Indian Military Helicopters

Cybaru · Post by **Cybaru** » 12 Jan 2018 01:18

shiv wrote:This accident is a classic example of how new and unexpected things turn up when a machine goes into regular use. Now that part will be inspected for stress failure in all the Dhruvs in service.

+1 New SOP for evaluation will take place and perhaps a redesign or two. Unfortunate someone got hurt, hope they are okay and recover quickly. Luckily it isn't a issue with the core machine!

Indranil · Post by **Indranil** » 12 Jan 2018 01:45

I did not realize that there were bolt holes in there.

ramana wrote:JayS, I was wondering if the stress guys reviewed the design? Putting bolt holes at the point where the bending moment is the highest for a cantilever seems a design weakness.

That is my thought too. But I am not a structural engineer.

ramana wrote:Need to look at the mating boom part. Both will tell the story.

ramana · Post by **ramana** » 12 Jan 2018 03:47

Those fasteners are called pin(bolt) and collar fasteners. The brand name in US is Hilok. They have a predetermined preload based on the collar breakoff and are very effective fasteners. Either High tensile strength steel or Titanium.
Looks like 1/4" fasteners.

The joint seems to be transition between composite (beam part) and base adapter.

The outer beam looks graphite epoxy see the rattle snake pattern hatching?
The beam failed in the base material (grey part). The tension in the upper part caused the material to fail in bearing.
The pins did not fail.

hnair · Post by **hnair** » 12 Jan 2018 06:24

From the pics, not just the none-metallic outer pylon, even the inner metallic one also seemed to have snapped off at the bolt holes.

JayS · Post by **JayS** » 12 Jan 2018 09:43

hnair wrote:From the pics, not just the none-metallic outer pylon, even the inner metallic one also seemed to have snapped off at the bolt holes.

Its actually the inner one which failed. The outer part would have had a clean separation if not for the two intact bolts at bottom. Note that this part is upside down in the picture. Its material failure of the base block. All bolts are intact.

I was thinking of single line of bolts. Now that we see multiple lines, its clearly a block shear type of failure. Only its more like block tensile failure. Block shear is common type of failure seen in even steel structures. The base block material doesnt seem to be ductile or else we should have seen elongated bolt holes. I cant see them. I have been resisting the feeling that its composite too. Because it makes more sense to have a metallic block there.

Ramana Sir, its definitely CFRP. In the first picture itself we could make that out from remaining portion of it. Thats how I colcuded its Composite right in the beginning.

ramana · Post by **ramana** » 12 Jan 2018 10:58

Exactly. Chopped fiberglass and not Metal
Then failure can be explained.
It's difficult to control it's properties.

ramana · Post by **ramana** » 12 Jan 2018 11:01

So it's a CFRP load transition block to which composite boom is attached with those pins and collars. That explains the pin and collar which are common for composites.

JayS · Post by **JayS** » 12 Jan 2018 11:56

ramana wrote:Exactly. Chopped fiberglass and not Metal
Then failure can be explained.
It's difficult to control it's properties.

ramana wrote:So it's a CFRP load transition block to which composite boom is attached with those pins and collars. That explains the pin and collar which are common for composites.

OK, some misunderstanding.?? I was referring to the boom, not the base block. The boom is definitely CFRP. I have half mind to think the base block is also composite looking at the type of failure, but from the exposed failed material section it doesn't look like composite. Also logically speaking one would use metal base block there. It looks like metal but failure looks brittle which is bewildering.

Glass Fibre (GFRP) will not be preferred for Aerospace application where the member is any type of load carrying let alone the primary load carrying member as its in this case. GFRP typically is used in places where high strength is not needed, weight is not critical, deflection is not critical factor, higher toughness is desired and most essentially cost is a important factor. Typically GFRP have lower stiffness but higher toughness. Some type of glass fibre can match Ultimate strength of CFRP but CFRP wins hands down in weight factor, but its significantly costly too. Only place where GFRP might be preferred over CFRP is in Radome due to their EM properties. Chopped GFRP is even cheaper type used in non-critical locations only, even in Auto industry.

