Method and Apparatus for Determining the Lead-angle in the Firing upon Moving Objects, or with Guns having a Translating Motion.
Year: 1891

page_text: Date of Application, 16th June, 1891-Accepted, 18th July, 1891
COMPLETE SPECIFICATION.
Method and Apparatus for Determining the Lead-angle in the
Firing upon Moving Objects, or with Guns having a Translating
Motion.
I, Dr. LUDWIG MAUTNER VON MARKHOF, of Vienna, I Fichtegasse 2, in the
Empire of Austria, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement :-
It is known that, in the firing of guns having a translating motion, or upon
moving objects, it is necessary to lay the sight-line ahead of the object aimed at by
a certain quantity which is proportionate to the translation velocity of the gun or
of the object aimed at, and to the distance. The determination of this lead is
effected by help of tables, according to the estimated distance and to the corre
sponding duration of flight, a process which necessitates the allowance of a large
margin for the accuracy of the firing, especially when directed on objects situated
on the high seas.
This invention relates to an aiming apparatus which is used for ascertaining the
lead-angle, that is to say, the angle at which the sight-line of a gun of given calibre
has to be laid ahead of the object fired at, for a given distance, when the object or
the gun, or both, are in motion.
The method employed for effecting this determination consists in first ascertaining
the angle formed when the moving object is aimed at, from a certain point, during
a fixed space of time, and in reducing afterwards this angle to the angle corre-
sponding to the duration of flight of the projectile.
The aiming apparatus consists chiefly of an alidade with sight-vanes, rotable on
a table, and through which the object is aimed at and followed during a given space
of time; in order that, from the angle, thus described by the alidade, the value of
the desired lead-angle may be accurately determined; the said angle is reproduced
in an enlarged manner, through the medium of a dial-and-pointer indicator operated
by the alidade.
From the angle shown by said indicator, the angle corresponding to the duration
of flight can be immediately ascertained, and through this angle the alidade is then
rotated backwards, in the direction contrary to that of the previous rotation, in
order that, for a given firing-distance, the point of impact may coincide with the
object fired at.
According to my invention, the reduction of the angle shown by the indicator to
the one corresponding to the duration of flight may be effected either by help of a
table or by means of the indicator itself.
In the first case, the dial-indicator is permanently fastened on a certain part of
the board of the aiming apparatus ; in the second case, it can be shifted, close to
the alidade or to the centre of rotation of the same, in a direction at a certain angle
thereto.
The accompanying drawings illustrate an aiming apparatus embodying this
invention.
Figure 1 is a plan view of an apparatus designed for ascertaining by help of a
table, the angle reduced to the duration of flight.
Figure 2 is a longitudinal section of the dial-indicator which, with this apparatus,
serves for reproducing in a considerably enlarged manner the angle described by
the alidade during a given space of time.
Figure 3 is a longitudinal section of the boards of the apparatus showing the
arrangement of a clock-work beating seconds.
Figure 4 is a longitudinal section of the apparatus, with the alidade and the top
of the stand.

page_text: Figure 5 is a plan view of an indicating dial of peculiar construction.
Fig. 6 represents to an enlarged scale, a portion of the table and the rule
that serves for ascertaining the number corresponding to the duration of flight.
Figs. 7, 8 and 9 are plan view, longitudinal section and front view of an
apparatus provided with a movable dial by means of which the angle reduced to
the duration of flight is found without it being necessary to use any table.
As shown, both systems of apparatus have in common the alidade B, rotating on
a pivot a on the board A, and having at its rear-end a handle b.
Before making use of the apparatus, both the alidade and the sight-line of the
gun are kept directed towards the object. From the moment when the object
intersects the sight-line a (Fig. 1), it is constantly aimed at and followed by
rotating the alidade, during a given space of time (10 seconds, for instance). It is
expedient to note that space of time by means of a clockwork C, beating the seconds,
which can be placed in a box c (Fig. 3) attached to an arm c¹ pivoted to the base-
plate D.
The angle described by the alidade whilst following the object, and which bears
a certain relation to the distance and translation velocity of same, is shown on an
arc scale a¹.
For the purpose of ascertaining exactly the lead-angle, and also of facilitating
the readings, as well as the ready use of the apparatus, the angle described by the
alidade is reproduced in a considerably enlarged manner by a dial indicator E set
in motion by the alidade.
