Bell 412

[TheMonk]

Just got a closer look at an airmed 412n the other day. Am I wrong or are the four blades just a combination of two 2-bladed systems set at 90* to each other? They llok as if they were two separate teetering hinges on two different planes.

Other four bladed rotor heads I've seen had all four blades in the same plane.

Monk

[paco]

I believe that was the original configuration, but improved since then

Phil

[Gomer Pylot]

The head is two pieces, bolted on top of each other. Bell hired Rube Goldberg to design the entire aircraft, and a wonderful job he did.

[oscar bravo]

Can be a real bear to track and balance one of these things, the blade tips look kind of funny from inside the cockpit too...as one would imagine, two different tip paths.

I haven't weighed one myself but it seems someone told me just one of those "dingle-balls" weighs 17 pounds!

http://i199.photobucket.com/albums/aa172/ajbart/DSC03220.jpg

[widgeon]

quite surprising how slender the mast is . Is it a lifed item on this aircraft ?

neat site shows many rotor heads.
http://www.b-domke.de/AviationImages/Rotorhead.html

[TheMonk]

Oscar Bravo,

Thanks for the pic. That's just like what I saw.

Wil

[ericferret]

The Hughes 500c has two overlapping strap packs.

When you set up the pitch links one pair are longer than the other to compensate.

So nothing new really.

[Gomer Pylot]

No, it's not new. It's just impractical. The blades are in different planes, and I've spent weeks trying to get one smooth enough to be acceptable. You can't really track them, you just get them to an acceptable ride. The first ones came out without the weights on the head, and most couldn't be tracked at all, so Bell put a couple of hundred pounds of weight up there to make it work, and that was payload lost immediately. The 412 is just a UH1 with 2 engines and a slapped-together 4-blade system, nothing new about it. Bell is so far behind the rest of the industry it may never recover.

[chuckolamofola]

Gomer Pylot said:

You can't really track them, you just get them to an acceptable ride.

You obviously haven't flown many of the later EP's. Typically they can be tracked in 3 flights or so. 4P's are a lot less too. EP's are a significate improvement over the early 412's in many ways.

The early 412's flying in the GOM are all getting long on the tooth, have had a lot of blade repairs done over the years which affects how they work. Many of the repairs were done in-house and the trailing edge of the blades got thinned out which greatly affects how the blades fly. At lot of rotor working troubles have been locally made. Like mis-matching blades across the fleet.

The pendelum absorbers had nothing to do with rotor working they were put on to reduce the 4P in plane vibration. Yes they do affect the payload...

Actually the 412 and its little cousin the 430 have stacked rotors and both can be worked quite well.

[Encyclo]

Having a stacked yoke is not all bad:

A lot easier for shipping; two long boxes in lieu of a huge rectangular box. Make's a big difference when you're grounded wayyyyy out there. Also the issue of tip path being different for each yoke has no negative effect on ride quality. The Bell 430 also has stacked yokes and has one of the smoothest rides of any helicopter. A lot of the issues with working Bell 412 rotors are related to either bad rubber (seperated/too old) or bad blades (too many repairs/paint touch-ups)

As for the weigths added to the M/R head, SPA (simple pendulum absorbers) weights, they are there for the 4/rev. They were not there originally but were added aerly on to help control 4/rev. Same type of device can be found on other four bladed system (BO-105/BK-117).

[skidsock]

I've heard that Bell is considering going to a composite head on the 412 due to a worldwide shortage of titanium. Not holding my breath!

[Matthew Parsons]

Monk, it is two pairs of rotors flying in two different planes, but they aren't on teetering hinges, they are semi rigid. If you look at other helicopters, you may see a similiar configuration on the tail rotor.

As far as track and balance, yes, normally complete in three flights, and normally very smooth.

[Blackhawk9]

Haven't had a 412 i couldn't get in limits some have taken 2-3 days and upward of a dozen flights , but got them eventualy!! even mismatched -104 blades, have used 8500 and Rads-at, like the rads better with problem blades, and yes the 412 is a bitch to balance compared to other helo's, get rid of any blade thats not a -109 and take your time with the balancing and start at basic with everything!, sometimes you may have to swap blades beside each other (not opposite)but a smooth 412 at 120 kn is possible.

