Field artillery materiel

by Unknown

THE CARRIAGE.

The gun is mounted upon a cradle which encloses the recoil and counter-recoil mechanisms. The device for elevating the gun through the angle between the horizontal and the line gun-target (angle of site) is interposed between the trail and the rocker while the device for giving the gun elevation for range is placed between the rocker and the cradle. This arrangement is known as the independent angle of site or independent line of sight. It has the advantage over the three-inch type in that it allows the range elevation to be altered without disturbing the elevation for site.

75 MM. GUN CARRIAGE, MODEL OF 1897 MI(FRENCH).
LONGITUDINAL SECTION

75 MM. GUN CARRIAGE
MODEL OF 1897 MI FRENCH
REAR VIEW

75 MM. GUN CARRIAGE
MODEL OF 1897 MI(FRENCH)
LEFT SIDE

75 MM. GUN CARRIAGE
MODEL OF 1897 MI(FRENCH)
RIGHT SIDE

75 MM. GUN CARRIAGE
MODEL OF 1897 MI(FRENCH)
PLAN VIEW

The principal parts of the carriage are: trail, axle, wheels, brakes, shields, angle of site elevating mechanism, range elevating mechanism, traversing mechanism, rocker, cradle and sights.

When traveling or resting, the tube rests on the cradle which supports it by means of the jacket. When firing, it recoils on the cradle by means of the rollers. The jacket has two pairs of rollers, and the muzzle hoop is provided with a single pair of rollers. On the upper part of the cradle are the lower slides, on which the jacket rollers, supporting the tube, roll during the recoil. When the jacket rollers are about to leave the lower slides, the muzzle rollers come under the upper slides; the tube is then supported until the end of the recoil by the muzzle rollers and the more forward of the two pairs of jacket rollers. This device gives the gun a long recoil upon short slides. Inclined planes are used in such a manner that when the gun returns into battery the rollers rise from the lower slides thereby relieving the slides from the weight of the tube when the tube is in the traveling position.

The carriage supports the cradle which in turn supports the tube. The cradle and the tube together are displaced, during the laying for elevation with respect to the carriage which remains stationary. The carriage is held steady on the ground by means of the trail spade which with abatage prevents the carriage from recoiling on the ground.

Abatage consists of elevating the wheels on the brake shoes which are provided with small spades which prevent lateral movement. The brake shoes are fastened to brake beams attached to a sliding rack beneath the trail in such a manner that the abatage frame may be placed under the carriage during travel. In preparing to fire, the frame may be adjusted to allow the brake shoes to slip from a position in rear of the carriage wheels to a point directly beneath the wheels.

75-MM. GUN CARRIAGE, MODEL OF 1897, MI(FRENCH) WHEEL BRAKE MECHANISM

Abatage is accomplished as follows: (1) The brake shoes are dropped to the ground in rear of the point of contact of the wheels with the ground; (2) The trail is lifted, turning around the axle, until the spade is about five feet in the air. Tie rods and a slide working on a rack beneath the trail move forward in this action; (3) The trail is then brought down. The rack prevents the slide from moving to the rear and the carriage turns on the abatage frame until the wheels rest upon the brake shoes. This gives the gun a three point support, two small spades under the wheels and a larger one at the end of the trail.

Laying in direction is accomplished by traversing the piece on the axle. The trail spade is fixed and the axle is straight and rigid so that in the movement of the gun to the right and left on the axle both wheels must turn—one to the front and one to the rear. The device for laying for direction is composed of a threaded axle, which is prevented from rotating by a spur and a sliding nut which is contained in a box fixed on the left flask of the gun. This nut bears one of the bevel gears, which is put in motion by the hand wheel. The traverse is three degrees either side of the center or a total of 6 degrees or about 105 mils.

Laying for elevation. To obtain greater accuracy and speed in firing the 75 has an independent angle of site. A rocker with two trunnions is interposed between the cradle and the carriage. The rocker trunnions are seated in the cradle trunnions and support them. This gives the same rotating axis to both rocker and cradle. This is necessary for the mechanical addition of the angle of site elevation and for the range elevation. When the angle of site handwheel is revolved it turns a pinion, which meshes in the rocker rack and thus causes the rocker to move in relation to the carriage. This gives the cradle through the rocker the elevation equal to the difference in elevation between the target and the gun. It is independent of the angle given to the gun for the elevation due to range to the target.

75 MM. GUN CARRIAGE, MODEL OF 1897 MI(FRENCH).
RANGE ELEVATING MECHANISM

The angle given the gun for range is effected through a telescopic screw. This screw is fastened at one of its extremities in the rocker and at the other in the cradle. The nut which receives the elevating screw is seated in an oscillating support which allows it to always remain perpendicular to the axis of the bore at any elevation.

The angular displacements of the cradle with respect to the rocker (angle of elevation) are recorded by the elevating system composed of a graduated arc and a range drum. The lower part of the arc is connected with the right arm of the rocker. The arc is graduated in meters. When the range handle is turned the arc does not move, but a brass slide block connected with the gun and the cradle and bearing an index slides along the arc. It is thus possible to set the range in meters.

However, the arc graduations are not very legible and it has been supplanted by a graduated range drum having more legible readings.

The black part of the arc bears a rack which meshes with a pinion, which in turn rotates around an axle fixed on the cradle. When the cradle moves, the pinion rotates and carries with it the range drum.

The elevation on level ground varies from a minus 11 degrees to a plus 20 degrees. Greater elevation may be obtained by sinking the spade.

The Recoil and Counter-recoil mechanisms are of the Hydro-pneumatic type. Their accurate description is a secret. The following brief description will give only a general idea of the working of the mechanism. The whole apparatus is inside of the cradle through which are bored two cylinders: an upper cylinder 40 mm diameter, and a lower cylinder 66 mm diameter. These cylinders may communicate through a large hole. A piston moves in the upper cylinder, the piston rod, 24 mm diameter, being fast to the gun.

In the lower cylinder are: (1) The valve carrier pipe screwed in the rear part of the cylinder supporting spring valves; in the inner walls of the pipe are cut two grooves; the valve carrier pipe is ended by a circular ring. (2) The diaphragm with its hollow rod. (3) The loose piston with its small rod, which may come in contact with the upper rack of the gauge. The two cylinders are full of liquid, usually Russian oil. The front part of the upper cylinder in front of the piston may communicate freely with the air through the Front Plug. The front part of the lower cylinder is closed by a plug and contains compressed air at a pressure of 150 kg. per sq. cm.

Operation. In recoil the piston of the upper cylinder compresses the liquid, which has to pass through the spring valves and between the circular ring and the hollow rod of the diaphragm. The passage of the liquid through these different openings constitutes the braking effect. In so moving the liquid opens the valves, which are widely opened at the beginning of the recoil and gradually close in proportion to the decrease of the speed of the recoil. At the same time, the air of the recuperator is compressed by the action of the liquid on the diaphragm.

When the recoil is finished, the compressed air pushes back the diaphragm. The liquid thus compressed acts on the small cylinder piston and obliges it to come back into its initial position, bringing with it the tube.

The liquid in flowing back completely closes the valves and must pass between the diaphragm rod and the inner wall of the pipe. At beginning of the return into battery, the space between the rod and the bottom of the groove is large. This space decreases in proportion to the progress of the return. The passing of the liquid through this constantly decreasing space causes the braking which at the end reduces the speed of the return to nil.