174 STORY OF EXPERIMENTS IN MECHANICAL FLIGHT. 



to see his great flying machine at Bexley, in Kent, where I was greatly 

 impressed with the engineering skill shown in its construction, but I 

 foand the general design incompatible with the conclusions that I had 

 reached by experiments with small models, particularly as to what 

 seemed to me advisable in the carrying of the center of gravity as high 

 as was possible with safety. 



In 1892 another aerodrome (I^o. 1), which was to be used with car- 

 bonic acid gas, or with compressed air, was commenced. The weight 

 of this aerodrome was a little over 4^ pounds, and the area of the 

 supporting surfaces 6J square feet. The engines developed but a 

 small fraction of a horsepower, and they were able to give a dead lift 

 of only about one-tenth of the weight of the aerodrome, giving rela- 

 tively less power to weight than that obtained in the large aerodrome 

 already condemned. 



Toward the close of this year was taken up the more careful study of 

 the position of the center of gravity with reference to the line of thrust 

 from the propellers, and to the center of pressure. The center of grav- 

 ity was carried as high as was consistent with safety, the propellers 

 being placed so high, with reference to the supporting wings, that the 

 intake of air was partly from above and partly from below these latter. 

 The lifting power (i. e., the dead lift) of the aerodromes was determined 

 in the shop by a very useful contrivance which I have called the "pen- 

 dulum," which consists of a large pendulum which rests on knife edges, 

 but is prolonged above the points of sui)port, and counterbalanced so 

 as to ]3resent a condition of indifferent equilibrium. ]!^ear the lower 

 end of this pendulum the aerodrome is suspended, and when x)ower is 

 applied to it, the reaction of the propellers lifts the pendulum through 

 a certain angle. If the line of thrust passes through the center of 

 gravity, it will be seen that the sine of this angle will be the fraction 

 of the weight lifted, and thus the dead-lift power of the engines 

 becomes known. Another aerodrome was built, but both, however 

 constructed, were shown by this pendulum test to have insufficient 

 power, and the year closed with disappointment. 



Aerodrome No. 3 was of stronger and better construction, and the 

 propellers, which before this had been mounted on shafts inclined to 

 each other in a V-like form, were replaced by parallel ones. Boilers of 

 the Serpolet type (that is, composed of tubes of nearly capillary section) 

 were experimented with at great cost of labor and no results; and they 

 were replaced with coil boilers. For these I introduced, in April, 1893, 

 a modification of the selopile blast, which enormously increased the 

 heat-giving power of the fuel (which was then still alcohol), and with 

 this blast for the first time the boilers began to give steam enough for 

 the engines. It had been very difficult to introduce force pumps which 

 would work effectively on the small scale involved, and after many 

 attempts to dispense with their use by other devices, the acquisition of 

 a sufficiently strong pump was found to be necessary in spite of its 



