LCA: News & Discussions - October 2016

All threads that are locked or marked for deletion will be moved to this forum. The topics will be cleared from this archive on the 1st and 16th of each month.
Dileep
BRF Oldie
Posts: 5846
Joined: 04 Apr 2005 08:17
Location: Dera Mahab Ali धरा महाबलिस्याः درا مهاب الي

Re: LCA: News & Discussions - October 2016

Postby Dileep » 27 Mar 2017 06:58

Rishi Verma wrote:
Dileep wrote:The continuous firing of Gsh will cause a 50-60Hz vibration with a very strong second harmonic at 100-120Hz. A single shot will cause a shock. Continuous firing at a constant rate will cause vibration onlee.

The tiny para above have too many factually incorrect statements, terminology etc. If discussing engineering it's important to use the right terminology and not throw in terms like "2nd harmonic" besides I think you are mistaking resonance with vibrations.

OK, kindly list at least some out of the 'too many', for knowledge sake. Also, if you know how the gun vibration looks like, please share it, since it would come useful.

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 27 Mar 2017 07:13

Eric Leiderman wrote:Dampening to a large extent depends on mounting. the weight of the source which is causing the issue, to control the recoil the amplitude of the force to be dampened. Taking a wild guess below. the dampening might cause inaccuracies in placement off shells on target, however that might be corrected with soft wear.

I suspect the guns have to have a rigid mounting or else they will be inaccurate. The recoil energy will be transmitted in full to the frame. After that it has to be dissipated safely.

I heard a funny story this last Aero India from a helo pilot who was involved with testing a gun on a helicopter - may have been the Mi 17. When he went to shoot at the target he found a man sitting on it and did not shoot. He was asked why he did not shoot and said that there was a man on it. He was told that if he had aimed properly the gun would have sprayed bullets everywhere but on the target and the man would have been perfectly safe.

JayS
Forum Moderator
Posts: 4547
Joined: 11 Aug 2016 06:14

Re: LCA: News & Discussions - October 2016

Postby JayS » 27 Mar 2017 14:07

shiv wrote:
Eric Leiderman wrote:Dampening to a large extent depends on mounting. the weight of the source which is causing the issue, to control the recoil the amplitude of the force to be dampened. Taking a wild guess below. the dampening might cause inaccuracies in placement off shells on target, however that might be corrected with soft wear.

I suspect the guns have to have a rigid mounting or else they will be inaccurate. The recoil energy will be transmitted in full to the frame. After that it has to be dissipated safely.

Actually gun need not be mounted on a rigid mount to be accurate. In theory it could be mounted on artificially stabilised platform. Just saying. Of coarse its too complicated a system for fighter gun mounting.

One would need both mass and stiffness of the structure to adjust the frequency response and springs/hydraulics to dampen the force and soft mounts (again a kind of dampening) to isolate the rest of the aero-structure from the gun vibrations. The overall vibration response of the system would depend on these three parameters - mass, stiffness and dampening. If you see the modal equation, you will see these exact three terms. The quantity of each parameter would vary in each system, of coarse.

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 27 Mar 2017 14:13

Yes but the recoil energy has to go somewhere and it will pass from the stabilization system to the mount - which is the aircraft.

Rishi Verma
BRFite
Posts: 1019
Joined: 28 Oct 2016 13:08

Re: LCA: News & Discussions - October 2016

Postby Rishi Verma » 27 Mar 2017 14:43

Dileep wrote:
Rishi Verma wrote:The tiny para above have too many factually incorrect statements, terminology etc. If discussing engineering it's important to use the right terminology and not throw in terms like "2nd harmonic" besides I think you are mistaking resonance with vibrations.

OK, kindly list at least some out of the 'too many', for knowledge sake. Also, if you know how the gun vibration looks like, please share it, since it would come useful.


ok, i will make a zimble list of what happens and one can find the incorrect premises in the para

0) hand held gun recoil is not the same as vibrations caused by gatling type of rapid fire gun, depending on how the gun is mounted, the barrel vibrations get transmitted to the support structure (here the LCA)

http://www.varmintal.com/atune.htm

(in above link a single shot results in vibrations of the barrel at about 80Hz, the freq depends on the length of the barrel, speed of the bullet, etc and is well understood with many software models available for simulations)

even a single shot from any gun can cause vibrations

1) you estimated 60Hz basic freq. based on firing rate of 3600 rounds per min, lets assume its the dominant "natural frequency", typical gatling type of guns have a wide range from 2000 rounds per min to 6000 rounds per min

