Well done Lu for being so candid.

I do feel that in general your arguments have been too diverse and all encompassing, when it comes to R22 bashing. If you had just concentrated on one flaw (as perceived by you) at a time I think things may have been clearer. The threads have covered all manner of topics such as low g behaviour, low Nr behaviour, excessive sideslip problems and even the consequences of showing off at low level to your friends. To have pinned all this on Frank and his 18 degrees of offset was a little bold I feel, and smacked of an obsession.

Some of your statements simply don't show themselves in practice,as quite a few pilots tried to point out. The R22 is a very clever piece of kit and reasonable competence in handling it should yield dividends when converting to larger types. I appreciate the high loss rate, but this is more of a regulatory and training issue than a design flaw. You simply cannot expect a 50 hour PPL to fly a helicopter with the safety that an equivelant fixed wing pilot could fly a Cessna (and that's debatable in it's own right). Similarly, a very experienced pilot on larger types, such as Bells, with more benign handling traits may find problems in some predicaments.

Anyway, keep up the contributions, they certainly keep the forum alive!

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Another day in paradise

To: Imlanphere

It is a well known fact that when a student graduates from a university, a technical school or say, a flight school he will have only that knowledge that was imparted to him by his instructors. If the student never expands on that knowledge he will only know what his instructors told him and nothing more.

Most helicopter flight schools start the student out in an R22. The instructors at that flight school may have been students at that same school only months before. Some of those instructors may have even attended a safety school at Robinson or at some field site where a Robinson Pilot taught the course. So, when one of the graduate students is asked a specific question he will provide an answer that fits the subject as he was taught. All Robinson helicopter pilots will respond in unison as if they were parroting the words as spoken by Frank Robinson.

First of all, the response that Frank Robinson made as quoted by you is totally false and this is why. Mr. Robinson mixed chickens and eggs so that you must really look at what he says in order to determine which came first.

The rotor head was designed from the very beginning as a teetering rotorhead with coning capability. Robinson knew from the beginning that the aerodynamics of a lightly loaded low inertia rotor would involve severe blade bending and blade flapping. In order to minimize those two negative actions they incorporated coning hinges.

Once coning hinges were installed they could never have a pitch horn that lead the blade by 90-degrees. To do so, would render the helicopter uncontrollable due to massive pitch coupling. By definition, the pitch horns could not pass the cone hinges. A 90-degree pitch horn would not force the pilot to compensate in the low speed regime. There would be no low speed or, for that matter high speed regime because when the pilot brought the helicopter to a hover, the pitch coupling would make it extremely difficult to maintain that hover and if he pushed forward cyclic the helicopter would most likely crash.

Robinsons’ theories, are fashioned to provide the neophyte pilot with information that the neophyte pilot believes to be true, and if that pilot never learns or accepts another alternate theory, then, when he is asked a question about a Robinson Helicopter, he will reply as if Robinson Helicopters signs his pay checks.


To: 212man

The reason that my posts are so diverse and I don’t address a particular point is because I have many interested individuals responding to the many points put forth in my report. Once I respond to a posting I get several more differing points of view that I in turn have to respond to. It is like playing a tennis match where I have 20-30 opponents at one time and they are all lobbing fuzzy yellow balls at me.

Regarding those statements that don’t show themselves in actual practice, I would refer you to those pilots that took up my challenge, and then reported back, that I was correct.


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The Cat

[This message has been edited by Lu Zuckerman (edited 14 December 2000).]

Lu, the response I spoke of in the above post was from Ray Prouty, not from a recent training school graduate. I completely agree that asking fellow pilots in a training school will more than likely yield similar results, but you have assumed too much for this was not the case.

To: Imlanphere

If Ray Prouty said that about the design of the Robinson rotorhead either he had not fully examined the problem or, if he did, he had his head up-and-locked.

A ninety degree pitch horn could never have been used on the R22/R44 rotorheads unless they got rid of the coning hinges.

If you would refer to my response to Frank Robinson I stated that I would buy the positioning of the cone hinges that resulted in the eighteen degree offset as a means of reducing certain pitch coupling. However, the lead in to this thread is that there is no 18-degree offset of the two parts of the swashplate.. The rigging is done with the pitch links over the lowest/highest point of the stationary swashplate which offsets the blades by 18-degrees. This makes Frank Robinsons' argument go away and as far as I am concerned, Ray Proutys' input is moot.

You mentioned having to compensate at higher speeds, discounting transverse flow effect, what compensation are you refering to.

Before you answer that I am including a response by The NR Fairy regarding my statements about the impreciseness of the Robinson cyclic control. This was in response to my claim about having to compensate for the so called 18 degree offset.

"On this occasion, I'd have to agree with Lu that the Robbie's handling is far from precise, but only when I'm trying to beat the little b*****d into submission" !!

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The Cat

[This message has been edited by Lu Zuckerman (edited 14 December 2000).]

Lu,

You CANNOT continue to preach that gyroscopic precession is the cause of rotor phase lag; it is incorrect and misleading. There are many good academic texts on the subject. Please see my post on page 9 of the R22 certification thread.

Grey Area

this is an excerpt from a letter written by Ray Prouty:

"...If you are on the ground and apply maximum cyclic pitch to the rotor when it is over the nose, the tip path plane will tilt up 90 degrees later on the left side (and down on the right) following the laws that apply to a gyroscope.

