Another rotor break off in flight

[Aesir]

https://www.youtube.com/watch?v=6A-tzAP-vs0

Seems that this was in Korea. What type helicopter is that?

[Nige321]

Is that a Surion? Puma gearbox...?��

[krohmie]

KAI Surion

https://en.m.wikipedia.org/wiki/KAI_KUH-1_Surion

[Aser]

Looks like a...KAI KUH-1 Surion"As the prime sub-contractor, Eurocopter has provided technical assistance in part for developing the power transmission, main gearbox, boom and tail gearboxes, automatic flight control system and rotor mast."
Just saying...

Regards.
Aser

[Nescafe]

That video is depressingly familiar.

[SASless]

Related development......332. Per that amazingly always accurate source....Wikipedia.

Sound familiar?

[Jimmy.]

MUH-1 Marineon, a Surion variant.

[peterperfect]

Thats the mast snapping/separating at the head, rather than a gearbox internal failure ?

[Nescafe]

If you slow the video right down at the 16/17 second mark, it actually looks like a blade lets go at the 12o’clock position, and then the head detached as a result of the induced imbalance.

https://cimg6.ibsrv.net/gimg/www.gmforum.com-vbulletin/1334x750/927ce314_9acc_45be_ab9a_2975bf47c570_a647fb1d2419eee5d3c5773 ab1c32cf340a369ff.png

[OnePerRev]

If you try to slow the video, or advance slowly, it seems as the coning angle is all over the place on takeoff. First it may appear normal, but seems to vary, then right around 9 seconds, when just over the last building, you can see the rotor tilt left, to the camera, then back forward. Then the cone angle drops, and raises again, before the rotor drops a lot around 10 seconds, one frame seems like blades are crowded in the front, spreads out flat again and one blade departs. The two other puma departures had intact heads and blades. I would not rule out a gearbox seizure as some have speculated, but probably not my first guess. But since this event was takeoff rather than cruise, all control positions and airflow vastly different, so the subsequent chain events could be different. Still, usually rotor heads and the blade roots tend to stay grouped, even after powered impact. This blade is missing at the head altogether, so I would suspect a blade attachment, or at least a blade control mechanism that could send this to extreme pitch, that would produce an extremely high load in the flatwise direction rather than chordwise, before separation. Who has graphics of rotor/ control system? Assume they are same as the AS332.

[Jimmy.]

If you try to slow the video, or advance slowly, it seems as the coning angle is all over the place on takeoff. First it may appear normal, but seems to vary, then right around 9 seconds, when just over the last building, you can see the rotor tilt left, to the camera, then back forward. Then the cone angle drops, and raises again, before the rotor drops a lot around 10 seconds, one frame seems like blades are crowded in the front, spreads out flat again and one blade departs.

Except for the blade departure, clear in a 0.25x reproduction, I really need to check my glasses or get a bigger screen.

[rotor-rooter]

https://scontent-sea1-1.xx.fbcdn.net/v/t1.0-9/37313514_760838730753453_3616649001975152640_n.jpg?_nc_cat=0&oh=ce23ec506e0aa507b5630e9cb7caf84a&oe=5BEA9490

[Harrynz]

Looks like leading edge pitch control horns. If the mast or transmission let go, the blade roots would rise up while the pitch links remain at the same point.
This would produce a brief period of low or even negative pitch. Kind of matches the footage at the 10 sec mark when the coning angle of the rotor disk goes negative.
I think the missing red blade flapped down enough to contact the fuselage and sheared off at the hub.

[212man]

It seems it was on a test flight after “major repairs”. I assume that means Heavy Maintdnance.

[Sanus]

The Surion fleet has only recently returned to flight following a prolonged grounding due to the Norwegian 225 accident. They share a common MGB. This is terrible news.
RIP to those departed.

[evil7]

To me it looks that the rotorhead shears off after one of the remaining blades hits the blade that departed. So more a „sudden stoppage“ failure. What do you think?

[Octane]

There was a big change in tail rotor rpm also. I'm going cross-eyed trying to tell if it was immediately before or simultaneous with the main rotor breakup/ separation.
Looks like first a rotor blade took out the windscreen with a simultaneous drop in TR rpm, then rapidly followed by main rotor separation.

