No. 3 LANGLEY MEMOIB ON MECHANICAL FLIGHT 249 



the hot water from the engine is by-passed through this grid and thus warms 

 the air as it passes into the carburetor. The small pipe that by passes this 

 water through the grid is seen connected to the outlet water pipe jusl above 

 the cylinders, a small butterfly valve in the outlet pipe enabling the amount of 

 heated water passing through the grid to be controlled. The return from the 

 grid is by means of the small pipe leading to the top of the large water tank. 

 The tachometer, which gives instantaneous readings of the speed of the engine, 

 is seen at G, where it is at all times in full view of the operator. 



These dynamometers proved to be excellently suited for the testing -work, 

 and far ahead of anything else the writer has ever found for engine testing. 

 Since the power required to rotate the rotor plates, with a uniform amount 

 of water in the drums, varies as the cube of the speed, if is readily seen that it 

 is impossible for the engine to race or injure itself by running away, as fre- 

 quently happens where there is no engine governor and Prony brakes are used 

 to measure the power. 



In the early tests the engine was never allowed to develop more than 40 

 horse-power, as it was feared that by letting it develop more, which it was 

 clearly seen to be capable of, it might be injured and cause a delay in the tests 

 of the aerodrome. In the second series of tests it was allowed to develop 5] 

 horse-power at 935 R. P. M., but it. was not thought to be advisable to let it run 

 at maximum power for more than an hour, for the same reason as before. In 

 the summer of 1904, after it was seen that there was no immediate possibility of 

 securing funds for continuing the tests of the aerodrome, it was planned to 

 enter the engine in the competitive tests at the St. Louis Exposition, where a 

 prize of $2500 was offered for the lightest engine for its power. As the condi- 

 tions specified in this competition required that the engine run at its maximum 

 power for one hour, and that this be followed by a durability test of ten hours' 

 continuous running, it was decided to make some durability tests of the engine 

 .before taking it to St. Louis. In these tests, the engine was run on three sepa- 

 rate trials for a period of ten hours l with a constant load of 52.4 horse-power 

 at 950 R. P. M. Even in these long durability tests the engine and the dyna- 

 mometers both worked so smoothly and evenly that the engine did not vary its 

 speed more than ten revolutions per minute, and the pull on the spring scales 

 varied less than ten pounds in the entire ten hours. Considerable correspond- 

 ence was had with the officials of the St. Louis Exposition regarding the en 

 1 ranee of the engine in the competition, in order to make sure that suitable 

 facilities for conducting the tests had been provided. After receiving assurance 

 that everything necessary had been provided, the engine and its testing dyna- 

 mometers were boxed for shipment to St. Louis and arrangements were just 

 being completed for their transportation when the following tele-ram was re 



1 Except for a ten minute stop to renew the supply of lubricating oil and change the sparking 

 batteries. 