[TheMonk]

Mathew,

Thanks for that info. I did noticed that it wasn't a teetering hub, 'cause I was very interested so I looked at it very close. The pilot let me hop up on it to get real close.

Blackhawk,

Can anyone (me) w/o an A&P just go out and buy a Chadwick, get familiar with the hows and the whys and get busy on these? In short, do blade balancers need to be certified?

Perhaps someone familiar with FAA regs can charm in. I'm in the US, private pilot helo with time in R22 and TH55 only. Oh yeah time in Cessnas too, buy never did finished the fixed wing add-on.

Monk

[Dan Reno]

Not to sound too harsh but if the best Bell can come up with after all these years is to simply plop one 2-bladed head atop another they, and their customers are in trouble. Are those metal to teflon PCR bearings also? One great step backward!

[toolguy]

The balancing gear should be either recognized or approved by the aircraft OEM. Tracking and balancing are maintenance actions so you need an A&P, AME, JAR66. It takes quite a while to master using this gear and some never do, but it is not something that can't be learned.

[Matthew Parsons]

Dan said,

"Not to sound too harsh but if the best Bell can come up with after all these years is to simply plop one 2-bladed head atop another they, and their customers are in trouble."

What do you believe is the problem with designing a rotor system like this.

You'll find other manufacturers have used this idea on tail rotors of such aircraft as the Apache, the Mi-28, the Mi-35, and the EH101. Bell is also using this arrangement on the main rotors of the 427, and the 407 (OH58D). The UH1Y and AH1Z use a similiar design on the main rotor and the tail rotor.

The claimed benefits are in reduced weight, reduced manufacturing complexity, increased blade flapping angles and reduced logistical problems associated with transport of rotor hub components.

What is it that you know that these manufacturers don't know, Dan?

[Simul8]

"Bell is also using this arrangement on the main rotors of the 427, and the 407 (OH58D)."

:= Not exactly...the 427 and 407 use the "soft in plane" rotor system. The only similarities between the soft in plane and the stacked are the elastomerics.

[Matthew Parsons]

Simul8, thanks for the correction. A quick look at a picture online looked the same as the 412, but the closeup revealed what you said.

[tottigol]

412 rotor is "soft-in-plane" too, you are correct about the rest.
While the 430 rotor is stacked, everything else is different about it, the lenght of the yokes, the way they attach to the blades etc.

412 rotor was adopted in the late 70s and it was a great impprovement over anything there was then.

[Salusa]

Bell only support the use of RADS-AT for rotor T&B.

[Dan Reno]

A one piece fully articulated rotor head is best for helos. Agree? If so, then the H-60 MRH looks like a better design.

[Matthew Parsons]

Dan,

I don't think you can say any one design is the best. It really depends what you want to do with the helicopter and what limitations reality impose.

[Dan Reno]

Yes, the fully articulate rotor head is the best. Anything else is a compromise. You sacrifice when ever you restrict the blade's movements in all planes. You reduce costs and ride comfort also. The US military can afford the best so go with it. These heads are out of the usual operator's price range so they compromise. US military would certainly go to a fully rigid or semi-rigid head if it was the BEST. They are not. As usual, deep pockets get you the best.

[Matthew Parsons]

Wrong again Dan. Check your facts before you post.

[tottigol]

A one piece fully articulated rotor head is best for helos

Hu?:eek::eek:

[Dan Reno]

"I don't think you can say any one design is the best. It really depends what you want to do with the helicopter and what limitations reality impose."

A fully articulated hub can do everything you want ANY helo to do, only better. Consequently, a rigid and semi rigid hub can't do everything a fully articulated hub can do so therefore what's best?

[Um... lifting...]

Dan-

"Consequently" means "as a result". That's what we call a non sequitir. Your conclusion doesn't follow from your premise. Or, your sentence makes no sense.

Neither does your argument.

Explain the below three machines as justifications for your argument. You might be able to pull off the last two, but only with a weak argument. You won't be able to do the first one. (Nor the Dauphin, BO-105, and several others). Extra credit if you can figure out what other physical characteristic these machines have in common (very approximately) other than broadly the type of rotorhead (I don't believe you will find that any of them are articulated... unless it means something different to you than it does to me).

Comanche (RAH-66)
Venom (UH-1Y)
Viper (AH-1Z)

I happen to side with Matthew on this one. Part of the "best" design is making sure it's light enough to get in the air, has the proper inertial characteristics for the helicopter it's made for, and the target customer can afford to buy it. A helicopter that's too expensive for the target customer is not a good design, it's a lost opportunity.

