Designing a hard-shell rooftop tent
 

Hey All, I'm attempting to design a rigid rooftop camper tent that will be permanently mounted to the roof of a Tesla Model S. This is going to be an around 7-foot diameter tube (I want it to be standing height inside) and 20 feet long so there's no overhang on the sides and about a foot and a half of overhang at the front and rear of the vehicle.

Here's a concept picture here, I used a plane fuselage model since that gets the idea across: imgur.com/BhKIclp

I'm making it out of carbon fiber and nomex honeycomb, I did the math and it'll come in around 300 pounds which is very light for such a huge structure. The Tesla has about the lowest center of gravity of any production car and I don't drive over 45mph so I'm not worried about crosswinds.

The two big aerodynamic concerns I have are:

1) how best to shape it (if it were 40-feet long, it would be easy to shape it like a killer whale with standing room in the middle and a narrower sleeping area in back, but 20 feet with a standing-height requirement makes it really hard to keep the drag coefficient down and still be practical

2) how much of a gap I should have between the floor of the camper and the roof of the car. If there's little gap, I'm worried the frontal area will act like a scoop and totally mess up the aerodynamics of both. The Tesla is 4.7 feet high and I would need to keep everything under 13.5 feet to be street legal.

I tried modeling everything in "Autodesk Flow Design" which is a 3D wind tunnel simulator but I'm not convinced it is giving me Cd values that are anywhere near accurate.

Uh....um....Is there any particular reason you wouldn't figure out a way to make a trailer out of this and pull it behind the car? I have no idea about the rooftop venture you propose, I don't believe it has been attempted.

Here's your pic/illustration.
http://i.imgur.com/BhKIclp.png

Thanks for posting the pic. The reason I want it on top is that it makes finding parking a thousand times easier, keeps it away from dirt and insects, and the Tesla's air suspension will "auto-level" the car when parked, therefore also leveling the camper. It also doesn't have to be licensed like a trailer. So most of the same reasons that rooftop campers are gaining popularity in general.

I know that is terrible for aerodynamics versus just towing it, but I live in an apartment with street parking, so if I want to go camping on the weekends and still have a place to park during my weekday commute, roof-mounted seems like the only way to go.

Might be some adverse behavior in windy conditions.

Consider bridge clearances can be as low as 13.5 feet. I would make a trailer and look for a rental storage bay. A canoe and a good tent would be easier.

Definitely paint it yellow and brown and put "Oscar Meyer" on the side. Also note the wiener is the perfect piercing shape. Much like a nuclear sub full of seamen in an emergency blow, or the famed No-Dong missile of North Korea entering a black hole. Forget these modern aerodynamic software programs, the wiener has been getting it done for a million years.

Welcome to the forums! :)

Have you considered a collapsible design something like roof top tents but with hard sides? No need to make it completely rigid all the time while traveling. ;)

Do you really have to have standing room while on top of the car? Consider the limitations you would have when driving through low clearance areas. ;)

Even parked, the Tesla will likely not have enough weight to keep that contraption stable in windy conditions.

I saw a guy lose a large toolbox he was using to weigh down a large cardboard box. A gust of wind lifted them out of the pickup bed.

Why not an actual tent that can be thrown in the back seat or trunk? Even a big cabin tent packs up small enough to fit easily in most trunks.

Where do you go camping at 45 mph in an electric car that doesn't have a cheap motel nearby?

A guppy airplane comes to mind...
https://i.ytimg.com/vi/dgZxOKNX1h8/maxresdefault.jpg

Have you considered a single wheel trailer and a Wacky Shack? ;)
WACKY SHACK