R-22 ROTOR SEPARATION? Florida Photo
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Hi BlarS. I am not sure what type of accident it is so it is not possible for me to comment, which would not be helpful anyway.
However I have seen this sort of failure of the rotor system before. As with all accidents I advise waiting for the investigators to complete their work.
However I have seen this sort of failure of the rotor system before. As with all accidents I advise waiting for the investigators to complete their work.
Me, being more familiar with the Bell 204/205/212 rotor system, can only iterate my amazement at the frugalness of metal quantity in that R22 rotor head. And of what metal there is, most of it is either torn/ripped/fractured/bent in that sorry looking set of photos in the above post.
Those clever technical boffins in the NTSB metallurgical department with their electron microscopes and xray machines and other fancy gadgets will no doubt quickly sort out what happened and why.
Those clever technical boffins in the NTSB metallurgical department with their electron microscopes and xray machines and other fancy gadgets will no doubt quickly sort out what happened and why.
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We sure hope so. I have a couple of photos somewhere of a set of blades with chord wise ripples clearly seen on the underside at about station - the inboard end of the torn sample.
We never figured it or got back a report but AFAIK the blades were sent somewhere for examination. I'll see if I can find the photos at least. They came off a helicopter R22 with the same blade dash number I think that the late pilot of which had a reputation for being - allow me to suggest - a tad aggressive at times.
As I chew I start with two fresh ideas the close ups has given me.
1. The steep nose down attitude of the helicopter as it was photographed on descent, which with 1 POB should have had C of G reasonably aft of fwd limit,
and,
2. I wonder -- where / if -- there is a nodal point for periodics when these blades approach compressibility?
well dammit there they are first go. see the crease marks underside of blades.
We never figured it or got back a report but AFAIK the blades were sent somewhere for examination. I'll see if I can find the photos at least. They came off a helicopter R22 with the same blade dash number I think that the late pilot of which had a reputation for being - allow me to suggest - a tad aggressive at times.
As I chew I start with two fresh ideas the close ups has given me.
1. The steep nose down attitude of the helicopter as it was photographed on descent, which with 1 POB should have had C of G reasonably aft of fwd limit,
and,
2. I wonder -- where / if -- there is a nodal point for periodics when these blades approach compressibility?
well dammit there they are first go. see the crease marks underside of blades.
Last edited by topendtorque; 14th Feb 2013 at 05:40.
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More photos?
Matari
The separated blade segment intrigues me. I can see several photos which show the adhesive on the front of the core, but there are no shots of the matching surface on the spar. Any chance?
Regards
Blakmax
The separated blade segment intrigues me. I can see several photos which show the adhesive on the front of the core, but there are no shots of the matching surface on the spar. Any chance?
Regards
Blakmax
So can we say your hunch is: blade segment fails, resulting in severe in-flight main rotor system imbalance, resulting in failure of main rotor hub, resulting in separation of main rotors?
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No hunch yet
gB, I am just trying to look at possibilities. I am not advocating any position yet. The fracture of the skin along the spar line makes me suspicious of one type of failure I have seen on an entirely different (F-111) aircraft, where an ineffective bond between a rudder mast and the core led to fatigue cracking of the skin and subsequent in-flight failure of the rudder.
Now almost every designer does not even consider this failure as possible, because the shear strength of core is an order of magnitude lower than the shear strength of the adhesive, so in many designs, this failure is not even analysed. In cases where the core-to-spar bond is ineffective (or fails) the out of plane shear loads must be carried by only the skins, and given that the R44 stainless steel skins are only about 0.006 inches thick, this failure mode is a possibility.
The photos of the rear of the spar will be of importance because if there is no adhesive on the spar (or minimal amounts of adhesive on the spar) then it is of fundamental importance to carefully check the skin failure using SEM or even just optical microscopy to see if there is any evidence of fatigue in the skin fracture. A further complication is that if they need SEM to find traces of adhesive, then there is another failure mode which can be significant and may lead to a different cause of failure.
If there is a significant amount of adhesive on the spar, then this failure mode is excluded.
If there is minimal or no adhesive and if there is evidence of fatigue in the skins then this approach must be further investigated. Again, I would expect that failure of the blade in this manner would result in blade impact on the fuselage as one blade looses lift, and apart from some indirect observations, I have not seen any evidence of such impact.
