'10 calibre head' shells

[Martin Bennitt]

Peter Hart in his masterly '1918: a very British victory' quotes Haig, presumably in his dairy, as saying that Churchill as minister of munitions, is "hurrying up the supply of '10 calibre head' shells, gas, tanks, etc."

grateful if one of our artillery experts could explain what is meant by '10 calibre head' shells and why it was important to have them.

thanks and cheers Martin B

[TonyE]

It is a measure of the degree of streamlining of the front portion of the shell, known as the ogive.

The curvature of the portion of the shell in front of the cylinfrical section is drawn on a radius, and the longer this radius is the more pointed the shell will be, and hence more aerodynamic. That ogive is often defined as x calibre radius head (c.r.h.)

In the early part of the war, most shells had a 4 calibre radius head, and were fairly "blunt". For example, a 3 inch shell with a 4 c.r.h. would have the ogive drawn on a radius of 12 inches, whilst a 10 c.r.h. shell would have a more pointed shape because the ogive is drawn on a radius of 30 inches.

Obviously the more aerodynamic a shell is, the greater the range for a given charge/muzzle velocity.

I hope that is sufficiently clear!

Regards

TonyE

[Martin Bennitt]

thanks Tony, it's as clear as can be to a bear of little brain like myself

cheers Martin B

[nigelfe]

It's slightly more complicated than that, however, in WW1 they were tangent ogive, meaning the crh was a radius from a point on a line at right angles to the long axis of the shell, drawn from the base of the ogive (ie where the curve ended). Secant ogive or fractional crh was a bit different.

In WW1 most shells had a crh of 2 or less at the beginning of the war. I'm not actually sure that 10 crh was introduced, AFAIK 8 crh of 60-pr was the most. 18-pr never exceeded 4 crh in WW1. There's a crh illustration and a bit more detail on my web site at this page http://nigelef.tripod.com/ammo.htm after Figure 6

[TonyE]

Tangent ogive was exactly what I was trying to describe Nigel, as it was a WWI shell he was talking about.

Regards

TonyE

[Old Tom]

Somewhat off topic but of interest; the OED defines ogive as terms in architecture; a pointed or gothic arch and one of the diagonal ribs of a vault. All shapes not too unlike a shell. Another thought; was the shape of a shell detirmined by the capability of machine tools of the period or aerodynamics? I suspect the first.

Old Tom

[truthergw]

An ogive is simply a curve. The term also arises in statistics. Machine tools were very well advanced at the time of the great war. Any curve could have been mass produced as required. We ought not to think that as far as mechanical engineering and production was concerned that our grandads had anything to learn from us. The main advance in the 20th Century was in electronics and the first giant strides had already been made by 1914. An industry that could build dreadnoughts, aeroplanes, submarines and machineguns would have no problem shaping a shell. The criterion would be efficiency. Would the improvement be worth the upheaval and cost of retooling.

[Old Tom]

Many thanks. My point was not that engineers of my father's generation - I'm getting on - were not capable of machining particular shapes but that such a shape was probably more convenient to make than that which would be ideal for supersonic speeds.

Old Tom

[Martin Bennitt]

a bit more off topic, but as I started the thread...

Am I right in presuming that only in shells, and possibly bullets, would aerodynamics have made much difference to performances at the time of the war? For instance, did the shape of the Albatros scout give it any great advantage over its blunter contemporaries in terms of speed, climb and dive rate, etc?

cheers Martin B

[Owen Hales]

.................... engineers of my father's generation - I'm getting on - were not capable of machining particular shapes .......

The was in the old science museum in Birmingham a machine dated sometime in the late 1800s that could "turn" an oval cooking pot.

Neccessity is the .........

Owen Hales

[Martin Bennitt]

returning to shell shapes, presume there was less room for explosive in the leaner and meaner shells? Or did it not really matter?

cheers Martin B

[centurion]

The was in the old science museum in Birmingham a machine dated sometime in the late 1800s that could "turn" an oval cooking pot.

Neccessity is the .........

Owen Hales

The ability to mass produce complex curves in very hard steel (as opposed to saucepan steel) is comparatively recent and effectively dates from the introduction of numerically controlled machine tools. One of my first jobs was running routines on an IBM 1401 to convert engineers drawings into open shop programs (The complex curves were turbine blades for the first RB211 fan jets). Before then a very experienced operator was needed for each machine who 'knife and forked' every blade which was a bottleneck. It isn't just cutting the curve but doing it in such a way as to avoid both unnecessary wear on the expensive tool bit and avoiding sudden strains on the same that might snap it (metal harder than very hard steel is often brittle) and indeed the supply of toolbits can itself be a bottleneck (and one that hampered the Germans in the later years of WW1). In the absence of NC machine tools producing substantial numbers of these shells would require a significant programme to ensure that enough experienced machinists were available especially considering all the other war industry demands for such men. It probably did require control at the ministerial level (which is probably be basis of Haigs comments)

[Old Tom]

The quote by Owen from my post left out the negative. Lapsing into aerodynamics, I seem to recall that drag which limits the speed that might be achieved with a given engine power depends on the square of the speed and hence at comparitively low speeds shape does not make much difference, it became much more important with for example aircraft of the Spitfire generation, leading to some beautiful shapes.

Old Tom

[SiegeGunner]

Lapsing into aerodynamics, I seem to recall that drag which limits the speed that might be achieved with a given engine power depends on the square of the speed and hence at comparitively low speeds shape does not make much difference ...

As the owner of a car that is shaped like a brick, I'd be inclined to agree, Tom - but why then do motor manufacturers put so much effort into the aerodynamics of road vehicles that do much the same speeds as Great War era aircraft? Physics is not my strong suit.