If you are in the air, the same thing happens as you call for an acceleration of a right roll by applying maximum pitch over the nose. (If the rotor has offset flapping hinges, the angle is not 90 degrees, but something less--maybe 85 degrees). However, once you achieve some rate of right roll, the situation changes and the tip path plane will not be responding at 90 degrees, but at some smaller angle depending on the design of the blades. This angle can be as low as 60 degrees depending on the design of the blades and results in rate crosscoupling.

Some helicopter designers arrange the cyclic control system such that a stick movement directly to the right produces maximum pitch over the nose and rely on the pilot to take care of the rate cross-coupling. Others, such as Robinson, rotate the controls to minimize this crosscoupling while accepting some acceleration crosscoupling.

There are some other sources of crosscoupling, so one value of control phasing will never be optimum....."

I typed this out because it was unfair of me to use Ray's name in the above post along with other information which was not given by him.



[This message has been edited by lmlanphere (edited 14 December 2000).]

To: Imlanphere

Ray Prouty said: "Some helicopter designers arrange the cyclic control system such that a stick movement directly to the right produces maximum pitch over the nose and rely on the pilot to take care of the rate cross-coupling. Others, such as Robinson, rotate the controls to minimize this crosscoupling while accepting some acceleration crosscoupling". My question is, how do the pilots counter this cross coupling. Which way do they move the cyclic?

The control movement and the resulting swashplate movement is exactly the same on a Robinson as it is on a Bell. Using the illustration above, when the pilot moves the cyclic to the right the Bell blade will have reached its' maximum pitch over the nose and its' minimum pitch over the tail and as a result the P R E C E S S I O N of 90 degrees will cause the blade to rise over the left side and drop over the right side and the helicopter is flying to the right.

The control movement for the Robinson is exactly the same. However, when the blades are over the nose or the tail they must rotate an additional 18 degrees to achieve maximum and minimum pitch change. When the have rotated this additional 18 degrees they will be at the maxim/minimum pitch change points and, the P R E C E S S I O N OF 90 degrees will cause the blade to rise 18-degrees past the lateral axis, and the helicopter will fly to the right, with a slight forward component. So, Mr. Prouty is wrong in this case. However, I do agree with his remarks about the laws that apply to a gyroscope. Grey Area are you reading this?

With regards to what Mr. Prouty said about articulated rotorheads or rotor heads with real or theoretical offset hinges he was talking about the positioning of the swashplate relative to the direction of flight. Most helicopters of this type follow what Sikorsky has been doing for years. The movement of the controls are the same as described above, however the movement of the swashplate is different. If the pilot moves his cyclic to the right, the swash plate will tilt up somewhere between the 10 and 11 o clock position and the swashplate will tip down somewhere between the4 and 5 o clock position. This offset is 45-degrees. The pitch horn lead is 45-degrees making a total phase angle of 90-degrees. With the right cyclic input as described above the disc will tilt up over the 9 o clock position and will tip down over the 3 o clock position. This movement is the result of PR E C E S S I O N which was caused by a force imbalance across the disc which was induced by the movement of the cyclic stick and the resultant pitch change.


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The Cat

[This message has been edited by Lu Zuckerman (edited 14 December 2000).]

[This message has been edited by Lu Zuckerman (edited 15 December 2000).]

Lu,

I am reading this and from personal experience know you are in error. For example the Lynx is rigged to accommodate a phase lag of 72 degs and is not too far off, a Squirrel at 78 degs and again does not suffer from too much cross couple. These cross couples will alter with density altitude (I have practical experience of this fact). In fact, with a cyclic pitch input aft it is possible to demonstrate on a cold, high pressure day, to demonstrate a pitch up and roll right whereas at high density altitude a pitch up and roll left. Please explain?



[This message has been edited by Grey Area (edited 15 December 2000).]

To: Grey Area

Please see my response to your posting on Certification of Robinson......

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The Cat

To: Imlanphere

You stated above that a helicopter can be designed so that when the cyclic is moved to the left or, right the pilot can take care of the cross couple and fly forward (or at least that is what I think you said.

FAA Advisory Circular 27-1 which governs Certification Of Normal Catagory Rotorcraft states that the direction of flight must be in the same sense of cyclic stick displacement. They allow a 1-2 degree deviation for control coupling but not 90 degrees as you had indicated.

[This message has been edited by Lu Zuckerman (edited 20 December 2000).]

Grey Area,

I'm afraid that I am going to have to disagree with you there about your statement about the Lynx. Firstly, the Phase Lag is 75 deg, secondly, with the AFCS OUT, it suffers massively due to this so called 'PITCH/ ROLL' couple - as in the R22 (note – this is not the ‘Acceleration Cross couple as explained by Ray Prouty/ not even he could explain this one!!). The only difference is that due to the nature of the Head - the rate of roll produced by an Aft/ Fwd movement of the cyclic is incredible. After a considerable amount of research and Flight testing into this subject, our conclusions are the same as for Lu Zuckerman. The only question that still remains un-answered is ‘Why has it been designed this way?’

