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United States. Army. Ordnance Dept.

Handbook of artillery : including mobile, anti-aircraft and trench matériel online

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riage is maintained in position by the spade, which sinks into the
ground, and by the friction of the wheels upon the ground. If the
force of the recoiling gun were communicated directly to the anchored
carriage the effect would be to make it jump violently, which would
not only disturb the lay, but would prevent the cannoneers from
maintaining their position. The hydraulic recoil brake is therefore
interposed between gun and carriage.

If the gun were rigidly attached to the carriage the latter would
be forced back a short distance at each. round, and the wjiole of the
recoil energy would have to be absorbed in that short motion. In-
stead of this, the gun alone is allowed to recoil several feet and although
the recoil energy is in this case greater than it would be if gun and
carriage recoiled together, yet it is so gradually communicated to the
carriage that instead of a violent jerk we have a steady, uniform
pull, the only effect of which is to slightly compress the earth behind
the spade. In a well-designed carriage the amount of this pull is
always less than that required to lift the wheels off the ground by
rotating the carriage about the spade.

The only motion of the carriage which takes place is that due to
the elastic bending and rebound of its parts under the cross strain
set up in discharge. These strains are inevitable since the direction
of recoil can not be always exactly in the line of the resistance of
the earth behind the spade. This movement of the axis is known as
jump and must be determined by experiment for the individual
piece in its particular mounting.

The principal parts of the typical gun carriage are the cradle;
a device for mounting the cradle called in the different models a
rocker, pintle yoke, or top carriage; the trail; the wheels and axle.
The gun slides in recoil on the upper surface of the cradle and the
the cradle contains the recoil controlling parts.

In the design of the carriage the constructional difficulty lies not
so much in preventing the carriage from recoiling, but in preventing
the wheels from rising off the ground on the shock of discharge.
The force of the recoil of the gun, acting in the line of motion of the
center of gravity of the recoiling parts, tends to turn the carriage

(28)



29

over backwards about the point of the trail or center of the spade.
This force is resisted by the weight of the gun and carriage, which
tends to keep the wheels on the ground. The leverage with which
the overturning force acts varies with the distance of its line of action
above the center of the spade; the leverage with which the restraining
force acts varies with the horizontal distance of the center of gravity
of the gun and carriage from the center of the spade.

It follows that the steadiness of the carriage for a given muzzle
energy may be promoted by four factors.

(a) Increasing the weight of the gun and recoiling parts. This
reduces the recoil energy.

(b) Increasing the length of recoil allowed. This reduces the
overturning pull.

(c) Keeping the gun as low as possible, either by reducing the
height of the wheels or by cranking the axle downwards. This
reduces the leverage of the overturning force.

(d) Increasing the length of the trail. This increases the lever-
age of the steadying force.

The well-designed gun carriage is one that combines these factors
in a practical way, so as to give the greatest possible steadiness to
the carriage, at the same time keeping within the limits of weight
imposed by the necessity of mobility.

Gun carriages are so constructed as to permit movement of the
piece in either a vertical or horizontal plane. These motions may
be simultaneous if so desired, and by a proper combination of the
two motions, the axis of a gun may be aligned in any desired direc-
tion within the limits of motion of its mount. The two kinds of
motion are designated as follows: Rotation of the piece about a
vertical axis, its inclination with the horizontal remaining unchanged,
is called " traversing "; movement of the piece in a vertical plane,
the horizontal projection of the axis of its bore remaining unchanged,
is called "elevating."

Gun carriages are provided with mechanisms for giving the pieces
accurately controlled motion in both azimuth and elevation. Two
types of elevating mechanisms are in common use. The first is the
telescopic screw. This gives a considerable length of screw for a
short assembled length and gives a rapidity of action (since the
movement of the inner screw is equal to the sum of the pitches of
the outer and inner screw for each turn of the pinion), combined
with the nicety of adjustment of a single screw of fine pitch.

In the second type 'the motion is communicated to rockers,
attached to the bottom of the cradle, through the engagement of
worms or pinions, with teeth cut on the circumference of the rockers.



30

This method is in use on all howitzers, and a great many guns.
It allows for a very high angle of elevation, and when fitted with a
quick-loading gear, allows for the rapid placing of the piece in load-
ing position after firing.

