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Indian Military Helicopters

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Re: Indian Military Helicopters

Postby JayS » 16 Jan 2018 19:53

Karan M wrote:
JayS wrote:
Karan, I am questioning the wisdom in designing and qualifying the rope system for only two persons at a time (which is what Indranil is pointing to) precisely considering the real life limitations on maintaining such SOP in strictest sense, especially in the actual war scenarios. There are multiple photos/videos which shows Dhruv has seen more than 2 persons on the rope in past. As I understand the separation in soldiers on rope is followed to avoid collisions. In my limited google search I could not find any reference to "design limits of insertion system putting limits on number of people on rope".


Typically, the design would have followed SQR which means the item either flowed directly from the SQR or was a result of any other SQR driven requirement, either way, it would be signed off by all stakeholders. I suspect it was not an issue all these days, because of the SOP, of using a second attachment point. Somewhere, in operations, it was discovered that SOP caused a time delay or was inconvenient and hence it was changed, precipitating this incident. Of course, this is all speculation at this point and the IA will find the real reason working with HAL.

To get back to my original point, If you have an engine power rating specified which means an engine of some weight, and so forth, and that means a bracket of some weight/rating, the designer would take the decision and services would not be so interested. Its the designers issue after all, but in an issue like deciding how many people on a hoist, there is no way HAL would take that decision on its own. That information has to come from the user.

Having an SOP of two soldiers on rope by Indian Army does not/should not imply "HAL designed the system only for 2 persons".


It typically would, because one thing I have realized about our designers & institutions is they are very risk averse about overpromising given past issues and hence will follow the SQR to the T.

Take the Tejas having R60 vs R73E for instance.

If HAL indeed do this then the wisdom behind this design decision is very much questionable. I would think its rather in favor of HAL not to point out that the boom was only qualified for 2 people. Because that's an absurd thing to do on the designer's side. Why would anyone design it only for 2 persons when designing it for even 4 or 6 is not going to add to the weight any significantly while making the design far more robust..?


Its hardly absurd, its sticking to the mandate very precisely and then what happens thereafter is another story altogether.

Wherever the designers decide to "out think" the SQR there is a tradeoff elsewhere and getting that cleared means more paperwork, more permissions from the services, more cribbing through out the design chain and your own people, easier to stick to a narrow mandate and be done with it.

Which is what makes the requirements projection so crucial.


Karan, SQR only specifies certain requirement and not how it is to be achieved. That's a designer's decision. Also lets not compare this with something like an engine bracket. Engine bracket design has far more involved design methodology. This particular bolted joint we are talking about can be easily designed with hand calculations based on simple conservative formulae. There is hardly any performance penalty by increasing load from say 200kg to 400kg. Its not going to increase weight by much, perhaps couple of kilos more on the metal component which failed.

Anyways, I have been trying to get the thing cleared that its highly unlikely to be a design issue, even if we consider its only designed for 2 person's load. I posted above, other references that show that's a valid design choice with some possible constraints forcing such decision and I stand corrected on that point. But at the same time I have noted that the weak links are the small metal links/clips, attachment points of rope to boom etc. Rope itself is pretty strong and I am very sure that the metal/composite components such as the boom itself are also far more conservatively designed.

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Re: Indian Military Helicopters

Postby srai » 16 Jan 2018 20:31

hnair wrote:...

We hopefully will know why this happened, considering there is this photo posted above by srai, which shows that along with the boom that snapped off, the rope is anchored on either the floor or pillar of the Dhruv. Did that anchoring also not work after the boom broke off?

Image


Valid point.

Here are more closer side views:
Image
Image

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Re: Indian Military Helicopters

Postby srai » 16 Jan 2018 20:56

Nice shot
Image

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Re: Indian Military Helicopters

Postby Karan M » 16 Jan 2018 21:51

JayS wrote:Karan, SQR only specifies certain requirement and not how it is to be achieved. That's a designer's decision. Also lets not compare this with something like an engine bracket. Engine bracket design has far more involved design methodology. This particular bolted joint we are talking about can be easily designed with hand calculations based on simple conservative formulae. There is hardly any performance penalty by increasing load from say 200kg to 400kg. Its not going to increase weight by much, perhaps couple of kilos more on the metal component which failed.