[hoss183]

The cone angle definitely goes very suddenly negative just before the break up, for me thats the cause. So perhaps a collective control link problem?

[aheoe26104]

I have NEVER seen a MR Mast shear off like that!!! I also see a very abrupt change in RPM at 17 sec.

[SASless]

While you Video Geeks are examining the video....consider the actions of the entire rotor system immediately prior to the apparent separation of the one blade from the Rotor Head if you will.

I am wondering how the Rotor System would react to a sudden stoppage of the MGB particularly in the way each Blade would react both individually and as an attached part of the whole Rotor Head.

If the MGB seized and the Mast sheared off.....that would also shear the Pitch Change Links I am thinking.

As that happens very quickly....the effect on the Rotor Blade movements would also be very rapid and should (I am guessing) transmit a somewhat common reaction to all of the Blades.

Meaning to me....the Rotor Head would act more or less in a common manner and not shed individual blades.

If that Rotor Head moved such that a single blade made contact with a strong object (say the fuselage) then I can see a single blade being lost from the Head.

Do you see the whole Rotor Head Tip Path Plane tilting in such a manner or are we seeing a single blade launching off for points unknown while the rest of the blades act in a common manner?

[Octane]

It's really odd. It's like the fuselage ascended through the rotor disc. A rotor blade strikes the roof of the forward fuselage, buckles mid span then hits the windscreen and separates. Then the rest follows.:sad:

[hoss183]

You have to use caution in determining rpm from video, aliasing can produce strange (even static) perceived rpm, as we see often on videos of rotors or props. It may be valid to say theres an rpm change, but whether it's positive or negative or how much is not really possible.

For me the accident sequence is:
- Sudden collective pitch change.
- 1 blade strikes fuselage & departs
- Out of balance rotor over-stresses the shaft and fractures

[NRDK]

Realise video can be deceptive with RRPM but there did look like a seizure & shock loading in the transmission just before the tragic detachment, the Tail rotor change may have been a signature of that. Tragic all the same.

[SASless]

By private message....a suggestion was made a Swashplate Bearing failure could also be a possible cause for such a tragedy.

[212man]

Whatever it was, it’s hard to imagine it happening on a test flight following major maintenance being anything to do with previous events.

[SASless]

Meaning there is a reason they are called "Test Flights"?

[OnePerRev]

The spindle fracture tells a big story.
This was not a repeat of the planetary failure chain of events, as I mentioned earlier, blades stay attached even after powered impact. Look at the tail rotor broom sticks, still attached. The separation is in a completely different spot, not at the conical housing, with struts and all.. No, I would strongly suspect that this started with the blade attachment shown broken in the photo.
fracture surface, even at the view shown, is not a clean shear, it has some jagged features on the aft side, and the area near it is clean from paint.
Then, there is an inward crushed area below and forward. This could be the indication of blade twist overload of the remaining segment of metal.
In this theory, crack exists, and is not detected, rigidity holds the geometry. Initial collective load is a "push" on push rod, blade twists, and crack opens further, BTM (Blade Twisting Moment). Damper loads contribute, possible to be complicit in root cause.
Airspeed increases, transitional lift allows collective to drop. Push rod "pull" begins local crushing, blade now unstable and flutters, before separating from rotor.
main shaft fractures from massive overload.

[gulliBell]

That was a difficult video to watch. I've never seen that before. I don't wish to see it again. Small mercy it was all over quickly for those aircrew on board. Only thing worse I can think of is the same thing happening from great height.

[Milo C]

If we didn't have enough whatching a 225 rotor autorotating alone.....now this. What's the chance to caption that on video?
Anyway, whatever are the causes, I find hard for Airbus to recover from these images. It's more emotional than rational now.
RIP

[SASless]

These kinds of videos are akin to watching a Mid-Air Collision occur.....have seen two of those!

Once seen.....they cannot be un-seen....ever.

[blakmax]

One per rev, the area near it is clean from paint. . I am intrigued by the loss of paint. It is unusual to completely remove paint like this. I am not familiar with this structure, but is there a chance it was bonded at that location?

