[aerohead]

Originally Posted by BigChief

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.

I don't think you'll have proper forwards/upper vision to see traffic lights while stopped at intersections.The sight line will be occulted by the overhang.