You are missing my point entirely. My point was that SQRs drive design choices & in some cases, the design choices can be done independently (eg the bracket example) since they are driven by a larger SQR which takes into account such down the road choices which have to be designer owned (services can't sit and say this should be x kg etc), whereas others require clarification or a direct point in the SQR itself (e.g. HAL won't come up with a 2 person/x payload for slithering ops on its own. At most it can do a literature study on its own OR have services provide what they want or have already on existing equipment). So, to claim a design decision is "easy" so it should be done, is not always the case, because the decision in some cases requires user involvement and that is not merely design ease of use, but also a lot of sign-offs required. For instance, will HAL decide the payload on each pylon is x kgs on its own even if the SQR says overall payload is X, or seek clarification because after all each pylon has to be rated for what the services will load on it (could be equipment in service or what they will procure). And even after that payload is known, they would have to go back to services to see what will actually be on it, after all, that integration needs to be taken into account to. Such stuff & back & forth creates interminable delays. From the viewpoint of the program manager he would prefer to minimize changes & hence low priority stuff (can we do this, even if it requires less effort and is more than SQR asked for) will almost always take a back seat in the Mk1 variant.

Anyways, I have been trying to get the thing cleared that its highly unlikely to be a design issue, even if we consider its only designed for 2 person's load. I posted above, other references that show that's a valid design choice with some possible constraints forcing such decision and I stand corrected on that point. But at the same time I have noted that the weak links are the small metal links/clips, attachment points of rope to boom etc. Rope itself is pretty strong and I am very sure that the metal/composite components such as the boom itself are also far more conservatively designed.


Which was my point that the design choice would have either been dictated by certain constraints or specific user input. Its unlikely that HAL did this choice on its own without user input OR it will make design choices because they happen to be easy. Given how process oriented our system can be & how even the smallest choice is discussed interminably, the ease of making an engineering choice is not the key determiner, IMHO but the fact whether it is signed off on by the user and whether the people involved in the process are willing to keep iterating on such choices or just go with "if its ok, don't fix it".

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 16 Jan 2018 22:48

Karan, have you seen the video from Patriot I have posted on Indian Army thread. See it you will like it.

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Re: Indian Military Helicopters

Postby Kartik » 17 Jan 2018 01:23

From AW&ST

BENGALURU—India’s state-run military aircraft maker Hindustan Aeronautics Ltd. (HAL) is working with French firm Safran Helicopter Engines to establish a unit in the southwest state of Goa for servicing military helicopter engines.

The two companies formed a joint venture in 2016 called Helicopter Engines MRO (HE-MRO) to provide maintenance, repair and overhaul services for Safran TM333 2B2 and HAL Shakti engines installed on HAL-built helicopters operated by India’s armed forces. But the project failed to gather momentum due to delays in the lease transfer process.

On Jan. 15, the Goa Industrial Development Corp. (GIDC) gave the necessary regulatory approval to the aerospace firm to begin work to build necessary infrastructure at the Honda industrial estate in Panaji city, Goa’s capital.

Once operational, HE-MRO will repair 50 helicopter engines per year in the country as well as those from other countries. After the formation of the joint venture, about 50 engineers were recruited, trained and certified by Safran Helicopter Engines. “We can ramp up to 150 engines in the near future,” a Safran official says.


HAL Chairman T. Suvarna Raju says it is useful to have an engine’s OEM as a partner in the venture.

“It will improve the average turnaround of engines, which means that one can make many helicopters ready for the armed forces,” he says. “It will also make it smoother to source components and spares currently imported from Safran.”

Officials at both companies say it will take up to 18 months to set up the MRO facility.

India is seen as having significant potential to grow into a global MRO hub, given its large pool of trained engineering talent and lower labor costs. Recent incentives from the Indian government have generated a lot of interest, particularly in domestic aviation MRO. With Indian carriers expected to increase their fleet size to 1,740 aircraft in the next 20 years, the local MRO market is projected to be worth $5.2 billion by 2026, consultancy KPMG says.

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Re: Indian Military Helicopters

Postby Cybaru » 17 Jan 2018 01:44

Indranil wrote:Absolutely. LUH flight testing is actually proceeding quite smoothly.