2) "2nd harmonic" is not caused by gun itself but is caused by gun + support (the whole system) and if 2nd harmonic is dominant then even harmonics are present so the "natural frequency " 60Hz is not present which is 1f

2f, 4f, 6f... Etc

If odd harnonics are caused by the system then
1f, 3f, 5f etc

(imagine a pendulum in free swing.. The natural frequency is 1 divided by the period of oscillation, but if someone taps the swinging pendulum at some frequency then harmonics will arise)

3) these frequency domain harmonics are not the be confused with fourier series approximations of signals where all harmonics extending to infinity are present to define any wave shape

4) if the pendulum (or gatling gun) are in resonance (pendulum being tapped with a hammer at same frequency or a frequency of any harmonic (odd or even) then the pendulum motion will reach "instability", and may cause destructive behaviour.

Dileep
BRF Oldie
Posts: 5846
Joined: 04 Apr 2005 08:17
Location: Dera Mahab Ali धरा महाबलिस्याः درا مهاب الي

Re: LCA: News & Discussions - October 2016

Postby Dileep » 27 Mar 2017 16:37

Oh.. KLPD. I was expecting some useful insight. :sigh:

To be clear, I was not talking about barrel vibration or the sympathetic vibration within the structures. I was talking about the source of vibration. If you fire a gun at 60 rounds per second, the resulting excitation at the gun mount will have the fundamental frequency at 60Hz and a very strong harmonic at 120Hz. How this excitation gets propagated within the structure entirely depend upon the structure itself.

There is no confusion between the 'frequency domain harmonics' and the fourier series harmonics. They are one and the same. If you haven't figured that out, then you are missing a lot of science.

JayS
Forum Moderator
Posts: 4547
Joined: 11 Aug 2016 06:14

Re: LCA: News & Discussions - October 2016

Postby JayS » 27 Mar 2017 20:10

shiv wrote:Yes but the recoil energy has to go somewhere and it will pass from the stabilization system to the mount - which is the aircraft.


True. So one has to design the structure which can absorb this energy and dissipate it in least harmful way. As Dileep saar explained in his post above, we are talking of response of the structure (gun mounting and the aero-structure together) to the forced excitation of given force and given frequency. So you play with the mass, stiffness and dampening parameters and adjust them so that the structure responds to the forced excitation in the way you want. For example, design it such way that its natural frequency does not coincide the excitation frequency or its harmonics (to certain orders, not all) of the originating force, the recoil in this case. Typically speaking stiffer the structure, higher is its natural frequency and tougher it is to excite it, because it take far more energy to excite higher frequencies. In contrast, lower mass gives higher frequency. But lower mass may also give less stiffness to the structure. So you have to optimize. The structural engineers do what is called as Modal analysis to check and optimize the vibrational characteristics of the structure, both natural and forced.

At a mounting locations where the amplitude and frequencies are in manageable range you can put dampeners in those mounts so that you reduce transmission of vibrations further into the structure. For example, in a bike, the engine produces vibrations and transferred to the frame which in turn transfer it to say the fuel tank. Now of coarse its difficult to mount engine itself on soft mountings. But you can easily attach the fuel tank to the frame using rubber grommets, so that the tank itself does not vibrate even if the frame vibrates somewhat.

I expect, even if the Gun is rigidly mounted to the Gun mounting structure, the gun mounting structure itself would be attached to the rest of the air-frame through some kind of vibration isolation points, away from the gun itself. And similarly the LRUs in the vicinity of the gun may themselves be attached to the main air-frame on such soft-mounting to isolate them from the vibrations somewhat.

Zynda
BRFite
Posts: 1910
Joined: 07 Jan 2006 00:37
Location: J4

Re: LCA: News & Discussions - October 2016

Postby Zynda » 27 Mar 2017 20:17

^^+10 JayS. Wanted to write the above but you have explained it eloquently.

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 27 Mar 2017 21:09

JayS wrote:
At a mounting locations where the amplitude and frequencies are in manageable range you can put dampeners in those mounts so that you reduce transmission of vibrations further into the structure. For example, in a bike, the engine produces vibrations and transferred to the frame which in turn transfer it to say the fuel tank. Now of coarse its difficult to mount engine itself on soft mountings. But you can easily attach the fuel tank to the frame using rubber grommets, so that the tank itself does not vibrate even if the frame vibrates somewhat.

I expect, even if the Gun is rigidly mounted to the Gun mounting structure, the gun mounting structure itself would be attached to the rest of the air-frame through some kind of vibration isolation points, away from the gun itself. And similarly the LRUs in the vicinity of the gun may themselves be attached to the main air-frame on such soft-mounting to isolate them from the vibrations somewhat.