[Dan Reno]

I apologize for my GED education that only allowed me to fly H-1s and then H-60s. Like us all, we are loyal to our helo and swear nothing is better...especially if your stuck with it. We were forced into the H-60 and like puppies our eyes were opened. I can only imagine what the H-53, H-92 and S-76 must be like since it was like night and day going from the H-1 to H-60. These two are the only helos I can speak to about but if you believe a rigid rotor is better than a fully articualed, more power to your superior intelect. Keep the shiny side up Pal. Best.
Dan

[Takan Inchovit]

... and you, yourself Mr Lifting, seem to have the view of an acccountant. The term "Best" has not been accurately defined.

[Gomer Pylot]

Please explain how it's possible to be both 'one piece' and fully articulated.

[Um... lifting...]

I didn't try to define "best", but as Matthew pointed out, it's going to depend upon a lot of things.

Dan, if I insulted you, I apologize. I've got no argument with you that an articulating head is a better performance choice than a semi-rigid underslung, and depending upon the machine, it can have better performance than a rigid head. But, it depends a lot upon the machine and what it's planned to be used for. In a light helicopter, a semi-rigid underslung is a good choice that has proven itself over time. It's not the best functional choice for an attack helicopter, but it works. It's not state of the art, but within its limitations, it does what it's supposed to. As Nick Lappos has pointed out to me on a few occasions, things aren't always what they initially appear to be to we pilots in helicopters and I've had more than one of my incorrect ideas put on a spit and barbecued. I went from flying a teetering head to flying an elastomeric head (with what is now about 30-year-old technology) to a different company's elastomeric head to going back to that same teetering head to a newer elastomeric head to an even newer elastomeric head with a few articulated heads tossed in there along the way for fun. To go from teetering to a more responsive head is like going from your Mom's Dodge to a sports car. You're really bound to like it. To go from a single-engine H-1 to a UH-60... well, same thing.

It's been my observation that a rigid head is a great choice for a small-medium size helicopter. They're simple to maintain, durable, can have a low radar signature, are resistant to battle damage, and with the right control system, can be fully aerobatic or nearly so. They haven't, however, scaled up real well into large helicopters so far, which may be part of why you'll see that Eurocopters don't use the same type of head in a SuperPuma as they do in a Dauphin. I wouldn't be surprised though, if somebody was working on it somewhere.

I've seen that an articulated head is terrific for medium-large helicopters and I wasn't saying an articulated head is a bad thing (The Hawk series I think is the most successful military helicopter line ever produced and the S-76 hasn't done too badly either). Since Sikorsky has concentrated their programs on machines that are about 5 or more tons these days, you won't see too many non-articulated heads on Sikorsky machines. Comanche is an exception and is one of the heaviest helicopters with a bearingless rotorhead that I know of. But again, I wouldn't be surprised to see technology from Comanche's rotorhead make it into Sikorsky's other product lines eventually, but I wouldn't know what, when, or how.

And while you, Takan, may think I sound like an accountant (I'm not, I'm an engineer by training, just not an aeronautical one, and I've flown all three basic types of heads, they all have their points) when an engineer figures out a design of any kind, he has to keep in mind that the machine or bridge or building or whatever needs to be able to be affordable to somebody who wants it or it will never leave the drawing board. It doesn't always make sense to use the most sophisticated technology on a simple design. And that's reality. And that was my point. Defining "best" is a slippery beast. I'm not going to ATTEMPT to define it for all helicopters or all things to all people.

And Dan, the military doesn't always get it right. I spent a couple decades in uniform and saw it enough. In the case of the Sikorsky Hawks though, I think they did. I think they got it right with the Hueys too... but that was then. I can't help you with how the H-53, S-92, and S-76 fly (I've only been a passenger in one of those), but my 53E buddies call it 'the sh*tter'. If you ask why, they say it's because it's like sitting on the can and flying your house around.

