520 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 39 



relation to its weight in such way as to give the required relation 

 between the two coefficients of lift and drag referred to above. 



Again, it is obvious that a performance such as this is without com- 

 mercial or economic value. The plane with only its operating 

 personnel is all that reaches the ultimate point. For economic pur- 

 poses, there must be something in the way of pay load, and this 

 necessarily reduces the possible supplj^ of fuel and hence, correspond- 

 ingly, the distance which can be flown. Eeference to this point has 

 already been made in speaking of carrying capacity. Here again, it 

 is clear that with a large fraction of the useful load allotted to fuel, 

 the plane will be able to carry a small pay load a relatively long 

 distance, whereas with ony a small part allotted to fuel, a large pay 

 load can be carried a relatively short distance. The question of pay 

 load and range are therefore mutually dependent, the one varying 

 inversely to the other within the limits of the total useful load 

 available. 



When we pass, then, to the question of commercial possibilities, 

 we find, for example, that the present China Clippers, making the 

 flight across the Pacific in successive steps of which the longest is 

 something over 2,000 miles, can, for this distance and with a reason- 

 able margin of fuel for adverse weather conditions, carry only a pay 

 load so small that, admirable as they have been as engineering 

 structures, they can scarcely be considered as economically suited to 

 this service. For successive steps of the order of 1,000 miles, on the 

 other hand, they would presumably be found economically well suited. 



It is confidently expected by both designers and operators that 

 the new Boeing flying boats already referred to, with a total lift of 

 82,500 pounds and carrying some 10,000 pounds of pay load over a 

 range of 2,400 miles at a speed of 150 miles per hour, will prove 

 distinctly superior in economic performance to the smaller boats 

 which they are expected to replace for this service. 



When we come to the question of trans- Atlantic service with an 

 uninterrupted flight of about 3,000 miles, it will be safe to say that 

 there are at present available no commercial craft capable of under- 

 taking such service with a pay load sufficient to give good promise 

 of economic success. For step-wise flight by way of Bermuda and 

 the Azores or for the shortest possible flight from Newfoundland to 

 Ireland, there are some possibilities. With reduced pay load or with 

 no pay load, the trans-Atlantic crossing is becoming almost a 

 commonplace. 



Earlier reference has been made to the competitive designs that 

 have been called for covering a structure that should give good 

 promise of successful economic performance. It will be remembered 

 that the specifications call for a structure weighing about 200,000 