A lucid explanation.

Getting back to what sparked this discussion was whether gun tests can be considered over and done with at an early stage and whether HAL were somewhat negligent in not thinking about the gun and leaving tests to the last stage, it still looks like that is an unfair assessment. Late Gp Capt Kapil Bhargava in the link I have posted says that the manufacturer's certification of the gun is different from the user's certification. The user, in this case the IAF, having lost men in crashes while certifying aircraft guns, is not likely to accept reassurances that gun tests were done long ago and. They will want to ensure that everything is pukka and I am sure HAL is aware of this. I am certain that despite all the facts listed out by people who have some in depth knowledge of vibration damping, gun tests will be done at the very end because gun firing increases vibration to levels that are several times higher than the highest design tolerances of all other aircraft sourced vibrations. A plane in a tight turn on full power with afterburners trying to put some lead into an aerial target will be producing the devil's death rattle in terms of vibration so I dispute the idea that the tests can be over and done with at an early stage.

As an aside - I am sure many forumites will not have seen what is under the hood of the old Fiat 1100s (later Premier Padmini) . Fiat 1100 engines were secured to the chassis with four dense rubber grommets to damp vibration. I was surprised to see that as a 10 year old boy in my father's car - I did not think a rubber component fitted in with the hard hot stuff near the engine. I still have a couple of those grommets at home - serving as door stops.

nandakumar
BRFite
Posts: 1202
Joined: 10 May 2010 13:37

Re: LCA: News & Discussions - October 2016

Postby nandakumar » 27 Mar 2017 21:26

I do not know anything about the technology of vibration dampners. But I know that during my days at Telco (Tata Motors) that a start up company based in Madras founded by a former professor of IIT Madras started supplying vibration dampners to the Tata vehicles. The company, if I remember correctly, was called Vibromech Engineers. Evidently they were a premium supplier that their bills cannot remain unsettled. The whole tech team would descend on the accounts department if there was any hitch on the payment side. They did use some kind of rubber pads. This was in the late 70s.

JayS
Forum Moderator
Posts: 4547
Joined: 11 Aug 2016 06:14

Re: LCA: News & Discussions - October 2016

Postby JayS » 27 Mar 2017 21:36

shiv wrote:A lucid explanation.

Getting back to what sparked this discussion was whether gun tests can be considered over and done with at an early stage and whether HAL were somewhat negligent in not thinking about the gun and leaving tests to the last stage, it still looks like that is an unfair assessment. Late Gp Capt Kapil Bhargava in the link I have posted says that the manufacturer's certification of the gun is different from the user's certification. The user, in this case the IAF, having lost men in crashes while certifying aircraft guns, is not likely to accept reassurances that gun tests were done long ago and. they will want to ensure that everything is pukka and I am sure HAL is aware of this. I am certain that despite all the facts listed out by people who have some in depth knowledge of vibration damping, gun tests will be done at the very end because gun firing increases vibration to levels that are several times higher than the highest design tolerances of all other aircraft sourced vibrations. A plane in a tight turn on full power with afterburners trying to put some lead into an aerial target will be producing the devil's death rattle in terms of vibration so I dispute the idea that the tests can be over and done with at an early stage.

As an aside - I am sure many forumites will not have seen what is under the hood of the old Fiat 1100s (later Premier Padmini) . Fiat 1100 engines were secured to the chassis with four dense rubber grommets to damp vibration. I was surprised to see that as a 10 year old boy in my father's car - I did not think a rubber component fitted in with the hard hot stuff near the engine. I still have a couple of those grommets at home - serving as door stops.


I agree fully. As I said already, my opinion has been that they have done enough testing already that gives them good confidence that the gun will not cause issues later. I would say they have tested the gun mounting structure for vibration and it already is absorbing vibration quite satisfactorily while not transmitting any harmful levels of vibrations further into the structure that may cause issues to LRUs. They must have done LRU qualification at the ground conditions as well, at least at the preliminary levels. The next step, that is testing all LRUs for vibration in all possible flight conditions and final certification can be done only when final configuration is in place. Which was not until recently. And if you have good confidence on the machine then you better do the certification at the end when everything else is finalised. That way you don't have to repeat tests if some LRU changes or layout of LRUs change. Of coarse there is risk of redesign due to gun vibrations but then this really depends on how much confident you are on the gun mounting structure which is based on what you saw in the butt firing tests (hilarious term BTW). Since we don't know actual results, we can only guesstimate based on what ADA says.

