Get over the battle [Archive]

Lu Zuckerman

4th Oct 2000, 07:57

Dear Tilt,

The report you referred to was taken directly from an NTSB report that I have in front of me at this very moment. I referenced this report I believe when I stated that I had contacted Mr. Jim Hall, Chairman of the NTSB. In My email to him which included a copy of my report I told him that his engineers didn't get it right.

As a result of his reading the report he contacted me and stated that he turned the report over to four of his investigators. One of the investigators was the man I originally addressed the report to in 1996.

I sent the report to Mr. Hall two days after a Robinson R22 lost its' main rotor in California. The NTSB report skirts around the certification issue and the problems with the main rotor design and it didn't even address the rigging procedure that can possibly introduce excessive pitch and the rotor design that can introduce even greater pitch settings. Add the increase of pitch when setting autorotation speed and you have a potential for blade stall. In every case the findings of the NTSB in their investigations of the 31 crashes ended up as pilot error. The reasons that the accident rate dropped to zero (until the last rotor separation described above) was that the FAA ammended the operational envelope and restricted the helicopters from being side slipped and flown out of trim.

I honestly don't know what else to say other than the helicopters should not have been certified and since they are in fact certified the FAA has restricted the flight envelope to the point that the R22 and R44 do not meet the certification requirements of the FAA.

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The Cat

[This message has been edited by Lu Zuckerman (edited 06 October 2000).]

[This message has been edited by Lu Zuckerman (edited 06 October 2000).]

tiltrotor

4th Oct 2000, 18:30

Lu,

You know, i think somewhere down the line you may have a valid point. I am sure that you have your stuff squared away, but what do you think you will be able to achieve?
The FAA will not change their opinion, neither will Robinson stop production or re-certify, not with that low accident rate.

And why it has such a low accident rate, I suppose people don't really care.

muffin

5th Oct 2000, 21:12

I will reply in this thread rather than spool the other one down 3 pages.

Last weekend I went to the UK Robinson Safety course run by Tim Tucker from Robinson. I asked him specifically if there was any prohibition in the R22 POH on sideslipping or flying out of trim. He replied that there was not, and that many users like cattle musterers in Australia spent most of their flight time in this part of the envelope.

Lu Zuckerman

5th Oct 2000, 21:55

Dear Muff,

Just wait. Keep your eyes on the Rotorheads
Forum.

It appears that this page is not in the UK POHs for the R22 and the R44. However, it is in the POHs carried in the R22s and R44s licensed in the USA. Does that mean that US pilots lives are more valuable than pilots in the UK or other areas outside of the US?

Does it mean that Mr. Tucker is keeping something from you and your fellow UK Robbo pilots?

Did Mr. Tucker address recovery from a zero G situation and if he did, what did he say you should do in recovery relative to how you should move the cyclic? Did he say anything about adding a "Tad" of left cyclic?
If he did, he was giving you good advice as this left cyclic compensates for the 18 degree offset in the flight control system.

However, in giving this advice, if he did, it is in direct conflict with the POH which does not take into consideration the 18 degree offset and tells you to pull straight back and not to add in left cyclic to combat the right roll developed by the tail rotor. If in fact you follow the POH and pull straight back you will introduce a right roll component because of the 18 degree offset. The instructions in the POH state that it is extremely dangerous to introduce a right roll when countering a zero G condition.

I think I'll stop for now to see what kind of response I get from this posting.

The Cat

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Lu Zuckerman

6th Oct 2000, 05:11

Dear Muff,

Please check out Helidrivers post which now leads the Rotorheads forum. That is what I wanted you to look at.

Regards,

Lu Zuckerman
[email protected]

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The Cat

Lu Zuckerman

6th Oct 2000, 18:46

Dear Muffin,

I am waiting for your reply to the above postings and, I want to know your response to the posting made by Helidrvr. If JoePilot is looking in I would appreciate hearing from him as well.

Will appreciate your feedback.

Cheers.

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The Cat

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[This message has been edited by Lu Zuckerman (edited 06 October 2000).]

WhoNeedsRunways

6th Oct 2000, 21:43

Lu :

Ref the page you refer to not being in UK R22 POH - it's in both mine (long story), one purchased in the UK and one in the US.

I get the sense you like bashing your head against a brick wall, and even when someone tells you its a bit silly you keep on doing it !!

Lu Zuckerman

6th Oct 2000, 22:22

If the pages are in your POHs and they contain the admonition against flying out of trim (balance) and the avoidance of sideslip then how do you explain what Tim Tucker told Muffin about there being no such restrictions on the R22 and the R44. Further, he told Muffin that the Wizards of OZ fly in that envelope all the time while mustering cattle. In your reference to "both mine" are you referring to two POHs, one purchased in the UK and one purchased in the US. is there a possibility that the organization you purchaced the UK POH from got it directly from Robinson. I would advise you to check a manual that was delivered with an R22 or R44 in the UK. I could be wrong but several respondents to my postings have stated that the page was not in their POHs.

The CAA is looking to this matter as we "speak". Please respond.

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The Cat

[This message has been edited by Lu Zuckerman (edited 06 October 2000).]

