cavelamb himself wrote:
Morgans wrote:

"Capt. Geoffrey Thorpe" The Sea Hawk @See My Sig.com wrote


... But pendulum's have nothing to do with it.


I'm not buying it.


I'm skeptical too.

"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