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Old 07-02-2011, 09:41 PM   #11 (permalink)
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Appreciate the compliment Cd. One cannot judge their own work. Actually, a friend of mine here locally did some extensive CFD testing on the cargo box. Some simulations were showing as much as a 24% reduction in Cd with the Aerolid / cargo carrier combination. The preliminary road tests are backing up what the computational fluid dynamics calculated.

Sorry basjoos, not meaning to highjack your thread but this cargo carrier seems to be quite aerodynamic.

Bondo

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Last edited by bondo; 07-02-2011 at 09:44 PM.. Reason: spelling
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Old 07-02-2011, 09:59 PM   #12 (permalink)
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If I was to stick to Basjoos' parameters and have one for the roof, I'd try to find out just how small the vertical height could be while still being functional, and spread the width out to the drip rails (or door gaps) on each side, and put a generous amount of tumblehome on the sides. I think the front would be the least influential of all the surfaces of the box but nonetheless either have it extend the curve and slope of the windshield, or heck make it square but have generous radii on the side and top edges. Let the back of the box follow the template down to a point.
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Old 07-03-2011, 10:56 AM   #13 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
If I was to stick to Basjoos' parameters and have one for the roof, I'd try to find out just how small the vertical height could be while still being functional, and spread the width out to the drip rails (or door gaps) on each side, and put a generous amount of tumblehome on the sides. I think the front would be the least influential of all the surfaces of the box but nonetheless either have it extend the curve and slope of the windshield, or heck make it square but have generous radii on the side and top edges. Let the back of the box follow the template down to a point.
Great imagineering Frank. You should build it!

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Old 07-03-2011, 11:41 AM   #14 (permalink)
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How would you design a cargo box to meld in with the roof line of a car to produce a minimum of additional drag?
Fitting flush on the roof - soft rubber seal all around.
Carrier arms to be fixed to the sides, not the bottom.

Use the carrier's front to recapture the air overshooting the windshield / roof transition - not overly blunt, say a bit blunter than the top half of the Yakima box that Cd illustrated.

Top and rear, template ending in a Kammback at say 70%.
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Old 07-03-2011, 01:11 PM   #15 (permalink)
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Nice work.
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Old 07-03-2011, 03:01 PM   #16 (permalink)
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Bondo, your designs look awesome !

I have noticed the same thing about roof top cargo carriers for years. They are all backwards.

Even the manufacturers show the carriers mounted the wrong way. Its the old idea that pointy ends are better than blunt ends.

If I already had one of these, I would investigate mounting it backwards and upside down, lining the front edge of the box up with the back of the windshield. This should allow the air coming off the windshield to continue flowing up and over the box. I'd also look at cutting the circumferential lip off (at least on the new "front" area) to allow the air to flow over it better. I don't know what effect mounting it upside down would have on the weatherseal (probably bad).
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Old 07-03-2011, 04:13 PM   #17 (permalink)
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That particular box would have such a horrid front if it was installed backward- looks kind of hopeless, unless one was to mount it backwards and fab up a nose cone for it.
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Old 07-05-2011, 11:14 PM   #18 (permalink)
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A while back, I was considering constructing a roof top carrier for my Vibe. On paper, it had many of Frank's parameters;

"...try to find out just how small the vertical height could be while still being functional, and spread the width out to the drip rails (or door gaps) on each side,...the front would be the least influential of all the surfaces of the box...but have it extend the curve and slope of the windshield... Let the back of the box follow the template down to a point."
and it looked like this;




But then I woke up and built this:

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Old 07-06-2011, 12:20 AM   #19 (permalink)
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Funny thing, I always notice these roof cargo boxes now for this reason....They're all put on backwards!! I swear Iíll crap my pants if I ever see someone who has it mounted tapered end back. The tapered end is invariably the front of the box, and unless you've been living under a rock, (or youíre not a frequent visitor to Ecomodder.com) we all know that the taper should be in the back. I wonder if the weather seal is different on the front & back which is the reason you never see them turned around by someone who would know better. Some boxes have a flat back, but others have a perfect aero shape, if mounted the other way. I think they should hang off the back as far as structurally possible as well.
They're not mounted backward. The big end is flat, not aerodynamic in any way. Air would hit that surface and spill out to the sides, effectively making a much bigger frontal area.
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Old 07-06-2011, 12:22 AM   #20 (permalink)
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Quote:
Originally Posted by Cd View Post
Bondo, your designs look awesome !

I have noticed the same thing about roof top cargo carriers for years. They are all backwards.

Even the manufacturers show the carriers mounted the wrong way. Its the old idea that pointy ends are better than blunt ends.

If that was a car, you'd call it a great example of a kamm shape. But because it's a plastic box, you think it's "backwards". Really? You think the front end should be a flat surface sloped to trap air like a parachute between itself and the roof?

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