[PaulB2]

I was looking at buying a volvo 850 wagon which has a nice boxy rear end. It occurred to me that that back end looks a lot like the back of a pickup cab.

There is that diagram floating around here about pickup aerodynamics, which shows the small wing on the roof and a half tonneau being the best aerodynamically. I imagine (correct me if I'm wrong) it establishes a stable vortex in the pickup bed, and the air just flows over that vortex down to the tonneau cover. I just wondered if we could move this to the back of my volvo (if I buy one).

The wing is easy, just stick it on the roof, projecting out the back. For the "pickup box", why not just get a receiver hitch arrangement and mount a short, wide box there. The vortex would reside in the box, which could also be used sometimes for carrying stuff. One could easily add a curved surface inside the box to make the vortex even more stable.

If doable, this should be a lot easier than adding a trailer with long, sloping sides and top. The box could physically touch the bodywork so there is no gap, unlike a trailer. Also the rear view mirror still works. The back door is accessed buy simply pulling the pin and removing the box from the receiver hitch.

I'm assuming the axis of the vortex is horizontal. Is that correct?