To: Helo Teacher Re 72-degree Vs 90-degree pitch horn

[Lu Zuckerman]

To: Helo Teacher

Log onto the following website that has the diagram that goes with this text:

http://www.pprune.homestead.com/files/pitchlink.gif

THE PURPOSE OF THIS ILLUSTRATION IS TO DISPROVE FRANK ROBINSONS' PREMISE OF CONSIDERING A 90-DEGREE PITCH HORN IN THE DESIGN OF THE ROBINSON ROTORHEAD.
IF HE HAD THE OPPORTUNITY TO CHOSE A 90-DEGREE PITCH HORN THEN ANY VERTICAL MOVEMENT OF THE BLADE (CONING) WOULD TURN THE BLADE INO A FIRST CLASS LEVER WITH THE CONE HINGE AS THE FULCRUM. IN THIS CASE, WHEN THE BLADE CONED UPWARDS, THE PITCH HORN WOULD MOVE DOWNWARDS AGAINST A FIXED PITCH LINK.
THIS RELATIVE MOVEMENT WOULD CAUSE THE BLADE TO INCREASE PITCH AS IF THE PITCHLINK HAD BEEN MOVED RELATIVE TO THE BLADE.

IN ORDER TO CONE, THE PILOT HAD TO PUT IN ENOUGH PITCH TO LIFT THE HELICOPTER OFF THE GROUND. AT THE SAME TIME, THE CONING ACTION WITH A 90-DEGREE PITCH HORN WOULD PRACTICALLY DOUBLE THE PITCH RESULTING IN BLADE STALL OR VERY CLOSE TO BLADE STALL. IF THE PILOT HAD SUFFICIENT POWER TO GET THE HELICOPTER OFF THE GROUND AND MOVED THE CYCLIC IN ANY DIRECTION HE COULD ADD ANOTHER 5-6 DEGREES OR MORE TO THE ALREADY HIGH PITCH IN THE ROTOR SYSTEM.

THE QUESTION IS, WAS FRANK ROBINSON TRUTHFUL WHEN HE MADE HIS STATEMENT? AND, IF NOT WAS HE BEING TRUTHFUL WHEN DISCUSSING DELTA 3 AND ITS' EFFECT ON ROTOR PHASE ANGLES.

You are all welcome to log on to the website and read the text above. After doing so, please make your comments regarding my statement about Frank Robinson not being forthcoming.

It should be noted that when the pitch horn terminates at the cone hinge then the above description does not apply. That is why the Robinson rotorhead has a 72-degree pitch horn.

[This message has been edited by Lu Zuckerman (edited 04 January 2001).]

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The Cat

[This message has been edited by Lu Zuckerman (edited 04 January 2001).]

[mark561]

Mr. Zuckerman:

Your drawing is quite pointless. It is by no means clear what you are trying to prove here.

I suspect you are attempting to illlustrate a mechanism by which blade flapping affects blade pitch. If so, you have completely neglected a rather important component of the linkage geometry. (Do you even have a clue as to what this might be?)

But more importantly, you seem unable to explain QUANTITATIVELY the relationship between coning and blade pitch. For example: assuming the linkage geometry in your drawing, suppose the coning angle were to change by 1 degree. How many degrees of pitch change would this produce?

With all due respect sir, you truly appear to be a buffoon. You continue to make unsupported and unproven assertions, while giving no evidence than you even have a clue as to what you are talking about. The fact that you were unable to even understand Frank Robinson's explanation of the 18-degree delta-3 angle proves this. The fact that the Robinson does NOT respond to cyclic movement in the way you predict it should (as attested to by numerous R22/44 pilots) proves this also.

[Lu Zuckerman]

To: Mark 561

You call me a Buffoon on an open forum accusing me of not knowing what I am talking about yet at the same time you expose your own ignorance of helicopter dynamic systems. Yes, I was trying to illustrate a mechanism by which flapping effects blade pitch and I am very well aware about linkage geometry. And yes I do have a clue as to what this linkage geometry is and how it relates to blade pitch change caused by blade flapping. Get a book on helicopter theory and look under pitch coupling.

I can’t answer your question about how much the pitch angle is effected by a one-degree change in cone angle. If you look at the diagram you would see that is a relationship between the input side of the lever (blade) and its’ relationship to the output side of the lever (pitch horn). Is it is greater or less than one-to-one,I can’t say. Then again, if the blade raises one degree the pitch horn will drop one degree. You do the math.

You mentioned my not understanding what Frank Robinson said relative to the delta three angle. It is obvious that you didn’t understand it either because he was talking about pitch coupling which is the subject of this thread. I’ll say it again, just because the words came out of the mouth of Frank Robinson it does not make it true. Pitch coupling as stated by Mr. Robinson has no effect on countering the 18-degree offset of the blades. The purpose of this particular thread is to prove that Frank Robinson was not truthful when he said he had considered the use of a 90-degree pitch horn but instead chose the 18-degree offset as a means of countering the effects of transverse flow.

You also picked up on the inputs of Robinson pilots that said the helicopter doesn’t respond the way I said. However, I made a challenge to those pilots to perform a test to see if the effects of countering the effects of transverse flow was in fact masking the tendency to fly left when the cyclic is pushed forward from the rigged neutral position. Until they perform the test or I can gain access to an R22 for an hour this will remain open to discovery of who is right or, who is wrong.

In any case, I would strongly suggest that you purchase the FAA ROTORCRAFT FLYING HANDBOOK or some other equally informative book prior to making any more accusations.


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The Cat

[This message has been edited by Lu Zuckerman (edited 04 January 2001).]

[HeloTeacher]

Lu, the desription you give above of what you see would happen when lifting into the hover with 90 degree lead seems flawed to me. Its like an older computer trying to run a newer game (no this is NOT an age crack!). The movement is blocky and jumps from instant to instant without a smooth flow.

Taken in isolation of factors such as dynamic instability in response to transient flight loads, if the pitch was applied to the blades, coning occurs as soon as lift is being produced, and it happens smoothly. The result would actually be the a/c lifting off the ground with less collective pull required, the additional pitch being supplied by the interlock in the pitch links. While this may have an adverse effect, sudden blade stall on loss of ground contact is definitely NOT it.

The situation must be explained dynamically, not statically. This same critique will apply to my take on the whole out-of-trim concern.

If the R22 is incapable of out-of-trim flight, then a crosswind hover is also unacceptable, as this is out-of-trim (90 degrees) flight. But this maneuver is not disallowed and has never (to my knowledge) resulted in rotor-fuselage contact. Why?

When flown in trim the R22 fuselage is a relatively aerodynamic body and flies smoothly and very responsively. When flown out of trim, the increased area being affected and (I beleive) the less aerodynamically stable attitude, not least because of horizontal stabilizer blanking, results in an aircraft that is very susceptible to pitch oscillations resulting from overcontrolling.