That's really good to hear. Any progress on IMRH?

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Re: Indian Military Helicopters

Postby Indranil » 17 Jan 2018 02:44

No info.

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Re: Indian Military Helicopters

Postby suryag » 17 Jan 2018 06:04

IR ji LCH front has been very quiet hope everything is going ahead of plan

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Re: Indian Military Helicopters

Postby Indranil » 17 Jan 2018 06:10

No 'ji' yaar :D.

ALH/LCH/LUH are solved problems. Don't worry about them :D. It's a matter of having new flavours now. CG wants a slightly different flavour. IN needs a slightly different flavour. It makes sense to have a different flavour for civil, and so on.

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Re: Indian Military Helicopters

Postby srai » 17 Jan 2018 10:34

IMRH will nicely round all the helo categories designed & built in India.

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Re: Indian Military Helicopters

Postby JayS » 17 Jan 2018 20:05

Just to confirm Indranil's chaiwalla account - 2 pers at a time, 300kg, indeed the limit for ALH.

Army knows what went wrong from their side (might not have stopped failure of that component IMO but definitely would have stopped the fall of Soldiers). I expect hole would be plugged soon enough from their side. We can expect the same from HAL once the loopholes on their side are zeroed upon.

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Re: Indian Military Helicopters

Postby Katare » 17 Jan 2018 21:42

The plate material is wrong for the application from what I can see from the picture. Recently i saw an industrial accident at one of my company’s plant where a large spin weld machine fell off clean from the holding fixture. This clean break happens when you use a cast metal instead of forged metal structure. A forged metal would buckle, mangle and elongate Before breaking off. It is cheaper to make cast structures, they are strong and lot more rigid than forged but you can never guarntee that you won’t make a bad part that will have catastrophic failure of clean break. The ALH boom material looks like a cast aluminum alloy to me.....

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Re: Indian Military Helicopters

Postby Singha » 17 Jan 2018 21:50

in tank armour front the cast turrets are said to be weaker than welded turret ?

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Re: Indian Military Helicopters

Postby Indranil » 17 Jan 2018 22:04

JayS wrote:Just to confirm Indranil's chaiwalla account - 2 pers at a time, 300kg, indeed the limit for ALH.

Yeah. It is in accordance to the FAR specifications.

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Re: Indian Military Helicopters

Postby ramana » 17 Jan 2018 22:13

Katare wrote:The plate material is wrong for the application from what I can see from the picture. Recently i saw an industrial accident at one of my company’s plant where a large spin weld machine fell off clean from the holding fixture. This clean break happens when you use a cast metal instead of forged metal structure. A forged metal would buckle, mangle and elongate Before breaking off. It is cheaper to make cast structures, they are strong and lot more rigid than forged but you can never guarntee that you won’t make a bad part that will have catastrophic failure of clean break. The ALH boom material looks like a cast aluminum alloy to me.....


Muh me ghee shakkar.

A few years ago had a chance to look at an Al casting which was received damaged. Everyone denied any wrong doing. The M&P engineer and I said it was mishandled and dropped on the floor while receiving inspection claimed it was received broken despite being bubble wrapped etc. We dropped the casting on the floor and the same exact mirror area which was still intact broke in similar fashion.


Its possible the boom attach bracket is not a machined part but a Al casting. However if they use A357 or equivalent alloy should have very good elongation.

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Re: Indian Military Helicopters

Postby dinesh_kimar » 17 Jan 2018 23:25

Singha wrote:in tank armour front the cast turrets are said to be weaker than welded turret ?


Yes saar. Welding joint can be stronger than the base metal structure, in some cases. Casting is used to make a complicated shape quickly ("net shape" as Ramana gaaru has explained in the past), but with weaker material properties like strength.

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Re: Indian Military Helicopters

Postby Indranil » 18 Jan 2018 00:32

Like many here, I 'think' the failure is fatigue related. Somehow, the 2-man restriction was not followed religiously. The heli itself seems to be very stable under the 3-man-on-the-rope load which may have provided a false sense of security. The boom got over-stressed again and again, finally leading to the catastrophic failure. The solutions may be simple. But I am little worried about the booms in the field now. How fatigued are they?