And since LCA project is governed by a body comprised of IAF/HAL/ADA and presided by RM, all the stakeholders are already in the loop. A crucial test like Gun testing could not have been deferred without a decent level of confidence by all the stakeholders. I haven't heard so much as noise from IAF on gun testing so far. They don't seem worried either.

ramana
Forum Moderator
Posts: 54701
Joined: 01 Jan 1970 05:30

Re: LCA: News & Discussions - October 2016

Postby ramana » 28 Mar 2017 00:24

To second Shiv, the gun trials with engine running to see effect of gun exhaust gases has not been mentioned.
Then all up flight testing is another test.

Thanks everyone for all the informative discussion.
Again avionics packages are qualified by to a 3 sigma level shock and vibration spectrum. g/sec^2 vs frequency.

How this is obtained is shock and vibration sensor data is measured from actual gun firing trials in g/Sec^2 format. Then 3 sigma levels are applied and then the spectra is smoothed whit a straight line approximations. This is fed to a shaker table on which the package is mounted in a fixture. Electronically active Pkg will have sensors to see the response.

All this is in S&V Handbook from McGraw Hill.

ramana
Forum Moderator
Posts: 54701
Joined: 01 Jan 1970 05:30

Re: LCA: News & Discussions - October 2016

Postby ramana » 28 Mar 2017 00:25

Anyone please post gun mounting sketches from Flight Intl or such cutout pictures of modern jet fighters.
Prefer fuselage mountings as opposed to wing mounted.

prasannasimha
Forum Moderator
Posts: 1200
Joined: 15 Aug 2016 00:22

Re: LCA: News & Discussions - October 2016

Postby prasannasimha » 28 Mar 2017 00:39

If I remember right the gun was fired while mounted on one of the Tejas prototypes when tested (remember the paper with marking where we did an analysis of bullet dispersion - that gun was mounted on a Tejas and there was even a video showing it firing albeit on the ground.That itself must have given a lot of data wrt vibration and other issues.

Indranil
Forum Moderator
Posts: 8186
Joined: 02 Apr 2010 01:21

Re: LCA: News & Discussions - October 2016

Postby Indranil » 28 Mar 2017 00:43

Nice posts all.

Jay, you are right. There is zero worry about the gun firing among anybody in the program. But it is they who told me that they should have cleared the gun first. Unfortunately, as the program was missing deadlines and they had to prioritize other deliverables for desired milestones. PV-3 has been fitted with the gun and instrumented for testing the same from the past 3 years.

None the less, they know how the vibration and shocks created by the gun, and every LRU is unit-tested for their capability to withstand those vibrations and shocks. Dileep sir would know.

Indranil
Forum Moderator
Posts: 8186
Joined: 02 Apr 2010 01:21

Re: LCA: News & Discussions - October 2016

Postby Indranil » 28 Mar 2017 00:47

prasannasimha wrote:If I remember right the gun was fired while mounted on one of the Tejas prototypes when tested (remember the paper with marking where we did an analysis of bullet dispersion - that gun was mounted on a Tejas and there was even a video showing it firing albeit on the ground.That itself must have given a lot of data wrt vibration and other issues.

You are right. Additionally, when on the ground, the aircraft is tethered while the gun is fired. This amplifies the effect of gun firing. In the air, they expect the firing to be smoother.

Fun fact: At maximum firing rate, the recoil from the gun is stronger than the maximum thrust produced by the engine on the A-10.

JayS
Forum Moderator
Posts: 4547
Joined: 11 Aug 2016 06:14

Re: LCA: News & Discussions - October 2016

Postby JayS » 28 Mar 2017 01:20

ramana wrote:To second Shiv, the gun trials with engine running to see effect of gun exhaust gases has not been mentioned.
Then all up flight testing is another test.


Gas ingestion should not be a worry given that the gun resides a bit downstream from the air-intakes or the axillary intakes.

JayS
Forum Moderator
Posts: 4547
Joined: 11 Aug 2016 06:14

Re: LCA: News & Discussions - October 2016

Postby JayS » 28 Mar 2017 01:28

Indranil wrote:
prasannasimha wrote:If I remember right the gun was fired while mounted on one of the Tejas prototypes when tested (remember the paper with marking where we did an analysis of bullet dispersion - that gun was mounted on a Tejas and there was even a video showing it firing albeit on the ground.That itself must have given a lot of data wrt vibration and other issues.

You are right. Additionally, when on the ground, the aircraft is tethered while the gun is fired. This amplifies the effect of gun firing. In the air, they expect the firing to be smoother.