[FlyAny]

Recently our HP came out of a 2500 hour inspection, if you've never seen a helicopter that you fly in that many pieces, including the main and tail rotor systems, you might not want to.
The aircraft was tracked and balanced in a day and a half with 4 or so flights.
Two of the engineering goals approached by Bell with the 412 were to increase speed and decrease noise as compared to the 212, they achieved both.
Since then, the 212 has been widely referred to as the lifter, and the 412 the cruiser. Ask the folks flying high altitude mining support in Malaysia, I think they will echo this.
I hear/read so many who feel that Bell simply recycles old technology. To the extent that it is functional to the market to do so, they do. After all, a derivative aircraft is normally much cheaper to certify. And, they continue to hold a fair market share.
They do make mistakes, Rogerson and Krados (sp) as a sole source provider for glass displays?

[Dan Reno]

Best means: “Better than ALL others”.

If a fully articulated rotor Can Do ALL the things a rigid or semi rigid rotor can do, then it is simply the Best.

So, regardless of the mission, weight, cost, small, large medium airframe, simplicity, complexity, cuteness, material, blah, blah blah, (get the idea?), if one rotor system can do ALL of this and the other rotor systems cannot, then it is “Better than the others” or BEST.

And yes, I agree the BEST thing to happen to rotor systems is the elastomeric bearing.

BTW, a one-piece fully articulated rotor system would look like the H-60, H-3, H-53 or H-92 not the two rotor hubs laying atop one another which has been described by the marines as the “homo-head”. Yeah, a lot of thought went into that system!

[Shawn Coyle]

Dan:
If a fully articulated head is truly the best design, why are all the new rotor heads bearingless rotors? (EC-135, MD900, Bell 430, and I'm sure there are others).

[Dan Reno]

Cost. (one of the qualifiers I mentioned)

[tottigol]

Manufacturing costs or maintenance costs?
Most rigid type rotors have a far smalller number of componensts, and most of those componensts are rated "on condition".

I really don't see why someone would continue to invest money in research and production of more expensive rigid rotor designs when we already have all the technology available for a 1960s design fully articulated rotor head.
Those bean counters have to be going ape over this.

[Dan Reno]

We're getting off track again with what is the BEST. Refresher:

If a fully articulated rotor Can Do ALL the things a rigid or semi rigid rotor can do, then it is simply the Best.

So, regardless of the mission, weight, cost, small, large medium airframe, simplicity, complexity, cuteness, material, blah, blah blah, (get the idea?), if one rotor system can do ALL of this and the other rotor systems cannot, then it is “Better than the others” or BEST.

[tottigol]

"BTW, a one-piece fully articulated rotor system would look like the H-60, H-3, H-53 or H-92 not the two rotor hubs laying atop one another which has been described by the marines as the “homo-head”. Yeah, a lot of thought went into that system!"

I am not sure how you can define "one piece" this:

http://www.b-domke.de/AviationImages/Stallion/Images/0423.jpg

or this:

http://www.b-domke.de/AviationImages/Rotorhead/Images/1642.jpg

or even this:

http://www.b-domke.de/AviationImages/Pelican/Images/HH-3F_1476_8580.jpg

Just to explain, rigid rotors, are not "rigid", but most of the hinges in traditional "fully articulated" rotors are replaced by elastomerics or virtual hinging built into the composite structure of the component itself, highly decreasing the number of components necessary to assemple a complete rotor head.
Does that make it more expensive?

[Dan Reno]

Anything other than the homo head is one piece...all spindles attached to ONE hub.

[tottigol]

It seems as if you have a personal case against the 412 rotor head, even though I am not sure you ever flew one.

[Dan Reno]

It's an inanimate object so nothing personal. Never flew one, don't have to since fiully articulating heads are the best. Anything else is a compromise. If you refer to the marine's nickname for it of "homo head", that refers to one two-blade hub laying on top of another two-blade hub. Get it? Gee, that certainly was quite a new rotor head design breakthrough don't you think?

[tottigol]

Well, to begin with they are two separate yokes but the are designed to act as if it was one.
They do not teeter and flap and hunt as individual yokes, they do not teeter at all since the rotation plan is the same as the oke mounting plan.

It's pretty much a single rotor head with staggered blade couples. the Bell 430 rotor head, derived from the 680 type rotor has the same characteristic (staggered yokes), however the yokes' arms are much longer and these are made of tightly wound composite materials rather than metal.
The main difference is that the pitch change links work on the blade in the 412 rather than the yoke in the 430.

I learnt not to criticize something I know nothing about, I may end up with the classic foot in mouth situation.

