FAR rules on "ground-effect" vehicles?

Does anyone here know if / what-section-of FAR rules govern the operation of
"ground effect" vehicles? Specifically, how high can a machine fly AGL before
its technically classified as an aircraft and not a hovercraft,
hydroplane-boat, Ecronoplan, etc.? Is there a loophole for a powered airplane
that can't climb to more than 5' AGL?

Second question: If a machine has tricycle gear with nosewheel steering, wings
and 3-axis control, and is solely propelled by thrust from an engine/propeller,
BUT CANNOT FLY, how is it classified? Trike motorcycle?

NOTE: Both of these questions relate to a proposed machine that will weigh
more than 254lbs dry, i.e. not Part 103 legal.

Serious responses please. I'm looking to find and verify a specific FAR rule,
as the correct answer to this question is critical for legal, operational, and
insurance purposes.

Thanks,
Harry Frey
Wright Brothers Enterprises