Lu – regardless of the analogy of ‘GYROSCOPIC PRESSESSION’ that Ray Prouty uses to explain the flapping of the disc, it is WRONG. If indeed the disc did act as a GYRO – then where is the secondary/ tertiary etc pressession? What about the OTHER property of a gyro – RIGIDITY IN SPACE? If the disc were a gyro, then it would be uncontrollable!! There is a far easier/ factually correct explanation, which holds true for ALL helicopter Principles of Flight. It involves the application of Pitch – due to the swash plate, and its effect on RATE OF FLAPPING!!

http://www.stopstart.fsnet.co.uk/Gif/SPericani2.gif

Lu, I can't find what you were refering to above about a 90 degree compensation (I'll assume a misunderstanding). All I've done is repeat what I've learned on the subject recently (which unfortunately does not include FAR's on allowable cyclic/rotor displacement discrepancies).

To: Imlanphere

It was a misteak on my part. Sorry for the confusion.

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The Cat

To: Baque Flip

Regarding the second paragraph of your post about gyroscopic characteristics. The rotor disc like the rotor on a gyroscope have two things in common. One, is rigidity in space. In other words, it will stay in the position you put it. The other is precession, as it will move to where you command it. In order to make the gyro/rotor disc move from its' rigid in plane position you have to input an external force. In the lab or in training school the instructor will demonstrate these characteristics using a multi gimbal gyroscope. With the rotor spinning, the instructor will perturb the rigid rotor by applying a force to the outer gimbal ring. The results of that force input causes the rotor to tilt in the direction of the force but 90-degrees later in the direction of rotation.

In the case of the rotor system it is either a direct force on the swashplate in the case of a Robinson or by a hydraulic servo such as those used on larger helicopters. The precession is still the same, 90-degrees and the precession will continue until one of two things happens, 1) the force stops or, 2) the control system or the rotor system comes up hard on the stops. In the case of 2 above the pilot becomes aware of the problem immediately as there is a very large vibratory force applied to the airframe from the rotorhead.

What you stated in the last sentence of your post discounts precession and states that the rotor moves because the swashplate position changes the pitch on the blades and the disc moves as a result. The change in pitch due to swashplate movement is the external perturbing force. The change in pitch creates a force differential across the disc, which results in precession.

Regarding the massive pitch couple on the Lynx when the AFCS is turned off I would direct you to read my post on the Piaseki Compound Helicopter where I made a comment about the Cheyenne helicopter.

The Cheyenne because of the design and the stiffness of the blades had a constantly changing phase angle (90 + or,- 5-10 degrees of precession). This little problem killed one pilot and destroyed a very large and very important wind tunnel in California. It took two years to figure out how to solve the problem. What they did was to measure and monitor cyclic stick position and when the blades went where they wanted instead of where the pilot commanded them the computer would sense this and command the servo system to instantly compensate. Say, the pilot pushed the stick forward and the disc tilted to the left, the computer would alter the servo input as if the pilot moved the cyclic to the right. The system worked very well but it was so complex and contained many single point catastrophic failure modes that the Army cancelled the program. I would assume that the AFCS system does the same on the Lynx as the flight computer did on the Cheyenne. Its’ too bad they can’t put one on a Robinson R22/44.

This principle of external force causing a gyro to precess is used in electro mechanical and air driven gyro instruments on the instrument panel of your ride. Only in this case it is the movement of the aircraft around the instrument that provides the perturbing force and the movement of the rotor is connected to the indicating needle or the ball on the gyro horizon.


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The Cat

[This message has been edited by Lu Zuckerman (edited 20 December 2000).]

[This message has been edited by Lu Zuckerman (edited 20 December 2000).]

Robinson: Tech Q's
 

Just A quickie..........
why have the robinson r22 and r44 got such long masts , ie the distance between the swashplate and the cabin. many different reasons sugested just wondering which one is right. whats the difference between the 206 setup and the r22/44 setup??

The precession theory for the rotor does not hold any water. Yes maybe as a ‘basic’ analogy/ comparison, but that is as far as it goes. To make the disc change attitude, you don’t just apply a force 90deg prior to its desired deflection. Consider the swash plate as a ‘swash plate’ and the blades as individual wings. All that the swash plate is doing is changing the AoA/ pitch of the ‘wings’ therefore causing them to increase/ decrease lift. Because they are attached to the rotor head, the blades flap up/ down respectively. This journey does not simply start 90 deg prior, but a full 180 deg prior.

Consider this. In order to get the blade to fly low over the front of the aircraft and high over the rear – you apply fwd cyclic. This will, in blades that turn counter clockwise, tilt the swash plate to the right (starboard)….As the blade leaves the 6 o’clock position (tail) pitch is slowly, but progressively being taken off – assume that it starts with neutral pitch. The blade starts to lose AoA = lift…therefore starts to flap down. As the journey of the blade continues to the 3 o’clock pos (starboard), the MAX amount of pitch is removed = MAX RATE of flap down. Towards the 12 o’clock pos (nose), note that the blade is still continuing to flap down, but at a ‘sustained rate’ because the amount of pitch is returning to neutral. Note – this blade will continue to flap down until positive pitch is applied. Funnily enough, this is what happens once the blade passes through the 12 o’clock. The swash plate now starts to apply pitch onto the blades, therefore the blades start to climb.

This is easily demonstrated in the hanger. Apply fwd cyclic and slowly rotate the disc and follow the journey of a blade from the tail to the nose. You will find that as the blade travels, the amount of pitch subjected to the blades is directly proportional to the swash plate. You don’t even need a swash plate – ANY rotor system.

