1921 firing trials against Baden

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Bill Jurens
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Formulas

Postby Bill Jurens » Mon Mar 28, 2005 5:36 am

Hi George:

Your package contains probably a hundred formulas, and it would not be feasible for me to comment on them all. What particular ones were you interested in?

Most (or all) of the formulas are fine. But when you work them out using real-life numbers you will indeed find that the drag effects of moderate yaws are really quite inconsequential. You seem to be claiming that after some computation is done, then 'the importance of yaw on flight dynamics quickly reveals itself". Well, I've done the computations many times, and it doesn't reveal itself to me, except as a second order effect, so please illustrate further...

A yaw of 2 degrees overall, which would be typical, would usually increase Cd by only about 0.015-0.020, which is easily taken into account by changing the form factor by (about) the same amount. (Actually, this amount of drag error was routinely within experimental limits before spark ranges became common)

If you have a copy of McCoy at hand, and you still do not believe me, you can look at charts 4:37, 4:40, and 4:43 which graphs the increase in drag due to yaw explicitly. It's not much. Further, McCoy reproduces yaw history graphs for a number of fairly typical trajectories in Chapter 9, in which you will note that the yaw rarely exceeds 5 degrees anywhere in the trajectory even with angles of departure of 45 degrees.

Accounting for yaw is completely routine in ordinary ballistics. Ho-hum, old-hat, and absolutely normal.

Can you be more specific please, and include actual values of the increase in drag due to yaw (and the dramatic effects that you imply accompany this) that are provided by "the modern literature" to which you allude? A bibliography of this 'modern literature' that you use to derive your assertions would be most useful and interesting as well. I'd frankly be fascinated in any information you could provide which would demonstrate where more conventional methods of computation have produced misleading answers because they failed to take yaw into account in trajectory computations, particularly any cases that have any relevance to WWII vintage ballistics.

So long as you talk in qualitative rather than quantitative terms you will continue to mislead yourself. So far as yaw-drag is concerned, you will fall on your face when you try to put numbers to this.

Honest.

Bill

George Elder
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See pages 10-13.

Postby George Elder » Mon Mar 28, 2005 5:04 pm

As you will note, one has to calculate yaw before measuring drag -- at least as this method applies.

George

Bill Jurens
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Yaw and drag.

Postby Bill Jurens » Mon Mar 28, 2005 5:47 pm

Of course.

and your point is...?

Yaw can be either calculated (but only if one knows the values of enough of the initial variables required, which is rarely if ever the case for old bullets), observed on the range via yaw cards, spark images, or yaw sondes, or -- at least in principle -- derived by subtracting observed drag from the known 'zero yaw drag' which must usually be measured in a wind tunnel. As supersonic wind tunnels were essentially unknown before c. 1940 or so, zero yaw drag coefficients were never determined before that date.

Usually, all the designer has to do, in practical terms, is to ensure that the gyroscopic stablility is OK at the muzzle and (sometimes) at the maximum ordinate as well. The equations to ensure gyroscopic stability are well-known and easily applied. If the gyroscopic stability is fine at these two points, then in virtually all cases the yaw and stability will be fine throughout the trajectory. Stability tends to increase downrange, which usually means that only stability at the muzzle is of major importance, and this only insofar as it is desirable to have the ejection instabilities (which are more-or-less unavoidable) damp in a fairly regular and promptly. Fowler and a few others derived the essential stability equation set in 1920 or so. This is not new stuff...

Bill Jurens

George Elder
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My point is that you...

Postby George Elder » Mon Mar 28, 2005 6:03 pm

... seem to be dismissing the influence of yaw while at the same time recognizing that it is one of the most fundamental variables involved in external ballistics calculations. Moreover, on occasion you make claims, as in the feasibility of inducing yaw in large projectiles (whatever defines large), that just don't correlate well with what I've read (e.g., see Pennekamp, Richard A. 1989). No, I do not dismiss your views, but it sure seems best to get a wide variety of inputs from many sources -- and especially from such luminaries as Werner Goldsmith (gone, but not forgotten). And yes, I have studies going back to the 1920s and up to recent times on external ballistics, not that they always agree or are very well done. And although I respect your views, it seems fair to ask if you have an advanced degree in ballistics?

George

Bill Jurens
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To George

Postby Bill Jurens » Mon Mar 28, 2005 6:24 pm

You are misquoting me. I can't recall ever suggesting that yaw "...is one of the most fundamental variables involved in external ballistics calculations." Anyone can read the thread up to date and confirm this -- one of the nice things about this sort of discussion is that it provides a full record of the written 'conversation'. If anything, I've consistently maintained the opposite.

