Contra-Rotating Coaxial Rotor Helicopters

[James Cho]

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.

[killfile]

"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

[N-6]

"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.

[Tony Williams]

"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/

[killfile]

"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

[Kevin Brooks]

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

[James Cho]

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?

[Henry J. Cobb]

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

[WaltBJ]

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

[Ralph Savelsberg]

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



>

[The Enlightenment]

(WaltBJ) wrote in message >...
> 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

Personaly, from an aestheic point of view, I prefer intermeshing
rotors. You avoid the complexities of a tail rotor and a coazial
linkage in a coaxial rotor.

They used to be quite common: Pieseki I think, Kaman and I think the
Germans had a little intermeshing Focker anti submarine unit in
service in WW2 circa 1943/44. What happened?

[Peter Stickney]

In article >,
(The Enlightenment) writes:
> (WaltBJ) wrote in message >...
>> 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
>
> Personaly, from an aestheic point of view, I prefer intermeshing
> rotors. You avoid the complexities of a tail rotor and a coazial
> linkage in a coaxial rotor.
>
> They used to be quite common: Pieseki I think, Kaman and I think the
> Germans had a little intermeshing Focker anti submarine unit in
> service in WW2 circa 1943/44. What happened?

Flettner in Germany, Kellet adn Kaman in the U.S. Flettner lost the
War, The Kellets had problems with the blades hitting each other, but
a lot of Kamen K-225s (Navy HTK trainers) and K-600s Navy HUK-1s,
Marine HOK-1s, and AIr FOrce H-43s) wer made. With theeir low disk
loading, they could lift like anything, setting a bunch of altitude
records, and they were, from what I hear, almost too easy to fly. But
the bik killer was drag. While they could climb lije anything,
forward fligh has been described to me as "Pushing your Grandmother's
Turkey Platter sideways through a hurricane". They weren't fast, but
they sure were slow.

Kaman has had a bit of a resurgence with the K-Max, a dedicated crane
based on the K-600, and a few K-600s are used in the Pacific
Northwerst for logging. Just don't try to make one go faster than 100
mph.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[Ralph Savelsberg]

The Enlightenment wrote:

> (WaltBJ) wrote in message >...
>
>>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
>>
>
> Personaly, from an aestheic point of view, I prefer intermeshing
> rotors. You avoid the complexities of a tail rotor and a coazial
> linkage in a coaxial rotor.
>
> They used to be quite common: Pieseki I think, Kaman and I think the
> Germans had a little intermeshing Focker anti submarine unit in
> service in WW2 circa 1943/44. What happened?
>

Kaman still builds a helicopter with intermeshing rotors: The Kaman
K-max, specifically designed to carry underslung loads for logging and
construction work. It has also been evaluated by the US Navy for use in
VERTREP missions and AFAIK Kaman is currently planning an unmanned
version for military work.

The German helicopter with intermeshing rotors was most likely the
Flettner Kolobri. The helicopters designed by Focke (not Focker) used
non-intermeshing twin rotors (side by-side).

BTW Fokker (also not Focker) never nuilt helicopters and at the time of
WW II had moved his business back to The Netherlands.

Regards,
Ralph Savelsberg

[robert arndt]

> BTW Fokker (also not Focker) never nuilt helicopters and at the time of
> WW II had moved his business back to The Netherlands.
>
> Regards,
> Ralph Savelsberg


Fokker does now as a contributing partner to the NH-90:


ww.globalsecurity.org/military/world/europe/images/nh90-731.jpg

Rob

[[email protected]]

(Peter Stickney) wrote:

>They weren't fast, but
>they sure were slow.
>

:)

Reminds me of the guy describing his steak "Well it wasn't
particularly tasty but it certainly was extremely tough"
--

-Gord.

[robert arndt]

> BTW Fokker (also not Focker) never nuilt helicopters and at the time of
> WW II had moved his business back to The Netherlands.
>
> Regards,
> Ralph Savelsberg

Fokker also had the XA-7 aircraft prototype for the US:


http://www.wpafb.af.mil/museum/research/attack/a2/xa7-3.jpg

Rob

[Ralph Savelsberg]

robert arndt wrote:

>>BTW Fokker (also not Focker) never built helicopters and at the time of
>>WW II had moved his business back to The Netherlands.
>>
>>Regards,
>>Ralph Savelsberg
>>
>
>
> Fokker does now as a contributing partner to the NH-90:
>
>
> ww.globalsecurity.org/military/world/europe/images/nh90-731.jpg
>
> Rob
>

Fokker, as in Anthony Fokker, never built helicopters.

The few remnants of his once thriving company, which although it built
rather nifty airliners had financial trouble and ultimately went
bankrupt sometime in the `ninetees, indeed survive by working as
sub-contractors for various projects, including on the NH-90.
Saying that Fokker builds Helicopters is like saying Messier-Bugatti
builds planes (for those of you who don't know, they do hydraulics for
landing gears, for instance).


Regards,
Ralph Savelsberg

[Ralph Savelsberg]

robert arndt wrote:

>> BTW Fokker (also not Focker) never nuilt helicopters and at the
>> time of WW II had moved his business back to The Netherlands.
>>
>> Regards, Ralph Savelsberg
>>
>
> Fokker also had the XA-7 aircraft prototype for the US:
>
>
> http://www.wpafb.af.mil/museum/research/attack/a2/xa7-3.jpg
>
> Rob
>
Indeed Fokker's company, after returning to the Netherlands from Germany
post WW I, sold quite a few planes outside of the country. My remark was
merely intended to point out that the German Focker helicopter (sic.)
referred to by an earlier had nothing to do with the Fokker company in
The Netherlands.

Regards,
Ralph Savelsberg

[robert arndt]

Ralph Savelsberg > wrote in message >...
> robert arndt wrote:
>
> >>BTW Fokker (also not Focker) never built helicopters and at the time of
> >>WW II had moved his business back to The Netherlands.
> >>
> >>Regards,
> >>Ralph Savelsberg
> >>
> >
> >
> > Fokker does now as a contributing partner to the NH-90:
> >
> >
> > ww.globalsecurity.org/military/world/europe/images/nh90-731.jpg
> >
> > Rob
> >
>
> Fokker, as in Anthony Fokker, never built helicopters.
>
> The few remnants of his once thriving company, which although it built
> rather nifty airliners had financial trouble and ultimately went
> bankrupt sometime in the `ninetees, indeed survive by working as
> sub-contractors for various projects, including on the NH-90.
> Saying that Fokker builds Helicopters is like saying Messier-Bugatti
> builds planes (for those of you who don't know, they do hydraulics for
> landing gears, for instance).
>
>
> Regards,
> Ralph Savelsberg

On small historical correction Ralph. Anthony Fokker, together with
Stork, helped build the Baumhauer helicopter in 1925. It was the
Netherlands first helicopter.

Rob