Coaxial Rotors

[mechanic]

Why don't American heli companies produce coaxial design heli's? Is it cost?

 

They seem to be far safer than single rotor types. No LTE, no RBS, no tail rotor for pax to walk into, higher Vne airspeeds, higher gross weights, less drive train part components.

 

There must be some reason they are not popular? Thougts?

 

Kamov Shark Youtube

 

Helicopter Gyrodyne Youtube

[bqmassey]

Why don't American heli companies produce coaxial design heli's? Is it cost?

 

They seem to be far safer than single rotor types. No LTE, no RBS, no tail rotor for pax to walk into, higher airspeeds, higher gross weights, less drive train part components.

 

There must be some reason they are not popular? Thougts?

 

Kamov Shark Youtube

 

Helicopter Gyrodyne Youtube

 

 

I've always wondered the same thing.

 

I have a remote control helicopter that's coaxial. Here are a few things that I've wondered about coaxials.

 

1.) It's extremely stable, almost too stable. Maybe it's beneficial to have a combat platform that you can throw around with more agility--something that doesn't resist irregular attitudes.

2.) High center of gravity. Maybe coaxial helicopter are less stable on the ground and more prone to dynamic rollovers.

3.) If I try aggressively to get my helicopter into an upset attitude, the rotors tend to collide. The solution to this may be found in different rotor head assemblies, I'm not sure, but the most obvious is to spread them apart. That'd result in an even higher center of gravity.

4.) Efficiency. Is it less efficient to drive one rotor right under another one, with dirty air, than to drive a tail rotor?

5.) More maintenance? Does it take more part and labor to keep two rotor heads running than a tail rotor?

 

Just some thoughts. I'd be interested to learn more about the coaxial design.

[Gomer Pylot]

Increased complexity, increased weight, increased cost. Two sets of blades, plus all the other moving parts, are far more complex, expensive, and heavy than a conventional tail rotor. Manufacturers will always go for the design that makes the most profit, and which they can sell easier. Igor's original design has kept on being used for good reasons.

[Goldy]

Increased complexity, increased weight, increased cost. Two sets of blades, plus all the other moving parts, are far more complex, expensive, and heavy than a conventional tail rotor. Manufacturers will always go for the design that makes the most profit, and which they can sell easier. Igor's original design has kept on being used for good reasons.

 

 

OK, I have a slightly different view. Manufacturer's will do whatever makes em the most money....quite true.

 

Tail rotors are loud, inefficient, unsafe HP sucking apparatus that do absolutely nothing for us. Coaxial rotors put all available HP into vertical or forward thrust, which is a good thing. I think the Kaman KMax offset twin solves a lot of the CG problems of a typical coaxial...and for the most part, both rotors are in clean air.

 

Basically it looks weird, so there is not a lot of demand. Remember Betamax was a better system than VHS, but it lost the race...and now they are both gone.

 

Its "acceptance"...which sells things, that is more important than efficiencies.

 

Goldy

[mechanic]

I had GOM ops in mind when I was thinking about coaxial types. Safety from tailrotor, greater speed and load capacity for deep water drilling, and better wind handling characteristics mainly. I was thinking special purpose situations. The Russians seem to like them.

 

Bell has kinda used GOM as a possible sale for their new Tiltrotor aircraft for deep water drilling. I think the tiltrotors are kinda cool but there are some things that worry me about those designs. Like, what will happen if a malfunction happens in transition from airplane to heli, like if one engine rotates to heli and the other is stuck in the plane position? Things like that bugs me about the tiltrotor. No matter how good it is sooner or later something is gonna happen to it.

 

Hummm, things to ponder..

 

Later

[HelliBoy]

Things like that bugs me about the tiltrotor. No matter how good it is sooner or later something is gonna happen to it.

 

Are you more dead if you flame it in with mast bumping etc.??

 

Technology is cool. bring it on. (are tiltrotor pilots all hermaphradites?)