I define large as 12"-16". I'm unfamiliar with Pennekamp at least at first glance -- the name doesn't "Google" -- so perhaps you can enlighten me further...

Goldsmith didn't have anything -- so far as I know -- to say about external ballistics. He did terminal ballistics. So how are his views (if they exist at all) relevant?

Don't have "an advanced degree in ballistics". Seeing as we are trading vitae, what is your doctorate in?

Bill Jurens.

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José M. Rico
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Postby José M. Rico » Mon Mar 28, 2005 7:19 pm

Permit me to interrupt you guys, but I think this thread is developing in the wrong direction, and has now little to do with Baden firing trials or British 15-inch shells. Perhaps you want to start a new thread on "Yaw Effects".

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Bill, I am fascinated by this conversation...

Postby Randy Stone » Mon Mar 28, 2005 7:33 pm

...insofar as many questions have been asked but precious few answered.

Bill Jurens wrote: You are misquoting me. I can't recall ever suggesting that yaw "...is one of the most fundamental variables involved in external ballistics calculations."

Bill Jurens


I distinctly recall similar misquoting before but perhaps it is nothing more than poor comprehension of your position. My complete understanding is that you never made the claim that yaw is a "...most fundamental..." variable, and I have been following this thread from Day One.

Bill Jurens wrote: Anyone can read the thread up to date and confirm this -- one of the nice things about this sort of discussion is that it provides a full record of the written 'conversation'. If anything, I've consistently maintained the opposite.

Bill Jurens


I was very happy when this Board altered its format to allow for exactly this kind of record, as you mentioned. That way the conversation can be 'researched,' as it were, and the "he said, she said" can be sorted out and 'quoted' as appropriate. This is a format I am suggesting to other Boards, primarily for this reason.

Although I have followed this thread from the beginning I nevertheless took your advice and reread your posts for any hint by you that yaw is a fundamental (and consequential) variable.

I found no such reference.

I did, however, brush up and reinforce my memory with the finer points you have made on the subject and for that I thank you.

Bill Jurens wrote: (I d)on't have "an advanced degree in ballistics". Seeing as we are trading vitae, what is your doctorate in ?

Bill Jurens


A lack of academic credentialing in specific curricula needn't be a hindrance to anyone, as you have amply demonstrated. For instance, I chose a Part 61 path through aviation rather than Part 141 or military training.

Yet, I was most proud when an aviator of some note, having evaluated me on a multi-engined heavy aircraft I had never flown before, commented that I was a pretty good 'stick and rudder' man. And he made that comment in front of a Board of Directors where his word counted for quite a bit.

If I can manage such a thing I would estimate that anyone -- or almost anyone -- can acquaint themselves with topics they are otherwise 'unfamiliar' with...provided they keep an open mind and exercise common sense in their research and deliberations.

At least, that is how I approach flying and topics such as we find here.

Randy

George Elder
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Message understood...

Postby George Elder » Mon Mar 28, 2005 8:00 pm

Hi Jose:

I think this is typical about how pointless dissagreements occur. Essentially, Bill is correct in most of the things he is saying according to much of the literature I have to hand. But we are miscommunicating on certain issues, and I cannot fully understand the points Bill is trying to make. For example, it appears that Bill does not agree with the notion that the afore mentioned yaw calculations are important -- even though one cannot use some of the drag formulae without considering yaw effects. I thus get confused about how drag cannot be considered as an important factor in using these tools. Perhaps I am simply misunderstanding Bill's intended meaning.
I also agree that yaw effects are small under 3 degrees, but do not extend that window to 5 degrees. As for Goldsmith, this was where I was hoping we go with with respect to one of the influences of yaw -- with the other focus being related to dispersion -- both of which can be tied in with the performance of the British 15" shell. With regard to Pennekamp, Richard A. (1989) citation, please refer to his, "A Large-Caliber, High-Velocity Yaw Inducer. ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD." But this would not meet Bill's criteria because it only involves 152 mm shells.
Overall, it may be pointless to pursue these issues because Bill and I do not seem to fully understand one another's intended meaning -- and now we get some predicatable, dreary and banal cheerleading being added to the mix. With regard to my degree, I have a Ph.D. from Penn State in Communication with the focus being on the neuropsychological undepinnings of how communication modulates memory formation, memory access, and subsequent behavior. This has nothing to do with the Bismarck -- or ballistics. My training served as a primer in understanding some fairly complex experimental methods and studies. My dissertation was published as a book, and then fate took me in directions that are far removed from neurons, Hebbian reverberations, and how the dorsolateral aspect of the amygdala interacts with the periaquiductal gray area -- IIRC.

George

Randy Stone
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I agree...

Postby Randy Stone » Mon Mar 28, 2005 8:44 pm

José M. Rico wrote: Perhaps you want to start a new thread on "Yaw Effects".


