That's a very good question. If you could build one that weighed 100kg (254
lbs) or less, then its an ultralight. Beyond that, things get very murky.
Kinda like trying to classify an aircraft that's so old that it can't turn or
fly our of ground effect, when it can get airborne. (BTW, most Wright 1903
Flyers are classified GA Experiemental.)

And that's the aircraft side of things. Trying to convince someone to issue a
license plate would be just as hard. If its got 3 wheels, then its still a
motorcycle. Four makes it a "car."

Fortunately, our perpetual cash-vaccum, uh... I mean source of inspiration,
Paul Moller has this issue well in hand and will no doubt pioneer legislation
that will license flying cars, etc. right after he builds one that can actually
fly.

Harry