Indian Military Helicopters

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Akshay Kapoor
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Re: Indian Military Helicopters

Postby Akshay Kapoor » 18 Jan 2018 20:43

Sure, I agree and I said I’m sure it’s happening. I’m just giving data for the analysis that’s happening here.

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 18 Jan 2018 20:50

Gents I add my compliments too. Great stuff gents.

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Re: Indian Military Helicopters

Postby Haridas » 18 Jan 2018 21:39

The exterior surface has composite elements thus weld marks not v clear, the weld line is however very clear on interior surface. Your arrow for weld line should point to the interior surface. BTW looks like high quality weld.

One can see the part is not welded on all 4 edges. Just bottom and top (can't be seen) which is consistent with application. Welded area is where stress is maximum, but that cross section didn't fail, what failed is the cross section that got hogged out due to fastener holes. (Staggered hole would have minimized the compromise) further close in holes would more easily allow manufacturing induced crack (s).
Last edited by Haridas on 19 Jan 2018 12:55, edited 2 times in total.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 21:52

Zynda wrote: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 :)


As I said, Welds are considered equivalent to casting in terms of material properties. Casting is typically cheaper than extrusion or forging, unless of coarse you are using COTS standard extruded rectangular section tubes. That could be cheaper than casting or comparable.

Place of failure would depend on how you have designed it. You can make weld location too strong and then bolt joint becomes weak link and vice versa. In this particular system, the weakest link should have been (IMO) the hook where rope is attached to the boom. The rope itself and the eye of the rope are very very strong for any COTS ropes.

Well, take my word for it - It is Al Casting.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 21:59

Akshay Kapoor wrote:Sorry just to be clear avg wt of soldier is 70 KG


Saar, I would use 95 percentile weight not the average. With that and max possible combat load ever, and some margin, 300kg looks OK for 2 Soldiers.

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Re: Indian Military Helicopters

Postby Zynda » 18 Jan 2018 22:14

Jay, I meant COTS extrusions...easily available in different standard sizes & shapes.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 22:25

Zynda wrote:
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.


Only single load path is there. Hi-lok are preferred for tight spaces due to installation ease. As such hi-lok has better quality than normal nut-bolt. I am thinking if they are preferred when bolt is in tension, but I cannot say for sure, looks unlikely though. Also if they have used hi-lok everywhere on ALH then why not keep same type..?

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Re: Indian Military Helicopters

Postby Zynda » 18 Jan 2018 22:31

^^I meant weld line already provides one load path...why have another fastener load path. Hi Loks are used instead of rivets rather than bolts because hi loks are permanent fasteners. Usually hi-loks are for high strength applications and they provide better fatigue resistance than normal rivets. Also preferred in tension clips where tension is the primary load...

We can take this further to Aerospace Engg thread if required. I am sure casual forumites might find these not that interesting and they are OT in a Heli thread.

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Re: Indian Military Helicopters

Postby JayS » 18 Jan 2018 23:02

Zynda wrote:^^I meant weld line already provides one load path...why have another fastener load path. Hi Loks are used instead of rivets rather than bolts because hi loks are permanent fasteners. Usually hi-loks are for high strength applications and they provide better fatigue resistance than normal rivets. Also preferred in tension clips where tension is the primary load...

We can take this further to Aerospace Engg thread if required. I am sure casual forumites might find these not that interesting and they are OT in a Heli thread.


May be there is some misunderstanding. Are you referring to bolts which attached composite boom to metal block ot the bolts on metal block flange which attaches it to Heli frame..?

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Re: Indian Military Helicopters

Postby Indranil » 18 Jan 2018 23:52

Zynda wrote:We can take this further to Aerospace Engg thread if required. I am sure casual forumites might find these not that interesting and they are OT in a Heli thread.

Please don't. This is why I come to BR: to learn.

High quality discussions are getting rare. Casual forumites who don't find this interesting can disperse and return when the conversation turns casual.

