228 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



Soon after this it became certain that the engines for both aerodromes 

 would have to be constructed in the shops of the Institution, and owing to the 

 greater importance of the experimental engine for the large aerodrome, all the? 

 facilities of the shops were devoted to the early completion of it. In Novem- 

 ber, 1900, however, it was seen that the experimental engine alone would not 

 furnish sufficient power for the large aerodrome, and that a duplicate of it 

 would have to be built or a new and larger engine designed and constructed, 

 and that therefore it would be impossible to get the first tests of the large aero- 

 drome in free flight before the following summer. It was therefore decided 

 thai it would be best to suspend work temporarily on the large aerodrome and 

 its engine, and put all the workmen who could possibly be employed on the con- 

 st ruction of the small engine, so that it would be ready in time to permit sonic 

 tests of the quarter-size model to be made during the following spring. 



In order to expedite its construction as much as possible, the attempt was 

 made to utilize all the available parts from the small engine which had been 

 undertaken by the engine builder in New York. The cylinders, which it had 

 been expected would he kept cool by their rotation around the crank pin, were 

 not well adapted for use as stationary cylinders, since they were not provided 

 with radiating ribs, but it was hoped that by using them an engine could be very 

 quickly constructed which would keep cool long enough to enable some short 

 flights to be made with the model. 



The work on this small engine was pushed forward very rapidly, so that 

 within a short time it was sufficiently complete to allow some power tests to be 

 made with it. In the first of these tests the attempt was made to measure the 

 power by means of the Prony brake, but as the engine had no fly wheel the 

 fluctuations in speed during each revolution were so great as to make it im- 

 possible to obtain readings of any value. When it was attempted to remedy 

 this by putting a fly wheel on either side of the crank shaft of the engine, it was 

 found that the sudden starting of the engine caused such severe strains in the 

 crank shaft, which had been built strong enough for driving the propellers but 

 in it for suddenly starting fly wheels having considerable inertia, as to make it 

 unsafe to continue the use of fly wheels. As without them the Prony brake could 

 not be used, it was decided to build a small water-absorption dynamometer on 

 tin' same principle as the larger ones which were under construction for the large 

 engine. As this larger dynamometer has already been described, it is only nec- 

 essary to add that the small one consisted of twelve rotating plates and twelve 

 stator plates twelve inches in diameter. In order to avoid the construction of 

 a special and elaborate testing frame for mounting the engine and the dyna- 

 mometer exactly in line with each other, it was attempted to connect them by 

 means of a universal joint. This " short cut " also proved the " long way 

 around." The strains set up in the universal joint by the sudden starting of 





