N 0. 3 LANGLEI MEMOIR ON MECHANICAL FLIGHT 



253 



the whole aerodrome had been originally designed with the expectation of using 

 a maximum of 24 horse-power, and as no margin had been left to provide Im- 

 possible increases in the size of the bearings, there was no room to permit them 

 to be increased without almost completely reconstructing portions of the trans 

 verse frame. While in the end it would have been cheaper to have reconstructed 

 these portions in order to put in larger bearings, yet, as is always the case in 

 experimental work of this kind, small changes which seem to hold out hope of 

 overcoming difficulties are usually followed, rather than reconstructions which 

 can be seen to involve considerable expense and delay. After a number of minor 

 changes had been made in the bearings, they were tinaliy able to stand up fairly 

 well under the severe strain to which they were subjected when the engine de 

 veloped its full power, and no further changes were made in them; a defective 

 race being, however, replaced by a new one as occasion demanded. 



These tests demonstrated very clearly that at speeds of approximately LO00 

 revolutions per minute ball-bearings which are subjected to considerable loads 

 should be calculated with a considerable margin of safety, as the yielding of 

 the frame, which must necessarily be far from rigid, causes more or less error 

 in the alignment of the shafts and bearings, and this introduces considerably 

 increased strains on the bearings. In the early tests before the bearings were 

 strengthened, the balls in some of the races were on a few occasions ground to 

 a very fine powder before it was discovered that they had failed. Such a result, 

 it will be understood, could and did occur in the course of a very minute length 



of time. 



In imitating as nearly as possible the conditions to which the carburetor 

 of the engine would be subjected during the period of launching, numerous tests 

 were made in which the engine was brought to its maximum speed and, without 

 changing the adjustment of the mixture-controllin- devices of the carburetor, 

 sudden blasts of air were turned on it from various directions, and these were 

 continued until the mixture-control devices were perfected to such a point that 

 -usts of thirty miles an hour suddenly directed from any point against any 

 portion of the apparatus would in no way effect the speed and power of the en- 

 gine. These tests were considered necessary in view of the very sudden changes 

 in conditions to which the aerodrome would be subjected during its brief run 

 down the launching track, the conditions changing in approximately three sec- 

 onds from absolute quiescence of the aerodrome to a plunge through space at 

 thirty-five feet per second. An aviator would be more than occupied with main- 

 taining control of himself and of the aerodrome, which at the moment of leaving 

 the track might require considerable change in the adjustment of the Penaud 

 tail, and he would, therefore, not be able to make any adjustments of the engine 

 control devices. This supposition was entirely confirmed in the actual tests of 

 the aerodrome which are to be later described, the rush down the track being 



