"James Cho" wrote in message
om...
Why aren't they more common? It seems like the advantages of them
compared to single main rotor + tailrotor helos are pretty
significant, not great enough to replace traditional designs entirely
but at least sufficient to be more popular than they are now.

It's the classic trade off. Co-Ax helicopters are more stable and don't have
a vunerable tail rotor, but they aren't as manouverable, and require a
vunerable and complex rotor linkage. Manouverability was what saved a lot of
helicopters in Vietnam, so I doubt we're going to be seeing a glut of co-ax
machines.

Matt