WHEELED VEHICLES 1 93 



of these wheels is ordinarily between 5 and 6 feet. The width of 

 tire is governed by the character of bottom over which the engine 

 is to travel. On ordinary roads from 20-inch to 24-inch tires are 

 satisfactory even for the largest machines. 



The forward part of the engine is supported on a pair of 

 wheels 3^ or 4 feet in diameter with from 6-inch to lo-inch tires. 

 These wheels carry only a small proportion of the total weight, 

 their chief function being to aid in steering. This is done by 

 means of a hand wheel placed at the rear of the engine in close 

 reach of the engineer. 



The engine which develops from 20 to 30 horse-power is usually 

 of the single cylinder type with a heavy flywheel. 



The daily fuel requirements range between i| and 2| cords 

 of hardwood, or between i and i^ tons of coal. About 2500 

 gallons of water are needed for the above amount of fuel. 



On a Washington operation a 30-horse-power traction engine 

 has made a daily round trip of 30 miles, hauling 20,000 board 

 feet of green lumber up 15 per cent grades, and down 30 per cent 

 grades. This is probably the maximum capacity of an engine of 

 this type. 



Holt Three-wheeled. — This type has been developed largely for 

 use in logging on the Pacific Coast and has a return-tube water- 

 leg horizontal boiler supported on an I-beam frame. Almost 

 the entire weight of the machine rests on the rear traction wheels, 

 each 7^ feet in diameter with a 24-inch tire. The fore part of the 

 engine is supported by a single 4-foot wheel used for steering. 

 Provision is made for the operation of the steering gear both 

 by hand and by power. A single cylinder ii-inch by 12-inch 

 balanced valve engine is placed on top of the boiler, and at 165 

 pounds' steam pressure develops 60 horse-power. Power is 

 transmitted to the traction wheels by chains, and either wheel 

 may be driven independently of the other. This is especially 

 advantageous in making sharp turns. A radius of 25 feet is 

 practicable in operating a train of five cars. 



Water tanks with a capacity of from 400 to 700 gallons are 

 carried on the frame directly in front of the boiler. The average 

 water requirement per day of ten hours is from 2500 to 3000 



