I guess the real question is why does the FAA feel it's necessary for
a homebuilder to have done 51% of the work? Is it to protect him from
himself, or to protect the public from him, or are there other
reasons? What of the prototypes built by Lockheed or Boeing; 51% of
them aren't constructed by a single individual.

It seems that there is some fundamental assumption that I am
overlooking, because the current FAA 51% mandate seems arbitrary and
unfounded to me.

All aircraft are licensed under one of a limited set of rules before being
allowed to enter our airspace. The only exception to this is a class of
flying machines, called "ultralights" that fall under part 103. These
aircraft are exempted from some of the oversight because they are so
lightweight that they do not present a serious danger to people who are not
committing the unnatural act of flight in one of the contraptions.

All larger and heavier aircraft can endanger people on the ground who have a
right to be protected from fools falling out of the sky into their homes.
Theoretically, anyway.

The 51% rule has applied since the EAA was first founded back in 1953.
Interestingly, building either wings or a fuselage is considered 51% of the
aircraft? The idea was to allow the builder to utilize scrounged aircraft
parts, and to use standard aircraft engines and propellors.

Why is it reasonable? Simple. To license an airplane as Experimental -
Amateur built the amateur in question must build a substantial portion of
the aircraft. Otherwise it is NOT "amateur built" and must be licensed in
some other category, such as Experimental - Exhibition, or Standard Type
Certified or some such.

How can it possibly be "unconstitutional" to restrict aircraft licensed as
"amateur built" to only aircraft that were built by amateurs. By definition
"Professionally Built" does NOT fit into this license category and should be
licensed in one of the other categories. And can be under the existing
rules. All that it requires is compliance with the appropriate regulations
to ensure safe operation and acceptable construction standards.

Highflyer