[This message has been edited by Lu Zuckerman (edited 06 October 2000).]

arm the floats

6th Oct 2000, 23:09

Lu

I flew R22's as a student and instructer 95/96,at a school which had previously suffered 2 fatal accidents classed as 'unexplained'.In my initial training ,subsequent Robinson factory course and 2 years of dealing with FAA examiners,flying the aircraft out of trim was never raised as an issue.Students of course were always taught to fly the aircraft in trim ,but the flight training standards document produced at the time required that in order to pass a Certified Flight Instructors Licence/Certificate you had to demonstrate stuck control procedures,which entailed flying the aircraft out of trim (stuck pedal).This ,I presume is still part of the syllabus.

Robinson produces a purpose built R44 ENG aircraft equipped with a ball mounted camera this type of operation requires the aircraft to be positioned out of trim on a regular basis to get the 'right shot'.
The only time side slip was ever mentioned was at the Robinson factory course concerning the Mariner and its adverse roll/negative dihedral effect.

[This message has been edited by arm the floats (edited 06 October 2000).]

eurocopter

7th Oct 2000, 02:51

I fail to see why people would be content with the findings of the above report.
I am concerned that a R22 flying at cruise speed/height can self destruct with a large input from a student. How near to a catastrophic failure have we been in the past without knowing?
I for one will be flying the R22 even more carefully in future.
Lu - Keep up the good work.

Thomas coupling

7th Oct 2000, 16:10

For goodness sake..and for the enjoyment of others on this web site, will you keep this monotonous drivvle (on R22's / 44's), under the same heading, so that those of us who want to steer clear of it, can! Get a life lads.

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TC

Whirlybird*

7th Oct 2000, 23:00

Thomas, even if you're not interested, that's unfair. This discussion has finally put some life into Rotorheads, which has often seemed to me to be in danger of dying out completely. I think we should be grateful to Lu for that at least.
Whirly

tiltrotor

8th Oct 2000, 12:12

Regarding the sideslip limitations, most other helicopters do also have entries in their POH/ Flight manual. No manual will specifically write that sideward flight above certain speeds is prohibited. Rather they state that successfull sideward flight has been demonstrated up to a certain speed.

To a previous posting by eurcocopter, no offense,but you probably don't know either how many times you have been close to something that could have killed you in any other type of helicopter.

rotorque

8th Oct 2000, 16:42

Hi guys,
Lu, I have always been under the impression that to try and put any left cyclic into a low or zero 'G' situation can be more detremental than just going with the right roll. I use to be a mustering pilot here in Australia. Alot of pilots early on when R22's took over from the majority of B47's found themselves in low g situations when they 'bunted' over from a steep pull up, either after 'hitting' some cattle or just coming up to have a look around. In this day and age it is a recognised sin, but back then it was the norm'. Anyway it was a common topic of discussion about how to avoid mast bumping in this situation. The way the whole thing was explained to me back then, was that when in a low or zero g situation, the rotor and the fuselage/tail rotor were two seperate systems independant of each other. Due to tail rotor roll the fuselage rolled right. Now if you were to put in left cyclic to correct the roll the inevitable mast contact would occur. Thats bad. For this reason we were told to simply put in the (in practice limited amount) aft cyclic and then hold the cyclic smack in the middle and let the hole ship take the roll to the right. The roll right is far more pronounced than the effect of aft cyclic by the way. This was demonstrated remarkably well when one of our students failed to lower the collective when the instructor rolled the throttle off, the desperated lowering of the collective by the instructor put the poor little helicopter in a vilant low g with the advertised right roll. The cyclic was centered as above - not only did they survive but were the first people to unofficially fly an R22 inverted (the story actualy includes oil on lower portion of main rotor blades). I am making light of the story but believe me it was deadly serious at the time and prompts me to write this. The point I want to make is that even an 18 degree input of left cyclic will put the rotor head that much closer to the mast in a low g situation. THAT should be avoided more so in my opinion than the right roll. Thats my own opinion and I take nothing away from the Robinson notices in the POH. If in fact they are 'teaching' that I would be very surprised.
The only other thing I should add is that in the mustering situation I describe above there is usually very little air speed at the top of the pull up, and the aircraft after rolling right was found to 'fall' out of the mess fairly quickly - it was then easy to load up the disc again.

See what you think. Cheers

arm the floats

8th Oct 2000, 17:11

I'd always been taught aft(to take up the disc load )then left cyclic(whilst holding your breath).
Never put it into practice ,but I'd wondered about going with the right roll,although when would it ever stop!!

Shelldrake Spin

8th Oct 2000, 23:31

I think that we all have to remember that if we have a healthy respect for the good ole' Robbo then you should not encounter any problems. However the best policy is to know the ins and outs of your a/c should you experience any problems. Thanks for the address of the report, I am sure it will be very useful.

Lu Zuckerman

9th Oct 2000, 00:29

This is in response to Both Rotorque and arm the floats:

If I understand you correctly, practical experience taught you and your fellow Robbo pilots that to combat zero G you should pull the cyclic back and then hold it in the center of its fore and aft travel. Then, you would ride out the right roll until you could gain positive control. If my assumption is correct then I will go from there. By pulling back to the neutral or centered position you would place the rotor system from a control standpoint in its’ neutral plane of rotation or as if you were in a hover.

