574 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



yses have shown that in normal times there are a hundred or more 

 passengers per day crossing the ocean in liners and who pay rates 

 comparable to those asked by Pan American for air passage. Already 

 Pan American, with over 100 crossings to its credit, is averaging about 

 20 passengers a trip on a twice-a-week schedule with occasional sched- 

 ules of 30 or 40. Mail, averaging about 1 ton a flight, has occasionally 

 gone to 3,500 or 4,000 pounds. It is rumored that more frequent sched- 

 ules will be justified in the near future in the expectation that even in 

 peacetime such frequency of schedule will be justified. 



The last subdivision of figure 2, graph (Z>), shows the improved 

 efficiency of the airplane as measured in terms of horsepower-hours 

 per ton-mile pay load. This factor has decreased (showing increased 

 efficiency) since the start in 1922 from a figure of seven to a present 

 figure of just over two. The fact that this curve has flattened out is a 

 clear indication that the difficulties of further improvement will be 

 great. It should be noted, however, that in general our air lines made 

 a profit in 1939. I previously mentioned a direct operating cost of 1.8 

 cents per passenger-mile for the Douglas DC-3 airplane. If a 66 per- 

 cent overhead is assumed and a 60 percent capacity load factor, it 

 means there is an actual operating cost of 5 cents per passenger-mile. 

 Subtracted from present fare averages of 5.7, a profit of 0.7 cents per 

 passenger-mile, or just over 12 percent, results ; so passenger air trans- 

 portation with present equipment can be made profitable. 



GROWTH IN SIZE 



The graphs of figure 3 are designed to illustrate the growth of the 

 airplane itself. It should be realized that average curves have been 

 drawn to show the tendency to increase in size. Naturally, there are 

 smaller pieces of equipment coexistent with larger. In fact, curves 

 (A), (//) , (C) of figure 3, rather than being averages of all equipment, 

 are more accurately a trend of the largest sizes for any given period. 

 The tendency of the weight curve, (A), for landplanes to flatten out 

 as against the nonexistence of any such tendency for flying boats is 

 significant in connection with the different type of service each pro- 

 vide. The long-distance service of the flying boat requires less fre- 

 quency of schedule and makes it likely (as indicated in graph {A) of 

 fig. 3) that greater and greater sizes will be developed. However, for 

 landplanes, the desire for a service "every hour on the hour" auto- 

 matically sets a limit on size increase. It is perhaps noteworthy that 

 the Douglas DC^ airplane which will first be placed in service is not 

 the original DC-4 but a smaller version. This flattening out in size 

 curve for landplanes will, of course, not persist if in the future, as may 

 well occur, landplanes are used for transoceanic service. 



