Morgans wrote:
"Geyser" wrote

"Charles Zimmerman, to the amusement of his engineering peers, proved the
theory that rotors on the top (i.e. helicopters) are inherently unstable."
http://www.hiller.org/flying-platform.shtml

So, what would you expect an article to say, that is trying to build support
for a rotor on the bottom craft? Of course that is what they would say.

Nobody is trying to build support for it. The Hiller Flying Platform is
a relic, 50 years old. Hiller built many helicopters since that time,
with the rotor on the top.

Also, it is taken out of context, since the next paragraph talks about the
fact that they believe a person over the rotor will be able to use shifting
body weight to make the rotor under craft stable.

But stability and controllability are different things. Weight shift
acts against the stability.
The relative wind hitting the draggy form *on top* keeps the platform
from tilting further-n-further and running away. It "wants" to
straighten up and return to a low speed.
If the drag were underneath, it would weathervane toward horizontal and
might be unrecoverable.

Anyway, the article also says that the duct's bellmouth leading edge
generates 40% of the lift. Wow! I wonder why the Martin jet pack missed
that.