Movement of the gun in azimuth is accomplished in several ways;
one is to pivot the cradle of the gun in a saddle which itself pivots
on a horizontal transom of the trail. Another is to mount the gun
and elevating gear on some form of top carriage, and pivot this
top carriage over the axle. Still another is to traverse the whole
piece along the axle, pivoting on the spade. This is a method used
by the French in some of their designs. It has the disadvantage of
only allowing for a small angle of traverse.

The above principles of design are, of course, modified considerably
in the case of semipermanent mounts which fire from platforms and
for anti-aircraft guns which have special mountings suited to their
special use.



RECOIL.



RECOIL BRAKES AND METHODS OF COUNTERRECOIL.

The stresses to which a gun carriage is subjected are due to the
action of the expanding powder gases on the piece. Gun carriages
are constructed either to hold the piece without recoil or to limit the
recoil to a certain convenient length. In the first case, the maxi-
mum stress on the carriage is readily deduced from the maximum
pressure in the gun. In the second case it becomes necessary to
determine all the circumstances of recoil in order that the force
acting at each instant may be known and the parts of the carriage
designed to withstand this force and to absorb the recoil in the
desired length.

Assume the gun to be so mounted that it may recoil horizontally
and without resistance. On explosion of the charge, the parts of
the system acted upon by the powder gases are the gun, the pro-
jectile, and the powder charge itself; the latter including at any
instant both the unburned and the gaseous portion. While the pro-
jectile is in the bore, if we neglect the resistance of the air, none of
the energy of the powder gases is expended outside the system.
The center of gravity of the system is therefore fixed, and the sum of
the quantities of motion in the different parts is zero. The move-
ment of the powder gases will be principally in the direction of the
projectile. By formula, the weight of the gun, projectile, and
charge being known, the complete relations between the velocity,
time, and length of free recoil may be established.

Thus far we have neglected all resistances and have considered
the movement of the gun in recoil as unopposed. However, when
the gun is mounted on a carriage the recoil brakes, of whatever
character, begin to .act as soon as recoil begins, and consequently
the velocity of recoil is less at each instant of travel than when
unopposed. It is evident that the higher the resistance offered by
the recoil brakes, the shorter will be the total length of recoil. A
little consideration will show that if the total resistance to recoil is
made constant throughout the recoil, its value will be less than the
maximum value of a variable total resistance which will stop the
gun in the same length of recoil. For a given length of recoil; the
constant resistance will therefore produce less strain in the carriage,
and for this reason is usually adopted, except where stability can be
increased by using a variable pull.
18322820 3 (31)



32




FIG. A.



The recoil system of a gun carriage consists of a recoil brake for
controlling the recoil and limiting its length, a counter-recoil mech-
anism for returning the gun to the firing position and keeping it
there, and a counter-recoil brake or buffer to soften the shock as the
gun runs into the firing position.

Recoil brakes of the friction type were formerly used. Pneumatic
brakes were also used to some extent. Both have been entirely
superseded by the hydraulic recoil brake.

A hydraulic recoil brake consists of a cylinder filled with liquid
and a piston. Relative movement is given to the cylinder and piston
by the recoil, and provision is made for the passage of the liquid

from one side of the head of the
piston to the other, by apertures
cut into the piston or in the walls
of the cylinder. The power of the
brake lies in the pressure produced
in the cylinder by the resistance
offered by the liquid to motion
through the apertures. ! f the area of the apertures is constant, it is
evident that the resistance to flow will be greater as the velocity of
the piston or the velocity of recoil is greater. Therefore, the pressure
in the cylinder, which measures the hydraulic resistance offered, will
vary with the different values of the velocity of recoil. If, however, the
apertures are constructed in such a manner that the area of aperture
increases when the velocity of the piston increases, and diminishes when
that velocity diminishes, the variation in the area of aperture may be
so regulated, that the pressure in the cylinder will be constant, or will
vary in such a manner as to keep the total resistance to recoil con-
stant, or it may be made to vary in
any manner desired.

