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# Certification of Robinson Helicopters (incl post by Frank Robinson)

Rotorheads A haven for helicopter professionals to discuss the things that affect them

# Certification of Robinson Helicopters (incl post by Frank Robinson)

2nd Nov 2000, 15:41
Whirlybird*
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SARcastic:

Well, if you were right, there wouldn't be so many people around to contribute to this thread, would there?

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To fly is human, to hover, divine.
2nd Nov 2000, 23:48
Try_Cyclic
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I'd like to jump in here with an observation regarding the R-22 rotor head. There are comments being made here concerning the swashplate offset not being 90 degrees.

This is being seen as some kind of design defect making it unwise to fly sideways and making it neccesary to move the stick in unusual directions relative to the flight path.

I believe that the phasing of the swashplate is the way it is because of the unique tri-hinge design of the R-22. There is a teetering pivot plus 2 coning hinges. The coning hinges are somewhat outboard from the teetering axis. So- what?
Well, you would expect to see the pitch links line up with the centerline of the teetering pivot. But in this case they are outboard by the coning hinges.
The result is that any flapping is now coupled to pitch. Teeter the rotor and watch the pitch change. This is a delta-3 mechanism. What it does is reduce flapping to provide for improved rotor-tail clearance.
It also provides crisper cyclic response.
It also changes the out of plane resonant frequency of the rotor. This is tough to visualize but mathematically it is crystal clear that the phase angle of the swashplate needs to be 72 degrees instead of 90 for the rotor to act like it is at 90.
Frank Robinson obviously knew this but now, years later, people are looking at this rotor head and saying its wrong because it doesn't fit their simplistic mental model of the way a rotor head works.
I'll say it again: The phase angle of the swashplate is 72 degrees or whatever it is instead of 90 because of resonance effects which cause a phase shift in the cyclic response. The offset cancels the phase shift and the head behaves like any normal helicopter. Push the stick in the direction you want the rotor to tilt, period.
I am not an engineer , just relaying what I have learned from studying things rotary.
3rd Nov 2000, 02:53
SARcastic
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Hello Whirlybird,
I posted the reply to see if anyone would bite - oops!! , and the more people flying them could lead to less available to answer the thread.
To fly is human, to hover(on two engines), divine. Now doesn't that sound better.

SARcastic
3rd Nov 2000, 05:31
Lu Zuckerman
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To: Try-Cyclic

Dear Try,

First of all, I would like to paraphrase your last sentence in your posting.

I too am not an engineer , just relaying what I have learned from studying things rotary since 1949.

I am going to send you a copy of my report and two diagrams that support the text in the report. Read this material and then come back on with your comments. If you were sitting in front of Regis Philbin on Who wants to be a milionaire you would not have gotten the first question correct.

The swash plate does not have a phase angle the blades do. I want you to rephrase your questions so that I don't have to go through trying to explain the dynamics of a rotor system again. I have done it so many times on various forums that I have developed carpal tunnel syndrome in my two index fingers and my left thumb.

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The Cat
3rd Nov 2000, 14:25
WhoNeedsRunways
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SARcastic :

Having never hovered on two turbines, don't suppose there's a chance you'd like to demonstrate to me, no ?

Lu :

If you've got carpal tunnel syndrome, isn't the way to alleviate symptoms to stop typing huge tracts on the computer ?

Lastly, when I built a R/C helicopter some years ago, before I could afford to fly the real thing, the swashplate links were offset by an amount other than 90 degrees. The details are hazy, but a combination of motion in all the links produced the required end result. At least my helicopter came to a good end - the cash I got for selling it paid for my first 2 hours flying !!
3rd Nov 2000, 16:18
helidrvr
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WhoNeedsRunways, was it bigger than an R-22?

3rd Nov 2000, 17:09
WhoNeedsRunways
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Helidrvr :

No. Otherwise I'd have stuck a seat in it and flown it for cheap !!!

The point I was making - being serious for a moment - is that the principles are the same, no matter it was only an R/C model - it's just thre magnitude of the forces involved.

