Jeff Duquette Posted July 4, 2006 Share Posted July 4, 2006 The 50% Zone is +/-0.67449σ. Run your Z-values. +/-1σ would imply you are referring to an ~68.27% Zone. I am referring to shot-to-shot dispersion -- systematic error related to the ammunition. As to what you are referring to with “muzzle dispersion”, well I am still confused as to what it is supposed to represent and how you developed this number. It’s not really nomenclature I have seen before. Is this your own term? Perhaps you can walk me through an example of how you determined this value so I have an idea as to what it is you are talking about. As to the numbers I have posted seeming too small – well I can’t help that -- they are what they are. The 50% zones for 88mmL56 firing pzgr. were 0.4-mils in height & 0.2-mils in width at 1000m. A pretty far piece from 1-mil, and this was crica-1940’s technology. 0 Quote Link to comment Share on other sites More sharing options...
Jeff Duquette Posted July 4, 2006 Share Posted July 4, 2006 Sorry. One more question. You said you were employing "Applied operations research: Examples from defence assessment", by R W Shephard et al. Which excercise are you refering to? #5? 0 Quote Link to comment Share on other sites More sharing options...
John D Salt Posted July 5, 2006 Share Posted July 5, 2006 Originally posted by Jeff Duquette: The 50% Zone is +/-0.67449σ. Indeed so. Serves me right for looking at the nearest thing to hand instead of digging out a table of standard normal variates. I am now slightly mystified as to why the figure 0.74 is given in PRO doc WO 291/1330, "The probability of hitting targets with artillery fire", but I s'pose a simple typo from not hitting the "6" key hard enough would be one explanation. Originally posted by Jeff Duquette: I am referring to shot-to-shot dispersion -- systematic error related to the ammunition. And the tube, surely? I imagine that it includes errors due to barrel whip and muzzle brake interference? It's not clear to me whether it includes jump -- since gun barrels tend to have pretty good rotational symmetry I can't imagine another reason for differences in horizontal and vertical dispersion, but, as you can probably tell, it's not really my subject. Originally posted by Jeff Duquette: As to what you are referring to with “muzzle dispersion”, well I am still confused as to what it is supposed to represent and how you developed this number. It’s not really nomenclature I have seen before. Is this your own term? Perhaps you can walk me through an example of how you determined this value so I have an idea as to what it is you are talking about. I suppose I should say "s.d. of projectile dispersion at the muzzle from all causes except range estimation error and laying error in tracking a moving target", but that's a bit of a mouthful. I determined this number through the long-established method of SWAG. I have a very limited quantity of gun accuracy data, so any pointers you can give to more would be most welcome. Originally posted by Jeff Duquette: As to the numbers I have posted seeming too small – well I can’t help that -- they are what they are. The 50% zones for 88mmL56 firing pzgr. were 0.4-mils in height & 0.2-mils in width at 1000m. A pretty far piece from 1-mil, and this was crica-1940’s technology. I'm not saying they're too small; I'm just impressed by how small they are. I suspect that ballistic dispersion makes a much smaller contribution to the error budget than I had previously thought. Originally posted by Jeff Duquette: Sorry. One more question. You said you were employing "Applied operations research: Examples from defence assessment", by R W Shephard et al. Which excercise are you refering to? #5? And 6, yes. I have browsed through the reports from the original studies on which exercise 5 was based, but I seem to have put the reference down somewhere very safe. All the best, John. 0 Quote Link to comment Share on other sites More sharing options...
WineCape Posted July 5, 2006 Share Posted July 5, 2006 John, Just couriered the material promised (Re: hopefully clarifying your understanding of adiabatic shear stress banding) today via TNT International. Will take between 12-16 working days to get to Wales. Please let me know when you receive it. Sincerely, Charl Theron [ July 05, 2006, 04:27 AM: Message edited by: WineCape ] 0 Quote Link to comment Share on other sites More sharing options...
John D Salt Posted July 5, 2006 Share Posted July 5, 2006 Originally posted by WineCape: John, Just couriered the material promised (Re: hopefully clarifying your understanding of adiabatic shear stress banding) today via TNT International. Will take between 12-16 working days to get to Wales. Please let me know when you receive it. Excellent! Very many thanks. All the best, John. 0 Quote Link to comment Share on other sites More sharing options...
Jeff Duquette Posted July 5, 2006 Share Posted July 5, 2006 On the first bit regarding WO 291/1330 – no idea why it says 0.74. Again, it is simple enough to verify yourself that this is in error. Determine the area under a normal distribution curve. My guess is that the original typist put in “0.74” instead of “0.674”…i.e. He or She accidentally dropped the “6” while merrily banging away at 65 words per minute. Shot-to-shot dispersion is an inherent or systematic error. It can’t be corrected by training your gunners more rigorously; or making sure you conduct your routine maintenance; or from sight & gun calibration; etc. Jump on the other hand is a well recognized constant error that is correctable. Calibration via zeroing is one way to correct for jump. The most modern MBTs account for jump via correction factors input into their CEU. These can be either fleet specific averages or they can be individual corrections determined for the specific foibles of a given tube via sight zeroing. Obviously P(h) is a function of more than inherent shot dispersion – wind, cant, parallax propellant temp, biorhythms of the TC and/or gunner on that particular day, etc etc. Many of these are automatically compensated for by the FCS of some modern MBTs. I look at it more from the perspective of how the MPI differs from the where the gunners aim point happens to be. Inherent shot spread follows the MPI about and radiates from that point. It doesn’t necessarily follow the gunner’s aiming point about. For example if the TC over estimates range to target, the gunner will still aim center of visible mass, however the MPI will be above the aim point some distance dependent upon the magnitude of the ranging error. It is still conceivable that the projectile will strike precisely where the gunner has aimed due to inherent shot-to-shot dispersion – and luck. But obviously the greatest P(h) will occur when the MPI and aiming point are coincident. 0 Quote Link to comment Share on other sites More sharing options...