In figure A is shown one type- of
hydraulic brake. It consists of a
cylinder on the inner circumference
of which are formed bars of varying
cross sections, called throttling bars (T), piston (p), and piston rod.
Either the piston rod is secured to the carriage, the cylinder moving
to the rear with the gun, or the cylinder is secured to the carriage,
the piston moving to the rear inside of the cylinder.

Through the piston head are cut slots or apertures through which
the liquid is forced from one side of the piston to the other as the
cylinder, or piston, moves in recoil. Each slot has the dimensions
of the maximum section of the throttling bar with just enough clear-
ance to permit operation. The area of orifice open for the flow of
liquid at any position of the piston is therefore equal to the area of
the slots minus the area of cross section of the throttling bars, and




FIG. B.



is so determined that the resistance to the flow of the liquid, or the
pressure in the cylinder, is made constant or variable, as desired.

In another type of hydraulic brake the throttling bars are not
used, but the varying apertures are obtained by cutting grooves of
varying width or depth on the interior of the cylinder.

Figure B represents another method of varying the throttling
grooves. The piston (P) is held rigidly from turning and the valve
(V) is rotated by means of a spiral groove cut in the cylinder walls,
in which the lugs of the valve slide during recoil, thus rotating the
valve and varying the size of the openings through the valve and pis-
ton. This method is used to a considerable extent in British design.

Figure C illustrates a method of central throttling. The throttling
rod (R) has a varying diameter; this causes the amount of liquid,
which flows between it and the hole in the piston (P) , to vary in the
manner necessary for correct throttling. This method is used in
some French designs.

Counterrecoil, or the return of the gun to battery after completion
of the recoil, may be effected by springs or by compressed air cylin-
ders; the latter, in connection with

the recoil brake, forming the hydro- . | [ p^ \ ~

pneumatic recoil system. (V c= Z__ J ^~

The spring method of effecting | ~f\

counterrecoil may be used in all
gun carriages on which the gun

recoils in the direction of its axis. These include pedestal mounts,
barbette carriages, turret mounts, and all wheeled carriages as shown
in figures F arid G.

In the smaller carriages of these types the springs, initially com-
pressed to the desired amount, may be placed between the piston
and the rear end of the hydraulic brake cylinder which is lengthened
for that purpose.

In some carriages of this type the hydraulic brake cylinder moves
with the gun in recoil, the piston being stationary. In such construc-
tions the springs are usually placed around the hydraulic brake cyl-
inder, and are compressed between a flange on that cylinder in front
and some fixed part of the carriage in the rear.

In larger carriages the springs are arranged in separate cylin-
ders with pistons of their own, two to four of these spring cylinders
being required, see figures F and G.

Figure D shows a spring counter-recoil mechanism (spring recu-
perator) consisting of two concentric columns of springs.

It is sometimes necessary to use telescopic springs as shown in
figure E, when a single column would not allow sufficient recoil.

These and other arrangements of counterrecoil springs will be further
discussed in the description of the carriages to which they pertain.



34







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>oooooooooo<






o






"joooooooooo
[>oooooooooo<







DOOOOOO o o o o {_








oooooooooooL




9


)OOOOOOOOO O<|~




-




ooooooooooon





FIG. D.



FIG. E.



Compressed gas (either air or nitrogen) is now very generally used
to effect counterrecoil. Figures H, J, K, and L are diagrams of two
designs of hydropneuniatic recuperators.

In Figures H and J the recuperator piston (P) forces the oil from
the recuperator cylinder into the gas reservoir through the port
(A) when the gun recoils. Thus the gas is compressed and the
necessary energy stored up to return the gun to battery. The piston
may be attached to the gun and move with it, the cylinder being
fastened to the carriage, or the cylinder may move and the piston



iRRIMGJ




FIG. f=- IN-BAT- TERV OR F1RIMC3 ROSITIOM



/SPRIMC3




F"IG.Gi EIMP OF" IREICOIL-

- SRRIMG RECOIL-



rod be fastened to the carriage. The gas is given sufficient initial
compression to hold the gun in battery at all elevations.

The type of recuperator shown in figures K and L is similar in
operation to that of figures H and J, but in the latter design the oil
is separated from the gas by the floating piston (FP).