One possible explanation could be quality issue of the metal in some batches. Material properties vary in a band and once in a while some batch tends to have lower than desired properties. Or it could be due to issue in Heat treatment.

Zynda · Post by **Zynda** » 12 Jan 2018 14:32

The failure is quite probably fatigue induced. Marks are clear. I will try to post a pic highlighting striation marks along with locations where crack initiation happened when I get some time.

shiv · Post by **shiv** » 12 Jan 2018 16:14

Zynda wrote:The failure is quite probably fatigue induced. Marks are clear. I will try to post a pic highlighting striation marks along with locations where crack initiation happened when I get some time.

Would appreciate that - I also saw a window/tear in the metal inboard of the actual break and felt it might be fatigue.

ramana · Post by **ramana** » 13 Jan 2018 00:51

Would like to see that.

JayS,

Chopped fiber also won't see the fiber. We need a good picture.

ramana · Post by **ramana** » 13 Jan 2018 01:40

shiv If you can please post that too. It could be load transfer to the helicopter structure.

Philip · Post by **Philip** » 13 Jan 2018 13:16

ONGC helo with 2 crew + 5 passrs . missing after taking off from Juhu to Bombay High around 1030am today.No news of helo type.

Indranil · Post by **Indranil** » 13 Jan 2018 13:40

Paanwalla, chai walla, cigarette walla everybody telling me that the boom is qualified for two persons at a time.

Those of you who can access the manual can check for yourself.

Meanwhile Army and HAL maintaining dignified silence as is desirable now.

I deliberated a lot before sharing this. But I am doing this because many worthies in Twitter land jumping up and down without knowing anything.

I will say no more on the subject.

Indranil · Post by **Indranil** » 13 Jan 2018 13:58

Philip wrote:ONGC helo with 2 crew + 5 passrs . missing after taking off from Juhu to Bombay High around 1030am today.No news of helo type.

Don’t know why the type matters. But it was a dauphin.

shiv · Post by **shiv** » 13 Jan 2018 18:12

ramana wrote:shiv If you can please post that too. It could be load transfer to the helicopter structure.

Ramana - you can see a jagged buttonhole tear on the top right of the inner metal rectangle just inboard of the line of shear in the image posted earlier above. The tear runs parallel to the shear line. as if the metal has been stretched repeatedly.The outer part is obviously fibre
https://pbs.twimg.com/media/DTOtlHbVAAAhuMS.jpg

Rakesh · Post by **Rakesh** » 14 Jan 2018 00:07

https://twitter.com/sandeepunnithan/sta ... 2554017792 --> Horrific from any angle. Another VIDEO of the January 9th ALH Dhruv slithering accident.

Rakesh · Post by **Rakesh** » 14 Jan 2018 00:09

https://twitter.com/sandeepunnithan/sta ... 6839389185 --> Chopper fall medical situation report. Commando #3 discharged on second day. Commando #2 - some months - back injury. Commando #1 minor injury. Para SF rules!

https://twitter.com/reachanshul/status/ ... 2617925633 --> Sandeep, looks like the 3rd commando fell on the 2nd one and part of the boom landed on both. Wish them an early and full recovery. Also a relook at SOPs.

https://twitter.com/sandeepunnithan/sta ... 1288084480 --> Yes. Hence the serious nature of #2's injuries. He'll be out in a few months hopefully.

ramana · Post by **ramana** » 14 Jan 2018 01:25

Shiv, I see it now. The tear or crack is due to the tension load. They grow only in tension loads. The tension load failed the joint at the pins. Or else it could have torn at that year or shear line.

As JayS says definitely a flaw in the material manufacture. Could be inclusion in ingot, heat treatment , flaws during the extrusion or rolling.

Thanks for pointing it out.
Material is a suspect.

