AIR TRANSPORT — DURAND 521 



pounds and carrying a pay load of 25,000 pounds (including 100 

 passengers) at a cruising speed of 200 to 250 miles per hour and with 

 a normal range of 3,700 miles but with fuel for a range in still air 

 of 5,000 miles. 



While we are thinking of the economic aspect of these matters, a 

 few figures of cost may be of interest. 



Thus if we take some of the most recent examples ranging in total 

 lift from 42,000 pounds to the giant trans-Atlantic plane of 200,000 

 pounds, we find investment costs range between $7.15 and $8.65 per 

 pound of gross lift, making the cost of the Boeing 307 of 42,000 

 pounds lift, $300,000, that of the new D. C. 4 of 65,000 pounds lift 

 (now undergoing trials), $470,000, that of the present China Clippers 

 of 52,000 pounds lift, $450,000, that of the new Boeing boat, No. 

 314, of 82,520 pounds lift, $612,000, and an estimated cost of the 

 proposed trans- Atlantic craft of 200,000 pounds lift, $1,500,000. 



For operation, the cost per hour for these planes, without stopping 

 for the individual figures, ranges from $108 to $337 with a cost per 

 mile from $1.62 to $1.23, and per passenger seat per mile from ll^ 

 cents to nearly 3 cents. 



It is fair to say that the economics of these largest structures is by 

 no means yet fully assured. Thus estimate places the cost per seat 

 mile for the new Douglas 4 of 65,000 pounds total lift at 2,10 cents, 

 which is practically the same as the figure 2.05 cents given for its 

 predecessor the Douglas 3, with a total lift of only 24,000 pounds. 



The same thought has apparently governed the design of a new 

 Curtiss- Wright 30-passenger twin-engined plane which is approaching 

 its first tests at St. Louis. 



The total lift is 36,000 pounds with a cruising speed of 200 miles 

 per hour at an altitude of 10,000 feet. 



It appears to be a not unreasonable assumption that a structure 

 of this relatively moderate size and capacity, but designed in the 

 light of modern scientific advances, may prove economically well 

 adapted to many types of air transport service. 



Perhaps brief note may be made of a characteristic of airplane 

 performance closely allied to range. That is, duration — the maxi- 

 mum time a plane can remain in the air regardless of distance flown. 

 It will be seen that this characteristic is of no great economic sig- 

 nificance. Obviously the economic purpose of an airplane is trans- 

 port. It will be clear also that this requirement calls for the 

 minimum consumption of fuel per unit of time rather than per unit 

 of distance as in the case of range. Here again, if we assume every- 

 thing subordinated to this one feature, and with similar assumption 

 as before regarding the optimum combination of all factors affecting 

 this one characteristic of performance, and likewise with no untoward 