And the experience helped me when I came to learning on the real thing, especially the hovering.
3rd Nov 2000, 23:04
Arkroyal
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Who needs

Sorry for late reply, been away.

Yep, point taken. I was just a bit miffed by the (not very)veiled threat in Frank Robbies post.:Mad:

The 'Nasty little helicopter' is just a personal view. Give me something a bit more substantial (though perhaps not a Merlin on last week's showing)
4th Nov 2000, 00:46
Lu Zuckerman
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To: Try_Cyclic,

Dear Try,

On the Bell rotor system when the pilot pushes the cyclic forward the swash plate tips down forward (on some Bell models the swash plate tips up forward and dips down at the rear in order to fly forward. On this type of rotor system the pitch horns are on the rear of the blades as opposed to being on the leading edge of the blade)

In either case, the advancing blade is at its’ lowest pitch when it is over the right side of the aircraft. The retreating blade is over the left side of the helicopter and is at its’ highest pitch angle and with a precession or phase angle of 90 degrees the blades will be down forward and up aft and the helicopters will fly forward.

On the Robinson Helicopter the swashplate movement is the same as on the Bell. When the cyclic is pushed forward the swashplate will tip down forward and up aft. The pitch horns on the Robinson lead the blade by approximately 72 degrees. So, when the advancing blade is over the right side of the helicopter and the retreating blade is over the left side of the helicopter neither blade has reached the maximum pitch change (+/-). The pitch horns must travel another 18 degrees for the blades to reach their maximum pitch change. I don’t care how much you think of the Robinson engineering designers, they are unable to counter the laws of physics that deal with rotating masses. When the stick is pushed forward the disc will tip to the left. The only way to counter this phenomenon is to displace the stick to the right.

Many years ago the Cheyenne helicopter had a related problem. On that helicopter the blades were designed in such a way that the phase angle would change and the engineers worked for about four years to figure out how to compensate for this condition. They finally solved the problem but it so complicated the control system that a single point failure (of which there were many) could cause loss of control.

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The Cat
4th Nov 2000, 06:30
YouWillSee
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Lu,

after reading most of your posts in that forum over the last days, i couldn't stay quiet anymore.
I try to keep up the good tone which still prevails here, but you start to bore me. After finding out that you're in fact 69 years old, everything made a lot more sense to me. You are just one of those guys, who have to find a problem otherwise they can't sleep at night. You sound like the typical old man, who can't enjoy life. I'm not saying, that everything what you are writing is wrong, but lets face it.
All those accidents in the R22/R44 are because of some maneuver the pilot should have never tried. Those helicopters are just not made for this kind of flying. I've been teaching for quite a while now and i just don't see any possibility to get even close to mast bumping. Quite frankly there is not one job in the R22/R44-World where you should even come close to those problems discussed over the last months. Ok, cattle mustering in Oz, ok, but like you said, they fly out of all limitations anyway.
From your point of view, every car being able of driving 250km/h should be banned or not certified. Going on a mountain road and pushing pedal to the metal will always result in an accident, but you can't argue against the manufacturers, just because the shocks and brakes weren't strong enough for that kind of driving. IT WASN'T BUILD FOR THAT!!! Getting the point???
I know by now, that you don't take advice from someone younger than you, but i'll try it anyway. Don't try to blame the design for those crashes, blame the pilots or the instructors, if it happend to students. The R22/R44 are great helicopters if you fly them the way they were supposed to be flown. Don't try any weird sh**, leave that up to guys in the factory, guys like Tim Tucker. And by the way, i tell you why he didn't mention the tad of left cyclic in the recovery. If he would've mentioned it, someone would've put to much left cyclic in, because his tad was bigger than Tims tad. Telling the pilots to pull back and DON'T use lateral (left) cyclic will eliminate the initial left move on the stick. When you pull back and the ship rolls right, everyone uses his common sense and applies a tad of left cyclic. Like a lot of other guys already wrote in here, you can't understand that, because you don't even have an idea about flying. Theory doesn't work up there, at least not always...
One last thing, Lu, if you want to find a potential problem, you're going to find one. I have one question for you, why did all the companies you mentioned never listened to you. Maybe because you are way to theoretical, maybe you lie. Something happens and sure enough, there is a post, i knew, i told them, they didn't listen. Something doesn't sound right, don't you think?

