Commanche

[FEBA]

Watching C5 the other night after a few glasses I see that the septics have made a brand new attack helicopter. Nice for the AAC having just procured the Apache.:}
Anyway this American chap said that the machine had a bearing less rotor :confused: So how does that work then ?

[FEBA]

Foxed you lot too, has it ?

[Bomber ARIS]

Well, in the case of the Eurocopter EC135 bearingless main rotor system, the hingeless main rotor blades are bolted directly to the mast.

[SEL]

A bearingless rotor is the same as a hingeless rotor, in most conversations. Instead of hinges allowing the blades to lag and flap, a section of the rotor itself is designed to bend under the loads. These rotor systems are sometimes called rigid rotors too but by design they are meant to bend!

The Lynx and the Bo105 were the first production types to get theses kind of systems, I think. This type of rotor system gives a much more agile manouevrability, a quicker response and higher control power but with the drawbacks of higher vibration, as the blade is 'rigidly' attached to the hub and some stability issues.

Also, I dont think the Commanche is to replace the Apache, I think its role is as an advanced scout.

SEL

[FEBA]

So as far as the rotor shaft to the gearbox, there'll be plenty of bearings there then? That's the bit that confused me.
It's probably apparent that I know the square root of diddly squat about helicopters, although I've been thrown out of lots of them. The C5 program got me wondering.

[Shawn Coyle]

Terminology rears it's ugle head, again.
To me, the term hingeless means and bearingless are more marketing terms than anything else. I have yet to see a clear technical definition of the difference.
However, it appears that the difference is as follows - Lynx and BO-105/BK117 have hingeless blades - all the flap and lead-lag is taken up by the rotor hub. These still have a feathering bearing to change pitch
Other more modern heads, (Bell 430 / H-1Y and Z / EC-135 / MD902 / Commanche are called bearingless because there is no feathering bearing - all the blade motions are taken care of by flexible elements in the head.
Hope that adds to the confusion.

[Bomber ARIS]

Shawn, I´d have to disagree.

In the cases of the Bo-105, BK-117 and the Lynx, the rotor hubs are rigid (i.e. NO FLAPPING OR LEAD-LAG MOTION POSSIBLE!), wheras the the blades themselves flex (about their virtual hinges) in order to accomplish flapping and leading/lagging. They do, however, have actual feathering hinges and the associated bearings.

The RAH-66 Comanche and the EC-135 are both developments of the MBB Bo-108 program which resulted in both types being truly bearingless (i.e. the evolution away from even feathering bearings).

The EC-135 does not even have a rotor head (in the conventional sense), just a rotor mast and four rotor blades attached directly to it. No hinges. No bearings. It's as simple as that.

However, on the question of terminology, I admit to being confused from first day I entered the "Rotary World". The seeming obsession with trying to put all the wierd and wonderful rotorheads (No,not you guys!) into three or four categories. People fretting over how to classify an A-Star, compounding these restrictive terms to come up with fully-articulated-semi-sigid as opposed to the traditional Mr Sikorsky-vanilla-flavoured-fully-articulated. Mister, how come my rigid rotor headed Bolkow's got bearings in it when I was told in training that.........? Can't we stop being "Head-ist" and just learn to love and respect each rotor head as an individual???

Sorry..... Low blood sugar level...... Must...Lie.....Down.....

[handysnaks]

and just to be even more pedantic the lynx head was always described as semi rigid, not rigid (a bit like a lynx pilots thingy!!)
:p

[Lu Zuckerman]

I may be wrong and many of you have accused me of that in the past but I believe the first helicopter to employ a bearingless rotorhead (tail rotor) is the Blackhawk. The opposing blades are made as a unit and the blade beam flexing accommodates any pitch change. A bearingless system requires a very powerful servo boost system and if it fails it would be difficult if not impossible to effect any pitch change. I think.

I believe the NH-90 also has a bearingless tail rotor relative to pitch change but unlike the Blackhawk tail rotor which is rigid in plane the NH-90 blades are free to lead and lag which means it has a bearing to accommodate the lead and lag..


:E :E

[Shawn Coyle]

Bomber ARIS:
you are correct- what I meant to say was that the rotor hubs / heads were classified as rigid, etc. The blades are the blades and they flex on their own.
And I don't believe that Sikorsky and MBB / Eurocopter collaborated to the point that the Commanche rotor head is a development of the BO-108! Bell's head on the 430 / H-1Y & H-1Z dates back to the mid 80's and I believe before the BO-108.

[widgeon]

If I recall correctly the Lynx flapping was in the titanium " cutlet" and lead lag was in the dogbone the original blades were very rigid stainless steel bonded abortions ( i think they were eventually replaced ) . I heard that one pilot put a permenant set in the dogbone after trying to roll the helicopter too close to the ground.
The 350 head has to be the shrewdest marketing invention , completely replace it every 2400 hrs , whereas the 105/117 , before they put a life on the TT straps ,was unlimited