These pitch oscillations can easily result in rotor loss of control if not contained.

This is not a helicopter problem, it is a pilot problem.

I have read many R22 accident reports fromt he NTSB, and in many I see an aircraft grossly mishandled or placed in lousy situations. When i weed those out I fail to see an accident rate that grossly exceeds other types.

A good example is the accident involving the ShowCopters machine. The incidents are written such that one would expect that a high-time student pilot and airshow R22 instructor is the safest combination to have. I disagree. High time fixed wing students, I've had them, have reactions that are completely inappropriate in a helicopter, because of their experience. And very experienced instructors, especially with inexperienced (helo) students, must guard against complacency. It is too easy to lose that alertness you start your instructing career with. I can't say what caused the accident any more than you can or anyone else, but I see a lot of potential cause factors, and they aren't all R22 design related.

Out of curiosity, how is the R22 accident rate in Canada? I'll try to find out myself. I bet it is much better, we have higher minmums required prior to getting a helicopter instructor rating, and few if any schools will rent a helicopter out to students or private pilots for purposes other than flight training. This keeps more experience in the cockpit and inexperience under supervision.

[Lu Zuckerman]

To: Helo Teacher

In references to your first paragraph, 90-degree lead or,for that matter a 72-degree lead had absolutely no relation to going into a hover. The lead comes into play when you push cyclic.

THIS IS TO CORRECT THE ABOVE STATEMENT: WITH A 72 DEGREE LEAD THERE MAY BE A MINOR DEGREE OF PITCH COUPLING WHEN LIFTING INTO A HOVER BUT ONLY IF THE PITCH HORN / PITCHLINK ARE NOT COINCIDENT WITH THE CONE HINGE. WITH THE 90-DEGREE PITCH HORN THE PITCH COUPLING WILL BE EXCESSIVE AND WILL ADD TO THE COLLECTIVE ANGLES SET BY THE PILOT WHEN HE RAISED THE COLLECTIVE.

The diagram is intended to show what happens if the pitch horn on the Robinson has a 90-degree lead. When the blade cones up the pitch horn goes down. The pitch link however is fixed. The pilot pulling collective has commanded the blade to feather and it can feather even more when it forces down on the fixed pitch link due to the coning action.

It is my understanding that the Robinson has a throttle correlator that will add the necessary power to match the collective input. If the pilot pulls a fixed amount of pitch the correlator will add the necessary power. What happens if the additional pitch adds additional drag? Also using your example would you want to fly in a helicopter that lifts off with only half the necessary collective. Also, think about this. What happens when the pilot pushes cyclic? Any cyclic pitch change will be amplified by some order of magnitude. The Robbie is touchy enough, what happens when the blades start to flap (change cone angle) the rotor head and dynamics of the helicopter will go crazy. Another point to consider is what happens when the pilot is in an autorotation and he can’t get the pitch low enough to establish descent rotor RPM and what happens when he pulls aft cyclic to flare? Also maneuvering at altitude could introduce rotor stall and possibly cause retreating blade stall (Maybe)

The diagram shows the blade in the pure radial position. I could have shown the blade in the cone position but since I can only illustrate on two planes it would be difficult to show the increased pitch due to coning.

You will either have to accept the fact that it would happen and what happens, when it happens.

Oh yes, if the Robinson had a 90-degree pitch horn on the existing rotorhead it would never have made it through certification. So, if Frank Robinson stated that he had considered a 90-degree pitch horn but settled on a 72-degree pitch horn he is not being truthful.

Regarding your comment aboutt Kent Reinhard the Showcopter pilot, I don't know if you said that he was a hightime fixed wing pilot that also participated in the Showcopters performance and he was at fault in the accident.. He had in excess of 20,000 hours with a great deal of helicopter time including a great deal of utility work, instructing and the Showcopters gig. his student however was on his first helicopter ride.


Think about it and come back and we will talk more.




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The Cat

[This message has been edited by Lu Zuckerman (edited 04 January 2001).]

[This message has been edited by Lu Zuckerman (edited 04 January 2001).]

[This message has been edited by Lu Zuckerman (edited 05 January 2001).]

[This message has been edited by Lu Zuckerman (edited 05 January 2001).]

[HeloTeacher]

""To: Helo Teacher
In references to your first paragraph, 90-degree lead or,for that matter a 72-degree lead had absolutely no relation to going into a hover. The lead comes into play when you push cyclic.""

You have stated that the 90 degree lead is prohibited because of coning problems, the rotor cones in the hover, therefore the hover is relevant to the discussion. The displaced lateral cyclic would be the problem in forward flight.

""The diagram is intended to show what happens if the pitch horn on the Robinson has a 90-degree lead. When the blade cones up the pitch horn goes down. The pitch link however is fixed. The pilot pulling collective has commanded the blade to feather and it can feather even more when it forces down on the fixed pitch link due to the coning action.""

agreed, that's what I was saying too

""It is my understanding that the Robinson has a throttle correlator that will add the necessary power to match the collective input. If the pilot pulls a fixed amount of pitch the correlator will add the necessary power. What happens if the additional pitch adds additional drag? Also using your example would you want to fly in a helicopter that lifts off with only half the necessary collective. Also, think about this. What happens when the pilot pushes cyclic? Any cyclic pitch change will be amplified by some order of magnitude. The Robbie is touchy enough, what happens when the blades start to flap (change cone angle) the rotor head and dynamics of the helicopter will go crazy. Another point to consider is what happens when the pilot is in an autorotation and he can’t get the pitch low enough to establish descent rotor RPM and what happens when he pulls aft cyclic to flare? Also maneuvering at altitude could introduce rotor stall and possibly cause retreating blade stall (Maybe)""

as I stated in my post, i am not going to go into stability of a potential system. yes the correlator is there, but isn't relevant to this topic. i am debating with you the merit of the statement that a 90 degree lead in the rotor system was impossible. additional pitch increases both lift and drag and as i stated,only the amount of collective movement would be affected, this does not make the design impossible.

i wish i had the documents i need, but intuitively i am surethat the teeter hinge is effecting the flapping, and the coning hinges the coning, so very little effect on coning from cyclic changes.

""The diagram shows the blade in the pure radial position. I could have shown the blade in the cone position but since I can only illustrate on two planes it would be difficult to show the increased pitch due to coning.""

""You will either have to accept the fact that it would happen and what happens, when it happens.""

i have agreed

""Oh yes, if the Robinson had a 90-degree pitch horn on the existing rotorhead it would never have made it through certification. So, if Frank Robinson stated that he had considered a 90-degree pitch horn but settled on a 72-degree pitch horn he is not being truthful.""

why not?