I wonder if there was a hidden flaw that caused this crack to grow under repeated loading. This is the fatigue part. But the metal broke for some other cause at the pin holes.

Deejay what is the standard person weight with equipment in Indian military helicopters?

Indranil · Post by **Indranil** » 14 Jan 2018 02:16

Rakesh wrote:https://twitter.com/sandeepunnithan/sta ... 6839389185 --> Chopper fall medical situation report. Commando #3 discharged on second day. Commando #2 - some months - back injury. Commando #1 minor injury. Para SF rules!

https://twitter.com/reachanshul/status/ ... 2617925633 --> Sandeep, looks like the 3rd commando fell on the 2nd one and part of the boom landed on both. Wish them an early and full recovery. Also a relook at SOPs.

https://twitter.com/sandeepunnithan/sta ... 1288084480 --> Yes. Hence the serious nature of #2's injuries. He'll be out in a few months hopefully.

The best news I have read. With Sandeep U reporting, I can trust it. Otherwise, the news on the condition of the jawans has been all over the place.

I had a sliver of hope when I saw the third guy fall. He was neither vertical nor horizontal, which is the best position to absorb shock.

Haridas · Post by **Haridas** » 14 Jan 2018 09:39

Manish_P wrote:I was referring to the brave unknown (to me) co-pilot, Shiv ji.

Unless i have read the post by Deejay sir wrong, Air Commodore P Sharma, the pilot, is the brother of BRF poster Arun_S.

Yes, real brother.

JayS · Post by **JayS** » 14 Jan 2018 14:19

ramana wrote:JayS,

Chopped fiber also won't see the fiber. We need a good picture.

I would expect fibres on the failed section whether its chopped or weaved. Generally glass fibres are chopped to like a inch or two length. (Using a finely chopped fibres would be basically defeating the whole purpose of using composites because it would give isometric properties more like metal). We should definitely see fibres poking out, it if was glass fibre.

In fact it seems metals are quite capable of this kind of brittle-like abrupt failure in the event of catastrophic failure without any appreciable signs of plastic deformation. Typical fatigue failure is a good example. But why I was not able to think of it as an obvious explanation is I cannot think how can such simple design fail like this without any indications by significant deformation. A good design, at least for such places where lives are at stake and are such simple regulation bolt joints, should have bb such that the metal would yield giving significant and sufficient warning of failure before it breaks completely. My most expected cause is some defect in the material, the material not being up to the specs (in other words quality control failure).

Also, when I said these kind of designs have significant FoS, it didn't mean by the single figure we use for defining Ultimate load using 1.5x Design load. The design methodology for bolt designs is typically based on simple theory which is highly conservative. I would have designed this particular bolt joint using hand calculations. That keeps it simple and conservative. When you design for 200kg the method ensures that it would withstand perhaps 400-500kg load without any kind of failure. On top of it you add FoS.

shiv wrote:
ramana wrote:shiv If you can please post that too. It could be load transfer to the helicopter structure.
Ramana - you can see a jagged buttonhole tear on the top right of the inner metal rectangle just inboard of the line of shear in the image posted earlier above. The tear runs parallel to the shear line. as if the metal has been stretched repeatedly.The outer part is obviously fibre
https://pbs.twimg.com/media/DTOtlHbVAAAhuMS.jpg

Shiv, the top part in that picture actually would be in the bottom when its attached to the base block, as I explained earlier in one post. Two bolts in that location still remained attached to the base block with a part torn off of the outer boom composite part, because that part is under compression. The failure would have started at the top since its a classic 'bending in cantilever' case. (the picture itself looks like its rotated upside down from its true orientation or the person held mobile camera upside down while taking snap. I think I see the floor tile on the top).

JayS · Post by **JayS** » 14 Jan 2018 14:45

Indranil wrote:Paanwalla, chai walla, cigarette walla everybody telling me that the boom is qualified for two persons at a time.

Those of you who can access the manual can check for yourself.

