400 Introduction to the Study of Science 



on the automobile has about ten pounds weight for each horse 

 power generated. 



Inasmuch as it is necessary to provide for airplanes engines 

 that will produce one to three hundred horse power, it is 

 evident that weight becomes a very important factor. Then 

 there must be included the weight of fuel necessary for an engine 

 of 100 to 300 horse power to make an unbroken trip of five or 

 more hours. For an engine developing 100 horse power, about 

 fifteen gallons of gasoline per hour may be used, and with this 

 must be included several gallons of lubricating oil. Counting 

 seven pounds to the gallon, a load of 100 gallons is seen to be no 

 small item. Should a transatlantic flight be attempted, its 

 success will depend in a very large measure upon the motor and 

 the fuel load that must be carried. 



Recent improvements in motor construction have brought 

 about a significant reduction in bulk and weight together with a 

 great increase in power and reliability. The " V" form of the 

 " twin-six " gives exceptionally great power with less weight 

 and less fuel. A motor of recent production, water-cooled, 

 weighs seven hundred pounds, and, with a normal speed of 

 1200 revolutions a minute, generates 150 horse power. An- 

 other of the two-cycle type, of the same form, and with twelve 

 cylinders, weighs only 600 pounds and gives with a speed of 

 1150 to 1400 revolutions a minute, 150 to 180 horse power. 

 These facts indicate the tendencies in motor design and con- 

 struction for airplanes. A weight of two and one half or 

 three pounds per horse power is now entirely possible. Such 

 an achievement will do much to make the airplane a ma- 

 chine of practical importance in transportation and travel. 



186. Commercial utility of aircraft. Thus far the airplane, 

 in spite of its many forms, has not had great commercial 

 utility. But the improvements which are being made in its 

 construction will undoubtedly be applied to machines for com- 

 mercial purposes. The perfecting of the motor will eventually 

 increase the carrying capacity of the airplane. The produc- 