Thank you

[This message has been edited by YouWillSee (edited 04 November 2000).]
4th Nov 2000, 07:19
Lu Zuckerman
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To: YouWillSee

It seemsthat you have answered your own question. Why don't the people i consult with or work for not follow my suggestions on how to make their product more reliable, more maintainable and more safe. Why don't you believe what I have said in my posts. The answer to that is that you have a vested interest in that you are a flight instructor flying R22s and maybe R44s. You have been to the Robinson schools and you quote Tim Tucker. The reason that people dont listen to me or my fellow RMS engineers has to do with money or the fact that there is an adversarial relationship between product integrity engineers and design engineers. When a suggested modification of the design is presented to engineering they have a NIH attitude (Not Invented Here) and totally reject the idea. Another point is that on most government design programs they bring the RMS engineers on board after the design is almost cast in concrete. No matter how good your ideas are it is too late to incorporate them as it would be too expensive. Regarding your comment abouut me being a liar that is totally untrue.

Here is another point about the "Tad Left Cyclic" comment made by Tim Tucker. Although he was correct in making the statement he violated the instructions of Robinson POH as well as the instructions in the latest FAA Rotorcraft Flight Handbook. Regarding your comment as to why he didn't mention pulling the stick a tad to the left, he did tell it to some students in a training course in the UK. That statement is located somewhere in this thread.

He told me in a telephone conversation that he does not always follow the Robinson line.
It is my opinion that he was aware of the 18 degree offset and he compensated for it by bringing the cyclic stick back to the left. This is contained in three diagrams and fully referenced in my report.

For the readers of this post, I have contacted YouWillSee and asked his permission to send him the report and the diagrams.

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The Cat
4th Nov 2000, 07:35
Lu Zuckerman
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To: YouWillSee

I lifted this from another thread in Rotorheads. This will explain what goes on in Aircraft manufacturing companies. It deals with the EH-101 and if you want more I can search other threads in which I pointed out major design deficiencies on the A-310 and A-300-600 and nobody took action including Airbus and three other companies in the Airbus Consortium. When I reported it to the FAA they took action and the VP and Program Manager in the firm I worked at were fired, but the design was never changed.

To:
Thomas Coupling,

What the Royal Navy bought was a potential for disaster in the EH-101. When the EH-101 was in the design stages I worked as a consultant at Agusta and In my position I worked very closely with Westland. Each company developed a means of compiling a FMEA (Failure Mode Effects Analysis)data base but in the three years I was there they had not developed a means to get the two systems to talk to each other. My position entailed the instruction and supervision of the Italian engineers in the development of the FMEAs. I also had systems responsibilities as well and I too constructed FMEAs. I stressed that they should consider the potential for single point failures that would be catastrophic and down the helicopter. We were about three quarters through the task and the Italian manager had them remove the catastrophic failures from the FMEAs as it was his feeling that there would be no catastrophic failures. I pointed out strongly that the EH-101 was similar in design to the SH3-D/S-61 which Agusta was building and they had suffered catastrophic failures and in some cases, had crashed and burned. Sorry to say, I was overruled. To date, there have been two single point failures that caused loss of life. Both failures had been noted on the original FMEAs.

Another sad point was that the engineering department and the product support department did not talk to each other. This adversarial relationship began in the early days when Agusta was designing the A-109. The respective managers of the engineering and product support had very bad feelings toward each other. Now fast forward to the then present time. Each department had three changes in management and the war was still going on. In my last six months on contract I was assigned by the Director of Agusta to find a means of getting the two departments together. This was imperitive as the product support department needed engineering input to make the manuals. Another point, The product support department because of the isolation from the engineering department and their IBM main frame computer bought an NCR computer that could not talk to the IBM so they (Product Support) had no access to the FMEAs which would be used to construct the troubleshooting instructions in the maintenance manuals. I busted my hump setting up meetings between the two managers, the director and myself.