[Dan Reno]

I bow to your superior intellect and will inform the marines of their mistake though perhaps they were just trying to be cute with the homo head thing. Cheers.

[tottigol]

The first correct statement from you on this thread. Thank you.

[Shawn Coyle]

Dan:
Attaching a cute name to a rotor head is no substitute for actual thinking. And in all the years I've known Marines, I've never heard any rotor head described that way.
If all you've ever flown is two types of helicopters and you compare the H-60 to the UH-1, and extrapolate from that to the universe, then you have a lot of learning to do. Many of us here have flown a lot more types than you could probably name, and would never make the sort of bold and unsubstantiated statements you make.
There is no 'best' rotor head, or it would be the only type used by everyone.
Articulated heads have their place, as do two-bladed teetering heads. There are many who would claim that in overall simplicity and straight and level ride quality in turbulence, for example, that the two-bladed teetering rotor is far better than the rigid head.
So, rather than try to pass yourself as the only person who knows what's 'best', pay attention to the experience and knowledge of the others in this forum. You just might learn something.

[Dan Reno]

Shawn. Perhaps you were too busy reading your own dribble when I wrote this (below)? I typed it a little slower just for you. Perhaps the PC amongst us would prefer the marines not refer to that fantastic peice of engineering as the homo head, but the gay head. Doubt it, the marines don't care what either you, I or anyone for that matter think they should describe a rotor head as.
---------------------------------------------------------
Best means: “Better than ALL others”.

If a fully articulated rotor Can Do ALL the things a rigid or semi rigid rotor can do, then it is simply the Best.

So, regardless of the mission, weight, cost, small, large medium airframe, simplicity, complexity, cuteness, material, blah, blah blah, (get the idea?), if one rotor system can do ALL of this and the other rotor systems cannot, then it is “Better than the others” or BEST.

And yes, I agree the BEST thing to happen to rotor systems is the elastomeric bearing.

BTW, a one-piece fully articulated rotor system would look like the H-60, H-3, H-53 or H-92 not the two rotor hubs laying atop one another which has been described by the marines as the “homo-head”. Yeah, a lot of thought went into that system!

[Um... lifting...]

Shawn-
I apologize for my ill-mannered and poorly-informed countryman.

Dan-
Do you have any idea who Shawn Coyle is? No, of course you don't. So, before you embarrass yourself further, here's a start:

http://www.helicopterseminars.com/Staff/ShawnCoyle

Be sure to pour yourself a nice coffee and then click on the 'resume' link. It's long, and it's comprehensive.

The only person on this thread who has an issue with intellect is you. Probably pretty hard to fly with that Cadillac-sized chip on your shoulder. So you've flown Hueys and H-60s. Who hasn't? I haven't flown a quarter of the types Shawn has flown, but I've still flown over four times as many as you have. I flew day-in and day-out with Marine aviators in a joint squadron for three years. They came from every community in the Marine Corps and we talked a lot about these sorts of things... daily. It wasn't one night of beer and bullsh*t with a Lance Corporal in a club somewhere, which is apparently where you get your information. In all that time, never once did any of these Marine aviators refer to a rotorhead as you have.

What you've demonstrated on this thread is that you're argumentative, poorly informed and don't know how to define what you're talking about. You also can’t take constructive criticism gracefully. People have tried to be pleasant to you and you respond by acting like an infant. There are reasons the Army doesn’t send guys like you on exchange assignments… two of them are called 'manners' and 'maturity', both things you don’t have.

While I could attempt to explain things to you as several of us have tried to do, I don't think it's worth the effort.

Dan, repeating yourself louder and louder doesn't make anyone think you're right. What it does do is tell them that you're not here to learn anything... you just want to stir the pot and show people how important you are. I saw enough clowns just like you in a quarter-century in uniform to know one when I see one.

You owe Shawn an apology.

[Dan Reno]

I’ll say again (3rd time) & last; A fully articulated rotor is the BEST. I included Webster’s definition of BEST and listed valid qualifiers, twice. Since some refuse to admit to that definition with guidelines specific to this subject, I repeated myself and for that you jump in speaking for Shawn Coyle (I’m sure he’s proud of you). And I’m sure his credentials are impeccable and his Papers Are in Order dear Comrade, but what does all that have to do with the fact that (now pay close attention here): A fully articulated head can do EVERYTHING the other type heads can do, but, those heads CANNOT do everything a fully articulated head can do? That simply follows Mr. & Mrs. Webster’s meaning of BEST, relative to the fully articulated head. I’m sorry if you formed some sort of symbiotic, maternal love affair for heads other than the fully articulated, but buck-up, accept it and move on Pal.

