A COMPARISON OF AIRPLANE AND AUTOMOBILE ENGINES

ANY aggregation of parts assembled to obtain a mechanical result is a series of compromises. The relative importance of the objectives governs the nature of the compromise. The major objectives to be considered in the design of airplane engines are

1. (1)
   Reliability
2. (2)
   Small weight per horsepower
3. (3)
   Economy of fuel and oil consumption
4. (4)
   Carburetion that permits of easy starting; maximum power through a range of 30 per cent of the speed range; and idling at one-quarter maximum speed without danger of stalling
5. (5)
   Ability to deliver full power through a small speed range without excessive vibration
6. (6)
   Complete local cylinder-cooling under conditions of high mean effective pressure
7. (7)
   Compactness

The automobile engine must have

1. (1)
   Reliability
2. (2)
   Silence
3. (3)
   Carburetion that accomplishes proper and even firing in all cylinders under varying throttle conditions, through speeds covering more than 90 per cent of the speed range of the engine. Great flexibility, with economy secondary
4. (4)
   Ability to deliver partial or full torque through its entire range of speed without vibration
5. (5)
   Compactness
6. (6)
   Small weight per horsepower

Starting from these basic qualities, the author makes a close comparison of construction, methods of use, adaptations and elimination of parts, weights and fuels. The question of design of crankshafts and crank cases is discussed. The action of an airplane engine in an automobile and the changes needed to insure success are specified. The conclusion is reached that none of the major features of the airplane engine can be grafted directly upon the automobile. The automobile will be improved as a result of airplane experience, but this improvement will be evident in the service the automobile gives, rather than in radical changes of design.