Meanwhile Army and HAL maintaining dignified silence as is desirable now.

I deliberated a lot before sharing this. But I am doing this because many worthies in Twitter land jumping up and down without knowing anything.

I will say no more on the subject.

1. If it was indeed qualified for only two persons, that itself is a bad design decision I would say. It would be nearly impossible to maintain that kind of idiotic SOP in the frenzy of operation (even in multiple demonstrations from Dhruv itself 3 persons on the rope situation has happened). Plus going from 2 to say 4 was not going to make them put on very many kilos in the boom. I would say both IA and HAL are stupid if they accepted this as a valid thing. I would have never. (Note that I am not against SOP of having 2 on rope at a time, its generally followed to avoid collisions. I was seeing a doc from US Army for heli insertion - FRIES, it put only one condition on number of people on rope - 3mtr separation to avoid collision. (Sorry to use US reference, they are very easy to find unlike anything related to Indian forces/Systems). But thats not the same as designing the boom for only 2 soldiers' weight).

2. Even if we say it was a valid design decision with 2 people on the rope at a time only and we consider in addition that the design was so perfect that it would fail even at 101% of the design load, that there was no margin whatsoever, the part failed with only 3 people loading it. (see the video Rakesh posted carefully at 0:30sec, only 3 at a time on the rope. The third one was almost on the ground just a fraction of second more and he would have landed alright leaving only 2 soldiers on rope). It should not have catastrophically failed at 150% of the load. (I saw the rope specs usd by US forces for Heli insersion/extraction, its design load is ~1600kg, breaking load is whopping >7000kg. Thats the kind of FoS one should have in such simple things which are simple but critical for life of soldiers). The design philosophy in Aerospace allows FoS of 1.5 only for the loading situations which are expected only once in a lifetime of the entire fleet, that is numerically close to 1 in a billion. The design load itself (to which this 1.5 is multiplied with to get ultimate load) is expected to occur only once in a life for a single aircraft/heli or 1 in a million. And even then some systems which are critical such as engine mounts, are not allowed to fail catastrophically leaving the functional requirement unfulfilled (thats achieved by having a separate standby backup). So with everything remaining within real life limits, the boom should not have failed like it did with 3 persons even if it was designed for only 2 at a time.

3. Yes, its stupid to castigate HAL on this issue. Such type of accidents do happen despite all the precautions. No one wants blood on his hand. But shit happens. But at the same time HAL has to take the responsibility and correct the possible errors, loopholes that might have led to the situation. There are many things that could have gone wrong. An enquiry would uncover possible issues and they will be plugged.

Lets wait for the enquiry report if it ever comes in public.

PS: I saw Angad Singh (photographer guy) tweets where he says earlier the rope was attached to two points, boom and near the door. Now it was only attached to boom, so no backup.

Indranil · Post by **Indranil** » 14 Jan 2018 17:10

No Jay, US special forces have a strict restriction of no more than three guys on the rope at any given time up to a maximum of 600 lbs. Even for heavy helis like the CH-53.

Weight saving on the boom is not an issue here.

shiv · Post by **shiv** » 14 Jan 2018 17:19

JayS wrote: Shiv, the top part in that picture actually would be in the bottom when its attached to the base block, as I explained earlier in one post. Two bolts in that location still remained attached to the base block with a part torn off of the outer boom composite part, because that part is under compression. The failure would have started at the top since its a classic 'bending in cantilever' case. (the picture itself looks like its rotated upside down from its true orientation or the person held mobile camera upside down while taking snap. I think I see the floor tile on the top).

Yes that is exactly what it appears like.
Here is the Helo side:
https://pbs.twimg.com/media/DTPDfkTU0AEk4Qi.jpg
On the helicopter side the rectangular boom shows a clean break on the upper part and one side and the tear is on the opposite side. The torn part would have been last to give I guess. That bar is subjected to what I think are called "torsion" loads because the rope with men is always swinging and not hanging directly down with no movement. It has been stressed round and round and round until 2 sides have failed at the bolts and the rest has simply torn off.