Blakmax

[gulliBell]

...I am intrigued by the loss of paint...

Maybe, the primer simply didn't stick to the metal and the top coat of paint ripped it off the way it did when the spindle fractured.
Given it was a post maintenance test flight, why would they have needed 6 people on board?

[workhorse22]

Regardless of the reason for the mainrotor to detach, it's a known fact that Airbus is heavily involved in designing and delivering main components to this aircraft programme.
Korean Aerospace Industries (KAI) is the prime contractor. As the primary partner, EADS Eurocopter will provide technical assistance, and supply the rotor mast, transmission, and autopilot subassemblies. Eurocopter has a stake of 30% in the development phase, and 20% in the production phase

How many airbus designed rotor disk detachments can be accepted within a relatively short timeframe? Regardless of the root cause, I belive airbus has a MAJOR problem.
The design of this main rotor mast looks very like the 225 mast, but with only four blades. It seems only to have small differences with the drag dampers, de-ice arrangement and dome fairing.
Pitch links, MRH sleeve and blade horns seems identical to the EC225.

This is my take on this accident:

Watch closely at the photo in post 12, you will see the lower blade horn nut sheared off, most likely due to direct hit from a ruptured pitch link. The same pitch link has impacted the MRH blade sleeve and caused
a major deformation of the sleeve tube which subsequently ruptured sending the fwd blade at the time flying. The MRH can no longer sustain the vibrations and it detaches from the aircraft.

What can cause a pitch link failure? Pitch link damage? Swashplate seizure/failure? Scissor failure?

edit: I also noticed that the pitch link connected to the blade horn of the ruptured sleeve has sheared off at the top, while the other two visible pitch links has sheared off/got the eyebolt pulled out of the pitch link tube at the bottom.

Again Airbus will put the blame on the maintenance crew involved in maintaining the aircraft as usual or they're gonna rule this out as a military prototype crash not in any way related to any other aircraft on the market today. Case closed! :mad:

Rest in peace fellow aviators. :(

[Cyclic Hotline]

Is this the straight 332L2 transmission and rotor system?

[Jimmy.]

Is this the straight 332L2 transmission and rotor system?

It's similar technology. The gearbox integration and rotor system are KAI's design, according to an AH subsidiary.

Correction: the rotor hub is KAI's design.

[Pablo332]

Spindle wall thickness looks a bit thin.

Surface finish looks a bit bright for paint adhesion.

[Mee3]

This is my take on this accident:



What can cause a pitch link failure? Pitch link damage? Swashplate seizure/failure? Scissor failure?

edit: I also noticed that the pitch link connected to the blade horn of the ruptured sleeve has sheared off at the top, while the other two visible pitch links has sheared off/got the eyebolt pulled out of the pitch link tube at the bottom.

Again Airbus will put the blame on the maintenance crew involved in maintaining the aircraft as usual or they're gonna rule this out as a military prototype crash not in any way related to any other aircraft on the market today. Case closed! :mad:

Rest in peace fellow aviators. :(
That's a cheap slap on EC.

[blakmax]

Pablo 332. Surface finish looks a bit bright for paint adhesion.

This is my concern as well. I fail to see how paint can fail in this manner. I am a specialist in adhesive bond failure forensics and such a failure in an adhesive bond should ring alarm bells even if it is not a direct cause of the failure. I ask again if any part of that structure is adhesively bonded? If it was bonded then adhesion failures such as that are an extreme warning of exceptionally poor bond strength. If not, then questions must be asked about how paint can just peel off like that. Such a surface finish provides absolutely no environmental protection whatsoever. Adhesion failures in adhesive bonds or paint are indicative of exceptionally poor preparation processes. And before anyone suggests it, a crash event can never change the failure mode in adhesive bonds or paints. The interface is already exceptionally weak and impact can not cause such a change in failure mode.

Regards

Blakmax

[workhorse22]

That's a cheap slap on EC.

Not to be discussed any further here, but my trust in airbus has worn very thin after the 225 accident in Norway.
Can agree that the last assertion is a bit cheap, but the first is a fact from the 225 accident.

Is this the straight 332L2 transmission and rotor system?

