"killfile" wrote in message ...
"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

Do you mean co-axial helos are not as maneuverable due to the danger
of rotor blade collision, or do you mean they are less maneuverable
because of slower yaw-control response due to there being no direct
thrust from a tail rotor? Or both?

Kamov has been building contra-rotating, co-axial helos for decades. I
wonder how many Kamov helos have gone down due to rotor blade
collision? Just curious if this is a very rare occurance or something
that a pilot (of, say, a Ka-50 or Ka-52) really has to be very careful
about during hard or evasive/aerobatic-type manuevering.

I also wonder why Kamov hasn't yet used rigid rotors on their coaxial
helos (like Sikorsky did years ago with their Advancing Blade Concept
demonstrator). Rigid rotors should eliminate some of the disadvantages
that exist with coaxial helicopters that have fully-articulated rotor
systems.