Another reason to consider this aspect is that it is unusual to have a segement of blade snapped off like that. If the segment was dislodged by impact, it must be out of plane to cause the skin to fracture at the back of the spar. The bond to the spar is only of the order of 0.5 inches long in the direction of rotation so impact with the water would be expected to cause peel failure of the skin-to-spar bond, rather than fracture of the skin.
These are my thoughts. I am NOT at this stage suggesting that this was the cause of the crash. All I am saying is that a simple investigation would exclude any further consideration of that factor.
Let's see what the photos look like. And in anticipation of the "leave it to the crash investigation experts" responses, I would bet the family jewels on the fact that adhesive bond failures constitute less than 2% of an average investigator's range of experiences, let alone expertise. This has been my bread and butter for forty years.
At 65 years old, the family jewels are not worth much these days.
Regards
Blakmax
Now almost every designer does not even consider this failure as possible, because the shear strength of core is an order of magnitude lower than the shear strength of the adhesive, so in many designs, this failure is not even analysed. In cases where the core-to-spar bond is ineffective (or fails) the out of plane shear loads must be carried by only the skins, and given that the R44 stainless steel skins are only about 0.006 inches thick, this failure mode is a possibility.
The photos of the rear of the spar will be of importance because if there is no adhesive on the spar (or minimal amounts of adhesive on the spar) then it is of fundamental importance to carefully check the skin failure using SEM or even just optical microscopy to see if there is any evidence of fatigue in the skin fracture. A further complication is that if they need SEM to find traces of adhesive, then there is another failure mode which can be significant and may lead to a different cause of failure.
If there is a significant amount of adhesive on the spar, then this failure mode is excluded.
If there is minimal or no adhesive and if there is evidence of fatigue in the skins then this approach must be further investigated. Again, I would expect that failure of the blade in this manner would result in blade impact on the fuselage as one blade looses lift, and apart from some indirect observations, I have not seen any evidence of such impact.
Another reason to consider this aspect is that it is unusual to have a segement of blade snapped off like that. If the segment was dislodged by impact, it must be out of plane to cause the skin to fracture at the back of the spar. The bond to the spar is only of the order of 0.5 inches long in the direction of rotation so impact with the water would be expected to cause peel failure of the skin-to-spar bond, rather than fracture of the skin.
These are my thoughts. I am NOT at this stage suggesting that this was the cause of the crash. All I am saying is that a simple investigation would exclude any further consideration of that factor.
Let's see what the photos look like. And in anticipation of the "leave it to the crash investigation experts" responses, I would bet the family jewels on the fact that adhesive bond failures constitute less than 2% of an average investigator's range of experiences, let alone expertise. This has been my bread and butter for forty years.
At 65 years old, the family jewels are not worth much these days.
Regards
Blakmax
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Spar side Honeycomb Surface
Blakmax,
Here is the matching surface on the spar side. Those barnacles do work quickly. One of the treasure divers mentioned that he was down for an hour or so and already had barnacles on his tank.
Here is the matching surface on the spar side. Those barnacles do work quickly. One of the treasure divers mentioned that he was down for an hour or so and already had barnacles on his tank.
Last edited by Matari; 14th Feb 2013 at 12:18.
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BM,
Isn't the R44 leading edge only Stainless, with the rest being ultra thin rolled Aluminium Alloy covering the honeycomb, with machined end caps?
Peter R-B
Lancashire
Isn't the R44 leading edge only Stainless, with the rest being ultra thin rolled Aluminium Alloy covering the honeycomb, with machined end caps?
Peter R-B
Lancashire
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No the -4's were very thin, 8 thou stainless steel over the honeycomb.
An over zealous and careless tap test is about all it takes to put a limiting dent in them.
Earlier -2 was alli - 25 thou..and now the later dash number I believe to be the same.
Poor old Dick musta got the poos and pinged off, measurements clarified if that is all he is on about as below I don't know.
An over zealous and careless tap test is about all it takes to put a limiting dent in them.
Earlier -2 was alli - 25 thou..and now the later dash number I believe to be the same.
