This week I unbent the aluminum bows I picked up.
Set up a stool on the driveway, got out the duct tape and taped one of the tubes between the stool and the car, extending the existing angle of the Kammback (~15 degrees). Spent a long time staring at things.
Fired up Photoshop. Drew some lines.
Then I chose 130 cm / 52 inches as the length of the boat tail (roughly to the vertical green line. Two reasons: partly for aesthetic proportions because it's close to length of the car's existing "sections" (hood / door / rear), and 2) partly because the longest aluminum tubes will fit crosswise in the back of the car.
I think I'm going to aim for a 6 degree bottom angle, approximately what's shown there (don't do the photoshop measurement to check my work on this image - it's 5 degrees there.)
Bicycle Bob advocates for no more than a 4 degree angle. Unfortunately, that will leave the end of the tail a bit lower than I'd like for departing slope angles from the back tire.
I've since made a cardboard "transom", and four struts. Mounted on the car.
Plan is to make an aluminum + cardboard skinned prototype tail based on these angles and tuft test it.
Should have a couple of photos of construction this weekend.