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Re: Indian Military Helicopters

Postby ramana » 19 Jan 2018 00:55

Zynda keep it here for focus and continuity.
A few questions to you:
- 2024 is weldable? What is its fracture toughness strength? Looks like 1/2 of good steel like 4340 (24 vs 50).
- So design has enough margins based on hand calcs. FEM will only to improve that margin.
- Looks like there was an initial flaw in the mounting/attach bracket.

Agree need photo micrographs of the bracket to determine nature of failure initiation.

JayS, The Hiloks are being used in shear. The break-off collar ensures sufficient pre-load to keep the pins in tension.
The failure shows the material failed at the joint.
The Hiloks and the welds were good.

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Re: Indian Military Helicopters

Postby Haridas » 19 Jan 2018 05:02

ramana wrote:Zynda keep it here for focus and continuity.
A few questions to you:
- 2024 is weldable? What is its fracture toughness strength? Looks like 1/2 of good steel like 4340 (24 vs 50).

Yes 2024 is weldable.
Al 6013 is more suitable, is welable and in addition stronger than 2024 & corrosion resistant.

I have more design experience with 7075 (not weldable, but much more stronger)
Last edited by Haridas on 19 Jan 2018 13:33, edited 1 time in total.

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Re: Indian Military Helicopters

Postby JayS » 19 Jan 2018 13:26

Haridas wrote:
ramana wrote:Zynda keep it here for focus and continuity.
A few questions to you:
- 2024 is weldable? What is its fracture toughness strength? Looks like 1/2 of good steel like 4340 (24 vs 50).

Yes 2024 is welable.
Al 6013 is more suitable, is welable and in addition stronger than 2024 & corrosion resistant.

I have more design experience with 7075 (not weldable, but much more stronger)


I suppose Al alloys are weldable so to speak, but not as good as some other alloys like Inconel, also not with all common techniques. But that's too many technical details which are not really needed in this particular case.

2024-T4 seems a good choice here since this part it under tension dominated fatigue as critical mode.

2000 series are good in tension fatigue so preferred for lower wing skin while 7000 are preferred for upper wing skin.

Ramana sir, I don't think we need to go to Fracture mechanics. This part must be designed with simple strength based criteria, which is conservative. Fracture mechanics would be needed for damage tolerance approach which is more for "high performance" structural components so to speak. Strengthwise Al alloys are comparable to or slightly lower to steel, but they more than make up in thickness while keeping weight same due to low density. So looking at comparative strength data also would not take us anywhere IMO.

Also, the bolts would be under significant tension along with shear, as its the case of bending, the bolts on the top especially.

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Re: Indian Military Helicopters

Postby Jayram » 20 Jan 2018 00:09

Two quick points..
The decision to use cast versus extruded manufacturing process is an important one. Casting does not have the same shock loading capacity as an extruded part mostly due to grain structure. Cast products are brittle and tend to fail suddenly without any of the plastic deformation. On close inspection of the failure it seems as if there was some reduction on cross section of the boom prior to failure at the top section but complete failure in the bottom and sides. So need more information. Elongated grain structures in extruded products give superior strength in the longitudinal direction ie the directional strength that is in question in this boom.
Secondly it is important to consider the shape of the boom. The boom shape should be maximized to increase moment of inertia to resist bending or twisting motions (especially in case of shock loading) that in turn are transferred on to the joint causing fracture under repeated loading as prima facie seems to have happened in this case. One point to note also if boom elongates elastically without failing (more ductile) under stress that is a good thing because that means less load is transferred to the joint. The boom shape can be cylindrical as well rather than rectangular as in this case. Perhaps a hollow cylinder will better serve to prevent stress concentration at the corners of the joint leading to crack initiation and fatigue failures. Case in point look at the freeway sign posts in most US Freeways. They are large cylinders holding the highway sign at a orthogonal direction and a subject to heavy fatigue and torsional forces due to wind. But failures are few and far between.

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Re: Indian Military Helicopters

Postby Haridas » 21 Jan 2018 15:42

Akshay Kapoor wrote:Sorry just to be clear avg wt of soldier is 70 KG

Equipment design will require worst case (i.e. max weight) number, not average of soilders wt & also max eqpt wt.

I am sure actual mission is not planned by allocating solider by weight quota to meet statisticaly fair allocation to proportional distribution :) .