The marines I talk with are like the in-country (Iraq) marine captain on the mil channel the other night who said: “I never met an Iraqi that didn’t lie”. Like those at the wrench-turner level, this captain wasn’t PC either, and if some people don’t like the term “homo head”, then perhaps they simply have an ulterior motive for that term, but regardless, they need to take that up with the marines and see how far they get with those who said it.

Unlike you Sir, I’ve been more than patient with this squabble while not being personally insulting. Smarten up and enjoy this vertical and above ground life as it’s too short and it would be too foolish to do otherwise. SF

[Um... lifting...]

The answer to your question is just one word:

Credibility.

He has it.

You don't.

Bye-bye Dan

[tottigol]

Dan, can you explain to us mere mortal pilots and aviators what are the differences between a fully articulated rotor system and a rigid one?

Maybe we can so understand why a fully articulated system is not rated for aerobatic manouvers, while a rigid system is.
Maybe we can so understand what other manouvers a fully articulated system can execute that other rotors cannot.

Can you also tell us what Marine unit flies or has ever flown the 412 to the extent that they have accumulated enough experience?

How's your other fishing, do they get bigger and bigger at the pub?

[Dan Reno]

Rotor Systems
As briefly mentioned in the lesson 1, there are three fundamental types of helicopter rotor systems: rigid, semi-rigid (or teetering), and fully articulated. These are discussed below, along with descriptions and operating principles of other important rotor components. To a large extent, the information is applicable to both main and tail rotor systems. Of course, the tail rotor does not have cyclic control, but its operation is similar to collective control on the main rotor, even though it provides the yaw reaction to main rotor torque on the airframe. Its operation can also be likened to that of a variable pitch propeller.
Fully Articulated Rotors
Fully articulated rotor systems allow each blade to feather (rotate about the pitch axis to change lift), lead and lag (move back and forth in-plane), and flap (move up and down about an inboard mounted hinge) independent of the other blades. As we will discuss, each of these blade motions is related to the others. Fully articulated rotor systems are found on rotor systems with more than two blades.
As the rotor spins, each blade responds to inputs from the control system to enable aircraft control. The center of lift on the whole rotor system moves in response to these inputs to effect pitch, roll, and upward motion. The magnitude of this lift force is based on the collective input, which changes pitch on all blades in the same direction at the same time. The location of this lift force is based on the pitch and roll inputs from the pilot. Therefore, the feathering angle of each blade (proportional to its own lifting force) changes as it rotates with the rotor, hence the name ‘cyclic control’.
As the lift on a given blade increases, it will want to flap upwards. The flapping hinge for the blade permits this motion, and is balanced by the centrifugal force of the weight of the blade, which tries to keep it in the horizontal plane. Either way, some motion must be accommodated. The centrifugal force is nominally constant, however the flapping force will be affected by the severity of the maneuver (rate of climb, forward speed, aircraft gross weight). If you ever get the chance to watch a helicopter hovering from the side (particularly a heavy helicopter), you can see all the blades ‘cone’. Appropriately, this is called ‘coning’. Some rotor systems have a ‘pre-cone’ but that is not important to discuss here.
As the blade flaps, its center of gravity changes. This changes the local moment of inertia of the blade with respect to the rotor system and it will want to speed up or slow down with respect to the rest of the blades and the whole rotor system. This is accommodated by the lead-lag hinge, and is easier to visualize with the classical ‘ice skater doing a spin’ image. As the skater moves her arms in, she will spin faster because her inertia changes but her total energy remains constant (neglect friction for purposes of this explanation). Conversely, as her arms extend, her spin will slow. An in-plane damper typically moderates lead-lag motion.
So, following a single blade through a single rotation beginning at some neutral position, as load increases from increased feathering, it will flap up and lead forward. As it continues around, it will flap down and lag backward. At the lowest point of load, it will be at its lowest flap angle and also at is most ‘rearward’ lag position.
