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Certification of Robinson Helicopters (incl post by Frank Robinson)

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Certification of Robinson Helicopters (incl post by Frank Robinson)

Old 25th Feb 2001, 13:21
  #261 (permalink)  
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Looks pretty reasonable to me, judging by the rightmost column (fatal accidents per 100,000 hours).

R22 has about twice the rate of Enstrom 28 and Bell 47. Slightly more than that when compared to Hughes 269.

Compared to FW types R22 also has a reasonably similar rate to Grumman AA1 (also an agile machine), worse than Cessna 150/152 but not wildly so.

Given what R22s are used for I don't see these figures as statistically significant.

If the fatal accident rate were an order of magnitude greater than other types in similar roles then yes I'd be looking for a problem. But not with these numbers.

Compare Enstrom 28 and Bell 47 fatal accident rate with Lu's beloved Bell 206.

In my mind that ratio makes the R22 ratio of R22 fatals to F28 and B47 look unremarkable. Therefore absolutely not justifying a witch-hunt concerning Robbies.

Of course, as with R22, the difference is down to what the types are used for, and in whose hands.

More volts, Igor
Old 25th Feb 2001, 18:57
  #262 (permalink)  
Lu Zuckerman
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To: Chips

In my original postings about the certification of the R22 and the R44 the main thrust was regarding the rotorhead design and how I felt it was the major cause of the in-flight rotor loss due to mast bumping and or fuselage incursions by the rotor blades. The chart reflects 23 such accidents. My report reflected 31 such accidents and last year that total rose to 35. This type of accident is analogous to a fixed wing aircraft suffering a loss of one or both wings. So, when you figure this type of accident on a fixed wing aircraft the rate of occurrence would be almost nil per 100,000 flight hours. Bell helicopters had suffered 53 mast separations when I first became interested in this phenomena in 1976. They have most probably suffered several more since that time but I honestly do not believe that any of the accidents other than the Robinson on the chart resulted from fuselage strike or mast separation.

FAR-AC-1309-1A states that all single point failures that could cause death or loss of the aircraft must be designed out of the system. If the design can’t be altered then the frequency of occurrence of death or loss of the aircraft shall occur no more frequently that 1 10-9 hours of accumulated flight for the specific model of aircraft. If in fact the rotorhead design on the R22 and R44 are determined to be defective then the Robinson design does not meet those criteria.

The Cat

[This message has been edited by Lu Zuckerman (edited 25 February 2001).]

[This message has been edited by helidrvr (edited 25 February 2001).]
Old 26th Feb 2001, 12:02
  #263 (permalink)  
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I, like most other "rotorheads", am acutely aware of the consequences of mast bumping and separation.

Once again you have to discriminate between pilot failure and aircraft failure in order to establish defective design. You have not done that.

I also dispute the idea that airplane wings don't come off. They do. Tails also.

Occasionally it's a plain structural problem (eg. corrosion, cracks or bad glue).

Usually, and tragically, it is a consequence of improper flying. Either g overloading, as in aerobatics or flying into thunderstorms; or the infamous graveyard spiral (as a consequence of control loss in instrument conditions).

A similar and sad state of misflying equivalent to misflying causing mast bumping. Also a case of exceeding the approved range of g (-ve).

Sorry Lu, you MUST prove that the aircraft is at fault, NOT the pilot. Rational thinking demands that, regardless of interpretation of regulations (and lies, damn lies and statistics).

The statistics you have presented not only do not show that the aircraft design is faulty, they also suggest that the Robinson R22 is not at all far from other types in similar roles, RW and FW alike. They actually support the assertion that the RW design is safe.

More volts, Igor
Old 26th Feb 2001, 20:54
  #264 (permalink)  
Lu Zuckerman
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To: Chips

Up until now the NTSB and the FAA have attributed almost all failures of the Robinson design that resulted in death to pilot error and therefore, my theory about the rotor design as the main contributor remains as a theory. I didn’t state that airplane wings or tails don’t come off as it is proven that they do. This type of failure is normally attributed to overstress which is pilot error or the onset of corrosion that leads to structural failure which can be attributed to poor maintenance. Very few if none of these failures are attributed to faulty design. Coupling all three types of failures that result in separation of a wing or tail and the frequency of occurrence per 100,000 flight hours would most likely be less than that of the Robinsons’ loss of the main rotor or fuselage incursion.

It is my theory that the design of the Robinson rotorhead can lead to mast bumping even in the hands of a high time pilot. This is evidenced by the rotor loss incident in Watsonville, California. This pilot had in excess of 20,000 hours much of it in helicopters and he was an airshow demo pilot flying in an R22. I believe it may have been the same aircraft used in the airshow that was involved in the crash.