Poor old Dick musta got the poos and pinged off, measurements clarified if that is all he is on about as below I don't know.
Last edited by topendtorque; 15th Feb 2013 at 01:16. Reason: find correct measurements from Robinson Maintenance
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It really scares me to see such misinformation on these sort of subjects!
cheers tet
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Thanks Matari but apart from a very small amount of the foaming adhesive which appears to be in an appropriate condition, I can not see sufficient to make any further comment.
Regards
Blakmax
Regards
Blakmax
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Thanks Morane and great to see the report out in the 12 months as predicted.
I will certainly need to read it several times, but so far the Florida case seems dissimalar to all mentioned by virtue of the visible blade damage / failure. Whether that failure occured prior to or after blade separation will need to be ascertained.
The only common denominator being the critical breakage point under extreme load - those pesky coning bolts.
once again Thanks
tet.
I will certainly need to read it several times, but so far the Florida case seems dissimalar to all mentioned by virtue of the visible blade damage / failure. Whether that failure occured prior to or after blade separation will need to be ascertained.
The only common denominator being the critical breakage point under extreme load - those pesky coning bolts.
once again Thanks
tet.
The pictures of the main blade at the root end with the pitch change arm look very similar to those in the UK accident that Morane links to - definitely worth a read!
In the UK case, the conclusion is that mast bumping leading to hub failure and blade separation was the cause but the reason for the mast bumping seems to be focused on a harsh cyclic input since there is no evidence of a pushover or turbulence.
What is interesting is that one of the blades flapped so much that it hit the left skid! If that wouldn't damage a blade badly, what would?
Ref the pictures of the Florida blade - was the detached section found with the main blade or not? If it was found with it then it is very unlikely that the separation occurred in the air.
Peter - like you I won't ever get in a R22 again - my last experience of one led to a write-off (dynamic rollover).
In the UK case, the conclusion is that mast bumping leading to hub failure and blade separation was the cause but the reason for the mast bumping seems to be focused on a harsh cyclic input since there is no evidence of a pushover or turbulence.
What is interesting is that one of the blades flapped so much that it hit the left skid! If that wouldn't damage a blade badly, what would?
Ref the pictures of the Florida blade - was the detached section found with the main blade or not? If it was found with it then it is very unlikely that the separation occurred in the air.
Peter - like you I won't ever get in a R22 again - my last experience of one led to a write-off (dynamic rollover).
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what happened.....
Standing on the shore.....heard a helicopter coming.....looked up and was just to about 1 o'clock position at about 500 feet, approximately 350 yards offshore.
I thought he was a bit low, but was flying level with no deviations, parallel to the coastline. Aircraft was operating as normal, engine sounded normal, was no evidence of any problems.
Looked back to the ground and at that same instant K-BLAM.....very loud metallic separation sound, looked back up and was already inverted and heading straight in.
Aircraft hit the water at a 12 o'clock position from where located on the bank. Did not see the blades splash, as was watching it hit the water. Was pretty shaken up, but watched as a person in a kayak paddled out to the site and recovered some body parts, put them on the bow of the kayak and paddled to position on the bank. Was not a pretty site, lungs and attached esophagus, had enough of that and left the scene.
Returned almost a month to the day after seeing the reward offered on the internet. Using side scan sonar, located blade one quite quickly, about thirty minutes searching from where aircraft was observed going in. Dropped a buoy on the site, 11.5 feet of water, my buddy hopped over, visibility very limited, no more than 1.5 - two feet..... tied a rope and buoy to the blade and recovered it. The blade as in the picture had the chunk broken out of the tip, but the chunk was still just barley attached by a bit of aluminum, and remained that way when turned over to the FAA.
Unfortunately did not have any more air on board and was forced to abort recovering blade two. Returned the next day with adequate air and searched...and searched....found some more anomalies on the bottom at site of blade one, got a grapple hook on them but was unable to lift them, looks like part of the air frame and one of the skids. Did not dive them as was more interested in the other rotor. Took many pictures of the bottom, don't know how I missed seeing blade two on the monitor but I did.
Returned home and downloaded the images. Looks to be part of the skid, and more airframe from what I can tell. Then upon review of the remaining images, there it was...blade two lying all by itself, not far from blade ones position. Close inspection you can clearly see the rotor hub, and complete blade lying on the bottom.
