A different style of Kammback & mounting discussion
 

could this be done for a hatchback?

you could imagine a flat clear plastic Plexiglas sheet spoiler coming up from somewhere near the wiper base. it could be supported by the wiper base, sealed at the bottom by duct tape to the car and supported at the top by coat hanger wire run from the hatchback hinges.

this would be much easier to make than a kammback?

maybe you would need a baffle running down the middle to guarantee non-separated bubble formation.

i apologize for crude photo-shop and poor image quality.

annotated

its just two coat hanger wires on the corners of the car that support the spoiler at the top. there is no roof to it and the non-separated bubble flow is used to change the effective angle of the rear taper, which would in effect follow the angle of the wire.

Two issues with the "Bubble Dam" spoiler that I can see.

A: What about flow from the sides of the vehicle into the bubble.

B: Doesn't the truck bed argument apply to this? (Tonneau better than open bed, tailgate up.) If this is the same, I should just build up the edge of my truck bed to get a 12 degree angle from the cab top.

P.S. Wouldn't you be putting a LOT of force on the Plexi panel? Even with .1 psi, that is 100 pounds of force.

you could cover up the sides no problem there. i have no idea about forces though. might just have to try it and see if it brakes.

if you cover up the sides it looks like a normal kammback thats been put on upside-down! perhaps some one could try this? it looks to me, like a short kammback would be more effective in this configuration than in the normal one because look at the relative lenghts of the orange and grey lines in my diagram

This reminds me of the Car & Driver Crisis-fighter Pinto. They added a 6-inch spoiler to improve the flow over the rear glass. It would be interesting to see the difference between a shorter and longer device.

What are some prices on plexiglass? I've been looking around and found some that I think would work or Ebay, no luck locally yet.

FunkSkunk -

In the size that I would need for a single piece, it seems like about $40 at OSH.

CarloSW2

heres my latest optimized spoiler plan. optimized for minimum material, maximum effect and to maintain driver visability.

you are right about the forces. i just found the plexiglas at my local hardware store and it was way too flexible to be a spoiler. on the other hand it could make a kammback.

i was thinking... can the plexi be heat bent round by 180* to form a hook to latch on to the hatchback like a cycle carrier? if so this would make for an easy mounting, may not even need the duct tape!