In the apparatus illustrated in Figs. 1 to 6, this is obtained by means of a curved
arm fixed to the alidade, the toothed sector 62 of which gears into a cog wheel
whose rotation is transmitted to the pointer e¹ by suitable gearing.
e,
In the construction of apparatus illustrated in Figs. 7 to 9, the arm ¹ is replaced
by a string ³, slung on a pulley of the dial indicator E which can be shifted along
in a slot a; from the loose end of the string is suspended a weight 64; the trans-
mission of motion from the alidade to the indicator E is combined in such a manner
that, if the alidade is moved over 1°, the hand e¹ is turned through 90° on the
diale, which is divided into 60 parts.
The angle, reduced to the duration of flight, which corresponds to the indication
given by the pointer & is found, in the apparatus represented Figs. 1 to 6, by means
of a table F, which is preferably hinge-jointed to the board A, so that when turned
over it serves as a lid for the apparatus.
In the first two circular rows and f¹ of this table are respectively inscribed the
firing distances and the corresponding durations of flight, the last named being
expressed in seconds. (For clearness' sake, these numbers have been represented
in Fig. 1 on the outside of table F).
As the duration of flight varies with the calibre of the guns and the nature of the
projectiles, the distance scale is so arranged that it can be changed.
In the radial columns 2 of the table are inscribed, beginning with 1 and going
towards the centre, proportionally to the series of the divisions 0-60 of the dial e²,
the angles which, for a given firing distance and duration of flight, correspond to the
various translation velocities of the object to be fired at.
In order that the values of these angles may be easily found, it is expedient to
make use of a graduated rule 1, pivotted at f³ to the centre of the table F,
(Figs. 1, 6) on which are marked division lines corresponding to the indications
given by the division lines 1-60 of the indicating dial &.
Let it be supposed, for instance, that for an estimated firing-distance of
2000 meters and for a given duration of flight of 6 seconds, the hand e' has turned
from 0 to 30 during the time employed in aiming at an object translating itself
towards the right, (see dotted position in Fig. 5); the value of the lead-angle
answering to that number 30 will be found to be expressed by 18 in the column f²
of the table F corresponding to the given distance (Fig. 6).
It will then be necessary to rotate the alidade B in the opposite direction, thereby
moving back the hand e¹ on the other side of its zero point through an angle

page_text: corresponding to the number read in the table F, the final result being to give the
sight line of the gun the desired lead-angle, determined by the position of the alidade.
It is obvious that the inscriptions of the table F can be contained in parallel
columns, in which case the rule must be so arranged as to be movable parallel to
the same.
In the apparatus of the system illustrated in Figs. 7 to 9, the table F is dispensed
with, as previously stated, and the angle corresponding to the duration of flight is
given directly by the dial of the indicating mechanism E. For this purpose, the
said mechanism can be shifted along in a slot a, parallel to a certain position of the
alidade, and provided with division lines corresponding to the time during which
the object is aimed at ; like divisions are marked on the alidade. In assuming the
time of observation to be 10 seconds, the alidade B and the slot a shall consequently
be divided into 10 equal parts, the alidade having a hole cut into it at each of the
division lines, for the purpose hereafter set forth.
As previously explained, in this system of apparatus, motion is transmitted from
the alidade B to the indicating mechanism by means of a string 63 passing over the
pulley of the pointer e³, and having a weight b suspended at its free end; this
transmission works on the same principle as the transmission which was operated, in
the hereinbefore described apparatus, by means of the toothed sector 12 and of the
wheel-work. If the indicating mechanism is moved completely forward in the
slot a³, as far as the division line marked 10, and if the pin attached to the end of
string is put into the hole, marked 10, of the alidade, the hand will be turned
through 90° to the right or to the left on the dial e², when the alidade describes an
angle of 1° in one or the other direction on the scale a¹.
Since the radii corresponding to the division lines marked on the alidade are
proportional to the arcs described by the same during its rotation, it follows that if,
previous to aiming at the object, the indicator is caused to slide along the slot till
it reaches the division-line corresponding to the given duration of flight, its pointer
being placed on the zero point, the indicator will give directly, after the object has
been aimed at during 10 seconds with the alidade, the value of the angle reduced
according to the time of flight.
