NO. 3 LANGLE1 MBMOIE ON" MECHANICAL FLIGHT L81 



and, second, that in order to get a thrusl which would equal fiftj per eenl of 

 the flying weight of the aerodrome it would be aecessarj to use propellers larger 

 than two metres in diameter unless a very large surplus of power were pro 

 vided. It was accordingly decided to make a sel of propellers intermediate 

 tween the two-metre, unit-pitch ratio, thirty-degree blade ones, and the original 

 ones which were two and one-half metres, one- and one-quarter-pitch ratio, thirty- 

 six-degree blade. A set was, therefore, designed two and one-half metres in 

 diameter, unit-pitch ratio, and thirty-degree width of blade, the hubs l>ein.<;' made 

 of steel tubing brazed up in the same manner as the two-metre ones, and the 

 wooden arms of the blades being one and three-eighths inches in diameter at I lie 

 hub end, and tapering to one inch at the end of the blade. 



Later, when the larger engine was actually tested in the frame, the inabil- 

 ity of the original transmission and propeller shafts to stand the extra strain 

 caused by the engine starting up very suddenly at times, together with the un- 

 satisfactoriness of the screw-thread method of fastening the gears and couplings 

 to the shafts made it necessary to provide new shafts, gears, couplings, etc. It 

 was then decided to change the ratio of gearing between the engine and the 

 propellers, which had been one to one, so that the engine might run faster and, 

 therefore, permit the use of larger propellers. For constructional reasons the 

 ratio chosen was thirty-one to forty, thus making the engine run approximately 

 one-third faster than the propellers. 



In the various tests made of the engine working in the frame there were 

 two or three instances in which the propellers were damaged either by the sud- 

 den starting of the engine or by their not being able to stand the strain to which 

 they were subjected by the power absorbed, but in everj case such breakages 

 were found to be due to imperfections of the brazing in the joints. While, 

 therefore, it would have been desirable to make the propellers somewhat heavier, 

 yet since the total weight of the aerodrome had been growing so very rapidly, 

 it was felt that this need not be done, as a pair of propellers winch had stood 

 quite severe service in shop tests might reasonably be expected to stand the 

 strain of actually propelling the aerodrome through the air. 



Nevertheless, when in the summer of 1903 the actual trials of the large 

 aerodrome were started, it was found that the very important difference be 

 tween a propeller working in a closed room and one working in the open air 

 had not been given due consideration. Several sets of propellers. ■_*.."> metres in 

 diameter, unit-pitch ratio, 30-degree blade, had been constructed and were on 

 hand, in order that no delays mighl be caused through a lack of such extra 

 parts. On September 9, 1903, when the aerodrome frame without the wings 

 was mounted on the launching car on top of the boat for some trial runs with 

 the engine to make sure that everything was again in readiness, before the en- 

 gine had made 500 revolutions, the port propeller broke; and a few minutes 