""Regarding your comment aboutt Kent Reinhard the Showcopter pilot, I don't know if you said that he was a hightime fixed wing pilot that also participated in the Showcopters performance and he was at fault in the accident.. He had in excess of 20,000 hours with a great deal of helicopter time including a great deal of utility work, instructing and the Showcopters gig. his student however was on his first helicopter ride.""

the high fixed time was in reference to the student, and i don't pretend to know the cause, anymore than anyone else. I was pointing out potential problems i see in the situation from my experiences

I look forward to your response...


Think about it and come back and we will talk more.

[Lu Zuckerman]

To: Helo Teacher

Check out the correction I made to my response to your post.

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The Cat

[Lu Zuckerman]

To: Helo Teacher

It seems our posts crossed each other.

Read the correction in my original response to your post.

The throttle correlater has everything to do with the subject. Once you have set up the rotor RPM and you pull collective the throttle correlater will add the necessary power (manifold pressure) to sustain the pitch setting made when the pilot pulled collective. If perchance the 90-degree pitch horn in effect doubles the pitch setting made by the pilot then the throttle correlater will be insensitive to this new load. Maybe the governor, if you have one, would sense this added load and increase the original power setting. However, in certain cases the Robinson is flown without the governor connected in the control circuit, which means that the pilot would always have to be twitching the throttle.

Regarding my terminology about coning and flapping, it is all based on semantics. The blade disc as a unit flaps about the teeter hinge. The individual blades cone about the cone hinge when collective is pulled. However if an individual blade moves out of the original coned position due to some external perturbation that blade will flap about the cone hinge.

On a 72-degree pitch horn the collective pitch coupling is minimal if non-existent when the pilot pulls collective. Under ideal conditions there would be no pitch coupling when the disc tilts forward as the cone angle has not changed. If an individual blade flaps out of the tip path plane it will be returned to the track via the effects of pitch coupling. In this case if the blade flaps up the pitch will be reduced thus returning the blade to the original tip path. Conversely if the blade flaps down the pitch is increased due to the coupling and that blade too is returned to the tip path.

With a 90-degree pitch horn on a Robinson when the pilot pulls collective the pitch coupling will be excessive and it could possibly double the pitch setting made by the pilot. Assuming the ideal conditions stated above when the pilot pushes forward cyclic any pitch input will be amplified by the pitch coupling. If a blade is perturbed and flies up out of the tip path, the pitch will not decrease and return the blade to the tip path, it will in effect cause the blade to fly higher out of the original perturbed condition due to the increase in pitch on that individual blade. This would make the rotor disc very unstable and quite possibly uncontrollable.

As far as autorotation is concerned the pilot may have returned his collective to bottom stop but the blades are still coned and even though the pilot has removed all of the pitch he set in, the coning will maintain a higher pitch setting thus decreasing the descent speed. Also when the pilot tries to flare the pitch maintained by the coupling effect will be further exacerbated when the blades start to flap either about the teeter hinge or, the cone hinge.

Flapping loads resulting from sideslip will be increased due to the 90-degree pitch couple and could result in mast bumping much earlier than if the rotorhead had a 72-degree pitch horn.

So, the only beneficial effect is that the pilot may be able to hover with less collective. As good as that might seem it would never happen because the FAA would have never granted certification.

Now we get back to my original premise. If the FAA would never have certificated the R22 with a 90-degree pitch horn why-oh-why would Frank Robinson have even considered it? The way I see it is that he provided an answer to my posts in such a way as to diminish my impact and at the same time add credence to his statement simply because he is Frank Robinson. The Robinson is already very "twitchy". A 90-degree pitch horn would make even "twitchier".

Why is that so hard to understand?


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The Cat

[This message has been edited by Lu Zuckerman (edited 05 January 2001).]

[Rotorbike]

From the Flight Manual, Flight and Maneuver Limitations, Section 2, Page 2-7, Flight prohibited with governor selected off, with exceptions for in-flight system malfunction or emergency procedure training.

So I guess you can't do that Lu :)

[Lu Zuckerman]

To: Rotorbike

In the Robinson POH that I have section 2 was last updated in 15 September 1987 and it has no reference to on or off governor operations. The latest revision to my manual was made 21 January 1993 Perhaps your POH is a later edition and does reference not turning it off. However as you indicated that in a training enviornment it can be turned off and as you stated it can even fail. This does not deviate too much from what I said

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The Cat

[Rotorbike]

Page 2-7 is dated FAA approved on 25 Jul 1996 you need some updates there Lu. Maybe you should give Frank some money and update the old subscription!!

The wording is straight from the POH and I haven't stated anything.

[HeloTeacher]

Lu, please, you are basing this argument on the idea that the only design change would be to extend the pitch horn a little and everything else remains the same and because it won't work this way then the 90 degree lead is impossible. Perhaps a tad unrealistic?

How about making it a 90 degree pitch horn on the other side of the blade such that increased coning angles reduce blade pitch and creates a restoring moment. Or maybe put in a touch of delta hinge in the coning hinges to mitigate the pitch coupleing. Or we could increase the swashplate diameter and adjust control throw to put the pitch horn on the swashplate coincident with the coning hinge.

Design, unlike engineering, is a creative process where one has to look at a problem in a non-linear manner in order to use the by-product of one solution to efect another.

I am not saying that a 90 degree lead is better or worse, or can be designed in a couple minutes. I am saying it is very possible even with the coning / teeter combination.

Many of the design details in the R22 speak of attention to cost and weight. It is simple and tough and has a minimum of things that can break. You advocate adjustable control stops because you are used to seeing them, but fixed stops require less weight and are more robust. Innovation, ain't it grand.

Now, does anyone know how to get the accident statistics fromt he TSB website, I can't figure it out?

[Lu Zuckerman]

To: Helo Teacher

I don’t propose adding to the pitch horn but if I had to make a suggestion I would suggest that they take 18-degrees out of the 90-degree pitch horn which would give you a 72-degree pitch horn which is what you already have in the existing design.

The basic premise I have put forward is that the design of the Robinson rotorhead from the very beginning incorporated cone hinges which precluded the use of 90-degree pitch horns like those used on the Bell single rotor helicopters. The design of any rotorhead requires that the pitch horn / pitch link attach point must terminate at or about the teeter bearing or the flapping hinge (cone hinge) to minimize pitch coupling.

Regarding a 90-degree pitch horn on the trailing edge as opposed to on the leading edge, this is already being used on some Bell Helicopters. But, in this case the swash plate movement is opposite to that on a Robinson or other Bell single rotor helicopters. If they put the pitch horn on the rear of a Robinson blade, it would provide a restoring moment but, when the blades coned up, pitch would be taken out of the blades so that the pilot might not be able to lift off or, he would have to add power and possibly rotor speed in order to generate sustaining lift for flight.

Regarding increasing the swashplate diameter to place the pitch link attach point under the cone hinge this is in effect the same as what they have with the 72-degree pitch horn.

I appreciate the comment in the last paragraph of your post. But, no matter how long you and I look at this problem the 90-degree pitch horn would never pass muster with the FAA.