Recurring to the example already chosen, let it be supposed that the lead-angle
is to be found, relating to a moving object, 2000 meters distant, that is to say, the
angle corresponding to a duration of flight of 6 seconds; in that case, the dial
indicator has to be pushed along the slot a as far as the division line marked 6, and
to be made fast thereto while the pin attached to the end of string 6³ is put into
the hole marked 6, situated opposite, of the alidade. If the object is thereupon
aimed at during the time fixed, that is, 10 seconds, the pointer e¹ will indicate the
angular deviation corresponding to a time of observation of 6 seconds, after which
the string and the indicator are pulled forwards and brought into their foremost
position, (Fig. 9) and the alidade B is rotated backwards until the pointer e¹ of
the indicating mechanism E shews the same angular deviation, but in the opposite
direction.
For the purpose of bringing back in a line with the alidade the object aimed at,.
which has travelled out of the sight line during the time employed for determining
the lead-angle by one of the methods previously explained, in consequence of the
corresponding displacement of the alidade, it will of course be necessary to turn
the support of the gun (the ship, for instance) as well as the aiming apparatus to a
certain extent, the gun being fired by means of an electric button at the very
moment when the object becomes visible in the sight vanes of the alidade.
In order to apply simultaneously the lead-angle ascertained with reference to a
certain object to several guns of the same calibre, the bores of which are differently
situated relatively to the original position of the alidade the following arrangements
can be made with regard to the dial indicator E.
The rim of the dial e² (Fig. 5) is surrounded by an outer rim e³, on which are
marked by division lines 1, 2, 3, 4, the positions in which the alidade B is parallel
to the sight lines of the various guns; on the pivot of the pointer e¹ is loosely set

page_text: another pointer e', which is placed on the zero point and fastened to the pivot when
the pointer e' has indicated the value of the lead-angle (18, for instance). In order
that the guns 1, 2, 3, 4.shall fire shots, the accuracy of which will be insured if the
distance has been reckoned exactly, the alidade has only to be rotated so that the
pointer be brought to coincide with the division line corresponding to the gun to
be fired, the firing of the charge being produced at the moment when the object
becomes visible through the alidade thus displaced.
For the purpose of easily placing the alidade in its proper position on the gun,
without being obliged to shift it beyond its zero point, the board A is mounted on
a pivot a² secured to the base plate D, and carries further two handles a³ a³, for
turning it round. The relative displacement of the plates A and D relatively to
each other is shewn by a pointer a on a scale d of the base plate D. When the
alidade has been brought into its proper position on the gun, the two plates are made
fast to each other by means of a set screw a³, the spindle of which moves in a
circular slot d' of plate D.
Finally, in order that it may be possible to fix up the plate D to suit local
circumstances, the said plate rests on the head of a suitable stand, where it is
movable on a horizontal axis and on a vertical axis d³, both of which can be
.locked by set screws.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. A method for determining the lead-angle in the firing of guns having a
translating motion, or in firing at moving objects, consisting in first ascertaining the
angle described by an aiming appara us pointed at the object during a given space
of time, and in then reducing that angle to the angle due to the duration of flight
of the projectile.
2. For carrying out the method referred to in the preceding claim, an aiming
apparatus consisting essentially of an alidade B with sight-vanes, mounted on a
pivot and operating a dial indicator E which indicates the angle formed by the
alidade during the time employed in aiming at the object, and enables the angle
corresponding to the duration of flight to be ascertained by means of a table F,
containing a distance scale, a graduation / for the flight durations and columns f
in which are inscribed the numbers which, for a given firing distance, represent the
angle shewn by the indicator after its being reduced correspondingly to the duration
of flight; said table being provided with a rule f pivotally connected to it, and
divided into as many parts as the dial of the indicator E substantially as described
with reference to Figs. 1 to 6 of the drawings.
3. In the construction of apparatus referred to in the second claim, arranging
the indicator E so as to be movable along a slot as which, as also the alidade B,
is marked with a scale having as many divisions as there are seconds in the
predetermined time for the observation of the object, in such a manner that if
the indicator is shifted to the division corresponding to the duration of flight, the
pointer of the indicator will directly indicate the proper lead-angle when the
object has been aimed at with the alidade during the said predetermined time,
substantially as described with reference to Figs. 7 to 9 of the drawings.
4. In an aiming apparatus, the indication of the lead-angle for several guns, each
of which corresponds to a different position of the alidade B, by means of a
pointer which can be made fast at will to the pivot of the indicating mechanism,
and of a rim e³, placed on the. outside of the lial e², on which are marked the
respective positions of the sight-lines of the various guns substantially as described
with reference to Fig. 5 of the drawings.
Doted this 16th day of Tune 1901