THE CREEPER TRACK AND STEAM TRACTOR.
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How the Super-Sentinel Steam Tractor has been Mounted on Roadless-Traction Units and is made Valuable for Timber and General Haulage in Rough ,Country.
THE application of the creeper-track mode of. vehicle propulsion to the steam tractor oi . rapidproduction lines is a distinctly neW departure, because, if our memory.on this subject is not at fault, the original creeper tracks, or caterpillars, were all allied to internal-combustion engines, whilst those manufacturers of steam-driven tractors who have employed the creeper track have done so in more or less an experimental manner, and we are unable to recall any model which has been maintained in production. The difficulty with which makers of such vehicles have, seemingly, been faced in the past is the unprecedented wear of the creeper tracks, a fault which was not overcome even in connection with the use of the Tanks in the war.
We have, as our columns have shown, dealt with all the developments of the use of the creeper track and it will have been noticed that, so far, vehicles of a type suitable for commercial and military uses and equipped with this mode of propulsion have been of the order of low or medium power and capacity. A two-ton load on a vehicle has almost been the maximum hitherto,. so that it has been exceedingly interesting, recently, to observe the results of the application oF the creeper track to machines of much greater capacity, with a commensurate amount of power behind them. The latest production is the " Sentinel-Roadless" tractor, which was shown to the Press at Shrewsbury on Wednes day last and put through its paces on difficult land adjacent to the works of the Sentinel Co. The demonstration had been arranged by the Sentinel Waggon Works, Ltd., and Roadless Traction, Ltd., the first being responsible for the tractor and the second for the transmission unit.
It is desirable at this point to look for a few moments into the evolution of the Sentinel wagon. The first vehicle possessed original—even curious— features, such as hydraulic steering, but, in a little while, it was shorn of these and developed into the successful machine upon which the company's business was built up. About 1919, advances in design and methods of construction were foreshadowed and followed up, the result being the production of the super-Sentinel boiler and engine, the super-Sentinel wagon being put on the market in May, 1923, and proving so successful that nearly 700 of these vehicles have been delivered to. customers.
The success of the two main components was so gratifying that new uses were sought for them. First there was produced the super-Sentinel tractor with the crankcase of the engine disposed to the, rear of the back axle, with the boiler placed almost amidships and with the water tank set over the rear axle, the. motive being the imposition of the greater portion of the weight upon the rear wheels. Following upon this, the boiler and engine were employed on the propulsion of rail coaches, and now they are
being applied to rail locomotives and stationary plants, because it is being found that the most modern types of engines and toilers developed for use on road vehicles are far more efficient and economical than similar components evolved for railway and other purposes, for the simple reason that road conditions are more strenuous and exacting and present so many variations in load, gradient, etc., that a high state of efficiency has had to be attained.
The next application of Sentinel practice to the crecper-track machine was, thus, an obvious development And, for the purpose, the tractor devised about a year ago was taken and its rear axle replaced by the Roadless-Traction unit. The boiler of this machine, as is well known, is of the vertical water-tube type, and is not called upon to carry any part of the weight of the tractor, it being contended that road work is too varied and strenuous for the locomotive type of fire-tube boiler. The boiler will evaporate as much as 1,800 lb. of water per hour, and it has been hydraulically tested to a presure of over 1,100 lb. per sq. in. It feeds a horizontal two-cylinclered engine, which will develop 60 h.p. to 65 h.p. continuously without being forced, and will put out 75 h.p. on emergency. With its -crankcase, as we have explained, to the rear it drives forward to the driving sprockets by a double-reducticn chain gear. The drive is taken from the rear sprocket to driving teeth formed on the top (or inner side) of each link of the track. Carried on forward arms is the jockey pulley which lays down the track, means of adjustment for slack or wear being provided, whilst, carried ori the bogie, are four rubbertyred rollers, which take the weight on the centre of the track unit. The unusual features of the Roadless-Traction patent unit are, first, that the track is made according to driving-chain practice, with hardened and ground pins and bushes, each lubri
B30 cated from an oil reservoir and protected for the loss of lubricant and the intrusion of dirt and grit, whilst a universal movement is given to every joint, altewing the track to take a curvature between sprocket and jockey pulley (actually, for effective purposes, between the weight-carrying rollers) so reducing materially the screwing, and therefore wearing, action between track and road whenever the vehicle is being steered out of a straight line. The net result is a track with a long life, silent on. hard roads and involving but a fraction of the maintenance costs of the Tank type of track.
The demonstration consisted of driving the machine without load through boggy ground, ponds 2 ft or 3 ft. deep and soft mud having to be traversed, in crossing hidden tree stumps and fallen timbers, in negotiating the sides of a trench about 7 ft. deep and climbing gradients of about 1 in 1, whilst, to show its capacity in haulage, a 31-ton tree log was easily pulled over rough ground, and a film display showed it hauling 74 tons of timber on a trailer through a very soft piece of country. A. drawbar test showed that the pull exerted was in
the neighbourhood of 5i tons, but 6 tons has been registered. A further test applied was the setting in motion of a number of derelicts with a total load
of 58 tons. They were, if anything, on a slight gradient and the load was got going without difficulty. The claim for the use of steam in conjunction with the creeper track is that it sustains its torque, which actually increases in inverse ratio to the speed of the machine and consequently the steam engine has a very great degree of elasticity, and a machine utilizing this source of power is able to surmount obstacles which would most probably stall a less flexible engine. The New Sentinel rail locomotive was observed during our walk through the works to be moving a train of railway trucks weighing over 80 tons.