A lot of good things were said in the meetings but when I left at the end of my contract they were still not talking. The system of communication that was eventually set up was written requests for information sent to engineering. These requests did not go directly from the questionor to the questionee, they went through a filter in the systems engineering department. These two guys would determine if the question was valid or not and if they felt it was not valid it never got to the questionee. The questionor was not told of the rejection and he sat on his butt waiting for an answer.

While all of this was going on, Westland was laying off a major part of their R&M department.

The EH-101 is in certification right now and the FMEAs are crucial in the construction of the safety hazards analysis which is required to gain certification. If the FMEAs don't have catastrophic failures then they will not be accounted for in the safety hazards analysis and another unsafe helicopter will be certificated. Does this ring a bell in the minds of the readers?

As they say, you get what you pay for.

If you want more on this subject go to the EH-101 Crash thread here on Rotorheads.

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The Cat

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The Cat
4th Nov 2000, 13:53
Whirlybird*
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YouWillSee,

Everything you said makes a lot of sense. So why spoil it with this ageist crap. I fly R22s, and I don't agree with most of what Lu's been saying either, but his age and mine and yours has nothing to do with it. Do you really think you're going to change that drastically because a few years go by? Well neither does anyone else. So let's stick to discussing RELEVANT points here.

Let's admit it guys, Lu has rejuvenated a forum which looked at times like it was in danger of imminent death - Rotorheads was never this active till he came along.

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To fly is human, to hover, divine.
5th Nov 2000, 04:23
YouWillSee
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To: Lu

First of all, I'd like to apologize for my age-related, like Whirlybird called it, crap!! Anyway Lu, thanks for that report of yours and the quick answer.
Like i mentioned in my earlier post, i never doubted the facts presented by you. My point is and was the probability of an accident because of the design. If you fly the R22/R44 in training, photo flights or the R44 in sightseeing tours, police or news work, you should never even come close to a problem related to your issue. And once again, to make it perfectly clear, you might be completely or at least in part right with your findings, BUT this is not the point. The point is, that no pilot flying the R22/R44 should even come close to mast bumping during everyday-flying.
Your issue with sideslips and out of trim maneuvers is another problem i have with your interpretation. Just because Robinson put a limitation on the helicopters doesn't mean they aren't capable of doing it (only one accident while cattle mustering, and they violate that limitation on a daily basis). Just because never-exceed-speed is 102kts, doesn't mean the helicopter can't go faster than that, it's just not legal. Just because 14000' DA is the service ceiling doesn't mean it won't fly above that. They demonstrated the sideslips and the out of trim flights during certification and later put a limitation on it. Where is the problem with that? Why do we have the limitation, thats a whole different world, but don't assume they didn't show it and Frank Robinson, in his function as the DER, signed something off.
Finally i want to agree with you on one thing. Companies and people don't listen to you and your fellow engineers, because of money and all that jealousy between the different groups. I have one question, though! Why don't you focus on changing that, because according to you, that's where the root of the problem lies??

YouWillSee
6th Nov 2000, 21:49
Lu Zuckerman
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To: YouWillSee,

First of all I will say (and this may come as a shock to some of you) the Robinson helicopters are just as good as any other helicopter as long as they are flown within the restricted flight envelope.

What started this whole thing off is that I wrote a report and sent it to the NTSB. I made two points in the report among others and every thing stemmed off of that.

The points are:

1) The design of the rotorhead is such that the helicopter does not follow in the same sense as the cyclic stick is moved. The certification requirements state that in order to determine the sense of flight in relation to cyclic stick movement the certifying party must use a device sometimes called a stick plotting board. The FAA allows a slight deviation between stick placement and aircraft direction of flight. This, the FAA says, is caused by pitch coupling. They allow a degree or two but not 18 degrees (approximate). This would have been discovered in the certification process. My report asked the question of Robinson and the FAA if this test was performed and was it determined that the differences between stick movement and flight direction were excessive.