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Re: Indian Military Helicopters

Postby Haridas » 21 Jan 2018 16:00

Just some nit pick observations.....

Jayram wrote:Two quick points..
The decision to use cast versus extruded manufacturing process is an important one. Casting does not have the same shock loading capacity as an extruded part mostly due to grain structure. Cast products are brittle and tend to fail suddenly without any of the plastic deformation. On close inspection of the failure it seems as if there was some reduction on cross section of the boom prior to failure at the top section but complete failure in the bottom and sides. So need more information. Elongated grain structures in extruded products give superior strength in the longitudinal direction ie the directional strength that is in question in this boom.

Good point.
Secondly it is important to consider the shape of the boom. The boom shape should maximized to increase moment of inertia
inertia?? I am sure you meant bending moment.
The boom shape can be cylindrical as well rather than rectangular as in this case.

Pls reconsider to choose shape that matches the demanded peak moment along the two orthogonal axis. Cylindrical is the inferior solution.
Perhaps a hollow cylinder will better serve to prevent stress concentration at the corners of the joint leading to crack initiation and fatigue failures. Case in point look at the freeway sign posts in most US Freeways. They are large cylinders holding the highway sign at a orthogonal direction and a subject to heavy fatigue and torsional forces due to wind. But failures are few and far between.
rectangular corners OTOH are superior on strength, due to shape and weld is always strongest there.

US traffic sign post cross section is a very bad example. BTW apart from overkill size, it doesn't fatigue because it is ferrous alloy (try non ferrous alloy in fatiguing application, it's a nightmare,
demanding careful engineering).

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Re: Indian Military Helicopters

Postby deejay » 21 Jan 2018 16:29

Haridas wrote:
Akshay Kapoor wrote:Sorry just to be clear avg wt of soldier is 70 KG

Equipment design will require worst case (i.e. max weight) number, not average of soilders wt & also max eqpt wt.

I am sure actual mission is not planned by allocating solider by weight quota to meet statisticaly fair allocation to proportional distribution :) .


Sir from memory, troop weight for calculations is taken as 100 kgs with eqpt. Special cases higher weight allowance can be considered. I have never heard of lower weight calculations.

Helicopters are an extremely weight sensitive machine. The rope or boom limitation (though the main factor in this case) comes later. Primary limitation will come in effect due to Free Air Hover to be established for slithering.

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Re: Indian Military Helicopters

Postby Haridas » 22 Jan 2018 08:46

Sure, I understand it is delicate planning.

My previous company had JV buyout of a Japanese automated material handling system (SHINKO), visited the parent Co factory next door, one of the products they made was winches for japani military helicopters; proud meticulous people.

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Re: Indian Military Helicopters

Postby JayS » 22 Jan 2018 11:54

Jayram wrote:Two quick points..
The decision to use cast versus extruded manufacturing process is an important one. Casting does not have the same shock loading capacity as an extruded part mostly due to grain structure. Cast products are brittle and tend to fail suddenly without any of the plastic deformation. On close inspection of the failure it seems as if there was some reduction on cross section of the boom prior to failure at the top section but complete failure in the bottom and sides. So need more information. Elongated grain structures in extruded products give superior strength in the longitudinal direction ie the directional strength that is in question in this boom.
Secondly it is important to consider the shape of the boom. The boom shape should be maximized to increase moment of inertia to resist bending or twisting motions (especially in case of shock loading) that in turn are transferred on to the joint causing fracture under repeated loading as prima facie seems to have happened in this case. One point to note also if boom elongates elastically without failing (more ductile) under stress that is a good thing because that means less load is transferred to the joint. The boom shape can be cylindrical as well rather than rectangular as in this case. Perhaps a hollow cylinder will better serve to prevent stress concentration at the corners of the joint leading to crack initiation and fatigue failures. Case in point look at the freeway sign posts in most US Freeways. They are large cylinders holding the highway sign at a orthogonal direction and a subject to heavy fatigue and torsional forces due to wind. But failures are few and far between.


Some valid points, but cylindrical shape is not the ideal solution. It lacks stiffness compared to polygonal shape.