Now, with a GENERAL helicopter, you would assume that with FWD cyclic applied, the blade over the 12 o’clock pos would have neutral pitch (indeed it shold not be effected) – and where you apply the phase lag offset – the max amount of pitch removed. As soon as the blade moves from the 12, the pitch 'should' start to increase again….Well, in the Lynx it is different. As the blade is moved through the 12, it is clear that it is still being subjected to pitch. It is not until 15deg past the 12, that the pitch becomes neutral. Therefore, the longitudinal axis does not run as we would expect - 12-6 o’clock. So AFT cyclic not only produces a nose up component, but also a roll to the right.. This can also be seen when applying collective pitch in fwd flight. One would expect the nose to ‘just’ flap back when raising the collective (try using precession to explain that one) and vice versa for lowering the collective. It doesn’t – you also get a roll, therefore confirming the theory. But you already know this.

As for the AFCS being advanced, believe me it is not. Maybe 25 yrs ago….It simply compares your control inputs with its vertical gyros and applies direct control inputs to the hydraulic servos.




[This message has been edited by Baque Flip (edited 20 December 2000).]

Lu,
Baque Flip has amplified what I sent you on e-mail regarding our thinking on precession versus aerodynamic forces causing phase lag.

Grey Area - you stated earlier that the pitch roll couple on the Lynx could be demonstrated to occur in different directions depending the Density Altituded. This might have been true with metal blades but the CMRBs only go one way - pitch up=roll right. As phase lag reduces with increase of DA you cannot achieve a reversal in this. Equally the negative DA required to increase the phase lag by the appropriate amount would be impossible to find even over the dead sea in the middle of winter.

[This message has been edited by [email protected] (edited 20 December 2000).]

Baque flip and Crab etc

I have been trying to argue the flapping to equality point with Lu for a while (see the big R22 thread). You are going to have fun convincing him.

I am in the process of putting together a missive on the subject of phase lag. Struggling with simplifying offset (displaced) flapping hinges at the mo. Watch this space. For the lynx the short answer is increased AUM, increased NR and new blades since the head was designed.

Crab. True about CRMB. I also agree that phase lag reduces with altitude, so the right roll component should decrease as you climb (Point of max tilt moves clockwise). In a CMRB cab the whole dynamics have changed I agree, but the roll rate should be reducing with altitude.

[This message has been edited by Grey Area (edited 21 December 2000).]

To: Baque Flip, Grey Area and everybody else that I have tried to force my beliefs on.

Our arguments are like trying to convince the other guy that your religion is better than his. You believe in God and he believes in Allah. You believe in Jesus Christ as being the Messiah and your Jewish neighbor believes that the Messiah is yet to come and when he does come, most likely he will find that it is Jesus Christ. When you get to heaven or your Muslim friend gets to Paradise and you meet up there you find that one god is judging you. What you see suits your beliefs and what the Muslim sees suits his belief. You both believe in the same thing but you see it in different ways.

What you learn about helicopters in the UK training programs suits you very well and you have a complete understanding of the subject. The student and pilot in the USA training programs gets a different understanding and that suits them very well, and they have a complete understanding of the subject. As long as you stay in the UK and the American stays in the States every thing is OK. Switch places and your whole concept about how a helicopters flies will immediately come under challenge.

I think Grey Area said it, it is a difference in language. I have often wanted Danny to incorporate a Lexicon or, thesaurus so that us Yanks understand what you Brits and especially the Wizards of OZ are talking about.

I think we should bring this aspect of these threads to a halt. No more talking about precession or phase lag.

I just received this from a pilot in the UK. I asume he was trained in the military.

It explains everything.

One aspect of rotor control that is not taught in the British Military is that of the rotor system acting as a gyroscope. Our belief is that the phase lag of 90 degrees exists between input of pitch change and desired blade position only because of aerodynamic forces. The blade starts to flap as the pitch operating arms follow the circular control orbit and the rate of change of pitch is at it's maximum 90 degrees later - for the next 90 degrees the blade continues to flap but at a reducing rate until at a point 180 degrees from where the pitch angle started to change - the blade reaches it's high or low point before completing the other 180 degrees doing exactly the opposite.
Whilst a theoretical solid rotor disc might exhibit some tendency to precession, the greatly reduced mass of a real rotor and the fact that the blades are free to flap mean that gyroscopic theory is not wholly applicable - are aerdynamic loads on a blade inertial or external and what produces the torque required to induce precession? - the pitch change happens gradually and is not the single point force that most textbooks illustrate when depicting precession in a gyro.

Grey Area appears to be ex-British Military, probably Navy and has questioned your use of the term "flapping to equality", we use it to describe the reaction of the blades to overcome dissymmetry of lift such as flapback or inflow roll, whereas you seemed to use it to describe the coning angle achieved once the lifting and centrifugal forces were in balance in the rotor system.



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The Cat

[This message has been edited by Lu Zuckerman (edited 21 December 2000).]

To: whatsarunway

I would assume that if the Robinson swashplate were lower down on the mast like a Bell 206 the pitch links would have to be very stiff in order to counter the centrifugal loads that would cause them to bow outward. Because of this tendency to bend or, bow outward the attaching adjustable hardware at each end of the pitch link would have to be strengthened as would the swashplate and blade attach points and this would add weight. If you add weight to the pitch links the stiffness must increase again because of the higher centrifugal loading.

