(12 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



Having determined this distance, the weight on AB was removed and the 

 aerodrome was allowed to regain its former position. The distance of the center 

 of thrust from B was then measured. The engine was next started and the Dum- 

 ber of revolutions of the propellers counted by a tachometer. The thrust of the 

 propellers, acting perpendicularly to the arm BD, produced rotation around the 

 point It, the angle of which was measured as above. 



In the power test of No. 6, the following data were obtained: 



W= weight of aerodrome = 120,450 grammes. 



0=angle of lift=19 3(K. 



Distance of CG from center of rotation= 198.2 cm." 



Distance of center of thrust from center of rotation =186.3 cm. 

 As the propeller thrust and the weight of the model are forces acting in opposite 

 directions at known distances from a center of rotation, letting L equal the "dead 

 lift," we may express the equation thus: 



W sin 0xl98.2=Lx 186.3, 



L= J|§^ x sin 19 J 30' x 20,450, 



L=7,263 grammes " dead lift." 



The flying weight of Aerodrome No. 6 was 12,064 grammes, and the per cent of 



this weight lifted was, therefore, 



12,064 =6(U - 



This was much more than was necessary for iliyht, but in order to insure 

 successful flights and avoid delay, the rule was made in 1895 that no aerodrome' 

 was to be launched until it had previously demonstrated its ability to generate 

 enough power to maintain for at least two minutes a lift of 50 per cent of the 

 total flying weight. At the same time other important data were obtained, such 

 as the steam pressure, the time required to raise sufficient steam, the total time 

 of the run, and the general working of the boilers and engines. 



As will easily be seen, these tests afforded a most satisfactory basis of judg- 

 ing what the aerodromes might be expected to do in actual flight if the balancing 

 were correct. 



At tbis lime, October, L893, the aerodrome (Old No. 4) was practically 

 complete, and the most anxious thought was given to lightening il in every way 

 consistent with the ever-present demand for more power, which necessitated an 

 increase in the weight of both burners and boilers to supply the requisite steam. 



On November 14, when the aerodrome was prepared to be shipped to Quan- 

 tico for trial, its condition was about as follows. The steam-generating appa- 

 ratus—the parts of which were of substantially the forms last described, al- 

 though some slight improvements had been introduced — bad been developed to 