But let me say this, lets not try to prove or say how there were bad choices in the design unless we have enough data to say so. There are n number of ways to achieve design solution for such simple system and with changing constraints one may be better than the other. But what matters is has the designer designed the system properly given the choices of design..? Else we could always say why the hell HAL didn't choose forged Titanium with some xyz shape for boom with more than one supports, that would have been the best. We do not have all the info that would have influenced design choices. Rule of thumbs are fine, but there are always exceptions to rules and with meticulous design and QC one can live with the exceptions.

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Re: Indian Military Helicopters

Postby JayS » 22 Jan 2018 12:29

Haridas wrote:Just some nit pick observations.....

Jayram wrote:Two quick points..
The decision to use cast versus extruded manufacturing process is an important one. Casting does not have the same shock loading capacity as an extruded part mostly due to grain structure. Cast products are brittle and tend to fail suddenly without any of the plastic deformation. On close inspection of the failure it seems as if there was some reduction on cross section of the boom prior to failure at the top section but complete failure in the bottom and sides. So need more information. Elongated grain structures in extruded products give superior strength in the longitudinal direction ie the directional strength that is in question in this boom.

Good point.
Secondly it is important to consider the shape of the boom. The boom shape should maximized to increase moment of inertia
inertia?? I am sure you meant bending moment.
The boom shape can be cylindrical as well rather than rectangular as in this case.

Pls reconsider to choose shape that matches the demanded peak moment along the two orthogonal axis. Cylindrical is the inferior solution.
Perhaps a hollow cylinder will better serve to prevent stress concentration at the corners of the joint leading to crack initiation and fatigue failures. Case in point look at the freeway sign posts in most US Freeways. They are large cylinders holding the highway sign at a orthogonal direction and a subject to heavy fatigue and torsional forces due to wind. But failures are few and far between.
rectangular corners OTOH are superior on strength, due to shape and weld is always strongest there.

US traffic sign post cross section is a very bad example. BTW apart from overkill size, it doesn't fatigue because it is ferrous alloy (try non ferrous alloy in fatiguing application, it's a nightmare,
demanding careful engineering).


He did mean Moment of Inertia.

Agree on Circular shape. To add, circular c/s is not great from shape stiffness perspective either, polygonal shape is better. There doesn't seem to be any issue with corners here.

Ferrous alloys also fatigue if designed with loads above endurance limit. Just nitpicking. :wink:

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Re: Indian Military Helicopters

Postby jaysimha » 22 Jan 2018 14:22

Image
The Siachen Pioneers”, Leh based Helicopter Unit carrying out casevac mission in Ladhak sector, at Leh on 19 Jan 2018

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Re: Indian Military Helicopters

Postby jaysimha » 22 Jan 2018 14:26

Image
“The Siachen Pioneers”, Leh based Helicopter Unit carrying out casevac mission in Ladhak sector, at Leh on 19 Jan 2018

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 22 Jan 2018 14:37

Haridas wrote:
Akshay Kapoor wrote:Sorry just to be clear avg wt of soldier is 70 KG

Equipment design will require worst case (i.e. max weight) number, not average of soilders wt & also max eqpt wt.

I am sure actual mission is not planned by allocating solider by weight quota to meet statisticaly fair allocation to proportional distribution :) .


You misunderstand. I was breaking down the total wt between a soldiers weight and equipment. So if soldiers wt is 70 kgs you equipment can be 30 max. Anything more than that can be dropped via a separate load - doesn’t need to be carried by the troops.

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Re: Indian Military Helicopters

Postby jaysimha » 22 Jan 2018 14:46

Image
Image
Image
Image
Image

ye dil mange more...

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Re: Indian Military Helicopters

Postby Jayram » 23 Jan 2018 05:30

Haridas wrote:Just some nit pick observations.....

Jayram wrote:Two quick points..
The decision to use cast versus extruded manufacturing process is an important one.

Good point.
Secondly it is important to consider the shape of the boom. The boom shape should maximized to increase moment of inertia
inertia?? I am sure you meant bending moment.
The boom shape can be cylindrical as well rather than rectangular as in this case.