You also stated that it was common theory at the time if you added in left cyclic you could cause mast bumping.

You have to understand how the eighteen-degree offset comes into play. Because of the 18 degree offset if you would pull straight back past the neutral position of the cyclic you would in effect put in a right roll component that would add into the right roll caused by the high mounted tail rotor.

In one of the previous posts, one individual stated that Tim Tucker, the Safety pilot that conducts the courses, told him that when you are countering a zero G condition that the pilot should pull the cyclic back while adding in a “Tad” of left cyclic. This is effect minimizes of not eliminates the right roll component introduced by the 18 degree offset.

Another point that I am not too clear on is that you stated that the cyclic was moved to the center. Now think hard about the word center. If you mean the rigged neutral center then the blades are in a hover position as described above. If you mean that the cyclic was moved to the neutral center in relation to the control stops then you are introducing a left roll input and this could exacerbate the control problem and quite possibly cause the mast bumping and resultant loss of both the helicopter and the pilot(s).

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The Cat

212man

9th Oct 2000, 02:07

Can someone explain this "high mounted tail rotor" expression to me? All the R22s I've seen/flown haxe the TR sticking out of the end of the tail boom, whereas 76s, 212s etc have it mounted "high" up on a vertical fin. Are we referring to the TR being higher than the main rotor head when pitched nose down?

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Another day in paradise

Lu Zuckerman

9th Oct 2000, 03:29

To 212 Man,

The term high mounted refers to the fact that the line of tail rotor thrust is located above the longitudinal center line that intersects the CG. This positional relationship allows the tail rotor thrust to introduce a right roll during the recovery from a zero G event. I remember seeing a reference to it in some Robinson literature but I am unable to locate it.

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The Cat

[This message has been edited by Lu Zuckerman (edited 08 October 2000).]

[This message has been edited by Lu Zuckerman (edited 08 October 2000).]

Outside Loop

9th Oct 2000, 08:09

Lu

Recovery from the low "G" roll is almost instantanious with application of aft cyclic. That is to say, that as soon as positive load is restored, the tail rotor no longer has authority over the main rotor and the right roll stops. Instantly. However, because the A/C is now banked to the right a little bit of left cyclic is needed to level it.I am speaking from personal experience and I think that this was probably what the instructor from the UK (previously mentioned) was trying to demonstrate.

Any left/right imput before positive "G" is restored will induce a mast bump and will not aid in recovery. I was also present when the incident as described by rotorque occured. The bottom of the mast fairing (on both sides) was bent up from contact with the cabin roof. The instructor,inexperienced on robbies, was not aware (at the time) of the low "G" problem nor the recovery and applied left cyclic with very little else. (that he could remember) The only reason it recovered, was as rotorque said, it went inverted and fell out of the sky. The instructor then instincively pulled back on the cyclic in order to pull out of the dive. Basically they did a half roll followed by a pull through and were very lucky to survive.

The POH page that you constantly refer to regarding out of balance flight states.

"Mast bumping may occur with a teetering rotor system when excessive main rotor flapping results from LOW "G" or ABRUPT CONTROL IMPUT. A low "G" flight condition can result from an ABRUPT CYCLIC PUSHOVER in fwd flight."

It also states that.

"High fwd airspeed, turbulence and excessive SIDESLIP can ACCENTUATE the adverse effects of THESE CONTROL MOVEMENTS."

It does not say anywhere, that sideslip or out of balance flight, alone, is responsable for main rotor flapping or mast bumping.

I hope this clears the air and puts every thing back in correct context.

Lu Zuckerman

9th Oct 2000, 17:00

Dear Outside,

I lost track of the conntrol inputs you described. But again, I don't know the control inputs necessary to cause a helicopter to roll or to loop.

Here is the problem as I see it. The positioning of the Robinson cyclic stick is imprecise to say the least. If you placed the cyclic in the rigged neutral position and lifted off directly and pushed the cyclic straight forward from the rigged neutral position you would be flying north north east assuming straight ahead was north.

Over a period of time you adjust to this problem and when you lift off and push the cyclic forward to fly straight ahead you move the cyclic to the right and forward.
This compensates for the offset differential between where the swash plate is directed to move by the cyclic input and where the pitchlink is in relation to that movement.

Because of the imprecise nature of the cyclic controls and if you enter a zero G situation this is what can happen: (and, I hope I get it right as It is very early in the morning where I am)

1) If the cyclic is maintained in the position of right of the center line of the rigged neutral position and you pulled straight back you only encounter the right roll developed by the tail rotor and not add to it.

2) If the stick is to the left of that imaginary line you will add to the right roll because of the offset when the cyclic is pulled back.

3) If the stick is even further left of the imaginary line you will be inputting a left roll component and encounter high flapping loads which will increase with additional left cyclic input causing high flapping loads and mast bumping..