Fun fact: At maximum firing rate, the recoil from the gun is stronger than the maximum thrust produced by the engine on the A-10.


hmm. I saw figure of ~3000kgf recoil force for Gsh-23 on one site.

Neshant
BRF Oldie
Posts: 4850
Joined: 01 Jan 1970 05:30

Re: LCA: News & Discussions - October 2016

Postby Neshant » 28 Mar 2017 06:09

Thank godness they did not put an even heavier caliber Gasha gun on the LCA.
Twin 23 mm barrels are at the top end of what it should carry given its size/weight.

Dileep
BRF Oldie
Posts: 5846
Joined: 04 Apr 2005 08:17
Location: Dera Mahab Ali धरा महाबलिस्याः درا مهاب الي

Re: LCA: News & Discussions - October 2016

Postby Dileep » 28 Mar 2017 07:16

Ramana, the spec is in g^2/Hz. One should test at the fundamental and second harmonic, plus a broad band at higher frequencies. This is because there would be a mix of frequencies there due of the resonance of a number of elements.

I haven't figured the unit/dimension of this. Mean while, how much does 1 g^2/Hz feels like? any idea?

Cain Marko
BRF Oldie
Posts: 4510
Joined: 26 Jun 2005 10:26

Re: LCA: News & Discussions - October 2016

Postby Cain Marko » 28 Mar 2017 07:24

FOC in 2018? Noooooooooooooooooooooooooooooooooooooooooooooooooooooooo! WTF - I thought derby was being tested as we speak and gun trials were almost done with already. Phuck it! This is very, very depressing...... :((

putnanja
BRF Oldie
Posts: 4487
Joined: 26 Mar 2002 12:31
Location: searching for the next al-qaida #3

Re: LCA: News & Discussions - October 2016

Postby putnanja » 28 Mar 2017 07:29

Might be a dumb question, but isn't there a difference in how the frequencies are transmitted in metal structures compared to composite ones? When the vibrations pass from metal structures to composite and back to metal (assuming there is no common metal structure to which both the gun and LRUs are mounted), there would be shifting of frequencies, right? And wouldn't composites dampen the frequencies to some level compared to metal?

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 28 Mar 2017 07:48

Regarding GSh 23

shiv wrote:OFB site says each projectile is 174 grams and is shot off at 720 m/sec at the rate of 50 plus rounds per second.

The barrel length of GSh 23 is 1 meter

I am gradually getting worse at all this but the little high school physics I can recall tells me that this is like a 4500 kg weight pushing back the aircraft (albeit for a brief period of time). Perhaps a person who is more in touch with such stuff can come up with a figure for a layperson to relate to - ie kilos as opposed to Joules

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 28 Mar 2017 08:01

ramana wrote:
How this is obtained is shock and vibration sensor data is measured from actual gun firing trials in g/Sec^2 format. Then 3 sigma levels are applied and then the spectra is smoothed whit a straight line approximations. This is fed to a shaker table on which the package is mounted in a fixture. Electronically active Pkg will have sensors to see the response.

ramana I may be mistaken but long ago on the forum someone had posted a pdf or image about "vibration testing" of the LCA airframe. Basically a shaker that shakes the thing up. This was, I am sure, done in the early stages of design

Rishi Verma
BRFite
Posts: 1019
Joined: 28 Oct 2016 13:08

Re: LCA: News & Discussions - October 2016

Postby Rishi Verma » 28 Mar 2017 08:22

shiv wrote:Regarding GSh 23

shiv wrote:OFB site says each projectile is 174 grams and is shot off at 720 m/sec at the rate of 50 plus rounds per second.

The barrel length of GSh 23 is 1 meter

I am gradually getting worse at all this but the little high school physics I can recall tells me that this is like a 4500 kg weight pushing back the aircraft (albeit for a brief period of time). Perhaps a person who is more in touch with such stuff can come up with a figure for a layperson to relate to - ie kilos as opposed to Joules


ShivJi, your curiocity is laudable but your assumptions are way off, and its not just "little high school physics"

Its not just a case of bullet exiting the barrel and counter-force is the "recoil".