I tried to prove my theory about the 18-degree offset by asking pilots on the forum to perform a test and you know where that led. Well, I doubt if I could ever get the test performed even if I bought an hour of flight time on an R22 however there is an agency that will have the test performed and that is the NTSB. In reopening the investigation of the rotor loss/incursion accidents their entire focus is on the rotorhead.

After the investigation by Georgia Tech at the behest of the FAA it was determined that sideslip and flying out of trim resulted in progressively increasing flapping loads which were dependent upon the degree of sideslip and the degree of out of trim flight. It was determined that these flapping loads could result in mast bumping and subsequent rotor loss or fuselage incursion. As a result, the Robinson R22 and R44 were restricted from performing these maneuvers. It was these restrictions and the increase in pilot training and awareness that resulted in no mast bumping or rotor incursions from 1995 until last year when the Robinsons' incurred four rotor separations / rotor incursion accidents. Was this due to relaxed flying standards by the involved pilots or, did the rotor design place them in jeopardy when the countered a zero G condition. All of this will come out in the NTSBs investigation.

The Cat
Old 27th Feb 2001, 02:07
  #265 (permalink)  
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Well folks, we seem to be running out of new stuff to debate on this one. Maybe the best thing is to now let the issue rest with the NTSB until they issue their report. When that comes out, we'll no doubt have ample fodder for a renewed debate.

Just my opinion, but don't let me stop you - continue if you must.


You are welcome to visit HELIDRVR here

[This message has been edited by helidrvr (edited 26 February 2001).]
Old 1st Mar 2001, 17:06
  #266 (permalink)  
Flight Safety
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Here's a link to the full text of the 1996 NTBS investigation of the R-22 rotor separation problem. The chart that Lu included in this topic is from this report. Sorry if this has been posted previously.


Later, to Lu,

I've been reading this report, and the discussion on pages 80-81 of the report (pdf pages 88-89) refers to the unique design features of the Robinson main rotor system. Specifically these pages address the feature that allows each blade to flap independently of the other, which is unusual in a semi-rigid design. At the same time, there's no mechanism that allows the blades to lead or lag (I understand ground resonance would be a severe problem on a 2 blade helo with lead/lag hinges).

What effect would the independent coning angles of each blade (and the accompanying tendency to change speed from the coriolis effect) have of this rotor system? The report in the pages I mentioned suggests there might be an instability in this configuration. Could some complication of the Hooke's Joint Effect stresses resulting from the independent coriolis stresses of each blade, create an instability that results in an uncommanded tilt of the rotor disk? Could a resonance of some kind be created between the independently flapping blades that induces a rotor tilt?

Where would the coriolis energy (or angular momentum energy) of each blade go if there are no lead/lag hinges? In a normal semi-rigid design, wouldn't the energy just be transferred directly to the other blade, and wouldn't the transfer of energy constantly be going back and forth between the blades as they advance and retreat, through the semi-rigid structure? With two flapping hinges between the 2 blades, how efficient would that transfer of energy be, and could some instability be created? I hope you can follow my thinking.

The report states that the aerodynamics of this particular rotor configuration may not be well understood and should undergo further study. I agree, something's not right here.

Safe flying to you...

[This message has been edited by Flight Safety (edited 01 March 2001).]
Old 1st Mar 2001, 18:36
  #267 (permalink)  
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I second that Helidrivr.
Old 1st Mar 2001, 20:24
  #268 (permalink)  
Lu Zuckerman
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To: Flight Safety

You have raised some valid points relative to the Robinson rotorhead design. I had posted on several occasions my thoughts on this subject and was ambushed by Robinson supporters and individuals that did not agree with my technical conclusions. You are the first to recognize that the flapping of the blade introduces leading and lagging forces (Coriolis).

It is true, when the blades flap they lead and lag. In the case of the Robinson rotorhead design there is no provision for leading and lagging and these forces are reacted by the coning bushings (hinges) and are transmitted directly to the teeter bushing (hinge) and are in turn reacted by the main rotor shaft and the transmission. The forces then pass to ground to the fuselage via the transmission attach points.

The magnitude of the leading and lagging is dependent upon the coning angle (flapping angle).
The frequency of the blade movement (tendency to move) is at a rate four times the rotational speed of the main rotor.

In reacting the lead / lag forces the cone bushings wear in an elliptical shape. In the wearing of the bushes the blades are actually allowed to move which exacerbates the condition. The teeter bush (hinge) will also wear but not at the rate of the cone bushes. It is my contention that in reacting the forces of leading and lagging the main rotor shaft can be fatigued as well as other structural parts of the blade.