In a conventional helicopter flight control system the pilot has an immediate reference to the position of the cyclic as it is between his legs. He knows where the cyclic is at all times because of this visual cue.
The Robinson on the other hand has a pistol grip that is essentially floating in space. I know that over time you get used to this and maybe you develop a system of visual references so that you (pilots with high time in Robbos) know where the pistol grip is in relation to the rigged neutral position of the cyclic stick. But, what about the trainees and the low time pilots that may not have developed this system of references. I talked to a Robinson pilot about the impreciseness of the control system and he said that when he lifts off he finds his point of balance. I asked him if that was in reference to CG type balance and he answered no. He said that he had to feel the response from his cyclic input and incorporate all control movements about that point. In other words, he was compensating for the cyclic offset between the swashplate movement and where the pitch link was in relation to that input.

I know I keep talking about this cyclic offset but have not explained it properly verbally. I do have a diagram that does explain it but I can't send it as an email attachment as it is done in Visio and to open it you have to have Visio on your computer. I have incorporated the diagram in my report so if you want to see it please contact me and I'll send it to you.

An easy way to demonstrate it is to place a Bell and a Robinson next to each other.
Place the blades on both helicopters over the longitudinal axis. On both helicopters, place the cyclic stick in the rigged neutral position. From that position move the cyclic stick directly forward and then backward. On the Bell the blades do not move. On the robinson the blade will move. On the Robinson rotate the blades until the pitch links are directly over the lateral axis of the helicopter. Repeat the movement of the cyclic forward and backward from the rigged neutral position. The blades won't move. Repeat the test with the blades over the lateral axis and move the cyclic sticks left and right. On the Bell the blades won't move but, on the Robinson the blades will move. Once again rotate the Robinson blades so that the pitch links are directly over the longitudinal axis of the helicopter and repeat the cyclic input. The blade don't move.

So, if you moved the cyclic directly forward you will fly 18 degrees (approximately) to the left. It is because of this 18 degree offset that it is so easy to get into a bad situation leading to rotor incursion and or rotor loss.

Another major problem on the robinson is the rigging procedure. It too is imprecise and very ambiguous and can lead to rigging in too much pitch which under certain maneuvering conditions or atmospheric conditions can lead to blade stall (Not retreating blade stall).

The R22 and the R44 helicopters are very unforgiving and the instructions that they have in the POH carry the weight of a feather. The only safety factor built into a Robinson is the pilot. And, from what I read in some postings some pilots don't pay much heed to safety and in the process place themselves and their passenger(s) in jeopardy. You might even fall out of the sky and hit several cattle.

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The Cat

rotorque

10th Oct 2000, 15:12

Hi Lu,
In reference to the above entry, I thought it would be a good idea to give you a pilots point of view with regards to the stick position of the Robbo'. You were right in saying that the 'cyclic floats' but really the cyclic grip actualy rests on your right leg. The design is quite good for the pilot as it alows you to rest your arm on your leg making control inputs alot smoother. To be honest the instructors have the hardest time, due to the fact that they must hold their hand up in the air when staying on the controls with a student. Obviously only the 'T' section of the cyclic setup can move like that. The point being, it dosn't get much better with regards to knowing where the cyclic position is as it rests on your leg.

I also want to add a little note to my earlier entry. The reason we were told to centre the cyclic in a low or zero 'G' situation after the aft cyclic input was, I believe, to maintain a degree of separation of the head from the mast (preferably 90 degrees). In other words when the fuselage rolls to the right the pilot instinctively tries to correct it by putting in left cyclic. Now, the rotor system is still being controlled by the pilot through the swash plate. Any input by the pilot will be reflected in the rotor disc. As I mentioned earlier the rotor system and the fuselage are acting independently of each other in a low or zero 'G' situation, so if we put in the left cyclic whilst the fuselage is rolling right the disc and head all do the right thing and tilt left relative to the fuselage, but the fuselage and therfore the mast are all tilted to the right. keep going and they contact each other. Thats bad.
By centering the cyclic and holding it there the swash plate and therefore the rotor system will be 'following' the fuselage as apposed to the fuselage following the rotor system when under positive 'G'. As the fuselage rolls to the right the rotor system is made to stay at '90 degrees' to the mast if the cyclic is centred. The neutral position you talk about may have an effect on the positon of the head in relation to the mast but the whole idea of what they talked about was the guaranteed displacement of the head from the mast.

I took it as gospel at the time and I find the idea easy to understand - whether its right or not I don't fully know.

The mustering example I used earlier in the thread may need extra input. I might have mentioned that at the top of the 'pull up' and subsequent low 'G' situation, the airspeed is next to nothing. This point is important. Because the Manual says put in aft cyclic - we do it!, but because of the low airspeed the result is bugger all (we used the last of our airspeed getting the low 'g' in the first place). In actual fact the disc tilts backwards (18 degrees aside Lu) and can mast bump just as easily as if it was to the left. No doubt other pilots have possibly had a machine in a very nose down attitude after a pull up or torque turn and have felt that pulling back on the cyclic gives them a bad feeling in the gut, as if you could chop your tail boom off if you went too far. Same idea.
The ability to gain possitive 'G' only comes with airspeed and for that we have to head back down, this usualy means going with the roll and waiting for gravity to help us out.

