Contra-Rotating Coaxial Rotor Helicopters

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.

"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

"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.

"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.

I haven't heard that the Ka-50 series of combat helos suffers from
poor manoeuvrability. I suspect that its more that manufacturers find
it easier to carry on making what they've always made, because they
understand it very well.

Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Discussion forum at: http://forums.delphiforums.com/autogun/messages/

"N-6" wrote in message
om...
"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.

The limiting factor is indeed the possible interaction between the two sets
of rotors.

Kamov have traditionally built naval helicopters, where the stability to get
you on the deck is more important than high-g manouverability. When the
requirement that was filled by the Mi-24 came out, Kamov offered a
land-based CAS version of their Ka-25, which was built and tested, but
ultimately rejected in favour of the Mil design.

Matt

(Tony Williams) wrote in message om...
"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.

I haven't heard that the Ka-50 series of combat helos suffers from
poor manoeuvrability. I suspect that its more that manufacturers find
it easier to carry on making what they've always made, because they
understand it very well.

I'd suspect it may also have to do with the fact that the transmission
of a helo is already a rather complex, and sensitive in some respects,
piece of equipment--a coax system would likely increase the level of
both.

Brooks


Tony Williams

I know that inherent to the contra-rotating rotors is an unlimited
turn rate, but as for other measures of maneuverability I know
nothing. Slower banking and pitching maybe?

(James Cho) wrote in message . com...
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.

How about excessive turbulence as the rotors cross each other?

-HJC

For one, I can see that the cyclic pitch control system is not a
simple setup. In essence you need two sets of them, one for each
rotor, and with modern helicopters you need a double set of hydraulic
actuators, and some way to get the controls to the top rotor
actuators. So - $$$$$.
Walt BJ

killfile wrote:

"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




A while ago this same subject came up.

I'll copy what I wrote then to this message:

World Air Power Journal vol 31, 1997 includes an article on the Mi-28 in
which a Russian test pilot by the name of Vladimir Yudin is quoted.
According to the article has flown both the Ka-50 and the Mi-28. A
General P. Bazanov also criticises the Ka-50 and a comparison is made
between the Ka-50 and the AH-64.
I'll quote parts of the article:

begin quote
"Coaxial-layout helicopters are great flying cranes, but I wouldn't
dream of going to war in such a helicopter, even the most modern one"
said Yudin.
One reason is that certain horizontal/vertical speed combinations are
unfavourable for this layout, e.g. , descent speeds from 3-4 to 9-10 m/s
and airspeeds around 30 km/h lie within the ring of turbulence zone.

Investigation of the crash of the first prototype Ka-50 ('White 01')
which encountered severe turbulence and crashed out of control, killing
the pilot) showed that critical speed increases as g loads grow.

....

At 2g critical speed is about 70-80 km/h, i.e. a helicopter's speed over
the battle area. In other words, some suggest that coaxial helicopters
are dangerous to fly in combat at 0-80 km/h. They also have directional
control problems at descent speeds of 5 m/s and higher and airpeeds up
to 60 km/h, which are also in the range of a combat helicopter in
action.
....
Coaxial helicopters have been under development in the USSR for the same
50-year period as conventional ones. Why are there so few then and why
have they never been used in real combat? The reason is that while a
conventional helicopter can land successfully after sustaining battle
damage to the main rotor, this is completely impossible for a coaxial
helicopter because a danaged blade can flap 1.5 m up and down and blade
collision is imminent.
General P. Bazanov, who often chaired state commisions during state
acceptance trials of new military aircraft is convinced that the AH-64
would emerge as the winner in a dogfight with the Ka50 because the
Apache can perform complex maneuvres in the vertical plane which the
'Black Shark' cannot.
....
The Ka-50's aerobatic displays at air shows certainly look impressive to
the public. However, General Bazanov points out that the Ka-50 makes
sharp turns only in a sharp climb , and then only left turns because a
right turn would very probably lead to blade collision. Conversly
Russian specialists judge the maneuvres demonstrated by the Apache as
usable in combat.
....
end quotes

Some more problems concerning coaxial rotors are mentioned like high
rotor loading and downwash and difficulties in protecting the rotor
system against wire-strikes.



Regards,
Ralph Savelsberg