Page:Popular Science Monthly Volume 90.djvu/730

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714

��Popular Science Monthly

��surmount seemingly impassable obstruc- tions, such as trees, boulders, ditches, shell craters, wire entanglements or trenches. Harveyized steel, so named after its in- ventor, made the tanks impervious to machine gun and rifle fire, shrapnel and everything except a direct shell hit.

How a Tank Is Built

The principal \ feature of the tank's construe- \ tion is the cater- pillar or track-lay- ing device. This consists of an end- less steel belt made up of short sec- tions like shoes, which lie flat on the ground. These support the vehi- cle wheels which mounted

��are mountea on trucks somewhat similar to those on rail- way cars. The insides of the shoes have double rails over which the truck wheels run as shown in the illustration at the top of page 712.

The endless chain made up of the shoes acts as a track, being laid flat under the

��The caterpillar tread is curved up in the arc of a huge circle at the front which gives the vehicle its wonderful tractive p>owers. This large curvature acts as a huge wheel with a tremendously long leverage equal to the radius of the circle or the six)kes of the imaginary wheel of the same di- ameter^ Only that portion of the assumed wheel which would come in contact with the ground acts as the lever, and it is just this portion that is reproduced in the front end of a caterpillar belt

��wheels and picked up again after the wheels have passed over it. The endless chains are driven by means of sprockets on the rear axle of the tank.

The real unusual adaptation of the cater- pillar device for which the British designer of the tanks must be given credit is the shape of the belts. This has been carried out in a very diff^erent manner from that y used on their farm tractor predeces- sors. Instead of being low and flat, they are strung out over frames thirty to forty feet long and from ten to fifteen feet high, depending upon the size of the tank. These frames are armor- ed with Harvey- ized steel to pro-

���vide protection for the tank operators and besides are curved up in the arc of a huge circle at the front to give the vehicle its wonderful tractive powers. This large curvature acts as a huge wheel with a tremendously long leverage equal to the radius of the circle or the spoke of the

���All tanks have the common characteristic of being divided into three main compartments between the two side caterpillar frames, the lookout, the ammunition, and the engine rooms. Part of the cater- pillar tread of this machine was shot away, thus revealing the construction beneath the outer belt

�� �