We then get back to why Frank Robinson stated that they had considered the 90-degree pitch horn and then settled on the 72-degree pitch horn. I can’t answer the first part but the reason he settled on the 72-degree pitch horn was because he incorporated the cone hinges. And, cone hinges were part of the design from the beginning.

Over


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The Cat

[HeloTeacher]

Speaking of getting off topic Lu, I though we were talking about the safety of the R22, not about what someone on PPRuNe who claims to be FR said.

Please, why would a 90 degree option not pass muster with the FAA? That's what I have ben trying to get from you.

[212man]

Just had a look at the diagram (is it supposed to move? it didn't seem to). The coning hinge is not a fulcrum; how can it be? it's a contadiction in terms. Even if it were, you don't show the teetering hinge which would be at the far left of the diagram. In an extreme case, if the coning (=flapping) hinge were half way along the blade, the inboard half would not be in any sense acting on the pitch horn. It would however, exert a moment on the head.

And another thing! What has auto rev settings got to do with any of this? If the pitch links are the wrong length then the pilot will have trouble with his Nr in auto. That's true of any type hence it being checked after work on the linkages etc. I feel some red herrings creeping in again.

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Another day in paradise

[Lu Zuckerman]

To: Helo Teacher

The FAA would not approve a 90-degree pitch horn on a Robinson rotorhead for two reasons.

1) It totally violates sound engineering practices for a rotorhead to have a pitch horn that extends beyond the flapping hinge and in the case of the Robinson the cone hinge.

2) See above and add in massive pitch coupling and the addition of pitch when the blades cone or when they flap about the cone hinge.

It is physically impossible to design a rotorhead that violates rule 2 above. It is because of these reasons that I believe Frank Robinson was not truthful when he said he had considered a 90-degree pitch horn. And, it is equally impossible to get that kind of design certificated.

Hopefully, this makes sense.

To: 212man

The purpose of the diagram is to show what happens when the blade cones or flaps about the cone hinge. All of these actions take place about the cone hinge. I used the term lever because I assumed that everyone was familiar with a first class lever. If you want, look at it as if it were a seesaw. When one end goes up the other end goes down. In the case of the diagram any upward movement of the blade will cause a 90-degree pitch horn to move down. As I stated previously I could only draw in one plane and the observer (you) has to visualize the actual action. This I believe is called imagery.

On the diagram the pitch horn is not a part of the lever but it will be displaced when the blade moves upward. The reason for this displacement is because the pitch link is fixed to the swashplate. The displacement of the pitch horn results in an increase in pitch on the effected blade or in the case of coning (blades).

I didn't picture the teeter hinge because it doesn't enter this discussion.

Regarding auto rev setting I’ll provide an example but it might be a bit convoluted.

Let’s assume that Robinson shipped you a brand new R22 or R44 and it was completely disassembled. This helicopter had never been flight tested and it incorporated a brand new rotorhead design that incorporated a 90-degree pitch horn as opposed to the old design that had a 72-degree horn.

You assembled the helicopter and set up the control system and rigged it according to the manual. Now, you take it out for a test flight. You immediately notice that it takes more power than a normal R22 in order to get it into a hover and once there, the helicopter had very strange handling qualities. You eventually get used to the problems of the rotor and it's control.

Now, you take it up to several thousand feet and you notice it still needs more power. You notice that your manifold pressure is running high and you might even have to speed up the rotor to the max in order to reach the altitude. You dump collective down to the stop and try to establish both forward velocity and rate of descent. You check your rotor system and it is starting to slow down and there is nothing you can do about it because even though the collective is on the bottom stop the blades are still coned and this puts more pitch into the blades causing them to slow even further. As they slow down the coning increases and the pitch increases further. If I go any further in this description you and the helicopter will both meet a violent end.

Why did this accident happen? The NTSB in their accident investigation found that Robinson had accidentally put on a 90-degree pitch horn instead of the regular 72-degree pitch horn.

I’m not a pilot so don’t jump me for any technical errors. I’m just trying to respond to your post.


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The Cat

[This message has been edited by Lu Zuckerman (edited 06 January 2001).]

[212man]

2 things: I say again, a hinge of the type described is not a fulcrum, it cannot transmit leverage from one side (outboard blade) to the other (inboard blade).

Why do people confuse auto rev settings with power required to hover? All that changes is colective position. What will change is the power being used at MPOG (flat pitch)and this will give some clue as to the likely auto revs. Once flying there is no correlation. It's similar to changes in density altitude, all that changes is the MPOG power and the flight collective settings.

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Another day in paradise

[sprocket]

212Man, in the diagram, I interperate that the teetering hinge is in line with the pitch link. Same as the 212 or 206.
To have the blade cone up like the Robbo (not teeter) then the pitch horn would tend to go down. If it is prevented from going down by the swashplate/pitchlink then the only thing that can move is the blade pitch angle and that would be in the upward direction.
This diagram does not reflect the actual R22 setup

[Lu Zuckerman]

To: Sproket

Thank you.

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The Cat

[Lu Zuckerman]

To: 212man

Please refer to the diagram. What you refer to as the inner blade is the pitch horn and although the pitch horn is not transmitting reflected mechanical energy when the blade cones or flaps it does in effect move in the opposite manner of the blade itself. In this case when the blade cones or flaps up the pitch horn since it is movable will rise in the opposite direction in reaction to the fixed pitch link. I used the term fulcrum for the cone hinge because I wanted to illustrate that all mechanical movement takes place about that axis jus like a fulcrum on a lever.

The fulcrum (cone hinge) does not transmit leverage as you indicated in you post. It provides a point at which the lever, in this case the blade can pivot around. If the pitch horn were not attached to the pitch link then when the blade rose due to coning or flapping the pitch link would move down just like a first class lever. Since it is attached to the fixed pitch link and because the pitch horn can cause the blade to rotate about its’ pitch axis the pitch horn will add pitch when the blade cones up or, flaps up. If you can visualize this, under the above stated conditions the lever will bend at the cone hinge (fulcrum). It is this bending that causes the undesired pitch change.

Please get away from your comments about autoratation and power. Lets’ say that you raise the collective to the point that you overcome gravity and you are in a hover. Let’s say that it takes an additional 10-degrees of blade pitch on a regular R22/R44. This is accomplished on a rotorhead that has a 72-degree pitch horn. Now, on a Robinson that has a 90-degree pitch horn the same collective movement used on the standard version would provide (for an example) an additional 5-7degrees. Now, maybe this will give you a jump takeoff capability but the throttle corellater will not provide the additional power to sustain the additional pitch so you have to tweak the throttle to compensate. This defeats the function of the throttle correlater and is strike one in the certification of the helicopter. You start to move forward and the rotor disc tilts. In order to effect this tipping of the disc you have to move the cyclic. The increased pitch will further amplify any movement of the cyclic in the rotor system that increases the already twitchy characteristics of the Robinson Helicopter. The same is true for flight maneuvering. Strike 2. It is true, you can decrease the collective setting but the throttle correlater will only provide the power for that collective setting and again you would have to tweak the throttle.