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Re: Indian Military Helicopters

Postby Cybaru » 18 Jan 2018 00:39

Indranil wrote:Like many here, I 'think' the failure is fatigue related. Somehow, the 2-man restriction was not followed religiously. The heli itself seems to be very stable under the 3-man-on-the-rope load which may have provided a false sense of security. The boom got over-stressed again and again, finally leading to the catastrophic failure. The solutions may be simple. But I am little worried about the booms in the field now. How fatigued are they?


Won't there be a system wide check to verify how prevalent this is?

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 18 Jan 2018 00:57

Indranil wrote:Like many here, I 'think' the failure is fatigue related. Somehow, the 2-man restriction was not followed religiously. The heli itself seems to be very stable under the 3-man-on-the-rope load which may have provided a false sense of security. The boom got over-stressed again and again, finally leading to the catastrophic failure. The solutions may be simple. But I am little worried about the booms in the field now. How fatigued are they?


Is there an easy way to test for this fatigue in the field ?

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 18 Jan 2018 01:01

Even if it’s 300 kg it should have some margin built in. A soldier with rifle and packs would not be more than 100 kg som3 soldiers at 300 kg should not create this stress.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 01:25

Akshay Kapoor wrote:
Indranil wrote:Like many here, I 'think' the failure is fatigue related. Somehow, the 2-man restriction was not followed religiously. The heli itself seems to be very stable under the 3-man-on-the-rope load which may have provided a false sense of security. The boom got over-stressed again and again, finally leading to the catastrophic failure. The solutions may be simple. But I am little worried about the booms in the field now. How fatigued are they?


Is there an easy way to test for this fatigue in the field ?


Short and simple answer - look for cracks.

All the components have a periodic check for cracks using non destructive testing NDT. Crack initiate after a while in service and grow over time. With proper inspection at intervals specified by designers for the parts, the cracks should be caught in regular inspections, ideally speaking. Any cracks seen or damage like dents, scratches seen, scrap the part. If you read the USMC doc I linked you will notice generic details for this. But the product inspection manual will have more specific instructions.

Now when root cause analysis happens, they will first check this failed part thoroughly to ascertain exact cause of failure, its manufacturing and operational history and so on. Then if its found out that the design may have been inadequate and its not a one of QC issue, then easy way is to simply redesign the part and replace fleet wide. Its cheap enough part to be replaced easily. Thats preferable. But if cost is prohibitive or logistics is issue and replacement is not possible, then next thing to do is to check very thoroughly and weed out parts with visible damage (using hi fidelity NDT) and make some feasible design changes to reduce stresses in critical area. For ex in this case, providing additional support to the fully overhung boom using a cross link or something. If even that is not possible, then from seemingly OK looking parts, take a handful of the components and lab test them for cyclic load (say equivalent to 3 battle ready soldiers) until they fail (Thats a simple enough test in this case, would need very basic infra). This to check residual life in components. And then suitably modify the usage/inspection instructions so as to avoid any more catastrophic failure.

This is exactly same as what NAL did with MiG21 to find out residual structural life left and based on that life extension was given for the fleet.

OTOH if its deemed as material or process QC issue, suitable measures would be taken to avoid such escapes further.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 01:38

Akshay Kapoor wrote:Even if it’s 300 kg it should have some margin built in. A soldier with rifle and packs would not be more than 100 kg som3 soldiers at 300 kg should not create this stress.


For all we know, there is enough margin. Until the root cause analysis points out to design deficiency, we cannot say there was not enough margin.

Why I have been stressing so much on not to think of it as a design failure or SOP lapse, is that, IMO either of the two should have shown systematic issue which should have been captured in the inspection multiple times as some kind of indications, given proper inspection procedures are at place. This is not a new system, recently deployed. Its been there for years now.

One thing is perplexing from IA side, is why earlier the rope would be attached to multiple points while now it was not..? Was it lapse in SOP..? Was the SOP changed...? One can never go wrong with a backup. Or was it there, but even second attachment point also failed..? very unlikely.

There is one more thing - in some pics I can see a thin thing attached to the boom somewhere in between and going back attaching the heli frame somewhere (see in image posted by hnair, next to head of the soldier standing in the door). While other pics do not show that. What is that thing..?

