Harry K wrote:
I wondered about that. Seeing 52 hp and ultralight and ref to 2 people
in the same description set off warning bells. Oddly, a google search
of 'ultralight airplane challenger II' returns many hits with
ultralight in the title.

They may be Canadian aircraft. See:
http://www.challenger.ca/faq.html
The article implies that the Canadian CAA has a different definition of
"Ultralight" than the US's FAA.

-Luke