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M1917 Renault FT-17 6 Ton Special Tractor - Design

The 6-ton tank, model 1917, is the Americanized Renault. This is a " two-man " tank, there being a driver and a gunner. The driver sits on the floor in the front of the machine and the gunner stands up just back of him, with his shoul ders and head in the turret, and so is able to operate the gun, which is mounted in one face of the octagonal turret.

The Renault was designed and first built by the Renault Co. in France. Four sample machines were sent to the United States, the first one arriving on December 1, 1917. Standard ordnance drawings were made, keeping the machine a Chinese copy of the French machine, except that all metric measurements were changed to inches and screw threads and gear teeth changed to American practice. An American engine was sub stituted for the Renault engine, the American engine being the Buda type H. U. with certain modifications of crank case and timing gear to fit the hull of the tractor.

The 6-ton tank, Mark II, is practically the same as the model 1917, except that the 6-cylinder Hudson engine is used.

The six-ton tank, model 1917, has no wheels of any sort directly bearing on the ground, but is completely supported and propelled by two endless-chain tracks, one on each side. Each track works on a side frame called a longeron. The track runs on two wheels, one propelling it by means of the engine and the other keeping up the tension and aiding it in the return of the track. Traction is obtained by the lower part of the track being forced into the ground by the weight of the machine, which weight is supported by rollers on the back of the lower part of the track. The axles of these rollers are fixed to two rockers, called the front and rear chariots, placed inside the lower frame of the longeron.

The front chariot has two trains of rollers, each train articulated to it by an axle. The forward train carries three rollers, the rear two rollers. The chariot is attached to the lower frame of the longeron by a large leaf spring which will support 1.200 kilos (2,645.5 pounds). The front end of this spring is fas tened to the longeron with an axle (fixed) and the rear end by a shackle . (movable). The spring is fastened to the chariot by an axle held to the spring by clips.

The rear chariot is similar to the front, with the following exceptions: Its trains each have two rollers; its spring has 14 leaves and will sustain a weight of 1,700 kilos (3,747.8 pounds). The front end of the spring is shackled and the rear end is fixed to the longeron. The nine rollers of these two chariots support the entire weight of the car, as mentioned above, and by their method of attach ment allow the tread of the track to conform to almost any inequality of the ground. This is a marked advance over other types, in which the rollers are fixed permanently to the plane surface of the bottom of the car and have no springs.

The superframe of the longeron consists of a train of six rollers whose function is to support the weight of the top part of the chain and to insure its tension. This train of rollers is at tached at its rear end to the main longeron by means of an axle and stanchion. At its front end it works vertically in a guide which is bolted to the main frame of the longeron, and its tension is secured by the action of a spiral spring placed just ahead of the guide and imprisoned between the lower end of the train of rollers and the top of the main frame of the longeron.

On the top of the main frame of the longeron and just ahead of the guide and spring above mentioned, is the support for the axle of the return pulley or tension wheel. This is a large metal disk wheel with steel shoe over which the track runs on its way to the ground.

The tension of the track is permanently altered by the advance or retraction of this wheel by means of the Y or fork which holds its axle. This adjustment is made by means of an adjust ing nut in the tail of the fork. The weight of the chassis is supported by the two longerons at two points on each side. At the rear end the articulation is fixed by means of a dead axle which serves as the pivot for both the rear end of the longerons and the spur-gear-driven sprockets. It is by means of these sprockets that the engine gives movement to the track. Front spring.At the front end, the weight of the chassis is trans mitted to the longerons through a large spiral spring working inside guides which allows play in a vertical plane. Fracture of the spring is prevented by means of a rubber bumper which comes into play in the case of excessive shock.

The movement of the tank is caused by two endless tracks, each about 12 inches wide with a single cross spur on each of the 32 links composing a chain. Each link is connected with the other by means of a connecting pin retained in position by a large cotter pin through each end. The whole chain is guided by the rollers and sup port wheels. At the rear of the longerons the chain rolls on the teeth of the sprocket, which, as above mentioned, is mounted on the dead axle at the pivot of the longeron.