The mast length on the Robbie like that on the 206 has to be long because of the low rotor blade/rotorhead interlock. It supplies a longer moment arm.
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The Cat

[This message has been edited by Lu Zuckerman (edited 21 December 2000).]

At last!! Some one talking sense. NOw can we continue please with no more talk of precession - unless related to aircraft instruments!

Happy with that. US/UK Aviation thesaurus on demand!

Will still post my explanation of <90 phase lag in rigid heads soon (sorry but it's written in UK Mil speak).

Grey area, I'm still interested in this subject and hope that you DO post some more info (at least one person will read it)- as for gyros and precession I think we can all agree that a helicopter rotor system is an "ineffective" gyro and therefore exibits SOME of a gyro's characteristics. The real thing requires much more mass and a much higher RPM (relatively).

Although a rotor disc might 'coincidently' display the 'odd' similar characteristic, it is NOT the same. Even considering them as having some of the same characteristics will only confuse the issue, especially when you try to explain some more complex helicopter effects. Trust me; leave the precession for a GYRO. The rotor disc is a completely different beast.

[This message has been edited by Baque Flip (edited 21 December 2000).]

I'm with Baque Flip on this one. The precessive qualities of a gyro stem from the inertial effects of the rotating mass. As has already been said the mass and rpm of a rotor are not sufficient. I once had a formula for the minimum mass/rpm for a gyro which I have (thankfully for most of you) misplaced, but I did use it on a helo rotor system (Lynx [grey]) and fell well short. Incidently it is inertial effects that cock up the phase lag in an offset flapping hinge.

[This message has been edited by Grey Area (edited 21 December 2000).]

Lu, Please explain. Also assuming your on the right track, where do alpha angles come into it?

To: Rotorque

Admitting my own ignorance, what is an alpha angle and what does it have to do with this thread? Just asking not attacking. Hopefully this doesn't generate into a discussion based on how you and I were taught the same subject.

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The Cat

thanks




[This message has been edited by whatsarunway (edited 24 January 2001).]

Lu's answer:
"The mast length on the Robbie like that on the 206 has to be long because of the low rotor blade/rotorhead interlock. It supplies a longer moment arm."

Means:
Long mast required to accomodate CoG range, since 'teetering' rotor heads supply no direct attitude changing moment - the CoG will hang directly under the center of the rotor head in a hover - to keep the angle between mast axis and disc axis small you need a long mast.
(any heads with flapping hinges (or virtual hinges) at a distance make a restoring force which resists attitude differences between helicopter and disc - (less g dependant for attitude control authority) - so they tend to have much shorter masts and have relatively more CoG range)

- I hope I haven't made it worse.

TO ROBINSON LAMEs AND A&Ps
 

To: LAMEs and A&Ps that work on Robinson Helicopters

In making this post I will make several assumptions;

1) In order to be able to work on the Robinson Helicopters you attended a factory school or, you attended a Robinson sponsored school that was operated by a Robinson distributor.

2) You were taught flight theory as well as how to rig the helicopter.

3) If you were taught in the USA you were told about gyroscopic precession and if you were taught in the UK or OZ you learned it in a different way. (Unless the subject was taught by a Robinson representative).

Although there are variants of the above assumptions it can be assumed that they are correct. If that were the case, I would like to pose these questions.

1) In learning about gyroscopic precession or the same phenomenon as taught in the UK or Oz did they use the Robinson system as a demonstration or, did they use a Bell system as a means of explaining the subject?

The reason I ask this is because there are at least two websites that are the home pages of two Robinson dealers and flight schools. These websites have a very good explanation of how a helicopter flies. They have excellent pictures of Robinson helicopters and the major elements of those helicopters. They show pictures of Bell and Robinson rotorheads and they then go into the subject of gyroscopic precession.

Although the preceding text on the website(s) dealt with a Robinson rotorhead they explained gyroscopic precession by using a Bell system as an example. The two systems are different.

2) In teaching the rigging process how did they explain the differences in the positioning of the Robinson blades as opposed to those of a Bell helicopter and, how did they rectify what they taught about gyroscopic precession as related to the positioning of the blades?

I assume they taught that the precession phase angle was 90 degrees and yet the Robinson blades are disposed 18-degrees from the respective axes during the rigging process. What did they tell you about where the blade disc would dip if the cyclic was pushed forward from the rigged neutral position?

To get a better understanding of what I am asking, log onto the following websites and download the diagrams.

http://205467.homestead.com/diagrams.html
http://pprune.homestead.com/files/rigging.jpg


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The Cat

Lu Zuckerman wrote:

I assume they taught that the precession phase angle was 90 degrees and yet the Robinson blades are disposed 18-degrees from the respective axes during the rigging process. What did they tell you about where the blade disc would dip if the cyclic was pushed forward from the rigged neutral position?

In a previous posting to this forum (to which you made several replies), Frank Robinson explained the reason for the 18 degree Delta-3 angle that is incorporated into the R22/44 rotor system. It seems that either you simply ignored his explanation, or you are incapable of understanding it.

Numerous pilots with experience flying the Robinsons have stated in this forum that the ship does *not* behave in the manner you claim. Not only do you continue to ignore these statements, but you refuse even the opportunity to gain first-hand knowlege of the situation by actually flying in the ship with an experienced pilot. Somewhat like the clerics who refused to look through Galileo's telescope, you choose to remain blissful in your ignorance.