PS: This image shows some more details. The rope is bound around boom and goes on to attach to Heli floor from the back of the boom. Also that thin link at the bottom of the boom attaching to the heli roof. (open image separately and zoom))

Image

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Re: Indian Military Helicopters

Postby ramana » 18 Jan 2018 03:54

Indranil wrote:Like many here, I 'think' the failure is fatigue related. Somehow, the 2-man restriction was not followed religiously. The heli itself seems to be very stable under the 3-man-on-the-rope load which may have provided a false sense of security. The boom got over-stressed again and again, finally leading to the catastrophic failure. The solutions may be simple. But I am little worried about the booms in the field now. How fatigued are they?


Is the boom made of composite which is fastened to the bracket?

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Re: Indian Military Helicopters

Postby srai » 18 Jan 2018 06:20

There is one more thing - in some pics I can see a thin thing attached to the boom somewhere in between and going back attaching the heli frame somewhere (see in image posted by hnair, next to head of the soldier standing in the door). While other pics do not show that. What is that thing..?

PS: This image shows some more details. The rope is bound around boom and goes on to attach to Heli floor from the back of the boom. Also that thin link at the bottom of the boom attaching to the heli roof


In the accident video, it doesn’t seem like the rope was attached to the cabin. If it was, one would expect to see a break in the fall (even if that cabin rope attachment failed). But in the video, there is no such “break” moment from what I can tell.

Two outcomes from this would be SOP to make sure that safety rope is securely tied to the cabin (if it hadn’t been attached that is) and to strengthen the cabin attachment point (if it had been attached but it also failed easily).

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Re: Indian Military Helicopters

Postby shiv » 18 Jan 2018 06:48

Akshay Kapoor wrote:Even if it’s 300 kg it should have some margin built in. A soldier with rifle and packs would not be more than 100 kg som3 soldiers at 300 kg should not create this stress.

There is one issue and I am not an engineer to speak with authority. There are two types of loads - static load and dynamic load. I think the latter is a temporary stress which can be very high and the latter a steady load. If you jump onto a spring weighing scale to check your weight - it goes ballistic for a moment and may register 200 kg before it settles down to show your weight. So when 2 men @100 kg each add their weight to a boom the sudden addition and the swnging to and fro will lead to stresses far higher than 300 kg. So we need to know if the 300 kg limit is for static loads - the dynamic limit should be higher.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 11:45

shiv wrote:
Akshay Kapoor wrote:Even if it’s 300 kg it should have some margin built in. A soldier with rifle and packs would not be more than 100 kg som3 soldiers at 300 kg should not create this stress.

There is one issue and I am not an engineer to speak with authority. There are two types of loads - static load and dynamic load. I think the latter is a temporary stress which can be very high and the latter a steady load. If you jump onto a spring weighing scale to check your weight - it goes ballistic for a moment and may register 200 kg before it settles down to show your weight. So when 2 men @100 kg each add their weight to a boom the sudden addition and the swnging to and fro will lead to stresses far higher than 300 kg. So we need to know if the 300 kg limit is for static loads - the dynamic limit should be higher.


What you are referring to is called - impact loading. During design one needs to consider this if significant impact loading is expected. Generally would be simply a factor multiplying nominal static load. In simple cases like jumping on a weighing scale, this factor which would be 1.x can be hand calculated with some simple formulae. (in this case this should be minor, in situation like catching a rope in midair while jumping would have much more pronounced effect).

Yes there is a lot of dynamics involved when the loading is initiated - that is a soldier transfers his weight on the rope. But in this particular case the rope is the most flexible part of the load path and it would absorb the initial variation by stretching. If you read the USMC doc I linked it specifically mentions that the soldier at lower end should take into consideration that rope will stretch a bit when second soldier at the top gets on the rope.

The boom and other solid parts are far far more stiff, so they will not see much of the effect of this dynamic part you want to point out.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 11:57

Akshay Kapoor wrote:
Indranil wrote:Like many here, I 'think' the failure is fatigue related. Somehow, the 2-man restriction was not followed religiously. The heli itself seems to be very stable under the 3-man-on-the-rope load which may have provided a false sense of security. The boom got over-stressed again and again, finally leading to the catastrophic failure. The solutions may be simple. But I am little worried about the booms in the field now. How fatigued are they?