 

Anyways- gomer hit the nail on the head in the coax debate, ask the maintenance dept how they feel about 'em...and I'm not so sure about the increased speed of a coax; sure less dissymetry of lift issues but a six foot high rotor mast above the fuselage is a boatload of drag. Throw in sluggish at best yaw control and the ruskies can keep 'em. I'd also like to know what's going on with the upper disk during an auto in a coax.

[slick1537]

mechanic, are you talking about the civilan version of the osprey? I don't know much about them, but I do know when the military started using them a few years ago and they were quite prone to accidents. I heard they have been revised since.

 

http://images.google.com/imgres?imgurl=htt...%3Doff%26sa%3DN

[Linc]

Sikorsky is working on their X2 demonstrator, a coaxial design, which they hope will reach 250 knots, which is the edge of the under 10,000' speed limit. Bet they want to show they can beat it without going the compound helicopter (gyrodyne) route.

[Vladimir]

I did try this one here in Russia, it is prototype yet but very promising. What do you think about this one?

Rotorfly.wmv

[RagMan]

It may only be the military version of the tilt rotor, but to my understanding, if one of the engines fail on a tilt rotor aircraft, the drive system is linked and can run off of the good engine. I'm not sure if they have incorporated that into the civilian tilt rotors yet.

Edited April 22, 2010 by RagMan

[d9aplus]

I'm not sure if they have incorporated that into the civilian tilt rotors yet.

 

Yes, they did / V22 do that with hydraulics and BA609 with shafts connecting

both MGB between each other.....

 

Concerning coaxial one,

see one nice proven design now with Turbomeca Arius>

 

 

1400 kg of load, removable cargo/PAX/or utility back

Edited April 22, 2010 by d9aplus

[lelebebbel]

so, according to Turbomeca ( http://www.turbomeca.com/public/turbomeca_v2/html/en/produits/version.php?aid=1407&sfid=502&mid=615 ), the engines are rated at 622shp continuous in the KA226, for a total of 1,200shp total. With that, the 226 will lift (according to wikipedia) 1500kg externally, and its maximum speed is about 200kph.

 

Comparable single rotor / tail rotor helicopters will lift pretty much the same and cruise faster. The twin rotor design can't be such a great advantage then.

[Vladimir]

so, according to Turbomeca ( http://www.turbomeca.com/public/turbomeca_v2/html/en/produits/version.php?aid=1407&sfid=502&mid=615 ), the engines are rated at 622shp continuous in the KA226, for a total of 1,200shp total. With that, the 226 will lift (according to wikipedia) 1500kg externally, and its maximum speed is about 200kph.

 

Comparable single rotor / tail rotor helicopters will lift pretty much the same and cruise faster. The twin rotor design can't be such a great advantage then.

 

Agree. But single rotor improved by a lot of companies. Coaxial Rotors died with Kamov and conserved in Russia but probably it has more prosper than single rotor. I did fly this tiny one in Russia without tail, while they were fixing it . So it can use engine power only for rotor it is 10-20%. Also for pilot coaxial rotors are much more better except autorotation.

[d9aplus]

So first "similar" example can be EC145

put some figures near each other and draw own conclusions....

 

Speed is not an designers dream here, aerodynamic either,

on the other hand steady hover and hot&high are better than average...

 

Only serious "problem" of KA226 is quite short time resource on MGB

[Eric Hunt]

Have a think about what takes away the efficiency of the main rotor - INDUCED FLOW - the stuff coming down from above.

 

The top rotor gets relatively clean air, sucked down and accelerated downwards.

 

The bottom rotor is now working in airflow coming vertically much faster than what the top rotor got - so the bottom rotor has to work a lot harder to get a reasonable angle of attack.

 

In the Sikorsky ABC, once you get a LOT of forward speed, the extra induced flow isn't so important, as the blades are almost in autorotation, but it is still a reason why the tried-and-true top and tail are still being built.

 

The Kaman has the blades offset, and each blade, when working, has clear air above it - no extra induced flow. Probably a better solution than Kamov.