The chassis is composed of a floor of armor plate 8 mm. thick; sides of armor plate 16 mm. thick. The nose is made of armor plate 16 mm. thick. The two doors on the top of the nose open to the right and left. Above the nose rises the case of the turret surmounted by the turret. Behind the turret is the tail section containing the engine, etc. All of these parts are composed of 16-mm. armor plate. At the front end of the base of the turret are slits through which the driver can see, also a small shutter which, opening in conjunction with the doors of the nose, permits the driver to enter and leave the machine. The turret can turn through 360 and is easily moved by two handles on the inside, the rotation being facili tated by a ball-bearing contact. In the back of the turret is a door opening outward which allows the gunner to enter and leave the turret. Behind the section carrying the engine is an additional flat piece of metal called the tail. The purpose of this addition is to give added length to the tank and thus facilitate the crossing of large trenches. It is hinged at its lower end and supported by movable brackets at its upper end, and it thus may be lowered so that the engine may be cranked from the outside.

The gasoline tank, with a capacity of 108 liters (114.13 quarts), is made of double sheet steel, the space between the two thicknesses of steel being filled with best-quality wool felt, so that if the tank is pierced by a bullet the expansion of the felt on being moistened by the gasoline will prevent excessive leakage. At the bottom of the outside case is a drainpipe leading to the outside of the tank, so that when the felt becomes thoroughly saturated the excess gasoline will flow outside. The carburetor is fed by a Stewart vacuum feed system.

The magneto is an Eisemann high-tension type. The carburetor is a Schebler model A. The radiator is of the ordinary Kenault tubular construction, with pump circulation. Cooling is assured by a large fan placed just forward of the radiator, which draws the air for the cooling of the radiator through the foot of the gun tower, the air entering the gun tower through a ventilator at the top. By this means the cooling fan also serves to ventilate the tank. Main clutch is of the inverted-cone type, contained in the flywheel. Universal joints are of special construction, allowing a certain amount of shock and strain to be taken up. It is a double hexagon ended dumb-bell type, with a male and female end connecting the engine to the gear box. The gear box has two trains of gears, giving four speeds ahead and a reverse, but at no speed does the engine drive direct, as in an automobile, but always through a gear. The power is transmitted from the gear box to the tracks by means of two pinions which receive their power from a beveled gear, as is usual in a differential, but it should be noted that in the tank there are no spider gears and both tracks always rotate at the same speed. The two track clutches, one on each side, are fastened to the two ends of this pinion by a slotted keyway. Beyond the clutch the power is transmitted to a train of gears and spur gears through an Oldham coupling.

Mode of steering is by means of the two side clutches which connect the engine to these two trains of gears the direction of the tank is altered. When, for example, it is desired to turn to the right, the right clutch is first released by pulling the starting lever. If a short change of direction is desired the starting lever is pulled more, applying the clutch brake on the right side, and the car spins round in place. At the back of the gun tower is situated the inside cranking device. A train of gears is used here because cranking from this end of the engine must be transmitted through the clutch and gear box.

The turrets are octagonal, made of rolled armor plate, and revolve through the full 360 degrees. Only one model of the machine is being built, but some are armed with 37-mm. guns, some with machine guns, and a few with wireless signal systems.

The exact ratio is five machines to carry 37-mm. guns to seven machines to carry machine guns. The 37-mm. guns are the field gun, model 1916, mounted suitably for tank uses, and the machine gun used is the Marlin aircraft gun modified for tanks. Two hundred and fifty rounds of 37-mm. ammunition will be carried per tractor and of machine-gun ammunition 5,000 rounds per tractor.

The armor is six-tenths inch thick on the sides and front and rear and the turret with thinner plates where not subject to direct fire. This machine is able to negotiate trenches up to 7 feet wide, and if chained two machines in tandem, wider trenches may be crossed.

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