When a gun is fired there is a mini explosion inside the barrel and most of the energy is dissipated as heat and in expanding gases, and the "left over" energy is then felt as recoil which is a small fraction of energy used to send the bullet out (hopefully to kill a paki)

A shot gun can cut a paki in 1/2 a km away, and if that force were 100% recoil then imagine what would happen to the shooter.
Last edited by Rishi Verma on 28 Mar 2017 08:29, edited 1 time in total.

srai
BRF Oldie
Posts: 4699
Joined: 23 Oct 2001 11:31

Re: LCA: News & Discussions - October 2016

Postby srai » 28 Mar 2017 08:29

shiv wrote:
ramana wrote:
How this is obtained is shock and vibration sensor data is measured from actual gun firing trials in g/Sec^2 format. Then 3 sigma levels are applied and then the spectra is smoothed whit a straight line approximations. This is fed to a shaker table on which the package is mounted in a fixture. Electronically active Pkg will have sensors to see the response.

ramana I may be mistaken but long ago on the forum someone had posted a pdf or image about "vibration testing" of the LCA airframe. Basically a shaker that shakes the thing up. This was, I am sure, done in the early stages of design


Check out Tests and Test Facilities (pages 7-8): DRDO Tech Focus Feb 2011: LCA Technologies

Ground Vibration Test (GVT) Rig Picture (page 8 ): ADA - Tejas Brochure (IOC)

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 28 Mar 2017 08:40

Rishi Verma wrote:
Its not just a case of bullet exiting the barrel and counter-force is the "recoil".

When a gun is fired there is a mini explosion inside the barrel and most of the energy is dissipated as heat and in expanding gases, and the "left over" energy is then felt as recoil which is a small fraction of energy used to send the bullet out (hopefully to kill a paki)

A shot gun can cut a paki in 1/2 a km away, and if that force were 100% recoil then imagine what would happen to the shooter.


No that was not the question. The question was - given a bullet of 174 grams, a barrel length of 1 meter, a muzzle velocity of 720 meters per second what is the force generated to push the bullet out and conversely what is the theoretical recoil force based on Shri Newton's 3rd law?

Do you have an answer to that question? Fuzzy answers like "some of it is lost as heat. Some more in barrel vibration resulting in more heat" etc only add more complexity. I am not even going there. How much force (preferably in Kilograms) is generated using the above facts about the GSh 23 gun barrel and shell.

Of course energy is dissipated at every joint and linkage. But at the outset - the moment the 174 gram shell is accelerated to 720 m/s at the end of the barrel what is the force generated? That is all. Simple. No complexity. This is a question that used to get asked in high school and for college entrance exams. Still does.

I am sure you know the simple physics formulae needed to calculate that.
Last edited by shiv on 28 Mar 2017 09:03, edited 1 time in total.

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 28 Mar 2017 08:54

Rishi Verma wrote:A shot gun can cut a paki in 1/2 a km away, and if that force were 100% recoil then imagine what would happen to the shooter.

I presume that when you use the word shotgun, you mean shotgun and you know what is meant by shotgun. If you are talking about hand-held shotguns, what you say is wrong

I believe you need to be more clear about what you are referring to when you say 100% recoil.

100% recoil is the recoil that is measurable exactly at the point when the bullet is about to emerge from the barrel and no gases have escaped yet. Once the gases escape and expand the recoil tapers off.

It is possible to Google for images of the results of shotguns on humans at point blank range, 1 meter 10 meters etc. At 500 meters a few eye injuries are possible. Most shotguns are ineffective beyond 100 meters. They will certainly not cut a Paki in half at 500 meters. At 500 meters one may not even be able to kill a pigeon with a shotgun. You check this out yourself if you visit a shooting range in Amreeka or if you join a local rifle association in India.

Rakesh
Forum Moderator
Posts: 9488
Joined: 15 Jan 2004 12:31
Location: Planet Earth
Contact:

Re: LCA: News & Discussions - October 2016

Postby Rakesh » 28 Mar 2017 09:02

Hakeemji....1/2 km away = 1,640.42 feet :mrgreen:

Image

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 28 Mar 2017 09:05

Rakesh wrote:Hakeemji....1/2 km away = 1,640.42 feet :mrgreen:

Image

I know Rakesh I know.

But you know - most people don't even know the difference between a shotgun and a rifle. The press in India certainly had no idea whatsoever when the eye injuries in Kashmir stuff was in the news.

Rishi Verma
BRFite
Posts: 1019
Joined: 28 Oct 2016 13:08

Re: LCA: News & Discussions - October 2016

Postby Rishi Verma » 28 Mar 2017 09:56

shiv wrote:
Rishi Verma wrote:A shot gun can cut a paki in 1/2 a km away, and if that force were 100% recoil then imagine what would happen to the shooter

....
I believe you need to be more clear about what you are referring to when you say 100% recoil.

100% recoil is the recoil that is measurable exactly at the point when the bullet is about to emerge from the barrel and no gases have escaped yet. Once the gases escape and expand the recoil tapers off.


