Traction and Non-Skid Devices for MotorDriven Fire Apparatus *
Your Topic 5, which has been assigned to me, is of such widespread importance to the perfection of motor-driven apparatus, that I must confess my inability to do this subject justice. I can only impart to you my limited knowledge, as I have gained by observation while acting in the discharge of my duties as Chief of the Calgary Fire Department. 1 have found the following conditions when operating a heavily loaded car: Most troubles, such as skidding and lack of proper traction, are the results of the construction of the differential as now used in motor apparatus and also of the road conditions we have to contend with, such as slippery streets and where of the largest motor would be useless, even if one wheel loses traction owing to mud, sand or slippery pavements. This is due to the wheels spinning, and the reason is that the present differential does not equalize the pull on both rear wheels. For example, the right wheel would spin the most when the weight is on the left-hand side; the left wheel, therefore, has greater traction and the present differential carries the power to the wheel having the least traction. This means that when one wheel has even the slightest traction, it gets all the power of the engine, until the other wheel gets traction, when the pull is equalized on both wheels. The latest device which I have noticed now being used with success, as far as my experience, is the individual cross chain that has a fixture fastened permanently to every other spoke, so that these chains can be snapped on with the least delay. I also find it important to have a. chain designed heavy enough for the load it is to operate under. Lack of attention to the weight of the chain has been the cause of unsatisfactory results in many cases. Regarding traction, it has been shown by actual tests that the high speed a car travels, say one hundred miles an hour, the rear wheels would turn over equal to a distance of 106 miles, showing a loss of one wheel would get into a mud hole and one wheel on a dry spot; in such case all the power traction and slippage of six miles. This always exists in proportion according to the speed of the car. This test was made on a level dirt road, so you can imagine the extra amount of traction lost on slippery pavements and the great wear in tires, owing to the loss of traction. A grade that has a raise of one foot in twenty feet is known as 5 per cent, grade; a grade with a raise of one foot in five feet, 20 per cent, grade; a grade that is a little steeper than a raise of one foot in two feet, is a little more than 50 per cent, grade, and is of such a height that gravity would overcome traction; a grade of one foot raise in one foot length would be 100 per cent., or an angle of 45 degrees, and not 90 degrees, as is believed by many. So, in summing up the conditions as they now exist, with the relation to the differential as now used and the many devices, we have room for improvement that will have the tendency to practically eliminate the present loss and danger that now exists from skidding and unequal traction conditions.
*Abstract of paper read at Convention of International Association of Fire Engineers, Cincinnati, O., Aug. 31Sept, 3, 19151