PERFORMANCE OF STEAM TRACTORS 



67 



rating. The mechanical efficiency will range from 85 to 93 per 

 cent. In the Winnipeg motor contest of 1910 the steam en- 

 gines carried an average of 97 per cent, of their rated brake 

 horsepower in an economy test and 132 per cent, in a maximum 

 test. The drawbar horsepower was 95 per cent, higher than 

 the nominal rating. Steam tractors are not as a rule over- 

 rated. However, their power for steady work is much less 

 than could be maintained on a short run, unless a much larger 

 boiler is provided than usual for a given size and speed of 

 engine. 



Steam tractors have competed in three motor contests held 

 in Canada during the last several years. The following table 

 shows the average coal and water consumption of all engines 

 in the economy tests in these competitions. It is not to be 

 supposed that the load in every case was exactly at or even 

 near the point of greatest economy, though this condition was 

 usually aimed at. There was but one test of a compound 

 engine on the brake, against six single and eleven double cyl- 

 inder engines. In plowing there were four single and six double; 

 and in hauling, one single and three double. To these figures 

 there should be added a certain percentage of coal and water 

 used in actual practice in getting up steam, and for waste 

 after the close of the day's work. 



POUNDS OF COAL AND WATER USED PER DELIVERED HORSEPOWER PER HOUR 



Steam tractors as a rule use from seven pounds to eight 

 pounds of water per pound of coal. Reports from 333 plowing 

 engines of all types in the United States and Canada indicate 