Pls reconsider to choose shape that matches the demanded peak moment along the two orthogonal axis. Cylindrical is the inferior solution.
Perhaps a hollow cylinder will better serve to prevent stress concentration at the corners of the joint leading to crack initiation and fatigue failures. Case in point look at the freeway sign posts in most US Freeways. They are large cylinders holding the highway sign at a orthogonal direction and a subject to heavy fatigue and torsional forces due to wind. But failures are few and far between.
rectangular corners OTOH are superior on strength, due to shape and weld is always strongest there.

Haridas, Jays ,
I have to respectfully disagree on the last point. I should have been more precise. My contention is as follows a hollow cylinder will resist both bending and torsional moments better as compared of a hollow square "for the same weight and length". The reason being the hollow cylinder can be made larger (more diameter) (with same wall thickness) while having the same weight as the square boom. This means then that the new cylinder will have a higher moment of Inertia which in turn will be better resistant to bending and torsional moments as compared to the square boom. for Ref see here http://mnhpva.org/tech/frame_tubes.html . The author was pointing out use of round tubes as opposed to square or any other shape for bicycles as a comparative example.
Image
Caveat I did not validate the calculations on that page. Further caveat I am metallurgist by training a long long time ago not a structural engineer so I could be very wrong. Here are some nice gifs of the motions the boom is being subject to.
Torsional
https://en.wikipedia.org/wiki/Bending#/media/File:Beam_mode_5.gif and
Bending
https://en.wikipedia.org/wiki/Bending#/media/File:Beam_mode_6.gif from here

https://en.wikipedia.org/wiki/Bending#Euler.E2.80.93Bernoulli_bending_theory.

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Re: Indian Military Helicopters

Postby Haridas » 23 Jan 2018 11:48

jaysimha wrote:Image
ye dil mange more...

The surroundings look very familiar.
I recall the Siachen Pioneers motto is painted on left side (not visible) it reads something like:
"we regularly do the difficult, impossible may take a bit longer"

Great airmen with wonderful airmen-ship.

BTW note the engine location. Cheetal !

AVM Manmohan Bahadur was the Commodore Commandent for the longest time.

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Re: Indian Military Helicopters

Postby Akshay Kapoor » 23 Jan 2018 14:45

Haridas, if I am not completely wrong we have interacted in a different environment before ? You are an IAF brat and your brother is from Deejays old hunting grounds ? Welcome to BRF.

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Re: Indian Military Helicopters

Postby Zynda » 23 Jan 2018 14:57

[quote="Jayram"]
Per my calculations, the beam was already oversized. Granted, I did a check just on the beam and joints and not the welds. Plus adding stuff to a rectangular beam would be easier from design & fabrication cost & effort. The only thing I would have done differently is to change the orientation of the beam. Instead of having the longer side orient horizontal (parallel to plane of rotor blades), I would have oriented it perpendicular. But I don't know what additional design constraints were present which made HAL go with the current config.

Anyways, it is quite possible that failure analysis may go to NAL. If we are lucky, the report could be made available for public consumption.

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Re: Indian Military Helicopters

Postby JayS » 23 Jan 2018 15:37

Zynda wrote:
Jayram wrote:

Per my calculations, the beam was already oversized. Granted, I did a check just on the beam and joints and not the welds. Plus adding stuff to a rectangular beam would be easier from design & fabrication cost & effort. The only thing I would have done differently is to change the orientation of the beam. Instead of having the longer side orient horizontal (parallel to plane of rotor blades), I would have oriented it perpendicular. But I don't know what additional design constraints were present which made HAL go with the current config.

Anyways, it is quite possible that failure analysis may go to NAL. If we are lucky, the report could be made available for public consumption.


Perhaps because the boom is not perpendicular to the base..? If you observe all pictures carefully you can make out that it has some 20-25deg angle to perpendicular. Its biased towards the front side (wrt helicopter). That means twisting moment (which is anticlockwise in this case) along with the bending moment at the base.

PS: Image

PPS: In above picture, it looks like from one side Soldiers are Fast roping while from other side they are rappling down.

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Re: Indian Military Helicopters

Postby Haridas » 23 Jan 2018 19:07

Abinandan AK ji.

