DURAND— MECHANICAL ASPECTS. 177 



4. The problem of auxiliaries. 



5. The problem of construction. 



Gasoline stands preeminent as the standard fuel for aeroplane 

 service. The chief objection is its high price. This will operate to 

 produce a serious limitation in the economic application of the 

 aeroplane and one of the most important problems with special 

 reference to an extension of economic use is the development of 

 prime movers capable of using cheaper grades of fuel. It will not 

 be without interest, at this point, to note the fuel cost per ton mile 

 for aeroplane service as compared with the same item for railroad 

 and for marine transport. If we take an aeroplane with say 130 

 h.p. carrying 300 pounds of cargo at a speed of 60 m.h. we shall 

 find with gasoline at 20 cents per gallon a fuel cost of about 30 cents 

 per ton mile. This will compare with about ^4o cent in the case of 

 a heavy freight train and with about ^4(i cent in the case of say a 

 10,000 ton steamer. The fuel cost for merely carrying dead weight 

 may therefore readily be from 300 to 1200 times as great as for 

 railroad or marine carriage. This unfavorable relation between the 

 economics of the fuel cost for aerial and for marine transport 

 arises from certain relations which develop in the two cases between 

 net cargo weight and gross weight, and between horsepower and 

 gross weight. 



Thus for the ship the net cargo weight may be, for moderate 

 speeds, as high as 50 per cent, of the gross weight, while for the 

 aeroplane as noted, it would be about 12 per cent. Again the ship 

 requires for a speed of say 15 miles per hour, a horsepower of 5,000 

 or less, or not exceeding i h.p. for 4.500 pounds gross weight while 

 the aeroplane requires something of the order of i h.p. for 15 to 

 20 lbs. gross weight. Again the fuel for the aeroplane engine 

 costs from 5 to 8 times as much per horsepower hour developed as 

 for the ship prime mover. 



While the fuel represents by no means the whole cost it is an 

 important item and it is clear that so long as the aeronautic engineer 

 is limited to gasoline fuel the economic uses of the aeroplane must be 

 seriously handicapped. 



There are other fuels cheaper in character and developed to a 

 point where they are satisfactorily employed in certain grades of 



PROC. AMF.R. PHIL. SOC., VOL. LVI, M, JUNE 20, I917. 