...as I see it, this issue of yaw -- which has been raised before -- could use its own thread.

As I have noted previously, this issue of yaw has been much advertised but insubstantially supported beyond some vague assertions.

Frankly, Bill has made some very convincing comments that boil down to a general summation that yaw is of little consequence based, in part, upon designing gyroscopic stability into the projectile and confirming such stability by the application of equations suited for the task.

That being the case he has commented that large projectiles are rather well behaved and that yaw produces a relatively minor effect upon drag and that yaw effects upon the projectile trajectory can be readily compensated for in the shoot.

If a separate thread can provide further illumination of the topic along the lines Bill has demonstrated, I am certain others -- as well as myself -- are interested. In any event, his comments have not been contradicted by any set of data and perhaps -- to the degree such can occur at all -- it will occur in a separate thread.

Randy

George Elder
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treads...

Postby George Elder » Mon Mar 28, 2005 9:23 pm

Hi Jose:

You may be right about a yaw-specific thread being in order wherein the expert literature can be examined. I seem to recall vague claims being made in another thread regarding the supposed ability to reduce a photo-based speed estimate to a 0.5 knot error margin when all available experts noted that 2-3 knots would be more in the proper and "viable" range. That was a very useful exercise. With respect to yaw, it is well known that at 4-5 degrees yaw has a measurable influence on the flight dynamics of many penetrators, and this grows as the yaw increases -- depending on the nature of the penetrator. These data have been shared with the whole community via TechSpec. With regard to terminal ballistics, the influence of yaw has been amply demontrated by Goldsmith and others. These are rather specific studies -- and none of the 70+ interested parties who received the studies seemed to dispute them when they were offered. As for a seperate thread on yaw, that depends on who joins it. I certainly respect Bill, but I would have nothing at all to do with some folks.

George

Bill Jurens
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Yaw

Postby Bill Jurens » Mon Mar 28, 2005 11:23 pm

I would be happy to participate in further discussions regarding yaw. We would have to be careful, however, to differentiate the discussion of yaw during flight, i.e. aerodynamic yaw, from the discussion of yaw effects on terminal ballistics and penetration.

The first of these is well understood, and the 'discussions' -- if that is the proper word -- therein would involve more elucidation than arguement.

The second, which essentially involves the detailed prediction of energy dissipation and conversion during high-energy (sometimes multiple) impacts, is much less-well understood and -- regardless of the quantity of discussion -- is likely to remain fairly opaque. This is largely because our understanding of most of these sorts of phenomona remains what might best be described as 'semi-empirical', i.e. based upon the quantification of experimental results. Unfortunately, because very few systematic experiments were conducted, certainly to modern standards, there has been little-to-no differentiation of variables and hense very little upon which to base an equation set, even if it were assumed that a closed-form equation set exists, which is unlikely.

There have, of course, been large numbers of systematic experiments with relatively small caliber projectiles of more recent design, and theory in these areas is relatively well established, though often difficult of access due to security restrictions. There never was, and there is now never likely to be, a large accumulation of measured data on large-caliber nearly solid projectiles impacting heavy plate arrays at what would now be called moderate-to-low velocities. It is possible, and perhaps most probable, that such impact sequences will be best studied via the application of high-speed finite analysis dynamic computer programs employing numerical integration, but these remain (as before) difficult of access, and are -- sadly -- also at their root largely semi-empirical in nature. What this means is that the variables in the equation sets in such programs have been 'tuned' in order to permit the program to produce results which in effect 'mimic' the results of testing. In the absence of a large test-derived empirical data set to begin with -- which is unlikely to accumulate in the case of large-caliber impacts, etc. -- then even the best of these are unlikely to provide more than approximations of reality.

It's sad but true that we are unlikely, at least within the forseeable future, to be able to reconstruct with much validity the post impact phenomena associated with early Twentieth Century naval combat. The theory to understand projectile/target interactions was not clearly developed while the technology was in use and, as the hardware of both ships and projectiles of this era has slipped into the past and is no longer available for study, accurate reconstruction of what 'might have happened' is difficult or impossible. Further, as the years slip away, it becomes increasingly clear that the 'motherlode' -- the "King Tut's Tomb"-- of contemporary data on these subjects, which many felt was just hidden away in some archive somewhere, never really existed in the first place.

Bill Jurens

George Elder
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A person who might help...

