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Robinson helicopters added to safety watchlist

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Robinson helicopters added to safety watchlist

Old 14th Nov 2016, 16:43
  #121 (permalink)  
 
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The added flap hinges are intended to relieve the bending stresses at the blade root when changes in G load produce changes in the coneing angle
Thanks Birdy, but I must be missing something. If the blades are free to flap, why then the teetering head? I'm working on the basis that there's no such thing as a stupid question here, so be gentle.
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Old 14th Nov 2016, 18:03
  #122 (permalink)  
 
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Wrong performance chart! It says R22 Alpha not Beta II. Maybe some more experienced R22 / IT nerd can upload the correct performance chart.
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Old 14th Nov 2016, 19:06
  #123 (permalink)  
 
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Paul Cantrell - thanks, every day's a school day on Rotorheads

aa777888 - that doesn't match what I saw of 2 of us with about 2/3 fuel struggling to get over the owners hedge without exceeding the MP limit. Or the lack of performance with the rather large examiner I did my check ride with - definitely not full fuel!
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Old 14th Nov 2016, 19:46
  #124 (permalink)  
 
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Hi Crab--can't speak to the conditions that obtained for your flight, but I've been near max. weight and the Beta II's that I've been flying all make their numbers, no problem.
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Old 15th Nov 2016, 06:52
  #125 (permalink)  
 
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OK It was 20 plus years ago and I can't remember which model of 22 it was but it was UK at not much above sea level. I didn't see the owner do a load sheet so I have no idea how heavy we actually were.
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Old 15th Nov 2016, 06:52
  #126 (permalink)  
 
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One of the problems of the difference between scheduled and real world performance of the R22 is the sensitivity of its small main and tail rotor blades to blade condition. Worst case scenario is warm humid day in summer and the leading edges plastered with bugs.The effects of humidity is not scheduled in the performance graphs as it used to be in old marginal performance helicopters (piston Whirlwinds for instance) and from memory could be up to 5 percent from dry to humid air. Cleaning the leading edges every sortie is a pain but can add the equivalent of about 5 bhp. Doesn't sound much but is the difference between a cushion creep and a more comfortable takeoff.
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Old 15th Nov 2016, 07:15
  #127 (permalink)  
 
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Spot on, rotorfossil, not to mention eroded and dinged up blade leading edges from flying through anything from rain to dust and debris blown up of dry landing sites.
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Old 15th Nov 2016, 10:22
  #128 (permalink)  
 
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Thanks Birdy, but I must be missing something. If the blades are free to flap, why then the teetering head?
The blades teeter on the central hub hinge, and can cone freely on the indervidual blade flap hinges.

You can split hairs if you like evil7.
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Old 15th Nov 2016, 11:23
  #129 (permalink)  
 
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That's really a grade3 mindset ...... if we take the millions of people killed every year in car accidents what now? Do we recall all cars?
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Old 15th Nov 2016, 12:31
  #130 (permalink)  
 
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If you have a specific car that has a serious defect causing deaths then yes, you would recall it.

You have to decide if the vehicle is fit for purpose or not.

Most people killed in cars are the victims of accidents of a variety of causes, very few of which are serious technical defects caused by design or manufacturing.
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Old 15th Nov 2016, 13:08
  #131 (permalink)  
 
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Crab

and to cap it all an automotive manufacturer will if in doubt recall his product. Does that happen in the aviation industry er NO
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Old 15th Nov 2016, 13:34
  #132 (permalink)  
 
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Originally Posted by [email protected] View Post
If you have a specific car that has a serious defect causing deaths then yes, you would recall it.

You have to decide if the vehicle is fit for purpose or not.

Most people killed in cars are the victims of accidents of a variety of causes, very few of which are serious technical defects caused by design or manufacturing.
If the car manufacturer had a uniquely designed steering system that on quite a number of unexplained instances caused the vehicle to drive into the central reservation at motorway speeds then I'm quite sure it would be recalled until rectified.