[MikB]

For instance, did the shape of the Albatros scout give it any great advantage over its blunter contemporaries in terms of speed, climb and dive rate, etc?

cheers Martin B

Made it fast enough to pull its wings off in a dive, so they say...

Regards,

MikB

[truthergw]

As the owner of a car that is shaped like a brick, I'd be inclined to agree, Tom - but why then do motor manufacturers put so much effort into the aerodynamics of road vehicles that do much the same speeds as Great War era aircraft? Physics is not my strong suit.

As well as affecting speed, shape also affects fuel consumption. A streamlined vehicle will be more efficient.

[centurion]

(MartinBennitt @ Jan 5 2010, 09:54 PM)

For instance, did the shape of the Albatros scout give it any great advantage over its blunter contemporaries in terms of speed, climb and dive rate, etc?

Might have done if the drag from the wings wasn't much greater. Albatross did not understand the need for lower drag wings so when they streamlined the fuselage of their C types (In the CX and CXII) they only gained an extra 2 mph over the previous model  (and that was probably because the engine was more powerful)

[nigelfe]

WW1 shells tended to have thick walls (incredibly thick by modern standards), if streamlining the ogive means thinning the walls then there would probably be little of no effect on internal volume. Alternatively streamlining may also have lengthend the shells to offset loss of volume. If you look at the 1930s gun handbooks, which tabulate some dimensions (weight, lenght, fill weight) for the different mks, then there are differneces, but I've never done any analysis looking for correlations. Of course the 1930s Hbs omit the earliest mks.

Another issue is the internal shape, a neat cylinder is easiest to machine and fill with explosive.

The need for streamlining depends on the shell velocity. You don't gain gain much from a highly streamlined low velocity shell (modern 40mm grenades vs 40mm AA shells are a prime example). Hence WW1 howitzer shells got less streamlining than guns

[Martin Bennitt]

thanks nigelfe

would velocity affect accuracy, then, especially in WWI shells (remembering how late WW2 fighters became unstable as they approached the speed of sound)?

cheers Martin B

[centurion]

thanks nigelfe

would velocity affect accuracy, then, especially in WWI shells (remembering how late WW2 fighters became unstable as they approached the speed of sound)?

cheers Martin B

The ideal shape for transonic and supersonic speeds is egg shaped (blunt end first). Aircraft such as WW2 fighters are an entirely different shape. More modern aircraft adopted a complex waisted fuselage shape to compensate for the wings which were a deviation from the optimum shape. The whole subject is rather complex but look for 'area rule'. Shells are much closer to the optimum shape and would have less problems. This is slightly simplistic as all sorts of factors would have an influence (for example the trajectory which would affect the various altitudes and therefore density of air passed through at different velocities) Then again the fact that the shell was fired from a rifled barrel and spin stabilized (unlike a WW2 fighter) would affect matters.

[Martin Bennitt]

thanks Centurion. I conclude that the answer is not a lot, then, at least as regards shape and velocity per se, disregarding the atmospheric factors, which I know were taken into account as far was known in artillery ranging and targeting later in the war

cheers Martin B

[truthergw]

I believe that inconsistency would be a bigger problem than shape. A shell which was nominally a certain size and weight would, under mass production, actually vary within certain limits. On the other hand, a shell is aimed into a box, not at an object. I remember how horrified I was, as an infantryman, to learn that. Also just how elastic the sides of the box could be.

[Rockdoc]

The History of the Ministry of Munitions, Volume X, Chapter 2, page 61, para 2: The chief design problem of 1917 and 1918 was to increase the range of the gun ammunition by various expedients, such as lengthening the head of the shell by means of ballistic caps or altering the shape of the shell and giving it a stream-line base.

It goes on to say that the first attempts began in 1916 when 6-in and 9.2-in shells with 4-calibre heads were requested by the C in C.

The tendency to lengthen the head of the shell increased, as it was found to increase the range by a marked extent. Shells with 6-c.r.h were adopted for many natures and 8-c.r.h. for the 60-pdr shell during 1917 and, on 22 April 1918, the War Office asked the Design Department to lengthen the range of the 9.2-in gun by producing an 8-c.r.h. shell.

[Further down page]

The ballistic cap - a false nose screwed on to the top of the shell in order to lengthen its range - was first used for the 9.2-in shell, a design giving an 8-c.r.h. being approved on 19 November 1916, manufacture on a small scale beginning soon afterwards.

It goes on, on page 63, Though it appeared that no marked advantage was likely to be obtained from the stream-lined shell with velocities over 2,100 ft per second, a trial in the case of the 6-in shell had proved very satisfactory. The 18-pdr shell had gained an additional 1,500 yards, part of which was ascribed to the increased muzzle velocity with the improved type of gun but pat to making them contour of the head of the shell more pointed and giving a slight stream-line to the base of the shell.

Hope this helps,

Keith

[Martin Bennitt]

Hope this helps,

Keith

Indeed it does, Keith. Interesting there is no mention of the 10 crh which Haig was hoping for. Were any such actually produced, at least during the war, and if so, for what size of gun?

cheers Martin B

[Rockdoc]

Nothing bigger than I quoted is mentioned in the book and, given the time it took to get things from successful trials into quantity production, I wonder how many of these shells arrived at the Front. It does say that the first trials of them in France were not a success because the accuracy was very poor and this was reported to a conference in September 1917. The French were consulted and things were improved (the hows and whys are not mentioned) but this does suggest that production wouldn't have begun before early 1918.

Keith