineering precepts and technical platforms. Recent fashionable designs 'carve' shapes to create desired dynamic highlight/shadow reflections. Even Hyundai's & Kia's ascendancy has plenty to be grateful to their great designers & studios. Earl, Buehrig, Gandini, Giugaro, Bertone, Loewy, Mitchell, Michelotti, Gale, Pininfarina, etc are just a few of great 'lizard brain' artists.
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Old 11-15-2010, 03:40 PM   #4 (permalink)
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Quote:
Originally Posted by rkcarguy View Post
Does it matter aerodynamically(keeping stability out of the equation) which way you "split" the air?
It does, but maybe not in the way you expected.
Splitting the air so it goes over or aside the streamlined vehicle rather than underneath helps (with an aerodynamically dirty underside) is beneficial.

Quote:
For example lets a take a 6'x4' rectangular frontal area, on one example the top and bottom taper to the nose while the sides are straight and flat.
On a second example all 4 sides taper to a point. Will one have any advantage over the other?
There's no point in aggressively tapering the front, as it's worse than a blunt spherical shape (at low airspeeds).

Weird as it may sound :
If you have to streamline a brick, you'll gain the most by streamlining the rear !

Quote:
In addition, when you look at "aerodynamic" cars, whats with the bulges around the wheels? Wouldn't it be more aerodynamic to have the sides flat and smooth with the wheels as flush to the panel as possible?
A bulge adds frontal area, which should be reduced as much as possible.
Even streamlined bulges add to the drag.

But reducing the rear track width reduces stability, so sometimes (as in the Insight picture) the upper body tapers in, reducing wake area, while the lower is bulged or continues almost straight aft (Insight) to keep sufficient track width.
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Old 11-15-2010, 03:49 PM   #5 (permalink)
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That's obvious, I admit myself that I find boxy shapes preferable.
There can be a balance of both however, and more people are going to be willing to give up the box when gas comes back to $5/gallon again. I've been drawing a MG midget sized car in autocad for almost 2 years now and am just trying to come up with an aerodynamic front end that I like. Specific feedback is needed regarding the shape, if I should chamfer the bumper at the headlights and have it sweep back(think S2000), or go more basic bullet shaped from the sideview like a 1st gen RX-7....
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Old 11-15-2010, 04:43 PM   #6 (permalink)
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Quote:
Originally Posted by euromodder View Post
It does, but maybe not in the way you expected.
Splitting the air so it goes over or aside the streamlined vehicle rather than underneath helps (with an aerodynamically dirty underside) is beneficial.


There's no point in aggressively tapering the front, as it's worse than a blunt spherical shape (at low airspeeds).

Weird as it may sound :
If you have to streamline a brick, you'll gain the most by streamlining the rear !


A bulge adds frontal area, which should be reduced as much as possible.
Even streamlined bulges add to the drag.

But reducing the rear track width reduces stability, so sometimes (as in the Insight picture) the upper body tapers in, reducing wake area, while the lower is bulged or continues almost straight aft (Insight) to keep sufficient track width.
I realize the rear is where the game is won, got that covered. So styling on the nose is trivial for the most part, choose a look I like?
I'm skeptical of ramping the air sideways by angling the sides of the bumper/body. I would think the air would be disturbed at the end of this "ramp" near the front wheelwells?
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Old 11-17-2010, 05:13 PM   #7 (permalink)
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Hucho

If you have access to Hucho's book,I believe that it contains these forms and their respective drag breakdown.
The short answer is yes,it makes a difference.
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Old 11-18-2010, 05:18 PM   #8 (permalink)
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How are you deciding on your shapes and curves? If you don't try it out in a wind tunnel are you designing surfaces by how it looks? I'm working on streamlining my XB with mods to the front and rear wheel cover.
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Old 11-19-2010, 08:27 AM   #9 (permalink)
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Quote:
Originally Posted by apryor View Post
How are you deciding on your shapes and curves? If you don't try it out in a wind tunnel are you designing surfaces by how it looks? I'm working on streamlining my XB with mods to the front and rear wheel cover.
Wind tunnels are expensive. Tufts are cheap. ABA testing is where the rubber meets the road. Full tank testing can be expensive and that kinda of data tends to be dirty (mixed inputs). A ScanGauge is your friend. Cardboard prototyping is prudent. Be scientific. Document everything. Learn from every improvement and setback. Take pix and share so others can help. A happy ending is inevitable.

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Old 11-21-2010, 07:16 AM   #10 (permalink)
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Could someone please explain tufting? I saw the pictures of it on the thread about the boat tail for the metro. But there was no explanation of just how you can get data from it. I'm working on some mental designs for reshaping the nose of my buick and making skirts for the wheel wells, which will have to be "bulges" since the car body is wider at the top of the wheel than at the bottom. You say that the real gains are at the back of the car, the back end of my car is already quite close to a wide boat tail, while the front end is like a brick.

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