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.