Not many similarities with the L2 on this one, more similar to the 225 but with only four blades.
Sleeves, pitchlink, blade horn, droop restrainer support seems by looking at the pictures very similar to the 225.
The sleeves are actually shorter on the this aircraft compared to the 225, if you compare to the photo of the rotor head of the norwegian crash you will see it.
At last it's no doubt where they adopted the design from.

Pablo 332.

This is my concern as well. I fail to see how paint can fail in this manner. I am a specialist in adhesive bond failure forensics and such a failure in an adhesive bond should ring alarm bells even if it is not a direct cause of the failure. I ask again if any part of that structure is adhesively bonded? If it was bonded then adhesion failures such as that are an extreme warning of exceptionally poor bond strength. If not, then questions must be asked about how paint can just peel off like that. Such a surface finish provides absolutely no environmental protection whatsoever. Adhesion failures in adhesive bonds or paint are indicative of exceptionally poor preparation processes. And before anyone suggests it, a crash event can never change the failure mode in adhesive bonds or paints. The interface is already exceptionally weak and impact can not cause such a change in failure mode.

Regards

Blakmax

Paint peeling off is not uncommon in this area, at least not on the 225 which by the pictures seems to have used the same paint type, AH replaced this with a glossy light gray color after a while. Maybe they replaced the paint type only for civilian aircraft, I don't know.

[OnePerRev]

Good insight on the adhesion or lac there of.
Who has infinite this part? What material?

[OnePerRev]

Sorry. Auto correct got me. Information. (And lack)

[gulliBell]

..I fail to see how paint can fail in this manner...

Maybe they forgot to apply a primer to the bare metal before painting. Wouldn't be the first time it happened on a helicopter.

[Pablo332]

We are clutching at straws at this point, but that’s PPrune.

The latest AH paint finishes are water based, good for the environment. Unfortunately they behave like a plastic. In the old days corrosion could reasonably easily be spotted as the paint fell off. Now it’s cocooned in a surface finish that expands to accommodate any change in original profile. Not good for the engineering people, they would literally have to coin tap the surface finish.

A shiney surface finish is a painter’s nightmare.

Back to the plot. Shaft has failed big time, don’t know what I’m talking about but I’d say this incident is head related. Smoking gun probably No 1 sleeve failure due to corrosion/not thick enough in the first place or No 2 damper failure.

But as I said, this is the point where everyone has their 2C worth.

[AnFI]

strikes me that holding blades on with paint is questionable anyway

As Pablo332 says
"Back to the plot. Shaft has failed big time, don’t know what I’m talking about but I’d say this incident is head related. Smoking gun prob ably No 1 sleeve failure due to corrosion/not thick enough in the first place or No 2 damper failure."

Would they really save metal and design margins in such critical areas?
This is a flawed aspect of the twin engined concept.
All that payload spent carrying a spare engine and its associated inefficiencies around when it could be spent on something important.
#whatanfinshameforthosedeadpeople

[Mee3]

The latest AH paint finishes are water based, good for the environment. Unfortunately they behave like a plastic. In the old days corrosion could reasonably easily be spotted as the paint fell off. Now it’s cocooned in a surface finish that expands to accommodate any change in original profile. Not good for the engineering people, they would literally have to coin tap the surface finish.
Totally not true. Water based paint are more brittle and more easier to fall of when attaching surface varied.

[rotor-rooter]

Helicopter engineer defends Surion after Pohang crash-INSIDE Korea JoongAng Daily (http://koreajoongangdaily.joins.com/news/article/article.aspx?aid=3051932)Helicopter engineer defends Surion after Pohang crashAug 16,2018https://pds.joins.com/jmnet/koreajoongangdaily/_data/photo/2018/08/15185514.jpg이미지뷰 (javascript:void(0))Hwang Jeong-seon, A former professor at the Air Force Academy and researcher at the Agency for Defense DevelopmentControversy still swirls over possible technical defects in the Korean military helicopter that crashed on July 17 in Pohang, North Gyeongsang, killing five Marines on board.

The helicopter in question is the MUH-1, or Marineon, a modified version of the KUH-1 Surion. It was the product of a strenuous four-year development process that cost more than 1.3 trillion won (＄1.1 billion). Over 90 of the helicopters have been deployed nationwide.