I think every one so far has the right idea just varying ways on how to explain it.

cheers.

Rotor Nut

11th Oct 2000, 03:12

I can't say I have noticed having to push the cyclic 'off centre' to achieve forward flight in the R22 or R44. I'll take a closer look next time I'm a passenger!

I have no trouble referencing where the cyclic should be despite the T bar arrangement. We are taught to rest our hand on our knee/leg but in time you instinctively know where it should be - that's the whole point of 45 hours training and why you balance the helicopter using outside references.

I gather that as forward flight is established there is a slight tendancy to role to the left because of extra lift from the advancing blade for which you have to make a slight adjustment for (although it is very difficult to demonstrate because you instinctively try to fly level). I also understand that some swash plates are rigged slightly left/right according to rotor direction to compensate for similar forces. Also the R22 has a simple but crude trim device to counter these forces during forward flight (otherwise the muscles in my right arm would be much bigger than the left arm!).

Further, you will notice that helicopters tend to hang slightly to one side in the hover - this is because some compensation is required to overcome the sideways thrust from the tail rotor. Also you compensate for wind/turbulence so the cyclic is never perfectly centred - its just a balancing act.

As for the cyclic stops - I have never approached the stops in flight - so I would be very surprised to have difficulty in achieving the control input I require even if the cyclic offsets that Lu talks about exist.

Lu Zuckerman

11th Oct 2000, 04:31

Dear Rotor Nut,

If you would be kind enough to send me your fax number I would be most happy to send you two diagrams that will help in explaining my point about offset.

Cheers,

Lu Zuckerman
[email protected]

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The Cat

Outside Loop

11th Oct 2000, 05:07

Lu

You say that in fwd flight,in a (normal) helicopter, the A/C flys to the position of the cyclic ie push the cyclic straight fwd and the A/C will follow.That in a robbo because of the 18 degree off set you must position the cyclic to the right. You are incorrect.

You have forgotten about a phenomena called inflow roll. As a helicopter accelerates fwd,we must progressively tilt the disc fwd. Now in straight and level flight, the induced relative airflow gives the tilted disc a greater angle of attack at the front, than the rear. The result because of gyroscopic precession is a slight roll to the right. So in (normal) helicopters, in straight and level fwd flight the cyclic position is actually fwd and slightly left.

Perhaps this explains the design of the 18 degree offset on the robbo. Next time I fly one I will take note of the actual stick position.

Secondly,the important thing in a low "G" situation is to avoid mast bump,(as rotorque pointed out) so it does not matter if the disc is slightly off centre as long as contact with with the mast is avoided. A neutral cyclic position will ensure this.

Thirdly, cyclic position during lift off is irrelevant.If a student or inexperienced pilot where to sit there making sure the cyclic is exactly neutral, whilst raising the collective, he/she will never achieve a smooth lift off. In any helicopter.If taking off with even the slightest X wind or sloping ground the cyclic must be positioned into wind/up hill in order to achieve a vertical lift off. The technique is to LOOK FWD,slowly raise the collective, make pedal adjustments to keep the A/C straight as you become light on the skids and compensate for drift with the cyclic. (fore and aft as well as laterally)

I can assure you that unless conditions are dead still, the ground is dead level and the helicopter is perfectly balanced under the mast, the stick will never be in the middle. Further more if you sit there watching it you will probably tip over or run into something.

Fourthly, after the head has been off or the controls are re-rigged, a flat pitch and/or autorotation rpm check will quickly reveal any rigging errors.

You made no reference to side slipping/out of balance flight in your last post. I take it you concede my point!

Outside Loop

11th Oct 2000, 06:53

Roter Nut

I agree with most of what you said however,your comment about rolling to the left in fwd flight, due to extra lift gained by the advancing blade lacks merit.

Gyroscopic precession insists that the lift gained by the advancing blade is employed by lifting the front of the disc. Hence if you where to push the stick fwd and hold it still,the nose would pitch up as you accelerated. Try it. To maintain level flight you must increase fwd pressure.

You actually do this without noticing it.

Lu Zuckerman

11th Oct 2000, 07:30

Dear Outside,

Dear Outside,

First of all the rigged position of the Robbo cyclic is right of the center of travel in line with the lateral axis and not in the center of allowed travel as dictated by the stop plate. In the rigged neutral position the stick is placed in the center of fore and aft travel and slightly to the right of the center axis of the aircraft. Because of the 18 degree offset if you moved the cyclic straight forward from the rigged neutral position the helicopter would fly to the left.

When a helicopter is in the certification process it is dictated that the helicopter fly in the same sense of cyclic stick movement. The FAA allows slight deviations in the amount of a degree or two, and they attribute this to pitch coupling. In order to demonstrate that the helicopter does in fact fly in the direction of cyclic movement they must employ a stick plotting board or some similar device that plots cyclic movement during flight. My report questions if this was done during certification.