ShivJi, dont change the subject about shotgun vs rifle (cutting paki in half was an enjoyable graphic) ... But if a bullet exiting the barrel has a kinetic energy of 2000 Joules at the moment, the shooter will feel less than 100 Joules as "recoil",
the rest is dissipated as heat, as gasses escaping, some absorbed by the inertia of the gun.. of course you will keep arguing and i dont get paid to convince you so enjoy...

Indranil
Forum Moderator
Posts: 8186
Joined: 02 Apr 2010 01:21

Re: LCA: News & Discussions - October 2016

Postby Indranil » 28 Mar 2017 10:04

Those eye injuries can happen Hakeem. Those pellets need not be travelling at lethal speeds and yet damage the eye. IA never refuted that. What IA is saying, what are we supposed to do to stay on top? What projectile may I use against their projectiles? Anyways that's well OT here.

Anyways, I will take a shot at your class XIth problem. I don't know the fluid dynamics in a gun. I am assuming that the bullet starts from speed of 0 and accelerates uniformly to a speed of 720 mtrs/sec within a distance equal to the length of the barrel = 1 mtr.

1/2 X a X delta_t^2 = 1
delta_v X delta_t = 2 (substituting a = delta_v/delta_t)
delta_t = 2 / delta_v ------ (i)

By Newton's second law
f = m X delta_v / delta_t
f = m X delta_v^2/2 (from i)
f = 0.174 X 720 X 720 /2 N
f = 45 kN (approx 4588 kgf)
So, what Jay read (3000 kgf must be the right number).

Impulse = f * delta_t = 45 kN * 1/360 sec = 125.28 Ns

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 28 Mar 2017 10:18

Rishi Verma wrote:
ShivJi, dont change the subject about shotgun vs rifle (cutting paki in half was an enjoyable graphic) ... But if a bullet exiting the barrel has a kinetic energy of 2000 Joules at the moment, the shooter will feel less than 100 Joules as "recoil",
the rest is dissipated as heat, as gasses escaping, some absorbed by the inertia of the gun.. of course you will keep arguing and i dont get paid to convince you so enjoy...

:rotfl:
This is called making a mockery out of physics. Joules is work done. Not force. Did not read the question.

I am sure you can enjoy yourself too if you can stop trying to attract my attention by replying to my posts and putting yourself in a rut with errors that you need to try and wriggle out of like that Paki cut-in-half analogy. Indranil has answered the question that you have wriggled out of answering.

But I have an idea and I will make it easier for you..

Dileep
BRF Oldie
Posts: 5846
Joined: 04 Apr 2005 08:17
Location: Dera Mahab Ali धरा महाबलिस्याः درا مهاب الي

Re: LCA: News & Discussions - October 2016

Postby Dileep » 28 Mar 2017 10:31

Good old Yakov Perelman had treated this in some detail. The calculations assume linear acceleration within the barrel, which gives the least impulse. The actual motion would be some kind of decreasing acceleration, since the gases are expanding. So, the actual impulse would be higher.

Philip
BRF Oldie
Posts: 20890
Joined: 01 Jan 1970 05:30
Location: India

Re: LCA: News & Discussions - October 2016

Postby Philip » 28 Mar 2017 12:15

Don't know if this was posted earlier.Xcpts only about the NLCA,carrier matters,though the rest of the interview is quite illuminating.

http://www.thehindu.com/news/national/w ... 664481.ece

Xcpts:
We back indigenisation, but Tejas didn’t fit the bill: Navy chief
S. Anandan MARCH 25, 2017 22:11 IST

Naval chief outlines his vision for the force based on timelines for projects and induction of personnel, especially women

The Chief of the Naval Staff, Admiral Sunil Lanba, in a wide-ranging interview with The Hindu, clarifies that the Navy has only taken a purely technical decision in turning down the naval version of the light combat aircraft developed by the DRDO despite its strong commitment to indigenisation. He highlights the need to step up training facilities to meet personnel shortage and the Navy’s strong ‘Act East’ focus.

All along, the Navy had placed thrust on indigenisation of assets, but is now facing flak for turning down the home-grown fighter LCA Navy which is being read as a retreat from its commitment to indigenisation.