Is there an easy way to test for this fatigue in the field ?


I thought of a simpler example which may make it little more clear how to look for fatigue in real life for a simpler structural component. If you have noticed/seen motor-cycle driving chain's inspection method - the way to tell when you need to change your chain is to measure how much it is elongated from original length, more the fatigue more is elongation (since every link goes from fully loaded to fully slack in every turn we have a cyclic loading, which mean fatigue is important). If material is weaker than intended it would elongate faster than intended and if your inspection interval is small enough (say every 500km) then you can most probably catch the eminent failure before it happens. The length for some 8-10 links is specified below which its OK to continue using. Any 8 or 10 links, you should check multiple sets on same chain. That's the proper way of checking bike chain. But since no one really check it that way, OEM give layman limits - change every 20000km and so on.

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Re: Indian Military Helicopters

Postby Zynda » 18 Jan 2018 13:15

I would want to point out that the following "analysis" is based on a lot of assumptions which will render it highly approximate.

IMO, the boom is fabricated using Aluminum 2024-T3 Extrusion and not cast.

1. Cast material is usually more brittle in nature and is bad from a fatigue POV. Since this component sees a lot of load cycling, I doubt cast material would chosen.
2. 2024-T3 has good fatigue & stress corrosion resistance properties. This component is exposed to a lot of elements and hence if I was designing the component I would be choosing the material as 2024-T3 along with Point 1.
3. From a procurement POV, 2024-T3 is easily available in different sizes and is most commonly used Al alloy on aircrafts.
4. I have very little experience working with cast materials and I am assuming that they would be available as blocks and hence need for machining to get a tube profile and very expensive for the given application.
5. To be there appears to be a good quality weld line between the tube & base plate materials which to me says that tube is probably an extrusion component purchased and welded to base plate.

I also did a quick & dirty calculation on the boom's static load carrying capacity. I took JayS's value of 300 Kg as Limit & did calc for UL = LL x 1.5.

I have to mention that the calculation I did was for C/S near the joint but NOT at the Joint i.e. the C/S where I did the calculation did not have any material cutout for bolt holes.

I will just mention that at that particular C/S, for the material to yield (not fail) the limit load limit should be 1650 Kg.

I also did an analysis of stress values near the fasteners for the joint config in the picture (assuming that there are just 3 hi-loks to carry the load) and for UL of 990 lbs...there is a slight margin (11%) before stress values reach the allowables.

Assuming that a solider weighs in around 80 Kg...then the boom is designed to hold UNDER static load conditions for up to 450/80 = 5 personnels.

I have a picture with probable crack origin locations marked but only way to be certain is to examine the fracture surface under a high resolution microscope for striation marks. I will have to upload the image to a hosting site...will do it once I am home.

I think unfortunately in this case, it could be a lapse of maintenance which allowed the crack to propagate beyond what was prescribed in inspection limits (or HAL could have specified that boom be replaced after so many hours of flying). At least from my approximate calculation, the boom seems to be solid from a static POV. I will see if I can do a quick fatigue calc. later on.

Katare, what you have mentioned holds true if the failure is due to static loading but if the failure is from fatigue, then the crack just propagates just like how crack flows in a paper. So even in ductile material, the fracture surface can look like a brittle failure.

Shiv, for practical purposes, impact loading would be minimal and hence will be considered as gradual or static loading from Analysis POV.

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Re: Indian Military Helicopters

Postby ks_sachin » 18 Jan 2018 15:02

May I complement all the recent posters on the quality of the posts. This is what makes BRF wortb it!

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Re: Indian Military Helicopters

Postby Zynda » 18 Jan 2018 18:17

I made a small error with respect to joint margins. Had considered the wrong load and up on review, the margin now is at a revised figure of 42%.

Anyways here is the picture with probable crack start locations.

Image

The white surface is freshly fractured one...while not all dark represents fatigue growth (some seem like smudge marks from dirt)...the marked locations, especially on top are suspected. Like I mentioned in my earlier post, only an examination under a microscope for striation marks can confirm fatigue marks.

If I can get to fatigue calcs, I will try to post life cycle numbers.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 18:37

Zynda wrote:I would want to point out that the following "analysis" is based on a lot of assumptions which will render it highly approximate.

