Most aerodynamic cargo box?

[slowmover]

While I agree that roof-mount carriers have an FE penalty (even beyond best design) they are generally small in both volume and weight capacity. Importantly, they are centered over the vehicle, between the FF/RR axles. The weight is hopefully not enough to affect COG meaningfully.

Whereas the hitch carriers may not have quite the capacity, they tend to exceed the TW (trailer Tongue Weight) capacity all too often as I have seen whilst running the roads. This is a safety concern: unloads the front axle which is a seriously bad idea for braking/steering control. Changes other handling qualities of the vehicle (polar moment of inertia) which is even worse in some situations.

I'd rather have a small trailer. The U-Haul "Sport Trailer" weighs 540-lbs, with a capacity of 39 c/f and a cargo weight of up to 965-lbs (TTW 1,500-lbs). Aero doesn't begin to describe this trailer.



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[Fat Charlie]

I've got one of the big Thule boxes. Before I started hypermiling it cost me about 1 mpg, dropping me to about 21 mpg on a long trip. Today it would probably cost me a lot more. Maybe some day when I've got nothing at all to do, I can do some A-B-C coast down testing, measuring car speed at the mile marker signs. What's more likely is I'll put it on and take it to work for a couple of days. A, B and C will be on three different days, but my commute is pretty consistent.

[orbywan]

Originally Posted by bondo

Correct.

Bondo, I don’t know which I like better, the box or the cap on the truck. Is the cap something you built also? Any mpg numbers on the before and after on the combination? Great work!

[kach22i]

Originally Posted by Fat Charlie

I've got one of the big Thule boxes. Before I started hypermiling it cost me about 1 mpg

Much better than I expected to read.

What do you guys think of this?
Random TRANSPORTATION pictures - Page 544 - Pelican Parts Technical BBS

[CFECO]

Component - Drag coefficient
Forebody - 0.05
Afterbody - 0.14
Underbody - 0.06
Skin friction - 0.025

This set of numbers is based on an existing car body (not a brick), which already has the front area reduced in size, compared to the maximum cross section area of the passenger compartment. I agree with NASA, streamlining the front does help, and it gets the overall shape closer to the "template".

[Varn]

RE Streamlined brick and roof carrier.

I have seen the diagram before. It shows a bricks with radius curves on both ends not true bricks. I also recall a quote from Hucho (I think) saying that a 4" radius (or more) was required to keep flow attached. I might assume that the 4" figure would vary depending on the size and speed.

I have found that the main body of air is detached from the roof about a foot back from the windshield on my MK 2 vw Jetta, all front radii on it are tighter than 4". a gradual slope on the front of a carrier might be better than blunt front in my example. Probably a gradual slope on both ends would be best.

[phreaddy]

I want to get a roof box for my 2009 VW Jetta Sportwagon. I understand the longer-is better argument, but I think that with wind coming off the windshield, you'd be better off with a shorter, stubbier (and/or shorter, wider) box placed as far back as possible -- that way more wind coming off the windshield would go over the box instead of getting shoved into the underside of it. And, yeah, I'd install it blunt-side forwards. Thoughts?

[Hersbird]

I like the looks of these, very pretty, but $900 or more.
Products | Packasport
sometimes I wonder if a kayak wouldn't be better. Hard to get big suitcases through the opening but you can't float the river in a Thule cargo carrier either.
$310 Walmart cheepie in 5 colors.
Sun Dolphin 1-Man Kayak - Walmart.com

[aerohead]

In Sighard Hoerner's 1951 book,Aerodynamic Drag,he shows aerodynamic drag of some wing-tanks,belly-tanks,and bombs.
The lowest drag was achieved with:
*wing-tip tanks based upon streamline bodies
*wing tanks,under-slung in pylons
*Half-body tanks blended onto the wing or fuselage itself were a little higher.(Me 109 belly tank)
The fiberglass fairing for the ADF loop-antenna on this North American SNJ trainer would be very low drag (Cd 0.08) on its pylon 'roof' mount.The distance above the fuselage helps mitigate super-velocity effects encountered on a 'blended' body.The 'blending' of the pylon helps kill any hook-vortice interference drag.

If you 'morphed' the carrier into the roof,you might treat it like a solar racer canopy from MIT's Goro Tamai

[freebeard]

What do you guys think of this?

I like it.

I'm bummed because I can't find the old logo for Gary Emory's Parts Obsolete Campout. Even the Wayback Machine didn't help. It was a picture of a Porsche 356 with a canoe upside down on the roof, in front of a teepee. (the teepee is the most aerodynamic dwelling ever)