88 'eXPERIMICNT station EECOED. [Vol. 43 



special reference to its develoimient as a satisfactory farm ami manufactui-iug 

 utility, is given. 



Some points in tractor design (Tractor and (las Engine Rev., 13 {1920), 

 No. 2, pp. 12-15, fi(iH. 10). — Cliarts are given showing grapbically tlie change in 

 some of the principal points of design of gas tractors through the years 1910, 

 1917, 1918, and 1919. 



In 1916, 65 per cent of the tractor nwdels had vertical engines ; in 1917, 70 

 per cent ; in 1918, 73 per cent ; and in 1919, 76 per cent. In 1916, 77 ix?r cent 

 were equipped with high tension magnetos, 19 per cent with low tension 

 magnetos, and 4 per cent with batteries. There was little change in the per- 

 centage of tractors using batteries during the four years, but low-tension mag- 

 netos were largely displaced by high-tension magnetos. In 1916, 69 per cent of 

 ti'actor models had 4-cylinder motors and this percentage inci'eased steadily to 

 80 in 1919. Two-cylinder motors decreased from 2.5 per cent in 1916 to 13 per 

 cent in 1919. 



In 1916, 27 per cent of the tractor models recommended gasoline for fuel and 

 73 per cent recom-mended kerosene. The.se percentages changed to 17 and S3, 

 respectively, in 1919. The data show that more engines operate at a speed of 

 from 700 to 900 r. p. m. than between any other limits. This tendency increased 

 steadily during the four years, and the tendency to design at higher speeils 

 also increased. 



In 19'i8, 63 per cent of tractor models had four wheels and 31 per cent had 

 three wheels. In 1919, 80 per cent had four wheels and 16 per cent three wheels. 

 Two-wheel drive held, the position of most importance during the four years. 

 The most iwpular weight during the four years was from 4,000 to 6,000 lbs. 



Fundamentals of tractor engine design, H. C. Buffington (Trans. Soe. 

 Antomotive Engin., 13 (1918), pt. 1, pp. 208-214, fl9S. 6).— A study of tractor 

 engine design is reported, particularly of the number of cylinders from the 

 standpoint of simplicity and operation. 



It is concluded that the 4-cylinder engine is the most adaptable and economi- 

 cal. A 2 or 3 bearing crankshaft, preferably the latter, with a stress not to 

 exceed 12,000 lbs. per square inch and an explosion pressure of 300 lbs., la 

 recommended. The crankpin diameter of the bearing should be about 57 per 

 cent of the cylinder bore and the length 1.2 times the crankpin diameter. The 

 stress on the front and center bearings should not exceed 400 lbs. i3er square 

 inch and on the rear 250 lbs. per square inch. The stroke should be about 1.4 

 times the bore. Other points of design are brought out. 



The ultimate type of tractor engine, H. L. Horning (Trans. Sac. Auto- 

 motive Engin., 12 (1917), pt. 1, pp. 65-73, figs. 2). — An analysis is given of some 

 of the factors that have Influenced tractor development. It is stated that con- 

 ditions on about 90 per cent of all farms require a 4-cylinder engine of between 

 16 and 40 h. p. operating on the 4-stroke cycle. The disadvantages of the 

 2-cylinder horizontal-oijposed engine are sunmiarized, and the following formula 

 is given for use in calculating the most satisfactory operating speed of an 



engine: S= \//wvi^iAR3- ^'^ ^^^^ fprmula, S is the most satisfactory working speed 



and B is the bore of the engine. 



In conclusion, a number of the most important general themes of design are 

 outlined, and pai'ticular mention is made of the lubrication system and of the 

 special provisions required for kerosene-burning engines. 



Principles of tractor engine cooling, A. B. Modine (Trans. Soe. Auto- 

 motive Engin., 13 (1918), pt. 1, pp. 435-4H< fio^- 5). — The author discusses the 

 radiator, air velocity, and fan power requirements as factors involved in engine : 