The Robinson rotorhead was not designed with the offset in order to compensate for rotor aerodynamics as described in your post above. The offset results from the fact that the pitch horn can not cross the flapping hinge. Take a look at a Bell rotorhead. You will see that the pitch horn terminates at or about the teeter bearing. Look at any other helicopter and you will see that the pitch horn terminates at or about the flapping hinge and if your helicopter has elastomeric bearings like a Sikorsky S76 the pitch horn terminates at or about the apparent flapping point.

Because the pitch horn can’t always be in the exact ideal position of dead nuts on with the flapping hinge or teeter bearing it results in pitch coupling and that is what the pilot in a helicopter compensates for in adjusting his cyclic stick position. Of course, I am describing an ideal situation with no wind. Every thing you said about adjusting for a crosswind or a not so level landing spot is correct.

On the Robinson which has both a teeter bearing and flapping bearings the pitch horn terminates at or about the flapping bearing. If it were like a Bell but with flapping capability and the pitch horn did terminate at the teeter bearing the pitch coupling would be so severe that the helicopter would be uncontrollable. If you were familiar with a tail rotor that has a delta hinge you would notice that each time the blade flaps in or out the pitch that the pilot put into it would change. This is to equalize the lift across the tail rotor disc. The same thing would happen on the main rotor if the pitch horn were at or about the teeter bearing.

When the pilot of a Robinson pushes his cyclic forward from the rigged neutral position the swash plate tips down at the front and up at the rear. If the blades are laterally disposed (left & right) the pitch horn lags the lowest point of the swash plate by about 18 degrees. If you think back to helicopter aerodynamics 101 you will remember that the advancing blade will be at its’ lowest pitch at that point and with precession the effect will be 90 degrees later in the direction of rotation. With that point understood take a look where the Robinson pitch link is in relation to the lowest point on the swashplate. The pitch link must travel an additional 18 degrees before it reaches the lowest point on the swashplate. With precession, the blades will fully react at approximately 18 degrees left of the longitudinal centerline of the helicopter. The result is that the helicopter flies to the left. In order to counter this offset, the pilot must adjust his cyclic movement to compensate for the offset.

Regarding the rigging procedure,if the mechanic follows the instructions he could build in a jam of some of the flight controls, he could place the swash plate in a bind and he can rig in too much pitch. Even when the aircraft is tested for autorotation the mechanic can add in even more pitch and under certain conditions it could result in blade stall (not retreating blade stall).

Regarding side slip and out of trim flight, I believe Helidriver said it all in his response to Tilt Rotor.

I don't know if either you Outside Loop or, Rotor Nut have requested a copy of my report because it covers all of this. In answering these many posts I have retyped my report at least twenty times.

Please provide your email addresses and your fax numbers and I will send the report and two diagrams that explain everything.

My email address is [email protected]

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The Cat

[This message has been edited by Lu Zuckerman (edited 11 October 2000).]

[This message has been edited by Lu Zuckerman (edited 11 October 2000).]

Rotor Nut

11th Oct 2000, 22:23

Outside Loop

In Flow role - that's the term I was looking for in my earlier post - although I thought in flow role and having to compensate for flap back in forward flight were two different things - I would be interested if anyone could confirm this.

Lu

Thanks, but you already sent me your diagram. I understand your arguement and the diagram does not help me any further. The point that no one has addressed from Joe Pilot is that if the blade flaps to position before 90 degree then Lu's arguement falls apart.

Lu Zuckerman

11th Oct 2000, 22:41

To: Rotor Nut,

You have a diagram that defines the difference between a Bell and a Robinson rotor system. The diagram I alluded to shows what can happen if the pilot does not follow the exact procedure when countering a Zero G event or countering retreating blade stall. I still need your fax number.

Regarding what Joe pilot said, I would appreciate it very much if someone would translate it from the language of OZ into the language of the so called mother country.
I don't mean to be mean spirited but I honestly could not follow his train of thought because of the colloquialisms (spelling) and idioms he used in his
descriptions. If that translation is forthcoming, I would like to respond (if I can).

Perhaps you may have heard the story about the American that was berating an Englishman for the spelling of the word tyre and the use of the terms boot and bonnet. The Englishman told the American that the Americans may have perfected the automobile but the English invented the language.

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The Cat

[This message has been edited by Lu Zuckerman (edited 11 October 2000).]

Lu Zuckerman

12th Oct 2000, 00:28

To: Rotor Nut,

In rereading Outside Loops’ description of inflow I think, maybe, perhaps, I know what he is talking about. He mentioned that if the advancing blade flaps up due to the increased relative and rotational airspeed of the blade then gyroscopic precession dictates that the disc will tip up and this requires the application of more forward cyclic to counter the raising of the disc at the front.

This sounds logical but I think it is incorrect. Somewhere in the Rotorheads forum, I described the effect of gyroscopic precession and I mentioned that you do not think of individual blades but that you think of the disc as being solid and the change in position of which is caused by the change in forces across the disc. Just like the rotor on a gyroscope that is mounted in dual gimbals.

