Bell 412
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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?
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.
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.
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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.
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.
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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.
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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!
---------------------------------------------------------
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!
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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.
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.
Last edited by Um... lifting...; 26th Sep 2007 at 16:12.
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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
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
Last edited by Dan Reno; 26th Sep 2007 at 17:56.
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?
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?
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Off the internet
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.
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.
Last edited by Dan Reno; 27th Sep 2007 at 14:25.
Good job of cut and paste, a fifteen years old could do that.
What's that from, "Aerodynamics for Naval Aviators 1962"?
You are yet to put any of your own material in it.
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.
What's that from, "Aerodynamics for Naval Aviators 1962"?
You are yet to put any of your own material in it.
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.
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All you 412 pilots out there..
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
The flight manual is your friend 
and it's also the law 
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.
and it's also the law 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.
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.