AIR




RIS-TOM(FP)



H IN-BA-TTETR^ OR F-|RNG



FLOAT-IMG PISTON





FIG. K IN- BATTER V OR F"IR>MC5 F>OS|-TlOrH




. L- ElfSP OF f?ETCOIL-

HVORO-PINEIUMATIC REZCQJL- S^



WITH



IM PIREICT OOMTAOT WITH THEI >AIR



36

The hydropneumatic recuperator (or counterrecoil mechanism) may
be separated from the recoil brake or the two may be combined in
one unit.

The principal advantages of air cylinders over spring cylinders for
counterrecoil are the reduction in weight and longer life. These
advantages are especially important in long-recoil field guns or how-
itzers designed to be fired at high angles of elevation. If springs are
used the columns are long and heavy, being liable to breakage; while
if air cylinders are used, the additional pressure needed when the
guns are fired at high angles of elevation can be obtained by pumping
more air into the cylinders.

It is evident that the energy, in whatever way obtained, which
effects counterrecoil, forms a part of the total energy of recoil. The
total resistance to recoil is composed of the resistance offered by the
brake, the resistance due to friction, the resistance either plus or
minus due to the inclination of the top of the chassis or the recoil

slides, and the resistance due to

M B X _ JJ the counterrecoil springs or air cyl-

/L c ^ "I (w L J inders, if there are such included



OIL



in the recoil system.



FIG M The counterrecoil buffer is pro-

vided for reducing the shock to the

carriage as the gun is returned to the firing position by the counter-
recoil mechanism.

In figure M is shown a type of buffer which is used to some extent.
It consists of a rod (B) which acts inside the hollow piston rod of the
recoil cylinder. A similar method to this is to provide a separate
cylinder in which a projection of the recoil piston acts during the last
few inches of recoil. It may consist of a dash pot formed at the end
of the recoil cylinder.

The use of the counterrecoil buffer increases the stability of mobile
artillery carriages by preventing their forward motion as the gun
runs into battery.

Modern field guns and howitzers are mounted so as to have a long
recoil on their carriages when fired horizontally. When certain types
of these guns are fired at high angles of elevation it is necessary to
reduce the length of recoil to prevent the breech of the gun from
striking the ground. This reduction is effected by a mechanism
which automatically reduces the size of the orifices in the hydraulic
brake as the gun is elevated. This is known as variable recoil.

If no counterrecoil buffer is provided, the velocity of the gun when
going into the firing position under the action of the counterrecoil
springs or air cylinders is at a maximum just as it reaches that posi-
tion. If an arrangement is made to automatically fire the gun when
it has this maximum forward velocity, it is evident that the maximum



37

velocity of free recoil will be reduced by the amount of the forward
velocity, and hence either the total resistance or the corresponding
length of recoil, or both, can be materially reduced. Systems based
upon this principle have been used abroad for small guns, such as
mountain guns. The gun is caught by a pawl in the extreme recoil
position and is loaded in that position. When it is desired to fire,
the pawl is tripped, the gun runs forward, and is automatically fired
as it reaches the firing position. The principal objections to this
system, which is known as the differential recoil system, are the
unsteadiness of the gun at the moment of firing and the possibility
of the gun being turned over in a forward direction by the shock of
counterrecoil if a misfire should occur.

In artillery of position, the gun carriage is rigidly bolted to a fixed
platform. Its mechanism is such as to allow the gun and the attached
parts to recoil on firing. The nydraulic brake cylinder and its piston
are attached, respectively,, to the moving and fixed parts of the car-
riage, or vice versa, in such a way as to cause the piston to be drawn
through the cylinder as the gun recoils. When constant total resist-
ance is to be exerted by the recoil system, which is always the case in
artillery of position, either the total resistance or the length of recoil
may be assumed, and the other determined. While the assumption
of a very long recoil would reduce the resistance and consequently
the strain on the carriage and permit its parts to be made lighter, the
necessary increase in the length of the recoil slides might overbalance
the saving in weight.

