18 SMITHSONIAN CONTBEBUTIONS TO KNOWLEDGE VOL. 27 



in Plate 1, with superposed wings, which was used for the purpose of compari- 

 son. S. I'. Langley was the observer, the place of observation t lie larger upper 

 hall of the Smithsonian building, at Washington, the time being taken by a stop- 

 watch, and the distance by a scale laid down upon the floor. The models were in 

 every case held by an assistant and launched by hand, being thrown off with a 

 slight initial velocity. In the case of No. 30, the preliminary calculation of the 

 position of the center of pressure had been made by the process already de- 

 scribed; the center of gravity, with reference to the horizontal plane, was deter- 

 mined by simply suspending the whole by a cord. 



The objects of these experiments, as of every other, were to find the practi- 

 cal conditions of equilibrium and of horizontal flight, and to compare the calcu- 

 lated with the observed positions of the center of pressure. They enable us to 

 make a comparison of the performances given by earlier ones with a light rub- 

 ber motor, with the relatively heavy motors used to-day, as well as a comparison 

 of single flat, single curved, and superposed flat wings. 



The average time of the running down of the rubber in flight was something 

 like three seconds, while the average time of its running down when standing 

 still was but one and a half seconds. It might have been expected from theory 

 that it would take longer to run down when stationary, than in flight, and this 

 was one of the many anomalies observed, whose explanation was found later in 

 the inevitable defects of such apparatus. 



The immediate inferences from the day's work were: 



1. That the calculated position of the CP at rest, as related to the CG, is 

 trustworthy only in the case of the plane whig. 



2. The formula altogether failed with the curved wing, for which the CP 

 hail to be carried indefinitely further backward. 



On comparing the previous flights of November 14, with these, it seems that 

 with the old rubber motor of :>"> grammes and 50 turns, the single wing, either 

 plane or curved, is altogether inferior to the double wing; while with the in- 

 creased motor power of this day, the single wing, whether plane or curved, seems 

 to be as good as the double wing. It also seems that the curved wing was rather 

 more efficient than the plane one. 



The weight of the rubber in each tube was 72 grammes, or 0.1G pounds; mean 

 speed of flight in horizontal distance 4! metres (about 15 feet) per second." 



From experiments already referred to, there were found available 300 foot- 

 pounds of energy in a pound of rubber as employed, and in 0.16 of a pound, 48 



fool pounds of energy were used; .,., ()()() or 0.00145=the horse-power exerted in 



•Subsequent observations indicate that the maximum velocity of horizontal flight must have been 

 about in met r< per .second. 



