A 28-ton Gun-carrying Trailer
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Ingenious Features in New Crane Product Mounted on I3.50-in. Pneumatics
AN interesting type of gun-carrying trailer to carry weights up to 2.8 tons has been delivered to the War Office by Cranes (Dereham), Ltd.,.the well-known trailer maker. This vehicle is to beemployed for transporting heavy ordnance, and as it will have to carry•the gun barrel, shields and gun mounting, it has been made particularly adaptable, as the pieces to be handled are of unusually varying shapes.
The basis of the machine is two Jourwheeled bogies on Goodyear 13.50-in. by 16-in, low-pressure pneumatics.
.11-ie bogies are identical, and on the front of each is a turntable carrying a transversely pivoting axle beam. The rear axles are fixed rigidly by clamp bolts and brackets to the under side of the bogie frames, a spacer bar in each case connecting front and rear axles, thus achieving the double purpose of transmitting the drawbar pull from the front to the back axle and acting as a distance piece to ensure the retention of the relative positions.
The bogie frames are rectangular, with permanent channel-steel crossbolsters of box-section, set midway between the wheels. Each bolster is secured by a kingpin on which it can turn to allow the vehicle to be steered. Segmental plates on each bolster act as bearings..
The main frame of the trailer is cornprised of two fish bellied, built up girders secured to the bolsters by anchor blocks, which are allowed a certain amount of float to allow for distortion in the frame caused when traversing uneven ground. The girders are fitted direct to the bolsters only when the gun barrel is being carried, and between them and resting on the top of each crossbolster are curved chock blocks to take the underside of the barrel, chafing being prevented by a covering of hardwood. The barrel is held by stout chains.
The steering is worthy of note. A standard form of pressed-steel drawbar is fitted to the front axle of the leading bogie, and the front wheels are free to lock to 21.5 degrees in each direction. Each bogie is free to move under its cross-bolster, but the two are coupled up so that the movement of that leading controls the path of the trailing bogie. This is achieved by means of two intermediate drawbars, the leader being of pressed steel, triangular in shape, with a central slot running for about half its length: It is attached by means of eyebolts and pins to the rear cross-member of the bogie. The drawbar on the trailing bogie is secured by the same means to the steerable front axle. It is of the same shape, and its apex has a large pin equipped with a roller, the flange of the pin resting on the upper surface of the front drawbar and passing through the slot in it, the roller reducing friction.
It will be realized that the intermediate drawbar must be supported. This is effected by a radius bar
knuckled under the forward axle of the rear bogie. It is spring-loaded and fits into a yoke on the underside of the rear intermediate drawbar, which it thus supports. When the front bogie turns, that at the rear is affected through the drawbars, the flanged pin and roller sliding in the slot provided or them, giving a turning circle of only 35 ft.
To provide for awkward conditions, a man-handling pole can be fixed to the front of the trailer, being coupled to the front axle by a universal
knuckle. It is also connected to the foremost drawbar.
An important feature is that steering can be effected from either end, as, by turning each bogie through 180 degrees, the trailer automatically faces the opposite direction.
In order to carry the shields and mountings, the main girders are dismantled from their positions on the permanent cross-holsters and are bolted to five sturdy cross-members forming a continuous rectangle which is stayed by two diagonal cross-braces.
The same frame-anchorage blocks a re used in the permanent cross-bolsters, but are now fitted into the front and rear cross-members of this rectangular frame. Thus the method of securing the bogies remains the same, and the necessary float is still ensured.
The frame so made is 7 ft. 6 ins, wide and 16 ft, 9 ins, long, and to alter the vehicle frame from one shape to another is quite a simple procedure, the overall dimensions of 25 it. long and 7 ft. 6 ins. wide remaining the same.
The vehicle will travel at only 4 m.p.h.. and it will be hauled by a traction engine. It is braked by two screw hand wheels fitted at the rear of each bogie and operating 113-in.
diameter internalexpanding brakes.