66 POWER AND THE PLOW 



load. The ratio of fuel per brake horsepower-hour to fuel per 

 drawbar horsepower-hour was 59.9 per cent, in plowing and 

 34.4 per cent, in hauling. During the two-hour hauling tests 

 the steam tractors,traveling at from 2.04 to 2.34 miles per hour, 

 developed individual averages of 25 to 34 actual drawbar horse- 

 power in moving the dead weight of other steam tractors rated 

 at from 25 to 36 h.p., one engine being used as a load in each 

 case. In plowing tests conducted in 1910, six steam tractors 

 plowing on firm sod ground showed a tractive efficiency, based 

 on comparative fuel consumption, of practically 48 per cent. 

 These figures quite effectively illustrate the tractive efficiency 

 which may be expected of the average steam tractor in con- 

 ditions where the footing is neither the very best nor the very 

 worst that might be found. 



A mean of percentages indicates that the weight borne by 

 the drive-wheels of the steam tractors at Winnipeg in 1910 

 was about 73.5 per cent, of the total. In plowing, the steam 

 tractors showed an average drawbar pull of 26 per cent, of the 

 total weight and 36 per cent, of the weight on the drivers. 

 In plowing, the preceding year, the drawbar pull was ap- 

 proximately 11 per cent, of the total weight in hauling and 22 

 per cent, in plowing. Averaging the plowing and hauling tests 

 for 1909, the steam tractors have credit for one tractive horse- 

 power for each 1033 pounds of total weight. 



Steam tractors are as a rule geared to run somewhat higher 

 than gas tractors, but owing to the many delays incident 

 to starting and taking on supplies, they actually net only about 

 15 miles of furrow travel in ten hours as compared to 17.5 

 for the latter. In the various motor contests, however, where 

 the start has been made with steam up, and every facility 

 provided for keeping outfits in motion, the steam outfits as 

 a whole have shown higher net speeds than the gas tractors. 



The indicated horsepower of steam tractors is sometimes 

 specified, and in general practice the indicated horsepower 

 will be from 20 to 25 per cent, above the manufacturer's brake 