Again I must use the tail rotor analogy. When the blades flap in or out they change pitch from the pitch that the pilot commanded using his anti torque pedals. The same is true for the main rotor. The pilot inputs the necessary pitch to get the helicopter off the ground (collective). He then incorporates cyclic input which changes the lift forces across the disc(cyclic). Now the helicopter starts to fly forward and the advancing blade because of its rotational speed is exposed to a higher relative wind, which it seems would cause the advancing blade to lift. However the advancing blade is also at a lower pitch than what was inputted for collective hovering. Meanwhile, the retreating blade is at a higher pitch. This causes a lift differential that results in the tipping of the disc, which is what set up the increased wind velocity over the advancing blade in the first place.

Now we get to Outside Loops’ posting. Due to the oncoming high velocity airflow the advancing blade will tend to flap up. If it does, the pitch link is still attached to a rigidized swashplate and if the blade flaps up or tends to, the pitch link will subtract pitch causing the blade to return to the in track position. This is aerodynamic and does not relate to precession. It is sometimes referred to as a Delta Hinge Effect.

I have said it before and I’ll say it again. With all of this pontificating, I can still be totally wrong.

I will add this point. If in effect what Outside Loop says is correct then when does this condition end. It would be like a short tailed dog chasing its' tail. As the forward speed builds up the lift on the advancing blade increases and precession sets in and causes the disc to raise in front then the pilot adds in more forward cyclic to counter the condition and the helicopter speeds up and the advancing blade lifts and the pilot adds in more forward cyclic until he hits the stops. The next thing that happens is the onset of retreating blade stall.

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The Cat

[This message has been edited by Lu Zuckerman (edited 11 October 2000).]

captain206

12th Oct 2000, 01:48

I have read all the threads regarding the R22. It seems to me that the only person who can answer the accusations is Mr Robinson himself. It is reasonable to expect he is unaware of this board, and equally unlikely to reply (although Mr Tucker has recently spent time in this country). So if we cannot expect an answer from a person who's knowledge and status is without question, perhaps we should ask who is Lu! I have 2000+ instructional hours on the '22 and have enjoyed all of them. Several unfounded theories and incorrect statements have appeared on this board (and others). There are several basic books that can explain Flapback, Inflow roll and phase lag. May I suggest a Q & A board. I would be happy to contribute. ( as long as it was friendly).
This is the first time I have ever posted a message so please be gentle.

Lu Zuckerman

12th Oct 2000, 02:04

Dear 206,

I'm sure Frank Robinson is both aware of this forum and the comments made by myself.

It all started when I wrote a report on why the R22 and R44 should not have been certificated. This report was sent to the NTSB. That was in 1996 and it has been a running battle ever since. My biggest detractors are individuals like yourself that have a vested interest in the Robinson line or people who just love these helicopters. That does not necessarily make them right and me wrong. That is the purpose of forums like PPrune. It allows an individual to present his opinions and others to object to those opinions. I was involved in a forum called Just helicopters and I was crucified. At least here they play by gentlemans rules. Start your thread and I will participate and I imagine a lot of others will as well. That way, Tilt Rotor can rest a while as this thread runs off at the end.

One other point, Tim Tucker requested a copy of the report and I am awaiting his response.

However, to bring you up to speed I would like to send you a copy of the report.

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The Cat

[This message has been edited by Lu Zuckerman (edited 11 October 2000).]

[This message has been edited by Lu Zuckerman (edited 11 October 2000).]

rotorque

12th Oct 2000, 14:40

Hey guys,
The question and answer idea is a good one. But for now we had better get this straight. What you are talking about is dissymetry of lift. In the teetering heads that we are talking about the blades 'Flap to equality'(the tail rotor does the exact same thing). Flapping to equality occurs when an advancing blade experiences increasing lift due to increased relative airflow. This causes the blade to rise (flap up). As it flaps up it experiences increased induced flow, which effectively reduces the angle of attack of the blade and limits the upward motion. On the retrating blade less lift is produced due to reduced relative airflow. This causes ther blade to descend (flap down), resulting in less induced airflow and a larger angle of attack. The larger angle of attack restores lift and limits the blades downward motion. Not, I'm afraid, because of a change of pitch produced by the pitch links. In fact it is all an aerodynamic reaction not a physical change in the blades pitch.

Cheers.

tiltrotor

12th Oct 2000, 17:44

Dear Lu, and others,

I guess some people already have given some hints aboput what cyclic inputs need to be made when transitioning into FWd flight. To talk about the rigging there are quite a few important factors to be considered, some are even variables. It all starts with the fact that the tailrotor, creating thrust, will pull the aircraft sideways. So, a means of counteraction is required, which in the R22/ R44 is a sideward tilt of the gearbox.
No 2, as you transition into forward flight and go through ETL, also the T/R gains more effectiveness, thus, an additional cylcic input is required and that is in the R22/ R44 and any other helicopter that uses a conuterclockwise rotating M/R to the FWD AND LEFT!!!! A variable factor e.g. would be the aircraft loading and CG.