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Re: Indian Military Helicopters

Postby shiv » 23 Jan 2018 19:23

Jayram wrote: My contention is as follows a hollow cylinder will resist both bending and torsional moments better as compared of a hollow square "for the same weight and length".

Please consider me a "near zero" in this discussion hovering around -272 deg C

But I have some empirical awareness based on seeing failures of everyday objects - some of which I have to repair as home Mr Fixit.

Your contention about tube vs square may well be correct - but the actual break that the helo suffered was at the mounting point, i.e. the point where the beam joined the main body of the helicopter. I would have thought that while the rest of the beam certainly is subject to all sorts of bending and torsion stresses - the point where it joins the helo is an especially vulnerable point where the elasticity (??) (is that the right word) of the beam meets the rigidity of the mounting. My guess was that a circular beam could develop a transverse stress tear/crack that extends circumferentially near this joint while a square beam would not allow such a tear to occur or extend. Just a guess. Please say that I am mistaken if this jugaadu information is wrong.

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Re: Indian Military Helicopters

Postby chetak » 23 Jan 2018 21:49

deejay wrote:
Haridas wrote:Equipment design will require worst case (i.e. max weight) number, not average of soilders wt & also max eqpt wt.

I am sure actual mission is not planned by allocating solider by weight quota to meet statisticaly fair allocation to proportional distribution :) .


Sir from memory, troop weight for calculations is taken as 100 kgs with eqpt. Special cases higher weight allowance can be considered. I have never heard of lower weight calculations.

Helicopters are an extremely weight sensitive machine. The rope or boom limitation (though the main factor in this case) comes later. Primary limitation will come in effect due to Free Air Hover to be established for slithering.


don't know if this was posted earlier

TIFWIW

✈Anantha Krishnan M ✈ Retweeted

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Replying to @writetake

270 Kgs or 3 Persons is max capacity of a steel winch.However in this case secondary tethering of the rope was not done.The rope should have been secured at secondary point as a failsafe measure.This is either a SOP flaw or plain carelessness.
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Re: Indian Military Helicopters

Postby ramana » 23 Jan 2018 23:56

chetak, The tethering was a personnel safety measure.

It would not prevent the bracket failure.

Zynda et al are looking at the root cause for the bracket failure.

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Re: Indian Military Helicopters

Postby Jayram » 24 Jan 2018 01:54

Zynda wrote:
Jayram wrote:Per my calculations, the beam was already oversized. Granted, I did a check just on the beam and joints and not the welds. Plus adding stuff to a rectangular beam would be easier from design & fabrication cost & effort. The only thing I would have done differently is to change the orientation of the beam. Instead of having the longer side orient horizontal (parallel to plane of rotor blades), I would have oriented it perpendicular. But I don't know what additional design constraints were present which made HAL go with the current config.

Anyways, it is quite possible that failure analysis may go to NAL. If we are lucky, the report could be made available for public consumption.

Completely agree. In the beginning of my career I have been exposed to HAL incident investigation team and they took all these failures very seriously indeed. The beam as you have calculated out is correctly( or even over) designed and as observed did not fail either elastically (yield stress reached) or completely (to failure) within the beam itself. The beam did resist all stresses as designed and transferred them correctly to the attachment point ie the joint. However failure did happen and it happened at the joint. This can mean one of two things 1) there was a manufacturing defect due to a previously existing crack/notch/inclusion/heat treatment etc etc again at the joint or 2)there was a stress concentration point that made crack initiation and propagation happen due to repeated cycles of loading. To prevent the former from going to failure better manufacturing practices and in some cases in-service visual/ultrasonic inspection techniques would be required. However to prevent the latter ie stress concentration points my contention is a circular form is better since there are no corners in a circle by definition. This will lead to a classic trade off - better resistance to moments but more challenges (cost/wt) in manufacturing. The joint design will get more complex leading to a joint that will look like the upper image in this pic..
Image.
So what happens next. An inspection of all booms in service is the logical next step. If root cause is found to be 1 above then no redesign is necessary however if it 2 then redesign and all options including boom shape/orientation will be on the table.