IMO, the boom is fabricated using Aluminum 2024-T3 Extrusion and not cast.


Just curious. How would a the component be extruded..? The flanged component which failed.?

OK saw the pic now. Never mind. The flange is welded, you propose.

You know if it was to be welded there, might as well have casted the whole thing. The weld will be the most critical location in this config and weld properties are taken to be same as Casting properties as a rule of thumb.

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Re: Indian Military Helicopters

Postby Zynda » 18 Jan 2018 19:37

JayS, I dunno how expensive a casting manf process would be...as Ramana pointed out, the inner surface is primed with chromate conversion coating to give a degree of protection from corrosion. Would be easy to apply on the inner wall surface of the tube if it was a separate component. I am sure it can be applied if the entire component was a cast as well. As a designer, one has to do a trade offs between cost & functioning. Functioning always takes priority but once it is determined that all design choices can accomplish it, then costing has to be factored as well.

Good observation on weld also being the critical point...I don't have experience with working with welded components but per my experience, almost all failures originate at joints.

I wonder what is the purpose of the hi-lok fasteners & attachment to a composite component. I think it may be to serve as an alternate load path to provide multiple load path capability.

Interesting design...would love to see the intact design in its entirety. May be next AI...one of the photographers who manage to get access to the other side of the static display line fence can do a favour and click some nice & detailed photos :)

Or if RaghuK is still lurking around and if he is in a position to shed some light...that too would be welcome :)

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 18 Jan 2018 20:01

Zynda wrote:I would want to point out that the following "analysis" is based on a lot of assumptions which will render it highly approximate.

IMO, the boom is fabricated using Aluminum 2024-T3 Extrusion and not cast.

1. Cast material is usually more brittle in nature and is bad from a fatigue POV. Since this component sees a lot of load cycling, I doubt cast material would chosen.
2. 2024-T3 has good fatigue & stress corrosion resistance properties. This component is exposed to a lot of elements and hence if I was designing the component I would be choosing the material as 2024-T3 along with Point 1.
3. From a procurement POV, 2024-T3 is easily available in different sizes and is most commonly used Al alloy on aircrafts.
4. I have very little experience working with cast materials and I am assuming that they would be available as blocks and hence need for machining to get a tube profile and very expensive for the given application.
5. To be there appears to be a good quality weld line between the tube & base plate materials which to me says that tube is probably an extrusion component purchased and welded to base plate.

I also did a quick & dirty calculation on the boom's static load carrying capacity. I took JayS's value of 300 Kg as Limit & did calc for UL = LL x 1.5.

I have to mention that the calculation I did was for C/S near the joint but NOT at the Joint i.e. the C/S where I did the calculation did not have any material cutout for bolt holes.

I will just mention that at that particular C/S, for the material to yield (not fail) the limit load limit should be 1650 Kg.

I also did an analysis of stress values near the fasteners for the joint config in the picture (assuming that there are just 3 hi-loks to carry the load) and for UL of 990 lbs...there is a slight margin (11%) before stress values reach the allowables.

Assuming that a solider weighs in around 80 Kg...then the boom is designed to hold UNDER static load conditions for up to 450/80 = 5 personnels.

I have a picture with probable crack origin locations marked but only way to be certain is to examine the fracture surface under a high resolution microscope for striation marks. I will have to upload the image to a hosting site...will do it once I am home.

I think unfortunately in this case, it could be a lapse of maintenance which allowed the crack to propagate beyond what was prescribed in inspection limits (or HAL could have specified that boom be replaced after so many hours of flying). At least from my approximate calculation, the boom seems to be solid from a static POV. I will see if I can do a quick fatigue calc. later on.

Katare, what you have mentioned holds true if the failure is due to static loading but if the failure is from fatigue, then the crack just propagates just like how crack flows in a paper. So even in ductile material, the fracture surface can look like a brittle failure.

Shiv, for practical purposes, impact loading would be minimal and hence will be considered as gradual or static loading from Analysis POV.


Just to give you some inputs re wieght. Average wt is about 70 Kgs. Equipment will be max 15 kilos for the demo operation. There will be very little ammunition carried in the demo. In operations equipment can be restricted to 20 - 25 kgs. Other loads can be dropped down. SF I can’t say - they do ‘impossible’ things so they may well take more loads.