Now, you are going to set the autorotation rotor speed. Under normal conditions when the helicopter is properly rigged the rotor will always rotate too fast during the initial autorotation.
This is compensated for by adjusting the pitch links on the ground to increase the blade pitch and in doing so decrease the rotor speed. However when you dump collective the blades do not go to flat pitch as you had indicated. Because the blades are still coned you may still have 5-7 degrees of pitch in the blades that can’t be compensated for because the collective is on the stop.

Now this might sound stupid and maybe it is but it just occurred to me. What if under certain atmospheric and weight conditions, 5-7 degrees of pitch were all that is required to get the helicopter off the ground? Then what would happen if the helicopter flew for an hour and burned off some fuel which would make the helicopter lighter and it came back in for a landing? At landing, the forward speed is arrested and the pilot lowered his collective to the stop and the pitch did not go below 5-7 degrees due to the coning action. How does the pilot get the helicopter on the ground? And don’t say wait till he runs out of fuel.


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The Cat

[This message has been edited by Lu Zuckerman (edited 06 January 2001).]

[212man]

Er...well the answer to that (is it really a serious question?) would be the pilot would close the throttle (or pull the ICO, but that's a bit drastic).

Now I know why some others have become so exasperated, I've managed to avoid it thus far. I cannot believe that the above is being proferred as serious, technically sound theory.

I don't think I'll bother with any more of these R22 threads.

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Another day in paradise

[Lu Zuckerman]

To: 212man

The bit about how the pilot gets the helicopter on the ground was said in jest. The other parts were in answer to your previous posts.

In each of your posts you concentrated on autorotation and collective settings. I still don't know if you fully understand what I was driving at relative to a 90-degree pitch horn Vs a 72-degree pitch horn.. Please don't go away.

I will sit at my computer and answer to the best of my ability any question you might raise about the thread subject..

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The Cat

[HeloTeacher]

Lu, explanations like that KILL my respect for your knowledge. Again you have ignored what I said, design does not consist of the process you are describing, I'll go point at a time.

1. Minimum (better than flat) pitch

I would expect that the minimum pitch setting would be rerigged a lower value such that the pitch realized at hover coning angles would approximate those experienced prior to the change.

2. Correlator

Simply put, if pitch is being added at a rate of say 135% to previous, the correlator gets rerigged to open the throttle at 135% the revious rate.

3. Jump T/O

Adjust the collectice rigging. If I need to explain how...

If you want to declare something impossible, try to use a reaalistic example of its implementation.

Sorry about the tone of the post, but I really expected better.

[Outside Loop]

Lu,

I mentioned earlier on a different thread that it is perhaps possible that the rotor head was designed around the 72' pitch horn concept (for the reasons explained by FR, transverse flow etc.)and that perhaps this very concept allowed the coning hinges and hence light weight blades to be employed.

You dismissed this possibility by claiming that the coning hinges were designed into the system first.

Do you have any hard evidence of this? Did FR tell you so or does it merely support your arguement to make such a claim?

It matters little which came first,the chicken or the egg, so long as there are chickens. The same can be said for the R22 rotor head. I does not matter which part was designed first.IT WORKS !

The fact that it works is indisputable.Every pilot who has ever flown one will tell you that the machine travels in the intended direction of flight.If you do not believe this then you must get your butt into one before you are eligible for further comment.

Assuming that you do believe it, then by continueing to attack the integrety of FR's explaination you set out only to prove/disprove FR's honour.This is of little consequence to anybody except maybe his friends and family and since it has nothing to do with the safety of the R22 is of very little interest in this forum.

[Lu Zuckerman]

To: Helo Teacher and Outside Loop

From the very beginning I referenced the FAA advisory circular 27-1 that addressed the Robinson rotorhead as a new and unusual design and, in order to get it certified Robinson had to perform testing over and above the normal tests to prove rotorhead structural integrity, reliability and safety. If Robinson had submitted the R22 with a teetering head similar to the Bell he would not have to perform the extra testing. What constitutes new and unusual was the fact that the R22 rotorhead was the first and only rotorhead that had both teetering capability and it also was comprised of two coning hinges. If you had read my report or, the questions I posed to the FAA and Robinson you would know that I inquired as to whether this extra testing had been performed. What prompted me to ask that particular question was the fact that both Robinson helicopters had been restricted from sideslipping and out of trim flight. The reason for the restriction was that in performing these maneuvers the helicopter could suffer a mast-bumping incident due to excessive flapping.

Why does a Bell not have these restrictions? Because, it is not subject to these excessive flapping loads. If the Robinson rotorhead was comprised of one teeter hinge and two coning hinges it could never incorporate a 90-degree pitch horn that Frank Robinson said he had considered. His entire explanation about delta 3 had absolutely nothing to do with compensating for the 18-degree offset. Absolutely nothing! Yet because he said it no matter his reason everyone thinks I am wrong and he is right simply because of whom he is. Do you remember in his explanation he stated that it would require a lot of highly technical descriptions to explain this phenomenon and that he also said that many helicopter engineers don’t even understand it. That might be true for a guy that designs landing gear or transmissions but not the guys that design the helicopter dynamic systems.

I think the reason that different individuals don’t understand what I am saying is because of several reasons. 1) They are blinded from the facts because they conflict with what Frank Robinson said in his response. Or, 2) they can’t conceptualize or they don’t have the capability of using imagery to visualize in their mind how mechanical things work or, 3) chose your own reason.

It all boils down to this.

1) The Robinson rotorhead was designed with the coning hinges

2) A rotorhead with flapping capability or coning can not incorporate a pitch horn that extends beyond the flapping or coning axis due to the generation of massive pitch coupling.

3) The FAA or any other certification authority would never certify a rotorhead that fell under (2) above.

4) Because of 1,2.3 above, what Frank Robinson stated about having considered a 90-degree pitch horn was totally untrue. In other words he lied and I state here and now that I strongly feel that he lied about the delta 3 effect compensating for the 18-degree offset. He then covered it up by stating that to properly explain how it works would involve highly technical descriptions. In other words he was saying that the participants on these threads were too ignorant to understand. He further buried the subject by inferring that many helicopter engineers don’t even understand the subject. This man is your god but he has feet of clay.

Now, how difficult is it to understand what I have been saying?

None of this is meant to be offensive or cutting any of you down, but I keep trying to explain by sending my message to you as if I were shooting a bow and arrow, but the target, seems to move around a lot and I can never hit the bulls eye. (Another sports analogy).

