Ranging of guns

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paul.mercer
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Ranging of guns

Post by paul.mercer » Thu Feb 17, 2011 9:13 pm

Gentlemen,
I have a question for the gunnery experts.
Obviously guns can be moved up or down for ranging purposes, but is there any method of moving them from side to side?
What I am trying to say is, if your pair of guns in a turret are spot on at say 15,000 yards and can place two shells within say 5 or 10 yards or so of one another on a target, at 20,000 yards the shells could be as much as 50 yards or more apart and so on as the range increases. Is this what is called dispersion and how was it cured if the guns cannot be moved sideways?

Bill Jurens
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Re: Ranging of guns

Post by Bill Jurens » Fri Feb 18, 2011 6:55 pm

Dispersion in range could be reduced in a number of ways. Dispersion in deflection was rarely large enough to represent a serious concern. In some systems, individual turrets were driven in azimuth so as to converge upon a target at a given range, but this meant slewing the entire turret, not adjusting individual guns. Individual guns in turrets could (and often were) adjusted for parallelism, but this was never done 'on the fly' in the middle of an action; it was usually a drydock/shipyard procedure.

Bill Jurens

Thorsten Wahl
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Re: Ranging of guns

Post by Thorsten Wahl » Fri Feb 18, 2011 7:35 pm

side only by turret train
individual elevation possible bot mostly not used

fall of shot dispersion follows a Normal Distribution
for SK 38 the 50% zones for individual shots are
of elliptical shape

at 10,000 m
95 m lenght and 1.9 m breadth

at 20,000 m
108 m lenght and 5 m breadth

at 30,000 m
142 m lenght and 10 m breadth
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

dunmunro
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Re: Ranging of guns

Post by dunmunro » Fri Feb 18, 2011 11:24 pm

Most FC systems had mechanisms to correct for convergence errors, so, for example, the bearing orders for A and Y turrets might be slightly different:
(ii) Transmits GUN TRAINING to the guns. Gun training is the sum of line of sight training, gun deflection (deflection plus deflection spotting), drift and cross levelling correction (or for H.A. fire, line of sight training, and total training correction transmitted from the fuze keeping clock). Convergence is corrected for at the training receivers at the guns.
http://www.hnsa.org/doc/afcc/index.htm (chapter 1, paragraph 2)

Keith Enge
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Re: Ranging of guns

Post by Keith Enge » Sun Feb 20, 2011 9:57 am

Although Bill Jurens is correct in saying that lateral dispersion is usually only a minor concern, there is one situation where it becomes enormous. Consider a chase situation aboard a smaller and thus lively ship in anything but calm seas. If the waves are coming from abeam, the ship is going to roll. Furthermore, since you are chasing your target, your guns are elevated and pointing over the bow. This means that as you roll, the muzzles of those elevated guns swing wildly from side to side. Unless you time your firing to exactly the point in the roll when the ship is momentarily level, your shells can be tens of degrees off the line of sight to the target (the more elevation and thus range, the worse the problem). This could also be a problem for directors but many of them, unlike the guns that they controlled, were stabilized.

Bill Jurens
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Re: Ranging of guns

Post by Bill Jurens » Mon Feb 21, 2011 3:06 am

A good point. This is commonly referred to as an error resulting from "trunnion tilt". It's quite difficult to correct for, which is one reason why ships tended to have such low hitting rates in stern chases when the range, if it was changing at all, was typically changing only very slowly. Almost all errors in that situation would be in deflection.

Bill Jurens

Thorsten Wahl
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Re: Ranging of guns

Post by Thorsten Wahl » Mon Feb 21, 2011 8:32 pm

In german this error is known as Kantfehler. It was automatically corrected by the fire control system. The turret was trained opposite to the roll and the elevation was slightly increased until the barrels are occupying the same orientation within space as without roll.
Meine Herren, es kann ein siebenjähriger, es kann ein dreißigjähriger Krieg werden – und wehe dem, der zuerst die Lunte in das Pulverfaß schleudert!

dunmunro
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Re: Ranging of guns

Post by dunmunro » Tue Feb 22, 2011 2:06 am

Thorsten Wahl wrote:In german this error is known as Kantfehler. It was automatically corrected by the fire control system. The turret was trained opposite to the roll and the elevation was slightly increased until the barrels are occupying the same orientation within space as without roll.
The RN used cross levelling gear to try and correct for this:
Canted Trunnion Error is the line error caused by firing the guns at a moment when their trunnions are not horizontal. The extent of canted trunnion error depends on the cant of the trunnions and the tangent elevation.

Cross Levelling Gear applies a line correction to neutralise canted trunnion error.
http://www.hnsa.org/doc/afcc/index.htm#pg40

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