Blade ones hub was still full of oil, although the seal was compromised by the twisting of the metal. I do not believe it was mast bumping, as the aircraft was flying straight and level, with no apparent issues until it went K-BLAM, in an instant and went in.
The chunk that failed out of the blade looked as though it was cut with a scalpel on the spar side, a very clean cut, not something that would have happened on impact I believe. The two sides of the chunk are ragged separations, not perfectly straight and clean as the spar side failure. From a layman's view, looked like the chunk came out of the blade, causing the rotors to be out of balance, shearing them off the mast.
this is blade two....
notice the scale 51 feet.....blade is about 20 feet
and this is the airframe parts, I believe part of the skid...and cabin...
I thought he was a bit low, but was flying level with no deviations, parallel to the coastline. Aircraft was operating as normal, engine sounded normal, was no evidence of any problems.
Looked back to the ground and at that same instant K-BLAM.....very loud metallic separation sound, looked back up and was already inverted and heading straight in.
Aircraft hit the water at a 12 o'clock position from where located on the bank. Did not see the blades splash, as was watching it hit the water. Was pretty shaken up, but watched as a person in a kayak paddled out to the site and recovered some body parts, put them on the bow of the kayak and paddled to position on the bank. Was not a pretty site, lungs and attached esophagus, had enough of that and left the scene.
Returned almost a month to the day after seeing the reward offered on the internet. Using side scan sonar, located blade one quite quickly, about thirty minutes searching from where aircraft was observed going in. Dropped a buoy on the site, 11.5 feet of water, my buddy hopped over, visibility very limited, no more than 1.5 - two feet..... tied a rope and buoy to the blade and recovered it. The blade as in the picture had the chunk broken out of the tip, but the chunk was still just barley attached by a bit of aluminum, and remained that way when turned over to the FAA.
Unfortunately did not have any more air on board and was forced to abort recovering blade two. Returned the next day with adequate air and searched...and searched....found some more anomalies on the bottom at site of blade one, got a grapple hook on them but was unable to lift them, looks like part of the air frame and one of the skids. Did not dive them as was more interested in the other rotor. Took many pictures of the bottom, don't know how I missed seeing blade two on the monitor but I did.
Returned home and downloaded the images. Looks to be part of the skid, and more airframe from what I can tell. Then upon review of the remaining images, there it was...blade two lying all by itself, not far from blade ones position. Close inspection you can clearly see the rotor hub, and complete blade lying on the bottom.
Blade ones hub was still full of oil, although the seal was compromised by the twisting of the metal. I do not believe it was mast bumping, as the aircraft was flying straight and level, with no apparent issues until it went K-BLAM, in an instant and went in.
The chunk that failed out of the blade looked as though it was cut with a scalpel on the spar side, a very clean cut, not something that would have happened on impact I believe. The two sides of the chunk are ragged separations, not perfectly straight and clean as the spar side failure. From a layman's view, looked like the chunk came out of the blade, causing the rotors to be out of balance, shearing them off the mast.
this is blade two....
notice the scale 51 feet.....blade is about 20 feet
and this is the airframe parts, I believe part of the skid...and cabin...
Last edited by susieqfish; 16th Feb 2013 at 18:34.
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I was browsing the other threads and I noticed this pic posted by a fellow PPruNer, showing a totally unrelated accident (T/R strike), different aircraft (206L), but with a very similar M/R blade honeycomb separation.
Funny how the failure is just aft of the leading edge, with what appears to be a similar sized chunk of honeycomb missing. Does it mean anything? I don't know, but just interesting in its similarity.
Funny how the failure is just aft of the leading edge, with what appears to be a similar sized chunk of honeycomb missing. Does it mean anything? I don't know, but just interesting in its similarity.
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30 days
Rotor was on the bottom almost exactly 30 days when we recovered it...and funny thing is the chunk that was hanging by a small piece of aluminum, was almost totally covered in barnacles, while the rest of the blade was sparsly populated. I think it is because the piece was slightly elevated off the bottom by the buoyancy from the air in the honeycomb. This would allow for better water circulation and faster growth of the barnacles due to increased feeding ability in the water column.
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