To: Outside loop

If you had read one of my previous posts I stated that the position of the coning hinges on the rotorhead may have been determined by design analysis and ended up as requiring a 72-degree pitch horn. True Frank Robinson referenced the location of the coning hinges in reference to transverse flow but the coning hinges have nothing to do with transverse flow, The pilot compensates for it by applying left cyclic. The coning hinges allow blade flapping to minimize flapping loads and they minimize blade bending. Because of the delta 3 effect the blades when they flap up and out of the tip path the delta 3 effect reduces the blade pitch and causes the blade to drop back in track. The opposite is true if the blade flaps down. This is common to all helicopters including a single rotor bell and especially those helicopters with flapping hinges.

It must be obvious to a lot of you that since I first entered into this forum my opinions have changed and that is due to these back and forth discussions. It is true that my opinions have changed but only to sharpen the technical aspects of those opinions. When I first discussed the 18-degree offset everyone jumped on me and said I was wrong. After a lot of bashing I started to look at this factor in a different light. That is when I considered transverse flow effect. I stated that the helicopter would fly left when the cyclic was pushed forward from the rigged neutral position. I still feel that way. But when you consider transverse flow effect and the left cyclic compensation it became clear that when the pilot moved his stick back to the right until he was flying in the direction intended he had compensated for the offset. In other words the transverse flow and the left cyclic masked the 18-degree offset. Does this seem plausible?

One other thing which I had mentioned previously is that I had asked why if the blade is offset by 18-degrees and it has a phase angle of 90-degrees (this was stated in two Robinson websites) why doesn’t it flap down to the left? Don't tell me because Frank Robinson said so.. The two websites that are supported by Robinson dealers stated that the Robinson blade had a 90-degree phase angle.


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The Cat

[This message has been edited by Lu Zuckerman (edited 07 January 2001).]

[212man]

Well, I've finally found a diagram (from maintenance manual) of the head, and it doesn't seem to tally with Lu's (funny old thing). For one thing, the pitch horn is exactly in line both vertically and laterally with the coning hinge (one side, hence singular). So any blade movement about this hinge will not result in any pitch change. However, as the main flapping takes place about an underslung teetering bearing there will be some delta 3 effect ( as Lu has stated before). From what I have hand written in my notes, the reason given was that it reduced the flapping forces that were being fed back to the stick. This is entirely logical, in that that flaping taking place about the coning hinges would not be felt, where as that about the teetering head would be.

Secondly, if you draw a line through the centre of the pitch horn bearing (where the pitch change link connects) to the centre of the axis of rotation, you get an angle of about 25 degrees, giving an advance angle of 65 degrees. So where does the 18 degrees come from? Is it from the direction the swashplate moves?

The reason for going on about auto rev settings was that the subject of different power settings required to hover had crept in. I had not realised that you were trying to relate this to pitch change due to coning. However, that is still a flawed argument because even if the pitch did increase with coning, the pilot would then have to lower the collective to reinstate the required net pitch angle for those conditions. If he did not, the a/c would rise. At the end of the day, power required is only a measure of blade drag which in turn reflects the blade angle of attack. For any given weight this will depend on the density altitude and will vary. However, within normal ranges, the drag will be much the same for any given weight and so will the power required. All that changes is the collective setting.

In the absence of more diagrams and not being able to locate FR's comments that's about all I can say for now.

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Another day in paradise

[This message has been edited by 212man (edited 07 January 2001).]

[Lu Zuckerman]

To: 212man

What you discovered in your drawing is what we have been talking about all along.

First you have proven that the pitch horn is almost coincident with the cone hinge. Which is what I had stated in other threads. When the pitch horn / pitch link connection is coincident with the cone hinge there is no pitch coupling when the blade flaps about the cone hinge. However as I had previously stated in other threads if the pitch horn / pitch link connection is above or below the cone hinge then there would be a delta 3 connection and when the blade flaps up the pitch will be removed. If the blade flaps down the pitch will be added thus in both cases restoring the blade to the in track position. If the blades (rotorhead) tilts in relation to a fixed swashplate the same thing will happen. The high blade has pitch removed and the low blade gets pitch added thus restoring the disc to the originally commanded position. It makes no difference if the pitch horn / pitch Inc connection is coincident with the cone hinge or not.

I’m confused by what you said about the underslung rotor head reducing the flapping loads. If you are talking about the Robinson rotorhead the reason for the underslung rotor design is to reduce lead and lag caused by the flapping of the blades. This obviously hasn’t happened because the cone bushings and the teeter bushings are high replacement items due to the leading an lagging of the blades. The purpose of the cone hinges is to reduce the flapping loads and the resultant feedback and also, to relieve blade bending caused by coning. Please note, a Bell blade also cones but it is allowed by bending of the blade and on some Bell rotor heads the head itself is preconed to relieve some of the bending loads on the blade and the rotorhead.

Regarding your angular measurement it probably is correct but the 18-degree offset is measured in circular degrees or, degrees of rotation. Log onto this website and download the diagram.

http://pprune.homestead.com/files/rigging.jpg

This shows the rigging position for setting fore and aft pitch setting on both the bell and the Robinson. You will note the position of the Bell blade. This is because it has a 90-degree pitch horn. Now, look at the Robinson blades. In order to set the fore and aft settings the blade is rotated in the direction of normal rotation until the pitch horn /pitch link are directly over the longitudinal axis of the helicopter just like the Bell. Please note the Bell and the Robinson swashplates move exactly the same when the cyclic stick is moved. The rotation of the blades to place the pitch horn / pitch link over the longitudinal centerline is about 18-degrees. This is because the Robinson has a 72-degree pitch horn. The reason the Robinson can’t have a 90-degree pitch horn like on the Bell is because the pitch horn can not cross the cone hinge. It would be bad design and the FAA would not allow it. Besides, you wouldn’t want to fly an R22 or an R44 if it had a 90-degree pitch horn.

Regarding your comment about auto rev I totally agree. I was only trying to construct a scenario about auto rotation if you had a 90-degree pitch horn.

Now, if and that’s a big if, you understand and believe what I wrote above then, is it possible the Frank Robinson told a falsehood.