2) The second point related to sideslip and out of trim flight. The certification requirements state that the helicopter under certification demonstrate both flight characteristics. The certification requirements state that the helicopter be flying at .6 VNE and the pilot pushes his left rudder pedal to the stops and hold it in that position and then return the pedals to the neutral position and repeat the test by pushing the right pedal to the stops and holding it there and then return to neutral. The helicopter must demonstrate out of trim by +/- 10 degrees.

Let us assume that these tests were performed and the design of the R22 demonstrated that it was capable of compliance. Several years later the R22 was dropping out of the sky in large numbers because the rotor systems either hit the fuselage or just came off. Because of this, the FAA the NTSB and Robinson launched an investigation. With out a consensus between the three parties the FAA commissioned Georgia Tech Aeronautics department to investigate the matter. Their report among other things concluded that sideslipping and out of trim flight would set up high flapping loads that could cause the rotor problems. As a result of this, the FAA set up the restrictions that are printed on the last page of section four of the respective POHs for the 22 and the 44.

My report asked the question if the restrictions were placed on flight operations and pilots were restricted from sideslipping and out of trim flight then the helicopter no longer met the requirements of certification. If either helicopter were presented now to the FAA and they were told that this helicopter can’t be sideslipped or flown out of trim it would be immediately be rejected.

Regarding stick input during zero G flight let us assume that the pilot has corrected for the 18 degree offset and the cyclic is placed forward and right of the rigged neutral position. As such, the helicopter is flying forward and not to the left. If the helicopter enters the zero G condition with the cyclic in this position the following can happen:

1) If he pulls straight back he will not add to the right roll set up by the tail rotor thrust.

2) If he pulls back and slightly to the left he will add to the right roll component.

3) If he pulls back and further to the left he will compensate for the 18 degree offset and not add to the right roll component

4) If he pulls back and even further to the left he will introduce a left roll component causing high flapping loads and possibly lose his rotor system or cause a rotor incursion.

With the intensity of pucker factor being so high during a zero G condition which direction would you move the cyclic if you were in that situation. Refer to my point 1 above and think about the sense of aircraft movement relative to cyclic stick displacement. Does this sound right? What if these same conditions existed in your automobile?

REGARDING YOUR LAST QUESTION ABOUT CHANGING THE RULES RELATIVE TO RMS Vs. ENGINEERING I WOULD STAND A BETTER CHANCE OF CHANGING THE BIBLE TO RECOGNIZE GOD AS BEING FEMALE.

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The Cat

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

[This message has been edited by Lu Zuckerman (edited 06 November 2000).]
7th Nov 2000, 05:41
Lu Zuckerman
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HELIDRVR IS GOING TO ATTEMPT TO PLACE THE THREE DIAGRAMS I MENTIONED ON THE INTERNET.

WATCH FOR HIS POSTING.

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The Cat
7th Nov 2000, 06:41
helidrvr
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Lu has been spending inordinate amounts of his (hard earned) pension to send copies of his report and diagrams to the farthest reaches of the world. I finally took pity on him and decided to give them to you all with a click of your mouse.

I hope this helps. Lu, you can also email this URL to anybody who asks.

Cheers
8th Nov 2000, 00:22
Lu Zuckerman
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Just trying to keep this thread alive until FR replies.

Also, why not log onto the web site noted above in the posting by Helidrvr. It might help explain what I have been shooting my mouth off about for the last month and a half.

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The Cat
8th Nov 2000, 21:31
Lu Zuckerman
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To: Joe Pilot and all of my other detractors.

Log on to the website provided in Helidrvrs'
posting above. Look at the diagrams and come back with your comments.

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The Cat
10th Nov 2000, 22:14
eurocopter
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I have heard the possible reason for Robinson not making the Pitch lead the Blade by 72 Degrees was to cure an oscillation in pitch when cruising.
If this was the case - what would cause the oscillation and how would the 72 degrees offset correct it?