A probe consisting of civilians, military and government officials is currently underway to investigate the causes of the crash, focusing on possible technical defects that may have led to the helicopter’s rotor breaking off from its fuselage just four to five seconds after takeoff.
The accident has given credence to critics who once called the Surion a “tin can chopper” due to its frequent mechanical defects. Voices have also emerged linking the helicopter’s potential faults to possible corruption in the defense industry.

Hwang Jeong-seon does not agree. He participated in the Surion’s development for six months after it began in January 2007 up until its completion in June 2012. A former professor at the Air Force Academy and researcher at the Agency for Defense Development, Hwang worked in the Korean Helicopter Program specializing in appraising static and dynamic loads and crashworthiness. He says it was an honor for him to participate in the development of the first domestically manufactured chopper in Korean history.

Though he retired in May, Hwang remains devoted to helicopter research, saying that he wants to be remembered as a person who made a good chopper. He says the current atmosphere in his industry is strained, and there needs to be more encouragement to those who built the country’s first helicopter.

The JoongAng Ilbo asked him about the development of the Surion at its offices on Wednesday.
Below are edited excerpts of the interview.

Q. What do you think are the causes of the crash?

A. First, I would like to express my condolences to the deceased as well as to their families. I have also served in the Air Force and am aware of the pain that comes with losing fellow comrades in the line of duty. Reports have said the recent accident was similar to the Super Puma helicopter crash in Europe, but I don’t concur. The Marineon’s rotor blades spin between 270 revolutions per minute (rpm) and 4.5 revolutions per second. Before the entire rotor detached from the chopper, one of its blades was seen breaking off. If this happens, the chopper is bound to lose balance and its weight will be pushed to one side. But it is wise not to make any foregone conclusions before the investigation.

Analysts often cite problems with the performance of the Surion, from which the Marineon was based on, as related to the recent accident. What do you think?

I want to stress that the Surion and Marineon are different helicopters. I can’t go into the details since I did not participate in its development, but the Marineon was adapted from the Surion after accounting for the Marines’ operational conditions. Many parts of it were modified or added, such as adding an anti-corrosive coating, foldable rotor blades for naval storage, inclusion of a supplementary fuel tank for longer flights and a tactical air navigation system. Usually when an aircraft model is developed, a variety of different offshoots eventually emerge suited for different needs. Because of this, whenever issues emerge with different models, we cannot simply attribute it to problems with the original machine.

Years ago, there were reports about issues with freezing in the windshield of the Surion helicopter. What do you make of this?

The helicopter possessed the capability to remove ice on its windshield since its development. Any defects or issues were resolved after two freezing tests we conducted throughout the months last winter in Michigan, and airworthiness authorities are currently reviewing changes made to the original designs. On top of the glass in front of the pilot seat, there is a cutting device that cuts away obstacles if the helicopter gets stuck in electric wires. We installed heating cables on the device to prevent ice from forming and breaking off and entering the engine. There is no precedent for something like this anywhere in the world.

Do accidents like this happen in the early development stages in other countries?

When we say helicopter, the model that comes up in most people’s minds is the UH-60 Black Hawk chopper, which the Army possesses. In the early 1970s, a prototype of the UH-60 developed to compete in the U.S. Army’s Utility Tactical Transport Aircraft System competition crashed in the mountains during a flight test while carrying armed personnel. There were light injuries to the passengers, but the chopper returned to base after changing its damaged rotor blades on the spot. This accident effectively led the U.S. Army to select the UH-60 as the winner of its competition. Accidents can happen, but the survivability of the aircraft was valued.

What do you make of the survivability of the Surion?

There is a word we often use as jargon called “crashworthiness,” which refers to the level of survivability guaranteed in a potential crash. This is a design principle which is kept in mind to ensure that the aircraft’s pilot and passengers survive in a variety of potential accidental circumstances. The Surion was designed to possess a higher crashworthiness in relation to the AS 532, from which it was based on. It is on a level comparable to the UH-60 Black Hawk.

Some point to the Surion chopper as a symbol of corruption in the defense industry and call it a tin-can chopper. What would you say to such criticism?