Jeff Duquette Posted July 5, 2006 Share Posted July 5, 2006 Regarding adiabatic shear banding – is someone here trying to determine why DU rods penetrate more RHA than WHA rods? 0 Quote Link to comment Share on other sites More sharing options...
John D Salt Posted July 5, 2006 Share Posted July 5, 2006 Originally posted by Jeff Duquette: Regarding adiabatic shear banding – is someone here trying to determine why DU rods penetrate more RHA than WHA rods? Nope -- I'm trying to understand more about the mechanisms of projectile shatter, and I understand that adiabatic shear stress is the mechanism that causes shatter. The background to this is that I have a program (currently in Java, I need to re-write in Python) that implements one of Dehn's penetration formulae (from Technical Report BRL-TR-2770, "A Unified Theory of Penetration", James T. Dehn, December 1986). Dehn's formulae seem to me to be nicer than the others I have met to date, but is not generalised to account for angle of strike (which I can fix with armour basis curves), nose shape and piercing caps (which I don't know what to do about) and projectile shatter (which is why I need to look at adiabatic shear stress). Dehn's formula is generlaised to cover the case of eroding projectiles, but as I'm interested in WW2-era weapons that isn't really relevant to me. All the best, John. 0 Quote Link to comment Share on other sites More sharing options...
Michael Emrys Posted July 6, 2006 Share Posted July 6, 2006 And here I thought you had just ordered a case of wine. Michael 0 Quote Link to comment Share on other sites More sharing options...
John D Salt Posted July 6, 2006 Share Posted July 6, 2006 Originally posted by Michael Emrys: And here I thought you had just ordered a case of wine. I'm not sure how drinking a case of wine would help my undesrtanding of adiabatic shear stress. But I'm prepared to give it a go. For SCIENCE. http://www.weebls-stuff.com/toons/science/ All the best, John. 0 Quote Link to comment Share on other sites More sharing options...
WineCape Posted July 6, 2006 Share Posted July 6, 2006 And here I thought you had just ordered a case of wine. ..... I'm not sure how drinking a case of wine would help my undesrtanding of adiabatic shear stress.Nor I for that matter, though Einstein claimed lucidum intervallum on certain occasions after finishing a glass of vino. 0 Quote Link to comment Share on other sites More sharing options...
Jeff Duquette Posted July 7, 2006 Share Posted July 7, 2006 Originally posted by John D Salt: Nope -- I'm trying to understand more about the mechanisms of projectile shatter, and I understand that adiabatic shear stress is the mechanism that causes shatter. The background to this is that I have a program (currently in Java, I need to re-write in Python) that implements one of Dehn's penetration formulae (from Technical Report BRL-TR-2770, "A Unified Theory of Penetration", James T. Dehn, December 1986). Dehn's formulae seem to me to be nicer than the others I have met to date, but is not generalised to account for angle of strike (which I can fix with armour basis curves), nose shape and piercing caps (which I don't know what to do about) and projectile shatter (which is why I need to look at adiabatic shear stress). Dehn's formula is generlaised to cover the case of eroding projectiles, but as I'm interested in WW2-era weapons that isn't really relevant to me. All the best, John. [/QB]I see. I am familiar with this paper, although I will admit I had only skimmed parts of it sometime ago. So your interest is not in modeling long rod penetration? There are -- as you may already be aware -- a number of DTD papers written on shatter. Have you looked at W-172-8a "The Shatter Effect"? I have no idea what the PRO cite may be on this one as a copy of it made it's way into American Archives and eventually into my hands via this circuitous route. 2-pdr and 6-pdr AP & APCBC shatter issues. As I recall the conclusion from this paticular study boiled down to higher t/d ratios combined with high obliquity angles of attack, and near muzzle shots – i.e. higher projectile velocities. Course this was all empirical. Do a bunch of shoots and find out what conditions resulted in perforation and what conditions resulted in shatter. Nothing detailed about the mechanics of what may have been causing shatter – aside from various brain-storms and guesses. 0 Quote Link to comment Share on other sites More sharing options...
John Kettler Posted July 8, 2006 Share Posted July 8, 2006 Jeff Duquette, Haven't seen you on the boards in months. Don't know where you've been, but welcome back! Regards, John Kettler 0 Quote Link to comment Share on other sites More sharing options...
Michael Emrys Posted July 8, 2006 Share Posted July 8, 2006 He's been right here in this thread for the last week. Where have you been, hmmm? Michael 0 Quote Link to comment Share on other sites More sharing options...
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