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Re: Indian Military Helicopters

Postby Haridas » 24 Jan 2018 02:03

chetak wrote:
deejay wrote:
Sir from memory, troop weight for calculations is taken as 100 kgs with eqpt. Special cases higher weight allowance can be considered. I have never heard of lower weight calculations.

Helicopters are an extremely weight sensitive machine. The rope or boom limitation (though the main factor in this case) comes later. Primary limitation will come in effect due to Free Air Hover to be established for slithering.


don't know if this was posted earlier

TIFWIW

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270 Kgs or 3 Persons is max capacity of a steel winch.However in this case secondary tethering of the rope was not done.The rope should have been secured at secondary point as a failsafe measure.This is either a SOP flaw or plain carelessness.
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Chetak ji, What you cite is for winch equipment (which is typically mounted on the starboard side of the ship) and is motorized to move human payload up/down.
The failure was in the slithering rope support that is on the port side (that failed). Apples and oranges specification.

ramana
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Re: Indian Military Helicopters

Postby ramana » 24 Jan 2018 04:28


Jayram
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Re: Indian Military Helicopters

Postby Jayram » 24 Jan 2018 10:22

shiv wrote:
Jayram wrote: My contention is as follows a hollow cylinder will resist both bending and torsional moments better as compared of a hollow square "for the same weight and length".

Please consider me a "near zero" in this discussion hovering around -272 deg C

But I have some empirical awareness based on seeing failures of everyday objects - some of which I have to repair as home Mr Fixit.

Your contention about tube vs square may well be correct - but the actual break that the helo suffered was at the mounting point, i.e. the point where the beam joined the main body of the helicopter. I would have thought that while the rest of the beam certainly is subject to all sorts of bending and torsion stresses - the point where it joins the helo is an especially vulnerable point where the elasticity (??) (is that the right word) of the beam meets the rigidity of the mounting. My guess was that a circular beam could develop a transverse stress tear/crack that extends circumferentially near this joint while a square beam would not allow such a tear to occur or extend. Just a guess. Please say that I am mistaken if this jugaadu information is wrong.

Shiv,
What follows is a simplistic explanation .. I am NO expert in this area.
Are you thinking the horizontal and vertical sides of the boom will be able to resist the bending forces better than a circular wall? I think that true and the Square is more efficient in pure orthogonal moments both horizontal and vertical. But as soon as you introduce twisting moments then the circular form is better since since stress are radial (highest at the circumference and reducing as you get to the center) and one of the rules of design is to fatten the area under stress. So for example an T or I beam (think H on its side) are better in pure bending because in pure bending the top and bottom are tension and compression respectively (and there are no radial stresses) and the center flange has 0 or very little stress. Therefore making the top and bottom flange thick increases the strength without requiring too much extra weight in the center flange except to prevent buckling. A square/rectangular section can be thought of a combination of 2 T flanges joined together on the side. But in twisting moments the square boom is not as efficient because at the corners where the radial stresses are at the highest there is no or enough material and what is worse a small crack or notch could act as a stress raiser leading to quick failure. The simplest example of a circular section is the tube of the bicycle frame.
BTW one example of fatigue loading that highway signs need to take into account that was surprising for me was "Truck Gusts". Every time a truck passed underneath a Freeway sign it induces oscillations in Road signs that are also cantilevered heavily over the 6 or 8 lane highways here.
Last edited by Jayram on 24 Jan 2018 11:03, edited 1 time in total.

chetak
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Re: Indian Military Helicopters

Postby chetak » 24 Jan 2018 10:48

Haridas wrote:
chetak wrote:
don't know if this was posted earlier

TIFWIW


Chetak ji, What you cite is for winch equipment (which is typically mounted on the starboard side of the ship) and is motorized to move human payload up/down.
The failure was in the slithering rope support that is on the port side (that failed). Apples and oranges specification.


Haridas ji,

There was some discussion on the load capacity of the winch. This post was in connection with that topic.

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Re: Indian Military Helicopters

Postby ramana » 25 Jan 2018 08:21


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Re: Indian Military Helicopters

Postby shiv » 25 Jan 2018 08:51

Jayram thx


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