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Re: Indian Military Helicopters

Postby Zynda » 18 Jan 2018 20:10

^^ Thx Sir. What could be the realistic total weight carried by solider during operations? 100 Kg max? SF may be an exception as you say. But dropping in SF folks packing 35+ Kgs becomes the norm (total weight 70 + 35 = 105...keep 110 Kg) then IAF/IA personnels should provide that weight to HAL on future improvements.

As you have pointed out, a non-operational personal like me could consider just the weight of soldier as norm (completely discounting their backpacks & equipments; of course in a design org. there would be some reviews and errors like the above should/would be caught early on) and design component. Onlee proves how important it is for end-user to involve in design process...the same logic can be extended to other complex systems.

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Re: Indian Military Helicopters

Postby titash » 18 Jan 2018 20:15

Image[/url]

It's been several years since I did failure analysis. Could be simple crack propagation near stress concentrations as opposed to high cycle fatigue. The fact that neither the weld nor the fasteners have failed is galling. That probably indicates a pre-existing crack...perhaps during the process of tapping the holes. Assuming that the dark colors are rapid crack propagation and the white fibrous colors indicate tensile deformation, one could speculate that since the dark colors are near all the holes tapped (and really the part has failed around the bolt taps), there was a small crack...

But then it has been XX years...so I may be wrong.

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 18 Jan 2018 20:22

Zynda wrote:^^ Thx Sir. What could be the realistic total weight carried by solider during operations? 100 Kg max? SF may be an exception as you say. But dropping in SF folks packing 35+ Kgs becomes the norm (total weight 70 + 35 = 105...keep 110 Kg) then IAF/IA personnels should provide that weight to HAL on future improvements.

As you have pointed out, a non-operational personal like me could consider just the weight of soldier as norm (completely discounting their backpacks & equipments; of course in a design org. there would be some reviews and errors like the above should/would be caught early on) and design component. Onlee proves how important it is for end-user to involve in design process...the same logic can be extended to other complex systems.


In slithering equipment weight will not be too much. Just rifle and pack. But on ground the soldier carries almost 70 pct of body wt which is too much. But that’s a discussion for another thread. Since you have done such a nice analysis I just wanted to give you realistic wt input. Agree with your points and am sure it’s done. Maybe we need to do better. User will be happy but the other side should should be happy to take the input. I’m sure it’s very easily solved.

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Re: Indian Military Helicopters

Postby Zynda » 18 Jan 2018 20:24

^^Yes...current practice in commercial aerospace at least (largely same philosophy is followed in Mil Aviaton as well but USAF/USN follow a slow growth analysis approach which is not acceptable by FAR/EASA agencies) is to assume that a small crack exists right from time the component is installed on aircraft and analysis is done to determine inspection intervals. So yes, a fatigue crack existed in the marked locations and grew as component was loaded cyclically until the failure event where 3 men load exceeded what the component could take with presence of a crack. Note: Even in fatigue failure, the failure always happens due to static load.

White surfaces are the regions where crack propagated rapidly (fresh fracture)...dark would be fatigue crack propagation.

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 18 Jan 2018 20:34

Sorry just to be clear avg wt of soldier is 70 KG

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Re: Indian Military Helicopters

Postby Karan M » 18 Jan 2018 20:42

Great stuff Zynda, Titash & Jay.

Also, I find it impossible to believe the ALH team would have not taken a loaded soldier into account. The user would have definitely included operational weights ie troop + equipment for a unit meant for slithering operations.

Likely, we need to provide more NDT kit to the field and probably lay down more rigorous SOPs.

Its also very likely that when an eqpt is inducted, its so heavily used that it uses up fatigue life earlier than planned and if not documented, such issues can easily arise. Or there is a QA/QC issue which accelerates under heavy load.

USAF post Vietnam war set up teams to visit each AFB and independently audit key items - eg missile serviceability, functioning EW etc. That saved them a lot of bother later on during ODS. Point being in large organizations and hierarchies, perhaps you need some extra support from the top to get the field units the support and attention they need, but would not otherwise get and have to make do.


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