Bell 412 and 407 rotor head

[TheMonk]

Why are they different? Why not just upsize the 407's rotor head?

Monk

[TheMonk]

412's
http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Bell_412_transmission_and_head.jpg/450px-Bell_412_transmission_and_head.jpg
407's
http://upload.wikimedia.org/wikipedia/commons/thumb/5/5f/Bell_407-rotorhead.jpg/800px-Bell_407-rotorhead.jpg
Which is better? Why?
Monk
PS: the 412's looks more complex, while the 407's looks straight forward.

[TheMonk]

UL,

I see what you mean about the 412 coming first. Shouldn't new 412's have "bigger" 407's head now?

I thought the 412's rotor head was not two teetering heads on top of one another. I don't see teetering hinges/bolts.

Monk

[outhouse]

When Bell wanted to upgrade the old 212 and give it two extra blades two rules applied I think. The easiest and the best cost effective solution, from that virtually nil maintenance costs between overhaul and a bullet proof design. The answer was as indicated. Additions to the original design to include the droop restrainers and the pendulum dampers went a long way to solve problems that became evident in service.
Ok so it can be a bitch to track and balance and if removed rarely returns to its original settings and generally needs a few tweaks to get it back to its previous ride.
The old girl is now in her twilight years and not really worth any fundamental changes to her running gear. A shiny flat screen display or two, improvements to the AP and a better power margin doooo quite nicely thank you.
Outhouse.

[Shawn Coyle]

Svenestron:
That design of blade is on the Bell 430, MD900, EC-135 to name just three. It is very nice - low vibrations and low maintenance.
The Bell 412 rotor head design story will be buried somewhere in a paper given to the American Helicopter Society. It was the start of production multi-bladed design by Bell, and the 406 and 407 built on that experience.
Like everything else, very complicated in the design, but very simple looking in the end.
And in the intervening years, a lot more was learned about composite materials and their strengths and weaknesses.

[ericferret]

The cost of certifying a new head and blades is immense.

All manufacturers have to consider how many aircraft they will sell in the future and whether the costs will be recovered.

Trying to get them to make even minor improvements requiring design changes is very difficult.

[CS-Hover]

"I believe the 430 has two spars placed on top of each other and each holding two blades. This reduces the rotor head to “merely” clamping the two spars together."

not easy to see, but hope it helps :hmm: (find those in the web :))

http://i86.photobucket.com/albums/k105/markm1245/pic3.jpg

http://i86.photobucket.com/albums/k105/markm1245/pic2.jpg

http://i86.photobucket.com/albums/k105/markm1245/pic1.jpg

http://img140.imageshack.us/img140/989/bell430headkd8.gif

http://www.aviationcorner.net/public/photos/1/8/avc_00019118.jpg

[Shawn Coyle]

Svenestron:
I meant to say the rotor heads of these are nearly the same - blades are obviously different.
As far as having two pieces 'stacked' on top of one another, it makes little or no difference to the handling. I have no idea why Bell did things this way, and from many points of view, it makes absolutely no difference to the handling or performance.

[Encyclo]

Bell being conscientious of helicopters that work for a living, always considers maintainability in their design. If the yokes on the Bell 430 (or 412 for that matter) where one piece, guess how easy it would be to send a main rotor head to Angola or some of the other places in the world where helicopters get up and go to work every morning. Two narrow long boxes are better than a huge square one:8.
As Shawn said, having stacked yokes has no negative effect on ride (Bell 430 probably has the best ride of all) or ease of working the rotor. Experienced techs will get a 412 rotor in, in about 3 moves, as long as you’re not trying to get beat-up/trashed blades and rubber to fly together:=.

[OverTq]

Experienced techs will get a 412 rotor in, in about 3 moves, as long as you’re not trying to get beat-up/trashed blades and rubber to fly together:=.
Blimey! I have some very experienced 412 engineers and it will take them at least 4 adjustment on the ground and another 4 plus in the air to get below vibration limits.