We are the pioneers of indigenisation, which we started back in the 1960s and have worked shoulder to shoulder with the DRDO, whose naval labs also have naval personnel. As for the LCA (Light Combat Aircraft Tejas) programme, the Navy was the first service to support ADA (the Aeronautical Development Agency) in its development and the Air Force came on board at a later date. What the Navy wants is a deck-based fighter, but the LCA Navy Mk 1 doesn’t meet that requirement. Its power-to-weight ratio, the thrust the engine generates [are insufficient] and it’s underpowered for the airframe. Unfortunately, even the Mk2 variant doesn’t qualify. That’s why we took this case up to the Defence Ministry. But let me be clear on this. We continue to support the ADA and the DRDO in the development of an indigenous deck-based fighter. A good 25% of the financial support for the project comes from the Navy. As and when ADA produces a fighter that can operate from the deck of an aircraft carrier, we will be more than willing to acquire it and fly it. The LCA Navy was supposed to be flying off from [the aircraft carrier] Vikramaditya. The second carrier Vikrant should be sailing in 2019. So we want a deck-based fighter today. The timelines that ADA promised to generate one was over a decade back. We are looking at a period of at least a decade for ADA to produce a deck-based fighter. In the meantime, the Ministry has allowed us to go ahead and look for a fighter that meets our requirements following which we issued an RFI.

Timelines have slipped for the under-construction maiden indigenous carrier Vikrant as well thanks to delay in delivery of aviation equipment from Russia. Also, what’s the latest on the third carrier?

There’ve been some delays in the delivery of equipment for the aviation complex from Russia. We’ve been working in close coordination with the Cochin Shipyard [which is building the carrier] and the Russians to compress the timelines of delivery of those equipment so that the programme continues on schedule. We are hopeful that Vikrant will start going to trials in 2019.

As for the IAC-II [second indigenous aircraft carrier], we are taking up the case with the ministry for which we will get an approval sooner than later. We are looking at a CATOBAR aircraft carrier above 65,000 tonnes and with EMALS and an advanced air strip.

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 28 Mar 2017 12:23

Dileep wrote:Good old Yakov Perelman had treated this in some detail. The calculations assume linear acceleration within the barrel, which gives the least impulse. The actual motion would be some kind of decreasing acceleration, since the gases are expanding. So, the actual impulse would be higher.

OT Dileep. Most gun propellants are slow burn and not a single quick bang so they keep producing gas as the bullet/ shell moves down the barrel causing constant acceleration. No drop in pressure as long as the propellant load is designed well.

Cordite burn video
https://youtu.be/CpbbyiE7xVw

JayS
Forum Moderator
Posts: 4547
Joined: 11 Aug 2016 06:14

Re: LCA: News & Discussions - October 2016

Postby JayS » 28 Mar 2017 13:00

*deleted - OT*
Last edited by JayS on 29 Mar 2017 11:24, edited 1 time in total.

JayS
Forum Moderator
Posts: 4547
Joined: 11 Aug 2016 06:14

Re: LCA: News & Discussions - October 2016

Postby JayS » 28 Mar 2017 13:15

shiv wrote:
Rakesh wrote:Hakeemji....1/2 km away = 1,640.42 feet :mrgreen:

Image

I know Rakesh I know.

But you know - most people don't even know the difference between a shotgun and a rifle. The press in India certainly had no idea whatsoever when the eye injuries in Kashmir stuff was in the news.


I find playing video games is a very good way to get acquainted with Guns, at least to the level where one can differentiate a shotgun from a pistol or from a rifle or from a Howitzer :lol: .

shiv
BRF Oldie
Posts: 34982
Joined: 01 Jan 1970 05:30
Location: Pindliyon ka Gooda

Re: LCA: News & Discussions - October 2016

Postby shiv » 28 Mar 2017 14:19

JayS wrote:
I am thinking I would rather have a profile with quick rise to max value and thereon decay in chamber pressure than a constant pressure or ever rising profile. Because having higher pressure at the end when the bullet is exiting the barrel is waste of energy. Ideally I would like to give all the energy to the gun in a single very short impulse.

All OT for this thread but I do recall reading about artillery shells where they try to design a burn for constant acceleration to end of barrel rather than "one kick" and reduced acceleration. That said since artillery shells come with different charges there must be situations in which it is one kick for lower ranges and a huge fireball from wasted propellant for maximum range.

There are gun enthusiast videos (obviously Amreeki) that show the difference between the same bullets fired with higher and lower propellant charges and typically the higher propellant does exactly what you say - ie waste some energy into the atmosphere with a big bang and flash + smoke.

JayS
Forum Moderator
Posts: 4547
Joined: 11 Aug 2016 06:14

Re: LCA: News & Discussions - October 2016

Postby JayS » 28 Mar 2017 14:54

*deleted - OT*
Last edited by JayS on 29 Mar 2017 11:24, edited 1 time in total.


Return to “Trash Can Archive”

Who is online

Users browsing this forum: No registered users and 18 guests