Perhaps you feel ignorance is bliss. But, if in fact you actually DO understand the effect of Delta-3, why do you believe it is *not* applicable to the behavior of the R22/44 rotor system in the manner that was explained by Mr. Robinson?

In this post you make several assumptions:

That this will begin another 100+ thread.

Not going to happen.

My assumption for 2001: Slowly, those who are on the board all the time will tire of endless repostings about the subject, and begin to ignore them.

The only way they will stay in the forum is if you add to them yourself.

Mark561, don't bother trying, he has an answer for everything except why it doesn't follow his predictions.

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Marc

To: mark561 and RW-1

First of all, I was trying to solicit responses from mechanics that work on Robinson helicopters as to what they were taught about the rigging of the two helicopters and what they were taught about flight theory. I was not looking for any criticism. Paul Cantrell writes the two web sites I often refer to and Robinson dealers and flight schools sponsor both. Mr. Cantrell addresses the function of various aspects of both the Robinson and Bell dynamic systems and then addresses gyroscopic precession indicating that it is 90-degrees (phase angle) for both the Bell and the Robinson. When he demonstrates the principles of gyroscopic precession he uses a diagram of the Bell control input and response which showed where the input and ultimate responses of the disc tilt were. On the RW-1 website you indicated that you got the information from a US Army flight instruction manual. Well the illustration used by Mr.Cantrell is the same as that used on your website so I can only assume that gyroscopic precession is addressed in your website as being 90-degrees.

In regards to this aspect of the control input Vs response, the Robinson is completely different in that during the rigging procedure the position of the blades during pitch setting are offset by eighteen degrees as opposed to where the Bell Blades are positioned for the same setting.

If the Robinson blades are offset by 18-degrees during rigging then the maximum pitch input on advancing blade is decreased to the maximum and the retreating blade which is also offset by 18-degrees and it is at its’ maximum pitch change then please explain to me the following. How in hell will the Robinson rotor system defy the laws of physics governing gyroscopic precession and tilt down over the nose and up over the tail. If you refer to what Frank Robinson said in his reply I will tell you both that you are full of S**t and so is he.

Listen to what I am about to say and then go out and look at the Robinson rotorhead. Frank Robinson stated that they evaluated the benefits of a 90-degree pitch horn Vs a 72-degree pitch horn and determined that the 72-degree pitch horn would solve a problem relating to transverse flow effect. He implied that the 72-degree pitch horn would eliminate this problem that effected the Bell with its’ 90-degree pitch horn. That is pure bull crap. RW-1 what happens to your R22 when you speed up from a hover to say around 20-30 Knots. Do you encounter transverse flow effect? If you do, then what Mr. Robinson stated about his choice of a 72-degree pitch horn and why it was selected is wrong.

Another point I have made regarding the rotorhead design is that from the very beginning, Frank Robinson incorporated cone hinges on his rotorhead. This was not done to counter the effects of transverse flow it was done to minimize the bending moments of the blade and to minimize the transmission of flapping (coning) moments so the design could never incorporate a 90-degree pitch horn.

He also stated that the delta 3 effect would make up for the 18-degree offset and result in a 72-degree phase angle and allow the blade disc to tilt down over the nose when the cyclic was pushed forward. This too is bull crap. The delta 3-effect causes pitch to be removed or added to the blade when it flaps due to external aerodynamic forces. If the blade flaps up pitch is removed and if it flaps down pitch is added. Just like on a tail rotor. However this can only happen if the pitch horn / pitch link attachment is above or below the cone hinge. If the two points are coincident then there is no pitch coupling. Explain this, if the points are coincident when forward cyclic is pushed then which way will the disc tilt? Will it tilt down over the nose or, will it tilt down left of the longitudinal centerline. You can’t have it both ways and state that it will tilt in one way or the other if you use the explanation used by Frank Robinson.

RW-1 here is something you can demonstrate since you like flying on the edge. Lift off with your cyclic in the rigged neutral position. Do not move it laterally. Push it forward and fly through the transverse flow effect. The helicopter should roll to the right but don’t move the cyclic. When you are through the transverse flow effect, let me know which direction the helicopter is flying.
This is for mark561.

According to your Bio, you are most likely working at the Lazy B but then again there are a lot of places in your area that employ engineers. Your Bio also indicates that you fly model helicopters.

I don’t know what kind of engineering training you have (ME, AE or, EE) but I assume that you learned the theory of gyroscopic precession and that barring any mechanical or, friction problems the gyroscopic phase angle is always 90-degrees. If you downloaded my diagrams especially the one that Helidrvr put on this thread you can see the difference between a Robinson blade and a Bell blade during the rigging process. The relative positions of the blade sets are the point that they have the maximum perturbing force and according to the laws of physics the blade disc will react 90-degrees later in the direction of rotation. It is my contention that there will be a left roll component added when the reaction takes place. Regarding the demonstration I asked RW-1 to perform, two pilots on this thread performed the test and their conclusions were that I was correct.