Here is Frank Robinsons' response

I have read some of the comments about the R22 helicopter printed in this forum. Most were favorable and I appreciated that. However, some were obviously misinformed, and I will comment on several of those.
SIDESLIP WITH THE R22
Concerning the caution against excessive sideslips in the R22 flight manual, this was in part due to a misunderstanding by the FAA. In the Army training film on mast bumping, it showed excessive side slipping as one cause of mast bumping. This was true for the Army Bell Cobras and Hueys, because both aircraft have high centers-of-gravity and relatively low side silhouettes due to their high-mounted powerplants and low-mounted tailcones. During a severe sideslip, the resultant fuselage drag could be below the center-of-gravity and cause the helicopter to roll out of a turn, instead of into the turn, i.e. a negative dihedral or adverse roll characteristic. Airplanes prevent this by having wings with positive dihedral.
The basic R22s and R44s have low-mounted engines, high tailcones, and aerodynamic mast fairings. Consequently, neither the basic R22 or R44 had any tendency toward adverse roll during FAA certification. However, all helicopters (including the R22 and R44) tend to have an adverse roll characteristic when they are equipped with inflated floats, because the floats move the side silhouette area down considerably. For that reason, I did not object to the caution in the R22 flight manual against extreme sideslips during forward flight.
R22 FAA TYPE CERTIFICATION
During the R22 certification, both the FAA test pilots and our own company test pilots flew the R22 through all required maneuvers and flight regimes, and it met all of the FAA regulations. No exemptions were issued for the R22 by the FAA during its certification. Also, I was not a DER (designated engineering representative) during the FAA certification of the R22. No DERs were used during its original certification. After it was certified, the FAA appointed me as a DER with limited authority, so I could approve some minor design changes which commonly occur during production of a new aircraft.
R22 ROTOR SYSTEM
I have read various explanations in this forum attempting to explain the dynamic and aerodynamic characteristics of the R22 rotor system, especially the 18-degree delta-three angle designed into the R22 swashplate and rotor hub. This is a highly technical subject which can only be fully explained using very technical engineering terms. However, since there appear to be a number of misconceptions and a great deal of interest by some pilots and mechanics, the following is a physical explanation of the reasons for the 18 degree delta-three phase angle.
First, keep in mind that the 18 degrees is only in the upper rotating half of the swashplate. The lower non-rotating swashplate is aligned with the aircraft centerline and always tilts in the same direction as the cyclic stick.
Many helicopter engineers have difficulty understanding how delta-three (pitch-flap coupling) affects the phase relationship between the rotor disc and the swashplate. Delta-three only affects the phasing when the rotor disc is not parallel to the swashplate and there is one-per-rev aerodynamic feathering of the blades. For instance, feathering occurs while the rotor disc is being tilted, because an aerodynamic moment on the rotor disc is required to overcome the gyroscopic inertia of the rotor. But once the rotor disc stops tilting, the rotor disc and swashplate again become parallel and the delta-three has no effect on the phasing. Aerodynamic feathering also occurs in forward flight, because it is necessary to compensate for the difference in airspeed between the advancing and retreating blades. Otherwise the advancing blade would climb, the retreating blade would dive, and the rotor disc would tilt aft.
The R22 rotor system was designed with 18 degrees of delta-three to eliminate two minor undesirable characteristics of rotor systems having 90-degree pitch links. In a steady no-wind hover, when forward cyclic pitch is applied, the 90-degree rotor disc will end up tilted in the forward direction, but if no lateral cyclic is applied, the rotor disc will have some lateral tilt while the rotor disc is tilting forward, sometimes referred to as “wee-wa.” This occurs because while the rotor disc is tilting, the forward blade has a downward velocity and the aft blade has an upward velocity. This increases the angle-of-attack of the forward blade causing it to climb, and reduces the angle-of-attack of the aft blade causing it to dive. If no lateral cyclic was applied, this would result in a rotor disc tilt to the right while the rotor plane was tilting forward. Pilots subconsciously learn to compensate for this by applying some lateral cyclic as the cyclic is being moved forward. The amount of delta-three required to eliminate “wee-wa” in the R22 rotor system was calculated to be 19 degrees.
The other undesirable characteristic in rotor systems having 90-degree pitch links is the lateral stick travel required with airspeed changes during forward flight at higher airspeeds. The ideal rotor control system would require only longitudinal stick travel to increase or decrease the airspeed. This is not possible with a 90-degree pitch link system, because the rotor coning angle causes the rotor disc to roll right as the airspeed increases. This occurs because the up-coning angle of the forward blade increases that blade’s angle-of-attack with increased airspeed, while the up-coning angle of the aft blade reduces its angle-of-attack. Consequently, the forward blade then climbs while the aft blade dives, thus causing the rotor disc to roll right with increased airspeed. To compensate for this with a 90-degree pitch link rotor, the pilot must apply some left lateral cyclic as the airspeed increases. The amount of delta-three required to compensate for this effect in the R22 rotor system was calculated to be 17 degrees.
A delta three angle of 18 degrees was selected as the best compromise angle to reduce or eliminate the two undesirable characteristics described above, which would have been present in the R22 had a 90-degree pitch link design been used. Subsequent instrumented flight test data confirmed the choice of the 18-degree delta-three angle.
Hopefully, this will help clarify a few of the misconceptions concerning the design of the R22.
Frank Robinson



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The Cat

[212man]

What I said (meant to say?) was that the pitch horn is ON THE CONING HINGE AXIS ie, as you say, there is no pitch coupling. That is what my diagram shows.

The bit about loads was that with the above accepted, some of the loads caused by flapping (ie those about the coning hinges) are not transmitted to the pilot, whereas some (those caused by flapping about the head) are.

I haven't had time to read FR's bit, I'll do that later.

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Another day in paradise

[Outside Loop]

Lu,

I understand your explanations on why a 90' pitch horn is not possible on this particular rotor system and I totally agree. You seem however to have missed my point completely.

FR stated that he had considered a 90'pitch horn for the R22. This does not imply that the design of the rotor head would have otherwise been identical.

The design as it stands is a package. You can't radically change one component of it and expect it to function as a unit.

It is quite possible that FR could have designed a more conventional system employing 90' pitch horns. Obviously the whole head would be different and it wouldn't have coning hinges.

It would also tend to fly to the right in forward flight and it would be necessary to apply a little left cyclic.

BTW I do not consider FR to be any sort of Diety.I have never met the man.I do not know whether he is a liar or not, much less care.I merely do not believe he has presented enough evidence in his response on this forum to be branded such.

[Lu Zuckerman]

To: 212man


What I said (meant to say?) was that the pitch horn is ON THE CONING HINGE AXIS i.e., as you say, there is no pitch coupling. That is what my diagram shows.

MOST LIKELY YOUR DIAGRAM LIKE MY DIAGRAM SHOWS THE SYSTEM AT REST IN A NEUTRAL POSITION. ON BOTH DIAGRAMS YOU HAVE TO VISUALIZE WHAT HAPPENS WHEN THERE IS RELATIVE MOVEMENT OF THE COMPONENTS WITHIN THE NEUTRAL OR, AT REST CONDITION. MY DIAGRAM SHOWS THE BLADE IN THE PURE RADIAL POSITION WITH FULL DOWN COLLECTIVE. ANY MOVEMENT OF THE COLLECTIVE WILL CAUSE THE BLADE TO CONE UP. WITH THE 72-DEGREE PITCH HORN AND NEUTRAL CYCLIC THERE SHOULD BE NO PITCH COUPLING. WITH THE 90-DEGREE PITCH HORN THE PITCH COUPLING IS MASSIVE. GETTING BACK TO YOUR DIAGRAM IF THE TWO ELEMENTS WERE NOT COINCIDENT AND YOU PULLED COLLECTIVE THERE WOULD BE SOME COUPLING.


