Metro convertible easy boat tail?
 

I have a 91 metro convertible. I also have an extra header(the part that joins the top to the windshield) I was thinking if I got a big roll of canvas, took off the rear bumper and trunk cover and mounted some tail lights on some arms about 2' off the current location I could just use the canvas to stretch between the header and the tail light pod, then down to the bottom of the spare tire well. Plausible? Good idea? Comments? Thanks!

something along the yellow lines here:
http://farm5.static.flickr.com/4139/...843f87f4b8.jpg

Since that isn't going to leave you much headroom, you might want to consider starting at a softer angle then gradually increase it after the seats.

I like it, but I don't know about canvas at the material. It seems like it will be really hard to get it tight enough so that it doesn't flap around. I think the easiest/cheapest/hack job lookingest way would be with a sheet of plywood. Or if you build a good frame for the canvas idea, but instead of canvas use woven fiberglass (often used for boat building) stretch it, then paint on epoxy. This will give you a hard shell that is light and stiff. I'd estimate you could do this for about $100 + the frame + a lot of time.
For boat building people don't really uses the fiberglass by it's self, it is rapped around wood before the epoxy is added, so I don't know how well this would work, but if well stretched it seems like it could. I've always wanted to make some body panels for my car in the same way as a wood strip canoe. About 1/8" thick, by 1 1/2" strips of wood laid together and bent into form, then fiberglass coated. It looks really beautiful, plus it's light and strong.

Just for those, who haven't seen this:
Another car for MetroMPG: convertible 1991 Pontiac Firefly (Geo Metro)

You want the roofline to start off somewhat flat, and gradually increase in curvature. Canvas has a tendancy to do the opposite of this. I think you're going to need to build your aero shell and boat tail out of something rigid.

http://ecomodder.com/forum/attachmen...0&d=1247946422 - it needs to be shaped more like this, with no "corners" on the roof.

okay, so this is making me dizzy if I look at it too long, but it may help your planning.
http://i779.photobucket.com/albums/y...g?t=1278435489

Thank you for the effort, Doctor. But the red dotted line is not correct. The big grey line is the correct one, and it calls for a very gently sloping roof and nearly flat underside.

The only correct way to use the template in a side view is to align the ground planes in both images, scale them so the roof has the same height as the template, then move the template left or right to align the arrow with the top of the roof as you did.

This results in a roof that's surprisingly flat near the driver's head, surprisingly high where the car's taillights currently are, and extremely long. Though you can truncate the boat tail at 50 or 70% of its full length with very good results.

A ground-plane reflection of the template is provided so you can use it in plan view as well. Line up the arrow with the widest part of the car, and build an extension that tapers inwards perhaps twice as fast as the roof could.

As the template was made for a flat bottom vehicle, it I was thinking that the additional curve on the underside would allow for a scaled-down curve (which would be quite helpful for this application on this short car).

template
 

The only parameter for the template is proper scaling of the subject vehicle image,such that the point of maximum roof camber ( typically just the high point of the roof ) matches that of the template when the bottom of the tires are along the same ground plane.