Regarding other semi rigid rotor heads some of them use drag links which transfer the loads directly into the rotorhead. On the Bell 206 series the blades are restrained from movement by an adjustable clamping arrangement and those loads are reacted by the rotorhead. Some of the in plane vibratory forces may be reflected on the opposite blade but they are minimal. Bell in trying to minimize the Coriolis forces underslung the rotorhead.

It well within the realm of possibility that the vibratory forces that are manifested in the leading and lagging can be reflected on the blade and cause an aerodynamic / aeromechanical instability that would result in divergence.

If you had read my report, I raised a question as to the level of developmental testing performed on the rotorhead. According to FAA certification regs, the rotorhead on the Robinson helicopter constituted a new and unusual design and it required a higher degree of testing to prove its’ efficacy as opposed to a conventional semi rigid rotor head such as that used on the Bell.

On several other posts I alluded to a report performed by the Georgia Tech Aeronautics Department at the behest of the FAA. This report which was never finished was adapted by the FAA and Robinson and as a result the R22 and R44 were restricted from flying out of trim (balance) and from being sideslipped because the rotorhead design would lead to high flapping loads and result in mast bumping. This should have been discovered in the certification tests and not 10 years after the design was certified.

Another point that should be considered is the design of the internal workings of the rotorhead. The Robinson rotorblade has an internal lug (stop) which establishes the static droop of the blades. When the blades cone, this lug moves in opposition to the blade coning and the blade is free to flap (cone) without restriction. However when severe flapping loads are encountered the blade can drop down to its normal static position and the lug will engage the stop. During the high flapping excursions the blades have a high degree of kinetic energy and in making contact with the stop the forces involved will / can force the rotorhead down (teeter) and the blade can contact the fuselage or, it can result in mast bumping.

There is one other point that bears strong investigation and that is the rigging procedure for both the R22 and all of its’ variants and the R44 and all of its’ variants. The procedure is vague and ambiguous and places the mechanic in the position of making a decision in the procedure with out adequate instruction in the Maintenance manual. There are also very confusing instructions which can lead to the binding of the uniball on the swashplate and possible contact between the control system and fuselage structure. The control limits for different variants of each helicopter are set by a rigging stop plate. When the cyclic is rigged it is placed in the mechanical neutral of the rigging plate which means that the cyclic can only be moved a given amount in any direction. When forward cyclic setting adjustments are made on the blades there is a fixed angular setting. That means, that when the cyclic is moved aft for the setting of the cyclic pitch settings the settings for aft should be the same as for forward. They are not, which requires that the pitch setting on the blade pitch link must be changed. In doing so, the mechanic is told to check the forward setting to see if it has been changed. It will have changed but the mechanic is not told what to do. This type of instruction or the lack of instruction is typical of the entire procedure.

All of this is contained in my report.

The Cat

[This message has been edited by Lu Zuckerman (edited 01 March 2001).]
Old 3rd Feb 2005, 15:07
  #269 (permalink)  
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Percentage of Robbo's flying

With all the crunches, bumps, bangs and destroyed R22's and R44's just how many of those built are still flying?

Would it be near 80% or something like 50%?
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Old 3rd Feb 2005, 16:35
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I'd say it's prob close to 50%, alot of them have been bent I reckon. None of them by me thank god!

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Old 3rd Feb 2005, 20:35
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I suspect closer to 90 percent. Some 5,500 Robinsons have been sold around the world so far, and RHC's production continues to outstrip that of all other civil helicopter manufacturers combined. The reason that every second accident seems to involve a Robinson is because they're working in such massive numbers.
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Old 10th Jun 2005, 09:01
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6000 Robbies delivered

Rotor and Wing announced in the June issue that Robinson Helicopter just delivered its 6000th machine - an R44 Raven II. As of April 2005, Robinson has produced 2,207 R44s and 3,837 R22s.
Sales are expected to exceed 700 machines this year.
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Old 15th Jan 2013, 11:51
  #273 (permalink)  
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R22 Report

I would like a copy of the report if possible. I am interested in Aviation/Aviation law in general but in particular inherent problems with Robinson choppers. [email protected]

Thanks in advance,

Jgilfedder is offline  
Old 15th Jan 2013, 14:43
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R22 Report

Jgilfedder - If the report you refer to is the one offered by Lu Zuckerman in 2000 then unless someone else has it you'll be unlucky as sadly he passed away in July 2005.
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