Coaxial rotor configuration

[Chizzy101]

The Ka-50 is a high performance chopper and one of the distinctive features of the Ka-50 is it's coaxial rotor. I started to wonder why Kamov seem to be the only major designer currently producing helicopters in this configuation. After a bit of sniffing around on the web, it seems that coaxial rotors have several advantages over the conventional tail rotor layout, such as being quieter, safer (no risk of tail rotor failure), more compact and (theoretically) faster. The main disadvantage I see mentioned is the mechanical complexity of the coaxial rotor.

 

Which makes me wonder, why don't we see more helicopters with a coaxial layout? Is the added engineering complexity really that much of an issue? Do helicopters with this layout have a higher incidence of problems with their main rotor? Are they much more expensive to maintain? I'm interested in your thoughts...

[RvETito]

Main disadvantage is the risk of blades intersection (collision). For that you need severe rotors separation hence the mechanical complexity. Also this makes the rotor mast pretty large - more drag. It's not quieter than a single rotor design, on the opposite. As for advantages- they are much more than the drawbacks- better power use efficiency, better performance (except for speed) and maneuverability, independance of the controls.

[ericinexile]

As mentioned elsewhere on the forum:

 

a) Other rotor designs do not have rotor blades intersecting...that trait alone scares the hell out of me. The prospect of blade collisions aside, coaxials tend to be taller and harder to store/transport.

 

b) Other designs don't potentially reverse yaw control during autorotation, admittedly corrected somehow by Kamov.

 

c) Other twin rotor designs do not place one of the rotor disks in an effective continuous climb state as is the case with the bottom rotor on a coaxial. (Again admittedly, losing the tail rotor more that offsets for this deficiency)

 

I think the overall answer is that the coaxial may be, after all sums are added, a more efficient design. But military philosophy (at least in the west) has determined that having the fastest, most maneuverable helo on the battlefield isn't as important as other traits, perhaps to include simplicity.

 

Smokin' Hole

[sobek]

Hey Tito, good to see you around the forum again!

[Frakin Toasters]

There hasn't been a new military grade heli of the gunship class in America for a very long time. The Comanche was probably the last gunship designed and fielded, wasn't it? granted that was only in 1996, comparatively young compared to the 30 or so year-old Apache. And that never made it into mass production (although that chopper's role wouldn't have really called for such a design). Also, the Ka-50 probably didn't get that much press until relatively recent years, since its inception in the 80's. I think the main thing is that a new gunship hasn't really been designed yet, since the Helix's and the Ka-50's coaxial design got attention. Even then, the Ka-50 never made it into full field production.

 

If America does ever design and build a new gunship, they will probably look into the coaxial technology. I certainly hope they do. One of the things in military technology that really gets me excited is when they design and build new aircraft! Although the new Joint ops F35 really disappointed me. It took away one of my favourite military birds - the Harrier. It also looks quite dull.

[GGTharos]

On the other hand, it does the Harrier's work three times over. ;)

[AlphaOneSix]

The Comanche was probably the last gunship designed and fielded' date=' wasn't it? granted that was only in 1996, comparatively young compared to the 30 or so year-old Apache. And that never made it into mass production (although that chopper's role wouldn't have really called for such a design). Also, the Ka-50 probably didn't get that much press until relatively recent years, since its inception in the 80's. I think the main thing is that a new gunship hasn't really been designed yet, since the Helix's and the Ka-50's coaxial design got attention. Even then, the Ka-50 never made it into full field production.[/quote']

 

The Comanche was never fielded. Only a few prototypes were built, and none belonged to the military. The Apache went into production for the military in 1983, the Ka-50 went into production for the Russian military in 1995.

 

As far as no new helicopters being designed, the Rooivalk went into production in 1999, the Tiger went into production in 2002, so both of those are more recent. China tried to buy the Ka-50, but the deal failed, and now they are producing the WZ-10, the originality of which can be debated ad nauseam.

 

Anyway, a very great number of new helicopters (both civil and military) have been designed and fielded since the inception of the Ka-32 and Ka-50.

 

Besides, if the coaxial rotor system was that much better than conventional, eveybody would be doing it. Maybe we;re just waiting for the technology to catch up (i.e. Sikorsky X-2).

[Frakin Toasters]

Oh really? I guess i'm just behind on the info.

 

When i said fielded i meant field-tested on the comanche.

 

Being drunk and on a forum isn't a good idea for reliability of information. Heh heh.

[GGTharos]

It wasn't field-tested, either (it was never 'on the field') ... it turned out to be too expensive for what it was supposed to do. The AH-64D serves quite well instead, and the Army is looking for a replacement for the underpowered OH-58.

[AlphaOneSix]

and the Army is looking for a replacement for the underpowered OH-58.

 

The replacement for that got canceled as well. ARH-70 Arapaho, canceled October 2008

[GGTharos]

Ah, I wasn't aware. Thanks for the info AlphaOneSix!

 

Yeah, I guess the budget is ah ... tight lately.

[joey45]

underpowered??? jus' wack new engines in it... thats what we did in the Apache.. hence why we can have the piece of cheese on top all the time.

[AlphaOneSix]

underpowered??? jus' wack new engines in it... thats what we did in the Apache.. hence why we can have the piece of cheese on top all the time.

 

The main gearbox on the Apache is a beast, and the GE engines it uses in the U.S. are not capable of producing enough power to overpower it. This is why you see that the U.S. is putting bigger and better engines on the Apache (and have done so for years, e.g. T700-GE-701, then -701C, now -701D). That beefy gearbox is also why there is no problem putting RR engines on the UK Apaches.

 

If things were only so simple for the aging OH-58D...

 

The OH-58D helicopter is equipped with a Model 250 485kW turbine engine from Rolls-Royce. The transmission has a transient power level of 475kW.

 

In other words, the engine it currently has already puts out more power than the gearbox can handle, so the engine has to be derated (derating an engine is like putting a governor on it, reducing maximum power output). To get a more powerful OH-58D, you need more than just a new engine, you need a new gearbox. And a new gearbox would undoubtedly larger and heavier, which defeats the purpose. The OH-58D simply suffers from having too much equipment being placed on too small of an airframe.

 

With the cancellation of the ARH-70 (which fixed the available power problem of the OH-58D with a bigger engine and gearbox and new tail), maybe another aircraft will come into the picture, such as the dual-engine Bell 429...or who knows, maybe a whole new aircraft...maybe (unlikely) the new MH-6M. I would guess that the recon/observation aircraft of the future will be a UAV, but that's just my own guess.