JayS · Post by **JayS** » 14 Jan 2018 19:19

Indranil wrote:No Jay, US special forces have a strict restriction of no more than three guys on the rope at any given time up to a maximum of 600 lbs. Even for heavy helis like the CH-53.

Weight saving on the boom is not an issue here.

Indranil, do you think that restriction is in anyway because of limitation of any component in supporting more than 3 soldiers..? Or that because of such SOP (due to some other reason) the heli designers design the FRIES system for 600lbs load..?

Raman · Post by **Raman** » 14 Jan 2018 19:25

Just 600lb for three operators and their equipment? These guys carry easily lug around 75 to 100lb each in addition to their regular weight, which I'm guessing is going to be about 200lb each.

If the limit is 600lb they would have to limit to two or even just one in extreme cases.

Karan M · Post by **Karan M** » 14 Jan 2018 19:26

JayS, what you are supposing is that only this demo saw three people on the boom. What if this has happened repeatedly because therebwas sone sort of miscommunication that >2 people could be on the boom. And if this occurred repeatedly wouldn't the metal age/ fatigue faster? Could that be a reason, and cant SOPs be changed.

Indranil the answer needs to be out on Twitter because this is arguably a very bad indictment afainst HAL QC otherwise.

SriKumar · Post by **SriKumar** » 14 Jan 2018 21:27

The picture of the broken boom shown inlined in Indranil's post (above) quoting ramana (
https://pbs.twimg.com/media/DTOtlHbVAAAhuMS.jpg) , seems to be a different broken boom than what is shown here https://pbs.twimg.com/media/DTPDfkTU0AEk4Qi.jpg bosted by shiv.
One can count 6 (or 8 ) bolts along the perimeter of the failed boom in ramana's picture. There are no bolts along the perimeter in the link by shiv. There are other bolt locations too that look different. Is each one the mating side of the other? ~~If so, it is not clear that they fit each other.~~
Added later: Seems plausible that they are mating portions of a single part.

srai · Post by **srai** » 14 Jan 2018 21:43

It looks really long and thin to take too much load.

srai · Post by **srai** » 14 Jan 2018 21:49

SriKumar wrote:The picture of the broken boom shown inlined in Indranil's post (above) quoting ramana (
) , seems to be a different broken boom than what is shown here bosted by shiv.
One can count 6 (or 8 ) bolts along the perimeter of the failed boom in ramana's picture. There are no bolts along the perimeter in the link by shiv. There are other bolt locations too that look different. Is each one the mating side of the other? ~~If so, it is not clear that they fit each other.~~
Added later: Seems plausible that they are mating portions of a single part.

Both the images don't look like they are from ALH. Look at the background to what they are attached to and the above pictures. Looks totally different.

shiv · Post by **shiv** » 14 Jan 2018 21:49

SriKumar wrote: Added later: Seems plausible that they are mating portions of a single part.

Yes. They are mirror images.

shiv · Post by **shiv** » 14 Jan 2018 21:51

srai wrote: Both the images don't look like they are from ALH. Look at the background to what they are attached to and the above pictures. Looks totally different.

One is the end of the boom and the other is the helicopter side. You need to turn one image 180 degrees to "mate" them

shiv · Post by **shiv** » 14 Jan 2018 21:54

A man with a total weight of 90 kg (man+ eqpt) hanging off the end of that boom would IMO be putting forces in the region of 1000 kg plus on the part where the boom is attached. That boom is at least 1.5 meters long
https://upload.wikimedia.org/wikipedia/ ... aining.JPG.

Rishi_Tri · Post by **Rishi_Tri** » 14 Jan 2018 23:48

https://www.youtube.com/watch?v=OvT1gm_I5lY

A little old but good video on LCH. Gives data points on performance.

Indranil · Post by **Indranil** » 15 Jan 2018 01:15

Karan M wrote:Indranil the answer needs to be out on Twitter because this is arguably a very bad indictment afainst HAL QC otherwise.