The bit about loads was that with the above accepted, some of the loads caused by flapping (i.e. those about the coning hinges) are not transmitted to the pilot, whereas some (those caused by flapping about the head) are.

PITCH COUPLING IS PITCH COUPLING NO MATTER IF IT COMES WHEN THE BLADES TEETER IN RELATION TO A FIXED SWASH PLATE OR, WHEN THE BLADES CONE ABOUT THE CONE HINGES WHEN THE TWO POINTS ARE NOT COINCIDENT.
THERE WILL BE SOME FEEDBACK REFLECTED IN THE CYCLIC. SOME OF THAT FEED BACK IS GENERATED BY PROPELLER TWISTING MOMENT AND SOME FROM DYNAMIC FLEXING OF THE BLADE IN FLIGHT. THAT IS THE REASON FOR THE HYDRAULIC BOOST ON THE R44 RAVEN. THE PILOT DOES NOT NEED EXTRA POWER TO INPUT CYCLIC, HE NEEDS THE BOOST TO CANCEL THE FEEDBACK. IF THE ROBINSON IS PLACED IN A SITUATION WHERE THE FLAPPING LOADS INCREASE TO THE POINT WHERE MAST BUMPING WOULD OCCUR THE PILOT WOULD FEEL IT IN THE CONTROLS AND IN HIS BUTT BECAUSE OF ALL THE SHAKING.

I haven't had time to read FR's bit; I'll do that later.


To: Outside Loop


I understand your explanations on why a 90' pitch horn is not possible on this particular rotor system and I totally agree. You seem however to have missed my point completely.
FR stated that he had considered a 90'pitch horn for the R22. This does not imply that the design of the rotor head would have otherwise been identical.

IF FRANK ROBINSON CHOSE A 90-DEGREE PITCH HORN HIS ROTOR SYSTEM WOULD LOOK VERY MUCH LIKE A BELL 206. THE BELL BLADES AND ROTORHEAD HAVE SUFFICIENT STRUCTURAL INTEGRITY TO RESIST THE CONING AND BENDING MOMENTS PLACED ON THEM. IF WE CAN ASSUME THAT THE ROBINSON DESIGNED BLADES WERE USED ON THAT 90-DEGREE ROTORHEAD THE APPLIED MOMENTS AND BENDING LOADS WOULD LEAD TO FAILURE VERY SHORTLY AFTER THE HELICOPTER LIFTED OFF ON THE FIRST FLIGHT. IF THE BLADES WERE DESIGNED TO ACCEPT THOSE LOADS WITH A MARGINE OF SAFETY YOU WOULD HAVE TO PUT A SECOND ENGINE IN THE AIRFRAME.
The design as it stands is a package. You can't radically change one component of it and expect it to function as a unit.

I ACCEPT THAT. MY ONLY ARGUMENT IN THIS THREAD IS THAT IF FRANK ROBINSON DESIGNED THE ROTORHEAD TO HAVE A 90-DEGREE PITCH HORN HE WOULD HAVE A MINIATURE BELL ROTORHEAD. THEN HE WOULD HAVE TO REDESIGN HIS BLADES TO ACCEPT THE BENDING, TWISTING AND VIBRATORY LOADS WITH A SUFFICIENT MARGINE OF SAFETY. THE ARGUMENT CONTINUES STATING THAT IF THE ROTORHEAD DESIGN WAS FIXED FROM THE BEGINNING (WHICH IT WAS) HE COULD NEVER HAVE CONSIDERED USING A 90-DEGREE PITCH HORN, WHICH IS WHAT HE CLAIMED IN HIS RESPONSE.


It is quite possible that FR could have designed a more conventional system employing 90' pitch horns. Obviously the whole head would be different and it wouldn't have coning hinges.

I AGREE WITH THE CONCEPT OF YOUR STATEMENT. HE MAY EVEN HAVE CONSIDERED USING A MULTI BLADE SYSTEM BUT THAT WAS IN THE CONCEPTUAL DESIGN PHASE. NOW THESE ARE MY WORDS AND THEY ARE BASED ON WHAT I HAVE READ ABOUT MR. ROBINSON. HE HAD WORKED FOR SEVERAL LARGE HELICOPTER COMPANIES AND HAD EXPERIENCE WITH A LOT OF DIFFERENT ROTORHEAD DESIGNS. MR. ROBINSON WANTED TO CREATE A HELICOPTER FOR THE MASSES AND HIS BOSSES AT THOSE COMPANIES WOULDN’T LISTEN TO HIM. HE PROBALLY GAVE CONSIDERATION TO ALL TYPES OF DESIGNS BUT WHAT HE DECIDED UPON WHEN HE INITIATED DESIGN ON THE R22 IS WHAT YOU HAVE ON THE R22 AND THE R44. HE NEVER INTENDED TO PUT A BELL TYPE ROTORHEAD INTO PRODUCTION OR, TO USE A 90-DEGREE PITCH HORN ON THE EXISTING DESIGN..

It would also tend to fly to the right in forward flight and it would be necessary to apply a little left cyclic.

ANY HELICOPTER WOULD FLY TO THE RIGHT AND WOULD REQUIRE THE APPLICATION OF LEFT CYCLIC TO COUNTER THE RIGHT ROLL. THAT IS CALLED TRANSVERSE FLOW EFFECT. HIS STATEMENT HAD NOTHING TO DO WITH THE 18-DEGREE OFFSET OF THE BLADES

BTW I do not consider FR to be any sort of deity have never met the Man. do not know whether he is a liar or not, much less care. I merely do not believe he has presented enough evidence in his response on this forum to be branded such.

LOOK AT IT THIS WAY, IF HE HAD ADMITTED TO ANYTHING RESEMBLING THE HELICOPTER FLYING LEFT WHEN THE CYCLIC WAS MOVED FORWARD HE WOULD HAVE IMMEDIATELY INCURRED THE WRATH OF THE FAA AND OTHER CERTIFICATION AUTHORITIES AND MUCH WORSE, OPEN HIMSELF UP TO A LOT OF LAW SUITS. WHY DIDN’T HE EXPLAIN IT EVEN THOUGH THE MAJORITY OF THE FORUM PARTICIPANTS INCLUDING MYSELF WOULDN’T UNDERSTAND HIS EXPLANATION AND WHY DID HE STATE THAT HELICOPTER ENGINEERS DON’T FULLY UNDERSTAND HOW A HELICOPTER FLIES?
IP: Logged

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The Cat

[This message has been edited by Lu Zuckerman (edited 08 January 2001).]

[This message has been edited by Lu Zuckerman (edited 08 January 2001).]