Mil Helicopters Blade Retention?

[Johnny31297]

Heyho,
I recently have been wondering how the Russians implemented blade retention on their helicopters, especially on the Mi-26, where the blades require a whopping 31t centripetal force to stay connected to the rotor.

Steel wire straps?
Shim packs?
Elastomeric solution?

Any insight is greatly appreciated!

Jonas

[RVDT]

You mean this great lump?

Doesn't look that special.

[[email protected]]

Looks like it was designed and built by Brunel

[500e]

Originally Posted by [email protected]

Looks like it was designed and built by Brunel

A lot of his stuff still about though & working

[Johnny31297]

That's nice and all, but does anyone have actual answers?

[[email protected]]

Have you tried google???

No elastomerics, no strap packs, just big bolts and shafts onto the titanium MRH.

[Johnny31297]

Originally Posted by [email protected]

Have you tried google???

No elastomerics, no strap packs, just big bolts and shafts onto the titanium MRH.

I have googled a lot, and haven't gotten any results, otherwise I wouldn't have posted. I kind of doubt that it's just bolts and shafts taking all the centrifugal loads while still allowing easy pitch changes.

[AnFI]

johnny
what are you trying to get at with this?
are you thinking that compressive elastomerics are better?

these (old fashioned) hinged heads are generally exceptionally smooth (when set up properly) and fly beautifully
the downside issue being bearing wear and lubrication (maintenance), otherwise pretty good eh?
or what is your thinking?

[albatross]

Perhaps you could contact them?

[[email protected]]

LMGTFY

Mil Mi-26 helicopter - development history, photos, technical data

[Johnny31297]

Originally Posted by AnFI

johnny
what are you trying to get at with this?
are you thinking that compressive elastomerics are better?

these (old fashioned) hinged heads are generally exceptionally smooth (when set up properly) and fly beautifully
the downside issue being bearing wear and lubrication (maintenance), otherwise pretty good eh?
or what is your thinking?

What I'm trying to do here is to gain knowledge.

For example, I know that a BO 105/BK 117 rotor head has four steel wire TT-straps with 12,000 windings of 0.25mm² steel wire each, which take the blades' centrifugal loads and allow smooth blade pitch change.

I've also seen a picture of an early version of that very head with laminated shim packs, similar to what the Hughes 500 series uses.

I know Bell also uses steel wire TT-straps on many helicopters, as well as elastomeric solutions on some. For most Western helicopters, a quick Google search brings up all kinds of material that answers the question of how things work, Robinson actually makes all their materials publically available I think.

I was just curious what is done in terms of blade retention in Eastern countries, as you obviously can't just look at a picture of the helicopter and see what's inside the main rotor hub. As many of the Mil helicopters were developed during the cold war, I suppose they might have gone a different way than the Western world, but that's just speculation.

It comes down to pure curiosity. I opened this thread because Google wouldn't bring up anything answering my question really, and I figured this would be read by people who might have worked with or on those helicopters.

[Droop Snoot]

It appears to be a fully articulated rotor with the lead/lag (vertical) hinge outboard of the flapping (horizontal) hinge, using antifriction (ball or roller) thrust bearings stacked to react the centrifugal loads. This is similar the CH-46 Vertol rotors, and not unlike many Sikorsky rotors.

[Vertical Freedom]

WoW what a Rotor Head.....a beauty & a beast

[riff_raff]

In the picture provided above, you can see that the main structural attachment for the blade is a multi-lug clevis joint with two shear bolts. The only thing that seems different with this design is the type of shear bolt used. Most of the similar blade attachments I have seen use an "expanding" shear bolt, which has a set of split taper bushings that expand in diameter when the nut is torqued, to eliminate any clearance between the bolt and clevis bores, creating an optimum fit.

[Droop Snoot]

rr:

The UH-60 originally had expanding pins, now has solid pins.

[riff_raff]

Expanding bolts do seem a bit complicated at first glance. But there is a good reason for using them with the clevis attachment shown. The multi-lug clevis attachment requires an interference fit between the lug bores and shear bolt body to prevent fretting damage. This type of fit is very difficult to achieve with solid body pins/bolts.

[[email protected]]

Not if you are a sub-contractor replacing the hinge pins in Tornado wings - if you can't get them in because you forgot to cool them first, you can just use a hydraulic press to force them in.........doh!!!