Evaluations of the chopper should be more nuanced than a simple good or bad label. There should be a greater range of options given for evaluations. But currently, the problem is that only negative voices dominate. In some cases, people accuse you of political bias if you are willing to defend the Surion. But how can there be political partiality when it comes to the development of defense armaments? A host of agencies, including three defense firms — the Agency for Defense Development, Defense Agency for Technology and Quality and the Korea Aerospace Industries — as well as the Army and the Defense Acquisition Program Administration were involved in the Surion’s development, as well as countless other technicians and scientists of subcontracted companies. It is unfair that all these people are being attacked.

Do you think plans to export the Surion chopper will be affected by the accident?

The aircraft has enough competitiveness in the international market due to its cutting edge avionics display systems and automatic engine control mechanism. As I said earlier, one must not equate the Surion and Marineon as the same helicopter. If the mechanical cause of the accident is attributed to machinery shared by the two choppers, we can make that conclusion, but we shouldn’t make any hasty judgments.

BY KIM SU-JEONG [[email protected] ]

[rrekn]

Interim report is out, cites defective main rotor mast supplied by Airbus

https://www.defensenews.com/global/asia-pacific/2018/09/12/defective-rotor-parts-from-airbus-blamed-for-fatal-south-korean-helicopter-crash/?utm_source=vertical-daily-news-news-from-the-web&utm_campaign=vertical-daily-news&utm_medium=email&utm_term=news-from-the-web&utm_content=V1

[Unregistered_]

More very disturbing but familiar video footage.
Everything including the coning angle looks fine, then suddenly the disk goes completely flat.
One blade then sweeps very low, a couple more rotations, then lets go, followed by the mast..the last part of what looks like four distinct events.

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/1280x720/pic1_f3fd06b24841a3a0f23422ea19e8dcec59ba677a.jpg

Normal coning angle on departure.
https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/1280x720/pic2_a8df0880cd7acce2796c24bc23badda137d01430.jpg

1 second later, the disk goes completely flat.
https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/1280x720/pic3_6e5889cc601487cb1ca398ac999fc64093550f8b.jpg

One blade flies very low
https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/1280x720/pic4_2d736dd5efe6249e85dde532058c221796072654.jpg

...then lets go.
https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1280x720/pic5_7bef2c24deb04d8cb358d14dc5c9be9c8722e4b2.jpg

followed lastly by the mast.

[joonkim83]

Hello. Do you remember the fatal accident of Korea marine helicopter in July ?
6 marines were dead for this crash.
Ministry of defense officially said that was the crack of rotor mast which was made by Aubert&Duval (france company)

“The interim results will be reported to the Ministry of National Defense this week before announcing them by Sept. 17,” a Marine Corps spokesman said. “Investigators have tentatively concluded that cracks in the rotor mast of the Marineon was a main cause of the crash.”

A member of the investigation team told Defense News that his team had found defects in a set of three rotor masts imported from Airbus during parts inspections.

“We found that the strength of a set of three rotor masts imported from Airbus was far lower than the standard, and one of them were confirmed to have been fitted in the crashed Marineon,” the investigator said, speaking on condition of anonymity. “Two other rotor masts in question were fitted in two other Surion troop-carrying helicopter[s] flown by the Army.”

The investigator said Airbus officials have confirmed the defects in the rotor masts.



Their scenario is..

the cracked rotor mast was broken by vibration > one of the rotor blade hit the body and took off > the rest of the blades and mast were took off from head

But as I see this picture and video clip, one blade took off from head first





it is not the blade, that is the blade sleeve! one of the blade sleeve was entirely cut off.
Even though the blade hit the body, blade sleeve could be cut off like that ????
I think that the blade sleeve had also fatigue crack.

Korea ministry of defense didn't investigate on this blade sleeve. they only blame on Airbus helicopter with the cracked rotor mast.
But the rotor blade parts for KUH made by KAI (Korea Aerospace Industries)

[Cyclic Hotline]

I don't have access to this site to get the entire story, but it appears to be headed to the Singapore International Arbitration Centre for resolution.
https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/945x923/image_7f081f2adf303fb4d052e5a59567f48f2fa4791b.png