230 SMITHSONIAN- CONTRIBUTIONS TO KNOWLEDGE VOL. '27 



ing by which il is connected to any driven mechanism. The inertia of the driven 

 mechanism, even though it be apparently small, becomes a most serious matter 

 when an attempt is made to start up very suddenly. This effect is very much 

 intensified if the driven mechanism is connected to the engine through even one 

 pair of gears, for there is always a certain amount of back-lash between the 

 teeth of the gears, and the effect of this back-lash is still further intensified 

 when the driven mechanism is turned over by hand in order to start the Sngine, 

 as this takes up the back-lash on one side of the years, and the moment the en- 

 gine starts permits a free movement until it suddenly takes up the back-lash 

 and strikes the other side of the gear teeth with a blow. The effect of this 

 sudden starting of the engine proved most disastrous to the thrust-recording 

 devices, and, although they were considerably strengthened, it was found after 

 a short time that in order to make them strong enough to withstand the shock 

 of the sudden starting of the engine it would be necessary to make them in- 

 ordinately heavy. It was therefore decided to abandon all attempts to incor- 

 porate the thrust-recording device on this quarter-size model, but it was hoped 

 to install it later on one of the steam-driven models, where the engine starts so 

 slowly that there would be no need for excessive strength in it. 



The engine for the quarter model when reconstructed with stationary in- 

 stead of rotating cylinders was found in the shop tests referred to above to 

 develop when working at its best between li and 2 horse-power, as measured 

 by the absorption dynamometers. However, it was impossible to maintain this 

 power steadily for more than 30 seconds. In the first place, the same difficulties 

 (heretofore described) that were met with in securing a suitable carburetor for 

 the experimental engine were experienced at the same time in the development 

 of the small engine. In the second place, as the engine had no cooling apparatus 

 of any kind, it was found that it could not be tested in the shop for more than 

 .'!() seconds owing to premature explosions. It was hoped, however, that by hav- 

 ing everything ready for a flight before starting the engine, it might be pos- 

 sible to launch the aerodrome before the cylinders began to heat seriously, 

 and that the greatly increased cooling effect due to the motion of the aerodrome 

 through the air would permit the engine to develop sufficient power to secure a 

 flight that would show whether or not the balancing was correct, as the final 

 disposition of some of the accessories on the large aerodrome could not be so 

 well settle. 1 until it was known just how the calculated balancing of this new 

 model corresponded with the actual balancing necessary for flight. 



On account of Mr. Langlcv's reliance on the generally sound theory that 

 where a successful method of conducting an experiment has been found only 

 after a long series of failures it is besl not to change to some unknown and 

 untried plan, it was impossible, especially where failure in the test might in- 

 volve a fatal accident, to get him to deviate from his original plan of launch- 