Because the rotor is a large, rotating mass, it will behave somewhat like a gyroscope. The effect of this is that a control input will usually be realized on the attached body at a position 90 degrees behind the control input. This is accounted for by the designers through placement of the control input to the rotor system so that a forward input of the cyclic control stick will result in a nominally forward motion of the aircraft. The effect is made transparent to the pilot.
There are a few other considerations to the placement of control inputs also transparent to the pilot, but still interesting to discuss. Location of the input links to the rotor blades is related to the phasing of the rotating and stationary controls and also to the amount of blade input rotation required. Because the lead-lag hinge and the flapping hinge are not necessarily coincident, the location of the input may be located such that as the blade flaps or lead-lags, there may be a change in blade pitch input as flapping or lead-lag occurs (or both). This is a little difficult to visualize, but imagine that the input link is located at the same distance from the center of the rotor hub as the flapping hinge. As the blade flaps, there will be no effect on pitch because the pivots are along the same line. If the input link is inboard or outboard of the hinge, some coupling (or change in blade angle as a result of an input from another control axis) will result. If an increase in blade angle results because of an increase to blade pitch, the situation will compound. This situation is nominally unstable, but depending on the rotor system, is not necessarily bad. This can similarly occur in lead-lag.
Older hinge designs relied on conventional metal bearings. By basic geometry, this precludes a coincident flapping and lead-lag hinge and is cause for recurring maintenance. Newer rotor systems use elastomeric bearings, arrangements of rubber and steel that can permit motion in two axes. Besides solving some of the above-mentioned kinematic issues, these bearings are usually in compression, can be readily inspected, and eliminate the maintenance associated with metallic bearings.
Semi-rigid (teetering) Rotors
Semi-rigid rotors are found on aircraft with two rotor blades, such as Robinson, Hiller, and many Bell products. The blades are connected such that as one blade flaps up, the opposite blade will flap down. Allowing the rotor system to ‘teeter’ at the top of the rotor mast accommodates this. The Robinson system, although basically teetering, permits some independent flapping of each blade and operates in a similar fashion. The Hiller design uses the large main blades for lifting, but relies on two smaller blades 90 degrees to these for cyclic control.
Because the rotors are tied together rigidly in-plane, there is no lead-lag between them. The rotor does not necessarily ‘cone’ but rather will tilt up on the side with more lift and tilt down on the other. Flapping is therefore self-balancing. Issues of phasing, gyroscopic precession, and flap coupling are still present, but easier for the designer to deal with.
Rigid Rotors
Rigid rotors want to behave similarly to fully articulated rotors, but do not provide flapping or lead-lag hinges. The blade roots are rigidly attached to the rotor hub. Instead, the blades accommodate these motions by bending. Because the kinematic loads are not resolved by actual blade motion (or blade reaction to load may be different from that desired), high vibration may result. Rigid rotor systems are rare, but may become more common as improvements in material properties and vibration control evolve. They are fundamentally easier to design and potentially offer the best properties of both teetering and fully articulated systems.

[tottigol]

Good job of cut and paste, a fifteen years old could do that.
What's that from, "Aerodynamics for Naval Aviators 1962"?:D

You are yet to put any of your own material in it.:rolleyes:

Neither you answered what Marine units are experienced on the 412 or why the fully articulated rotor system can do things a rigid one cannot.

Failing to do so shall make you a troll and no more of your posts shall be answered.

[globalindian]

I have some d....heads telling me here that it is good to bring the Helicopter to complete idle to conserve fuel.. This seems completely against what the manual says...as per the Flt manual NR 26%to 77% is to be used only for transient operations .. Some comments in here please..Thanks:ugh:

[Encyclo]

The flight manual is your friend :ok: and it's also the law :eek: Chapter 1 as in LIMITATIONS SECTION :=

Running below 77% is not good for the yokes. Cf loads are not high enough and damage may be caused to the M/R head.

[gulliBell]

I'm surprised someone would suggest explicitly otherwise to what the RFM says...only to save a bit of fuel. Mumbai, India...interesting. For as much curry as they can buy for those fuel savings, you need to spend a hellava lot more curry to fix unnecessary wear and tear on the main rotor head.

[oldbeefer]

Not sure I'd like to try this http://www.youtube.com/watch?v=1MfFStR_fA8 with a fully articulated head (not sure I'd like to try it in a Lynx either, really!).