Now, I believe that a lot of facts in Lu's postings here are based on theoretical knowledge out of very interesting books, e.g. Prouty is a great specialist. I think that;s very admirable. However, let's not forget that even Prouty keeps his explainations rather simple and general with the idea that people like myself can understand it. So when we talk about different model helicopters, I guess that the manufacturers will use their leeway to optimize any aerodynamical principle, thus, if Robinson has figured out that they need an 18 deg. offset, well, I guess it will suite them.
Lu, when you write in your posting that people are pestering you when you question the R22, well I guess as you say, this forum is here for everybody's opinions. Never the less, please don't fight over things or make certain statements that only really people that actually fly the aircraft can tell.

In many fields the therory turns out to be quite different from the actual performance.

Thus, my theory was always to become a brain surgeon- instead I turned out to be a stupid helo pilot- not that I regret it because I have met the most fantastic people in this field- though some of them would need brain surgery, hehehe

Lu Zuckerman

12th Oct 2000, 21:24

All great inventions including the helicopter began with a theory or perhaps many theories. It was not until those theories were reduced to practice that the engineers determined which theory was correct and which had to be modified or discarded and replaced with a new theory.

Take for instance when the engineers realized that the blades on an articulated rotor head had to have the ability to lead and lag as well as flap. It was originally thought that the advancing blade because of the increased air loads would lag and conversely, the retreating blade would lead because of the assisting air loads. This theory would be considered fact by all helicopter engineers.

That is until Sikorsky put a movie camera on an S 51 rotorhead. They wamted to see what happens to the blade in flight. They were not interested in lead/lag just the flexing of the blades. When they developed the film, the engineers were astonished at what they saw. The blades had a traveling wave starting at the tip leading to the root with the wave moving above and below the static center of the blade by four or five inches.

NOTE

IT WAS FOR THIS REASON THAT WHEN HELICOPTER MANUFACTURERS SWITCHED TO NON SYMMETRICAL AIRFOILS THAT THIS WAVE GOT SO BAD THAT THEY HAD TO PUT SOME TYPE OF DAMPENING SYSTEM EITHER ON THE ROTORHEAD, IN THE BLADES THEMSELVES OR UNDER THE PILOTS SEATS ON THE ch 47

Then somebody noticed something else. The advancing blade was leading and the retreating blade was lagging. So much for that theory.

It is true that my statements about the Robinson Helicopters are based on theory. But that theory comes from a strong background in helicopters. I am constantly told that my theories don't hold water by pilots that claim to have thousands of hours using that fact that their theories are more valid than mine.

I only have about 800 hours in helicopters and that was as a flight mechanic. I can't hover a helicopter to save my butt. However, I became associated with helicopters as a wrench turner in 1949 long before many of you were born. I worked in an engineering capacity on helicopters starting in 1955.

I worked for Sikorsky, Bell, Lockheed Helicopters, Hughes Helicopters, Agusta Helicopters and Bell-Boeing. I worked for Litton Ship systems integrating helicopters on two different ship designs. While at Sikorsky,Hughes and Lockheed I worked with Ray Prouty. I think he has a great mind but there are certain things that he says that I don't agree with.

These are my 2000 hours and I think that although my theories don't agree with yours that does not mean that I am wrong. It is my ultimate goal to get the Robinson design changed to make it more safe and at the same time lift a lot of the restrictions that are presently placed on them. I'll keep posting even though I am preaching to a very small Choir.

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The Cat

captain206

12th Oct 2000, 23:37

To Rotorque, Dyssimetry of lift: Splendid answer, quite right.

To Tiltrotor, During transition to forward flight the tailrotor does experience ETL which increases with fwd speed. plus it has to work less hard due to influence of vertical stabiliser. These effects require right pedal input not cyclic as you suggest. Notwithstanding above, I agree with your sentiments.

To Outside loop, re: transition. The left offset actually cancels out inflow roll on the R22. The need to apply further forward cyclic during a fwd transition is to combat flapback.

Lu. You have been trying to prove your point for several years (according to your reply to my first message), if you are right and have been crucified on 'just pilots' site, why continue?

Rotor Nut

13th Oct 2000, 02:58

Thanks guys for explaining flapback - I remember it well now. Rotorque's explanation was excellent and agrees exactly with the Robinson R22 instructors manual (exercise 5) by RNK Aviation (http://www.rnk.co.uk/himan/) - an excellent colour manual, well worth the read.

Thanks also to Captain206 for your comments. I'm assuming the forces felt on the cyclic stick in forward flight without trim on are directly due to differential lift from the advancing and retreating blades.

LU - Outside Loop's description was correct after all and although the rotors can be considered as a disk for basic flight theory they still are quite individual beasts and will try to flap according to the forces on them at any given time. The repetitive rotation just happens to average out the motion to appear like a disk.

Lu - Yes, I have your diagram, but having it doesn't explain it all away. Yes, the R22 is set-up differently to a 206 and if Joe Pilot is correct about the blades flapping to position before 90 degrees then it doesn't help me, sorry. The fact that the helicopter goes exactly where I push the cyclic stick without having to allow for this 18 degrees offset just leaves me unconvinced. Also, your quick dismissal of Outside Loop's explanation of flap back and in flow role leaves me even more unconvinced that your opinions are sound, sorry.

I'm still going flying the R22 on saturday!