Postby George Elder » Mon Mar 28, 2005 11:50 pm

I hate to ask him because he is so busy, but Dr. Don C. may be of considerable use here. You probably already know him. He is a no flame sort of guy, and that is why I am hesitant to get him into this food-fight arena. But he is from the old school, and even uses problems involving large naval shells and FH armor in his courses. This area still has applications to "new" science.
I agree that we must seperate items into their natural catagories. I get the distinct idea I was talking about the use of formulae and you were talking about effects -- and thus we ended up on different pages -- so to speak. I don't know how to avoid mixups in this except to ask questions when miscues happen. Now, there is a document I should have in a few days that may be a good way to open -- but first we have to define what we are talking about.
I presume the initial topic is exterior ballistics as it relates to yaw and shell form. Is this a good way to focus?

George

Bill Jurens
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Sure

Postby Bill Jurens » Mon Mar 28, 2005 11:52 pm

Sure.

Bill Jurens

Randy Stone
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Actually...

Postby Randy Stone » Mon Mar 28, 2005 11:55 pm

George Elder wrote:Hi Jose:

I seem to recall vague (my emphasis -- Randy) claims being made in another thread regarding the supposed ability to reduce a photo-based speed estimate to a 0.5 knot error margin when all available experts noted that 2-3 knots would be more in the proper and "viable" range.

George


...the comment was quite specific that a 0.5 knot error margin could be deduced and such appears now -- by the evidence we have to hand -- to be a very reasonable evaluation.

I know of no 'expert' who has staked out the position that Bismarck's speed at the Battle of the Denmark Strait could be estimated to within only 2 or 3 knots. Perhaps they'd be willing to come forward and justify the positions you have asserted for them.

George Elder wrote: ...With respect to yaw, it is well known that at 4-5 degrees yaw has a measurable influence on the flight dynamics of many penetrators, and this grows as the yaw increases -- depending on the nature of the penetrator. These data have been shared with the whole community via TechSpec. With regard to terminal ballistics, the influence of yaw has been amply demontrated by Goldsmith and others. These are rather specific studies -- and none of the 70+ interested parties who received the studies seemed to dispute them when they were offered (sic).

George


This all, of course, overlooks the valid points which Bill has made in his presentation on the topic -- again, the valid subject of a separate thread.

However, at this time, you have not made any points which contradict the information Bill has shared.

As Bill pointed out, Goldsmith has nothing to say about external ballistics and Bill challenged you to provide some indication as to how Goldsmith's views are relevant to the discussion at hand. Yet here again you merely assert Goldsmith's work without citing anything which we can evaluate vis-a-vis Bill's position.

As to the assertion that none of the 70+ parties disputed the studies fails to address whether these folks actually read and digested the material or whether they had concerns which they have not not bothered to voice.

Additionally, one may note that even if all 70+ people agreed with the findings this would fail a basic test of logic. After all, how many people believed Iraq had WMD ? The fallacy of common belief looms large in this assertion.

Nevertheless, insofar as you raised the topic, I feel the ball is in your court to articulate a valid observation and justify it with some manner of discussion which addresses Bill's position. Then we can form a better opinion as to whether your assertions are robust enough to rebut the comments Bill has generously posted.

I'm all for establishing a new thread on yaw and it would be interesting to see what results you may be able to manage with the formulae which have been noted here. I find it fascinating work and I would very much like to review any data you may present.

As Bill has pointed out, it is important to keep the focus on external ballistics rather than drifting -- if you'll pardon the pun -- off into terminal ballistics, which was not the basis for your initial comments regarding yaw as it relates to drag. It does strike me as a matter of education and rather than argumentation.
Randy

George Elder
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People can read the prior thread on speed estimations...

Postby George Elder » Tue Mar 29, 2005 10:56 am

... and see how totaly out in la-la land you truely are, and especially after shooting yourself in both feet on the subject. As for the Goldsmith article, how can you disscuss the efficacy of a study you never read -- let alone judge anyone's reaction to it? You're just blowing hot air and everyone knows it. Now I promised Jose to avoid your antics, but here you are -- interjecting your sorry butt into an affair that folks like Bill and Dr. C. are more than able to handle. Indeed, I honestly don't think Bill needs any of your rah-rah cheerleading because he is more than able to articulate his own views and he has a damnsight more knowledge about the subject matter to hand than yourself. I and others can and do learn for him -- but seldom from the likes of you. Furthermore, if Bill and others knew the true nature of your soul I doubt they'd want very much to do with you. You can't send people some of the trash e-mails you've sent to me and expect to have any credibility. You cannot deny others access to studies and expect to garner any respect from accademics. And you sure as heck cannot pretend things did not happen as a means of avoiding rersponcibility for past bad behavior -- as in your Nazi taunts and the like. You cannot run away from that record, and I think it best that we both abide by Jose advice -- and avoid these silly confrontations. I think it is a big enough world for you to go your way, and for me to go mine. That is all I have to say about the subject.

George


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