Karan,

I am not on Twitter. And even if I were, I wouldn't write about it. A few journalist have been made aware of the 2-person limit. They won't write about it. I don't know what their motivation is, but I am with them. It is not the right time or place. But when you hear "better SOPs have to emerge", know what they are talking of.

I am a big critique of HAL's marketing and QC. Forget the fixed wings, how they botch up sales of ALH, arguably one the best helis in its class is beyond me! However things are starting to look up. HAL is now taking up orders with PBL support package, i.e. a minimum availability guarantee. That is what is jacking up Mk 1A's prices to 400 crores per plane .

But, I hate it that the worthies on Twitter, the so-called bastions of patriotism in this country immediately jump to "Dhruv/ALH maimed our soldiers. We deserve better (aka imports)". You can compare the headlines of ONGC accident and the Army Day accident. How many even know the correct event and location where latter happened? But, everybody can tell you that an ALH/Dhruv was involved (and caused it!). Even here, are we even discussing the ONGC accident? 7 people died on a routine sortie on a clear morning! One poster asked about the make of the heli. When revealed that it was a Dauphin, no questions followed!

Hakeem, with his years of watching the military has rightly said: out of this accident will emerge better equipment and SOPs. Something else that I would like to emerge out of this is putting the pseudo-patriots/nationalists in their rightful place.

Karan M · Post by **Karan M** » 15 Jan 2018 04:51

Indranil, even I am not on twitter, but here is the issue:

I am a big critique of HAL's marketing and QC. Forget the fixed wings, how they botch up sales of ALH, arguably one the best helis in its class is beyond me! However things are starting to look up. HAL is now taking up orders with PBL support package, i.e. a minimum availability guarantee. That is what is jacking up Mk 1A's prices to 400 crores per plane .

The PBL stuff is great news.

But, I hate it that the worthies on Twitter, the so-called bastions of patriotism in this country immediately jump to "Dhruv/ALH maimed our soldiers. We deserve better (aka imports)". You can compare the headlines of ONGC accident and the Army Day accident. How many even know the correct event and location where latter happened? But, everybody can tell you that an ALH/Dhruv was involved (and caused it!). Even here, are we even discussing the ONGC accident? 7 people died on a routine sortie on a clear morning! One poster asked about the make of the heli. When revealed that it was a Dauphin, no questions followed!

Exactly my point! A lot of the commentators are shills (excluding the alarmed ex-forces guys). If above has to be addressed then we have to change things:

I am not on Twitter. And even if I were, I wouldn't write about it. A few journalist have been made aware of the 2-person limit. They won't write about it. I don't know what their motivation is, but I am with them. It is not the right time or place. But when you hear "better SOPs have to emerge", know what they are talking of.

There is no better time or place than to be open and transparent about these issues from the beginning itself.

Now ALH is again besmirched with another attack and HAL given its prior record in managing media, appears to come out clueless and shoddy.

Cybaru · Post by **Cybaru** » 15 Jan 2018 05:30

Before we start a twitter war about this being tested for 2 soldiers only, can we really confirm its there?

srai · Post by **srai** » 15 Jan 2018 06:02

Cybaru wrote:Before we start a twitter war about this being tested for 2 soldiers only, can we really confirm its there?

We would need to know the design load limits qualified for that slithering boom extension and the designed fatigue life tested.

Other questions:
What the was the load factor during that particular event?
How many times that particular piece was used under what conditions?
When was the last time it was checked for failures? What is the maintenance schedule for it? What sort of failure analysis are done on it to keep it safe for use?
What was the standard SOP and has that been in practice at all times (or most times)?
How are other booms doing under fleet-wide checkup post this accident?

etc.

Not a simple straight-forward answer. After a detail investigation, we might come to know the series of events that lead to the structural failure of the boom. It's too soon to pass any judgement on this matter without knowing all the details.