When the Robinson accelerates forward the pilot will counter the transverse flow effect by adding left cyclic. This is in addition to the left roll caused by the 18-degree offset. When he passes through the transverse flow effect he moves his cyclic to the right. In doing this he is reestablishing the helicopter in forward flight as opposed to rolling left. Is there a possibility that in the process of moving the cyclic to the right he is not only recovering from the transverse flow effect he is also countering the effect of the left roll induced by the offset? This is why I asked if in the certification process they used a stick plotting board, then they would have noted this problem.

This is also for mark561. You seem to have taken a stand based solely on what Frank Robinson said in regards to my postings and not from a detailed understanding of the mechanics of the Robinson Helicopters. If this is an incorrect assumption then I stand corrected. I stated this in a previous post, if Frank Robinson makes a counter statement to my postings it doesn’t mean it is true. He is not Jesus making his Sermon on the Mount and he is not God in the form of a burning bush giving the Ten Commandments to Moses. He is an engineer and businessman that will say anything to protect his interests and if you are a pilot that buys the farm in a Robinson Helicopter then he will be your survivors’ worst enemy.


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The Cat

To: RW-1

The reason I became so belligerent is because of your attitude in responding to my posts. It is obvious that you and I will never agree on this point so do two things. Perform the test I described and tell me the results and the second is please refrain from participating on this particular forum as I am trying to elicit responses from mechanics that work on Robinson helicopters and not try to defend my ideas.. Oh yes, a third thing, please talk to the mechanics at Volar and pose the same questions I asked on this post.

YOU NEVER SEEM TO ANSWER THE QUESTIONS DIRECTED AT YOU. HOW ABOUT THE QUESTIONS POSED ABOVE BY CRAB?

AND HOW ABOUT THIS WHICH I COPIED FROM A POST ABOVE. PLEASE REPLY.

When the Robinson accelerates forward the pilot will counter the transverse flow effect by adding left cyclic. This is in addition to the left roll caused by the 18-degree offset. When he passes through the transverse flow effect he moves his cyclic to the right. In doing this he is reestablishing the helicopter in forward flight as opposed to rolling left. Is there a possibility that in the process of moving the cyclic to the right he is not only recovering from the transverse flow effect he is also countering the effect of the left roll induced by the offset? This is why I asked if in the certification process they used a stick plotting board, then they would have noted this problem.


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The Cat

[This message has been edited by Lu Zuckerman (edited 31 December 2000).]

YOU NEVER SEEM TO ANSWER THE QUESTIONS DIRECTED AT YOU. HOW ABOUT THE QUESTIONS POSED ABOVE BY CRAB?

In the post, I answered twice.

You can be belligerent, I have nothing I have to prove, I do it everytime I fly it.

You have the burden of proof, not I, not FR, not anyone else, not the rotor gods that be.

Just you. Again, you haven't made it.

You should really get off you hang up on gyro precession, you're like an 11 year old I know on another forum who believes he knows all, but hasn't touched an aircraft.

I certainly don't know all, but I know enough that you are not correct in your assertions and your hangup on GP is what keeps you from seeing the whole picture.

You have already been told, not informed, that the cyclic doesn't respond as you predict, and why. But noooooo, you know more than the designer, other engineers, phd's, aerodynamicists, the rotor gods, etc. .... not!

You need to go drive over to a R-22 and get in it, and perform the test I outlined: and then you would be silent. Why can I ask that? Because. (that's a good Lu answer. Because.)

It's as simple as that!

To: RW-1

Do you want to shut me up? If so, please do the following

Ask these three questions of the R22 mechanics at Volar. Then, come back on to this thread.
Better still, print the questions and hand them to the mechanics. That way there will be no confusion or no influence by you in phrasing the questions.

1) In learning about gyroscopic precession or the same phenomenon as taught in the UK or Oz did they use the Robinson system as a demonstration or, did they use a Bell system as a means of explaining the subject?


The reason I ask this is because there are at least two websites that are the home pages of two Robinson dealers and flight schools. These websites have a very good explanation of how a helicopter flies. They have excellent pictures of Robinson helicopters and the major elements of those helicopters. They show pictures of Bell and Robinson rotorheads and they then go into the subject of gyroscopic precession.
Although the preceding text on the website(s) dealt with a Robinson rotorhead they explained gyroscopic precession by using a Bell system as an example. The two systems are different

.
2) In teaching the rigging process how did they explain the differences in the positioning of the Robinson blades as opposed to those of a Bell helicopter and, how did they rectify what they taught about gyroscopic precession as related to the positioning of the blades?
3)
I assume they taught that the precession phase angle was 90 degrees and yet the Robinson blades are disposed 18-degrees from the respective axes during the rigging process. What did they tell you about where the blade disc would dip if the cyclic was pushed forward from the rigged neutral position?

Please provide your thoughts on this following paragraph.

When the Robinson accelerates forward the pilot will counter the transverse flow effect by adding left cyclic. This is in addition to the left roll caused by the 18-degree offset. When he passes through the transverse flow effect he moves his cyclic to the right. In doing this he is reestablishing the helicopter in forward flight as opposed to rolling left. Is there a possibility that in the process of moving the cyclic to the right he is not only recovering from the transverse flow effect he is also countering the effect of the left roll induced by the offset? This is why I asked if in the certification process that they used a stick plotting board, then they would have noted this problem.

Please perform the following test (Providing it does not compromise flight safety).