Robinson has a unique design of rotor head (teeter and coning hinge layout) and it also has a unique problem that happens very occasionally and is as yet largely unexplained. A number of people feel the issue lies is in the balance between the teeter hinge and coning hinges (including some of the recognised world experts in the field). If someone unloads the rotor slightly (not as in an extreme low G situation) changing the coning angle and a coning hinge has any kind of change in standard resistance (sticks slightly / reacts slower for any reason) things can get out of hand very quickly. Unexplained rotor divergence is in the Robinson rotor head design - no other manufacturer has the unique design and no other manufacturer has the problem. Yes, we all know a Bell 206 can mast bump under extreme low G like any 2 bladed system but the Robinson is unique in that it has a history of largely unexplained rotor divergence incidents.
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Old 15th Nov 2016, 20:29
  #133 (permalink)  
 
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Originally Posted by TTSN View Post
If someone unloads the rotor slightly (not as in an extreme low G situation) changing the coning angle and a coning hinge has any kind of change in standard resistance (sticks slightly / reacts slower for any reason) things can get out of hand very quickly. Unexplained rotor divergence is in the Robinson rotor head design - no other manufacturer has the unique design and no other manufacturer has the problem.


From quite a number of accidents and the witness descriptions it is blatantly clear that there must be something hidden in the Rotor systems dynamics that occasionally makes them go wild with little or no obvious trigger. A lot of witness reports describing a helicopter smoothly cruising along or at worst tail- wagging a bit (what they do seem to have in common that it almost always happened at >80kts) and all of a sudden a popping noise and bits'n pieces raining out of the sky. Far from the scenario Robinson is clinging to in their opinion of what happened in all those cases where the Robbies sliced their tail and spit their rotor.
Yes there is surely a number of traditional low G accidents or low RRPM accidents included but there is a number of accidents where both these scenarios quite obviously do not seem to be the case. (see witness descriptions and state of warning lights in some of the highlighted accidents).
And this is the really worrying part. Much beyond a helicopter which ultimately demands not to exceed stated flight limits.
Whether the underlying cause is rather in the triple hinge mechanism or in blade elasticity or lead/lag issues would potentially be a worthwile subject of study for NASA.
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Old 15th Nov 2016, 22:01
  #134 (permalink)  
 
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I had a look back to 2004 at a Robbie thread where the head design was discussed at length.

A contributor called Delta 3 had done a great deal of mathematical modelling and talked about how both the coning and the flapping (teetering) hinges had a delta-3 effect designed into them.

This 'double' delta-3 effect appeared to have the potential to give more than desired flapping in certain circumstances.

Don't suppose Delta-3 is still watching this forum?
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Old 16th Nov 2016, 02:44
  #135 (permalink)  
 
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A couple of points about the condition of the head hinges, if a flap hinge had more friction than the other, to the point where the many tones of centriphical tension couldnt break the binde, itd have to be sceezed compleatly. At worst, itd create a head shake that a pilot would notice an land asap. These hinges only need to move with G load ( coneing) changes, so itd only shake with a change in G load. If the central hinge sceezed and wouldnt allow the hub to rock, the teetering action would be transfered to the coneing (flap) hinges, again, only creating a stick shake.
If all 3 hinges bound, there would be a heavy left roll tendancy.
None of the above would cause the blades to suddenly and without warning, attack the machine.
In the list of incidents, the only pattern is that the blades suddenly, and without warning, violently depitch and mince the airframe.
Its been recorded to happen at any speed from hover to @90 kts, so AS can be rueled out.
Its happened with a wide range of AUWs, so disc loading can be rueled out.
Its happened, generaly at a steady cruise, but also dureing normal manouvers, but never recorded to happen with high rate, high magnitude control inputs ( mustering ops), so ham fisted pilots could almost be rueled out.
Low G roll is to the left. The incident reports list rotor strikes on every point of the compass, not consistant with low G strikes.

Probably millions of hours have accumulated in robbys, only 32 (?) have been recorded to self destruct with no indication as to why.
Sounds more like a rare structural failure, like maybe, phase lock.
Afterall, MR phase is only locked with two ball joints, loaded in shear, and not their intened design, tension.

Ready to stand as im corrected.
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Old 16th Nov 2016, 07:28
  #136 (permalink)  
 
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Birdy2

I understand low G roll is always to the Right (not the left). A low G right roll can be at rates of 100 degrees per second, 25 years ago or so they used to be demonstrated by instructors along with the correct recovery actions. The tail rotor would need to be on the other side to make it roll to the left.

