NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 103 



When the aerodrome was balanced for flight so as to bring the theoretical 

 " center of pressure in motion " over the center of gravity, it was found that it 

 was not possible to carry the center of gravity in front of this point, although 

 it was known by experience to be necessary. Accordingly in the first trial the 

 outer ends of the tail were pressed down by the guys so that the wind of ad- 

 vance tended to lift the tail and throw the head down more than if the tail had 

 been flat. Furthermore, the float, weighing 200 grammes, instead of being placed 

 in its normal position near the base of the bowsprit, was carried out to its ex- 

 tremity, this change in the position of the float alone being sufficient to carry the 

 center of gravity forward three or four centimetres. The curved wings were 

 set at an angle of nine degrees at the root and eleven degrees at the tip. They 

 were well guyed, and in flight appeared to be not materially twisted or altered. 



It was anticipated that the pressing down of the outer ends of the tail and the 

 shifting of the center of gravity would cause the aerodrome to point downward in 

 flight, and this anticipation was verified in the test. At 6.15 a. m. the aerodrome 

 was launched at a steam pressure of 120 pounds. A perfect calm prevailed at 

 the time and the machine started straight ahead. There was no perceptible 

 drop at the moment it was released from the launching car, but a smooth and 

 steady descent until it struck the water, nose down, at a point approximately 

 200 feet from the boat. Dr. Bell noted that the length of time the aerodrome 

 was in the air was 2.8 seconds. One of the propellers was broken and the other 

 one was found to have twisted its shaft one-fourth of a turn. 



At 9.45 a.m., the wings having been dried, No. 5 was again tried. The 

 float was moved back to its normal position at the base of the bowsprit, and the 

 guys, by which the outer ends of the tail had been depressed in the previous 

 trial, were so adjusted that the tail was flat. The machine was, therefore, in 

 the condition of theoretical equilibrium for rapid motion with a plane wing. All 

 the other conditions were precisely as in the previous trial, except that the 

 round-end 100-centimetre propellers were substituted for the 95-centimetre ones 

 which had been broken, and a new paper-covered tail was used. The mechanic 

 in charge was directed to let the steam reach its highest pressure consistent 

 with a flight of one-half a minute, before launching the machine, but he seemed 

 to have lost all sense of the length of time the fuel and water would last, as he 

 let the engines run until almost the whole charge was exhausted before launch- 

 ing it. The aerodrome went off almost horizontally, then turned up into the 

 wind and rose to an angle of about twenty degrees; then (while moving for- 

 ward) slowly sank as though the engine power had given out, as in fact it doubt- 

 less had. The actual distance travelled was 123 feet and the length of time 7.2 

 seconds. While the exhaustion of the fuel and water prior to launching the ma- 

 chine had prevented what apparently would otherwise have been an exceed- 