RW-1 here is something you can demonstrate since you like flying on the edge. Lift off with your cyclic in the rigged neutral position. Do not move it laterally. Push it forward and fly through the transverse flow effect. The helicopter should roll to the right but don’t move the cyclic. When you are through the transverse flow effect, let me know which direction the helicopter is flying. Or, try this. With the cyclic in the rigged neutral position lift off in a hover and hover taxi the helicopter by moving the cyclic straight forward on the rigged neutral centerline. Do not move it off of the rigged neutral centerline.

If after accomplishing the above please let me know the results. This also goes for the rest of you R22/R44 pilots participating on this forum and on this thread.

One final note. Instead of constantly referring to what Frank Robinson said in his reply why don’t you respond to the points I made in disproving his statements about the 90-degree Vs 72-degree pitch horns? You seem to completely ignore my points and simply say that I am wrong because I disagree with what Mr. Robinson stated in his reply. I called them Bull S**t and you said I was a Bull S****er




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The Cat

Lu, for myself, I have never tried to contradict your assertion that there is a 72 not 90 degree offset in the rigging. The only fact I have disputed with you about is your original assertion that the R22 should not have been certified for a couple reasons:

1> the stick will not move in the correct sense to aircraft movement.

...several times we have stated that it does perform in a sense that is NOT objectionable to the pilot. I would like to note that the 1-2 degree difference you reference several times, near as I can tell, is your own number.

2> the flight manual restriction against sideslip means the certification sideslip could not be performed.

...Lu, all aircraft are required to perform during certification some procedures that are NOT normal procedures. The Bell 206 has a limiting crosswind component. This limit is less than .6 VNE. Does this mean that the 206 could not pass the certification test? Absolutely not. Is is capable of performing the test, but it is NOT a normal procedure.

===

I have wondered many times if you are reading my posts with the intent of learning from them. Obviously not. You asked another pilot to perform a test, lifting into a hover with the cyclic in the rigged neutral position, not moving it laterally and then accelerating forward. Lateral cyclic is required to maintain position against tail-rotor drift, left cyclic. I told you this before.

I have learned a good bit of information from your posts about the R22 rigging, accident statistics, and general perception of the aircraft, but I am tempering that with my own experience. When I get a chance to fly one again (sson I hope) I will try to answer some of my own questions, but I still find that I must contend that the primary assertion in your paper to the NTSB questioning the R22 certification is flawed in its most basic logic.

That is the point I tried to address, and I'll post a single response here vice the many other R22 threads to avoid dredging them up from the void.

To: Helo Teacher

Point 1) the certification requirements dictate that a stick plotting board is used to determine that the helicopter will move in the same sense as cyclic stick displacement. The certification standards indicate that the displacement of the helicopter could be up to 2-degrees from cyclic stick displacement and could be attributed to pitch coupling. It is not intended to be up to the pilot to determine if the stick displacement is objectionable or not. It states that under ideal conditions if you moved the cyclic forward from the rigged neutral position the helicopter would fly straightforward. If it deviates from that sense of movement the difference can be no greater than +/- 2-Degrees.

Point 2) The certification requirements dictate that the helicopter demonstrate sideslip at .6 VNE by pushing hard to the stops on the pedals. First one pedal and returning to neutral and then on the other pedal. The helicopter must comply with this requirement as well as to demonstrate flying out of trim. Now you have to think on two planes at once. 1) The restrictions were placed on the sideslipping and out of trim flight because it was determined that in doing so you could induce severe flapping loads to the point of causing mast bumping and loss of the rotor. 2) If it was determined that these two actions would result in mast bumping then what happened when these same actions were demonstrated in order to gain certification. My premise about the Robinson not being certifiable stems from the facts above. If the Helicopters were presented for certification with the restrictions against sideslipping and out of trim flight they could not pass the certification requirement requiring demonstration of these flight maneuvers. It is not to say that they could not do these maneuvers because the OZ pilots do it all the time. However the fact remains that if you do these maneuvers and something happens it is your fault because the AD and the POH tell you not to do them.

Regarding the crosswind component on the Bell 206 this limitation was established during the sideslip demonstration during the certification trials. The test sets the maximum outer limits that can be obtained by the specific design. On the Bell it just happened that because of the test it was determined that the restriction be put in place for certification. I am assuming this because of what you said in your post.

Regarding what you said about lateral cyclic having to be used to counter the propeller effect of the tail rotor, I was under the Impression that there is a left tilt of 2-degrees on the mast to counter this effect. Regarding the report, if I had it to do all over again I would have made some changes. These changes would have been prompted by what I have learned from the postings of others including your self which caused me to look deeper into the subject. The most illuminating of all of those changes of mind occurred when I reread the rigging procedures and I found out the following. http://pprune.homestead.com/files/rigging.jpg


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The Cat

My mistake, in reading your report I got the impression the 1-2 degree sense of direction allowance was yours. What I would really like to read at this point is the report that established these limits. You wouldn't happen to have a link would you?

I still feel, from my experiences with the aircraft, is that the biggest threat in a sideslip in the R22 is overcontrolling by the pilot. The limit being there to prevent inexperienced pilots from getting into trouble.

Also, can you please explain how the coning hinges prevent a 90 degree lead but allow a 72 degree lead??

Surely the mast bumbing that can occur with large sideslip is due to the aerodynamic effects of trying to fly a fueselage sideways at great speed? rather than in its normal 'clean' sense. Hence the different effect of fixed floats etc.

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Another day in paradise