Related thread something happened in the hover which was posted in 2012 copied below:

anti-talk's 10th Dec 2012 15:30

This is very interesting, we had a 22 Roll over in the hover about 3 years ago that appeared to throw a blade - it was thrown well clear of the wreckage with no bending or discernable damage, the mast sheared at the gearbox and then the mast wrapped under the machine causing a pre impact fire due to ruptured fuel tank (as the mast cut through it)
Fortunately both occupants escaped the wreckage , the pilot stated he didnt grab a skid (dynamic roll over) and the machine literally inverted itself very violently (both occupants lost their shoes)
We were convinced this was a blade separation (query bolt failure??) we recovered the blade with hardly and damage, the Hub broke in two and the bolt was no where to be found.
As a result everytime the blades come off the machine we now replace with new bolts (never did like the 'stretching' idea.)
The local FSDO felt there was some mileage in the blade seperation idea but the NTSB had no appetite to investigate further due to there being no injuries. We retained the hub and I still have it to this day.
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Old 16th Nov 2016, 07:45
  #137 (permalink)  
 
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And a case where a blade bolt failed (luckily when parked in a hangar) also from 2012 thread titled R22 Rotor Seperation Florida:

helichoppers's , 14th Jan 2013 13:55
Bolt Failure
Just to throw something else in to the pot..

We had an R44 Raven II that fortunately whilst sat in the hangar and not flying suffered a Blade Bolt Failure!

We returned to the machine after it had sat for a weekend to find a thrust washer sitting on the hangar floor! The full horror then dawned as you looked up to see one of the main Blade bolts sticking out from the Hub. If this had failed in flight and not whilst sat with the full weight of the blade on the droop stop I am sure the bolt would have totally departed from the aircraft along with the blade etc and you can imagine the rest....

The bolt was sent to our local CAA for inspection who then sent it to the FAA via Robinson, the opinion in the end was that it was a one off caused by Hydrogen enbritellment of the bolt and was not considered to warrant further investigation. The bolt had a total time of 80 hours from new.

I appreciate this was on an R44 not an R22 but the bolts must go through a similar manufacturing process??

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Old 16th Nov 2016, 07:52
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This is just an opinion as I have no more evidence than anybody else about the unexplained breakups in cruise flight. However 20 plus years of teaching and examining in R22's suggests to me the following. If there is an unexpected power loss, the first reaction is "what's happening"? Followed by either far too slow lowering of the lever or no reaction at all. Result- massive drop in rpm, rotor blow back and break up. I have had two examples of this lack of reaction to real engine failures but not in R22's and in each case I had to slam the lever down. Sadly Robinsons edicts about simulations of engine failures result in most people have no experience of the rapid rundown in rpm in the event of power loss (and it doesn't have to be a total loss). Again my observation of people's behaviour suggests that the most likely cause of the power loss is due to lax operation of carb heating and undue reliance on the carb heat assist. Whatever the reason, if you get an unexplained power loss in an R22, after the inevitable " this can't be happening to me", you have to slam the lever on the bottom as fast as you can move your hand. Even then, the rpm will go down into the 80's. Unfortunately the autorotation entry as normally taught is much slower than this scenario and unexpected complete shutting of the throttle discouraged.
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Old 16th Nov 2016, 09:36
  #139 (permalink)  
 
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I hear what your saying TTSN, yes, some of these incidents could slip past the keeper as another low G boo boo, and some low G incidents could look like angry rotors.
Authorities seem fixated on head design/ blade stability.
After watching these machines for years being pushed way past Frankies limits and never a hint of blade instability tends to make me think they are very much under control.
Oh, and you caught my deliberate mistake with low G roll.
Just checkn your on the ball.
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Old 16th Nov 2016, 09:51
  #140 (permalink)  
 
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Again my observation of people's behaviour suggests that the most likely cause of the power loss is due to lax operation of carb heating
Yes, this always amazes me - a lot of people around where I am treat the carby heat as if it should always be locked off, even though the conditions (often very humid air and usually somewhere between 20-30 degrees C when airborne) are perfect for it.

Unfortunately the autorotation entry as normally taught is much slower than this scenario and unexpected complete shutting of the throttle discouraged.
I agree totally on the importance of making sure the lever goes down as quick as you can - the POH says not to do throttle chops because of the chance of the student doing the wrong thing or the engine stopping, but it's certainly a massive difference between a gentle coordinated throttle roll-off while the lever's going down and what would really happen if the power suddenly went away with the collective up, not to mention the oh shit factor.
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