In carriages, such as mortar, anti-aircraft gun, and the latest type
barbette carriages, all of which permit the firing of the gun at high
angles of elevation, a very long recoil can not be used, because the
distance from the breech of the gun to the supporting platform will
not permit it. Furthermore, the use of a long recoil would necessi-
tate the use of long and heavy columns of counter recoil springs.
Lack of space also prevents the use of a long recoil on turret mounts.

In disappearing carriages, the length of recoil is determined more
by the necessity of giving the gun the proper movement in recoil than
by limitation of the strains brought upon the carriage.

With the exception of the disappearing and the older type of
barbette carriages, the recoil for artillery of position is comparatively
short.

The construction of all modern wheeled carriages is such as to
allow the gun to recoil in the direction of its axis. The resistance to
recoil developed by the recoil system pulls forward on the gun and
backward- on the carriage, tending to move the latter to the rear.
Actual motion of the carriage to the rear is prevented by a spade
sunk in the ground at the end of the trail of the carriage and so con-
structed as to present a broad surface to the ground in the rear.



38

Under ordinary conditions the ground will resist a pressure of 40
pounds per square inch of spade surface, and knowing the pressure
developed by the pull of the piston rod, which is the only force acting
on the carriage, the size of spade can be determined.

Another effect produced by the resistance to recoil is a tendency to
rotate the carriage around the point of support of the trail, or to
cause the wheels to jump from the ground. Such a movement is
very undesirable, as it interferes with the rapid aiming and firing of
the piece. In order to prevent the wheels from jumping off the ground
when the gun is fired, it is necessary that the product of weight of
the carriage including its recoiling parts and the horizontal distance
of the vertical through their center of gravity from the point of sup-
port of the trail, should at any instant be greater than the product
of the force opposing recoil and the perpendicular distance from its
line of action to the point of support of the trail. The value of the
total resistance to recoil, that will be just insufficient to cause the
wheels to rise from the ground when the gun is in the firing position,
is obtained by equating moments which will show that a value of this
resistance small enough to prevent jump of the wheels in the early
part of the recoil might still cause jump toward the end of the
recoil, as the moment of the weight of the recoiling parts becomes less.

It is evident that safety against jump can be maintained and the
necessary length of recoil shortened if, instead of assuming a constant
total resistance, we assume it as decreasing to such an extent as to
remain parallel to a line showing the maximum permissible values of
the total resistance to recoil and plotted as a function of the length of
recoil. If the length of recoil is such as to provide a factor of stability
when the gun is fired at horizontal, the carriage will be stable at all
higher elevations, as the lever arm of the total resistance of recoil
decreases as the gun is elevated. For this reason, reduction of the
length of recoil with increase of elevation in howitzer carriages does
not affect their stability.

The initial strength of the counterrecoil spring columns or air
cylinders is the force which they exert. against the gun in the firing
position. This force must be great enough to hold the gun in that
position at the highest angle of elevation at wilich it is to be fired, as
well as to overcome the friction on the recoil sides as the gun runs
forward to the firing position.



AIMING DEVICES AND SIGHTING METHODS.



Sights will be discussed briefly in this pamphlet merely to indicate
their application to field, anti-aircraft, and trench materiel.

In order that a projectile from any gun may hit the target, the
gun must be fired at a certain angle of elevation depending on the
range, the ballistic characteristics of the gun, and upon the relative
level of the gun and target. It must be given such a direction to the
right or left of the target as to offset the deviation of the projectile
due to drift and wind. The sights of the gun provide means of de-
termining when the axis of the gun has the predetermined direction.

When the piece is sighted, both in elevation and direction by sight-
ing directly 011 the target, the method is known as direct laying.
This is precisely the same operation as sighting a shoulder rifle or
pistol. The line of sight may be fixed in one of two ways. The first
method is to use plain or open sights, the rear one of which has a
peep, or notch, capable of adjustment in a vertical or horizontal
direction. This rear sight is equipped with an arc reading in frac-
tions of the range, or degrees, by which the necessary elevation can
be set off. In some cases the rear sight is designed to automatically
correct for drift; if not, the drift must be set off on a scale provided
for this purpose on the rear sight. It is always well to bear in mind


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Online LibraryUnited States. Army. Ordnance DeptHandbook of artillery : including mobile, anti-aircraft and trench matériel → online text (page 3 of 19)