A brief update: Here's a Sonex airplane that my friend Mike Smith is building
from scratch:
Sonex -- The Sport Aircraft Reality Check!
I think the 4-cylinder 80HP engine weighs ~130 pounds, and the dry weight of the whole plane (including the engine) is 570-620 pounds. 22' wingspan, and the fuselage is 18' long. +6G and -3G in a 440-490 pound structure is great! This
construction method is pretty straightforward. It uses 0.025" and 0.032" 6061-T6 Aluminum sheets, and some aluminum plate and angle stock -- and thousands of pop rivets.
What my friend did is he drew the patterns full size in DataCAD (which the way you always draw things!) and he plotted them out full size (you can choose any scale for plotting) and he used spray adhesive to stick the paper onto the aluminum sheets. Then he cut them out, drilled all the holes, deburred them, clamped them in wood forms (two halves cut out of OSB board and wing nut and bolted) and used a soft plastic hammer and a pair of special pliers to pleat the flange around curves.
He's spent about 500 hours and he has almost all the components made. He's spent ~$1,600 on stock and ~$900 on tools.
Doing a similar process on a car would not seem to be all that hard.
Oh, and I'm continuing on the drawings -- I'd like to be able to test the aerodynamics of it before committing it to reality...or at least before building a working chassis!