14(5 SOME AERONAUTICAL EXPERIMENTS, 



that the curves give pressures more favorable in amount and direction 

 than planes; but we find marked differences in the exact values, 

 especially at angles below 1(P. We were unable to obtain direct 

 measurements of the horizontal pressures of the machine with the 

 operator on board, l)ut b}^ comparing the distance traveled in gliding 

 with the vertical fall it was easily calculated that; at a speed of 24 

 miles per hour the total horizontal resistances of our machine when 

 bearing the operator amounted to 40 pounds, which is e(iuivalcnt to 

 about 2i horsepower. It nuist not be supposed, however, that a motor 

 developing this power would be sufficient to drive a man-l)earing 

 machine. The extra weight of the motor would require either a 

 larger machine, higher speed, or a greater angle of incidence in order 

 to support it, and therefore more power. It is probal)le, however, 

 that an engine of «> horsepower, weighing loo pounds, would answer 

 the purpose. Such an engine is entirely practicable. Indeed, work- 

 ing motors of one-half this w^eight per horse]X)wer (9 pounds per 

 horsepower) have been constructed by several different l)uilders. 

 Increasing the speed of our machine from 24 to l>3 miles per hour 

 reduced the total horizontal pressure from 40 to about 35 pounds. 

 This was quite an advantage in gliding as it made it possible to sail 

 about 15 per cent farther with a given drop. However, it would ])e 

 of little or no advantage in reducing the size of the motor in a power- 

 driven machine, because the lessened thrust would be counterbalanced 

 by the increased speed per minute. Some years ago Professor Lang- 

 ley called attention to the great economv which might be obtained 

 by using very high speeds, and fi'om this many were led to sup- 

 pose that speeds of 50 or OO miles an hour were essential to suc- 

 cess; but the introduction of curved surfaces as 'su])stitutes for 

 planes has very greatly reduced the speed of greatest economy. The 

 probability is that the first flying machines will have a relatively low 

 speed, pcirhaps not nuich exceeding 20 miles per hour. l)ut the i)rol)- 

 lem of increasing the speed will be much simpler in some respects 

 than that of increasing the speed of a steamboat; for, whereas in 

 the latter case the size of the engine must inci'ease as the cube of the 

 speed, in the flying machine until extremely high speeds are reached 

 the capacity of the motor increases in less than simple ratio; and there 

 is even a decrease in the fuel consumption per mile of travel. In 

 other words, to double the speed of a steamship (and the same is true 

 of the balloon type of air ship) eight times the engine and l)oiler capa- 

 city would be required and four times the f\wA consumption per mile 

 of travel; Avhile a flying machine would recjuire engines of less than 

 (loul)h' tlie size, and there would ho an actual decrease in the fuel con- 

 sum})ti()ii per mile of trav(d. Hut, looking at the matter conversely, 

 the great disad\'antage of the Hying machine is apparent; for in the 

 latter no flight at all is possil)l(> unless liie ))r(>])()rti()n of horsepower 

 to flying caj)acity is \-ery high; but, on the other hand, a steamship is 



