NO. 3 LANGLEY MKMilIll ON ,M VA ' 1 1 \ N !( 'Al , h'UGHT 25 



retical capacity possibly realizable under such conditions, but if we take 1/1000 

 we shall probably be nearer the mark. Even in tbis case we have, when using 

 gasoline as fuel, 15,625 foot-pounds per minute, or nearly 0.50 horse-power, as 

 against .0091 horse-power in the case of the rubber, so thai even with this waste 

 and with the weight of the engines necessary tor a single minute's service, the 

 unit weight of fuel employed in the steam engine gives 55 times the result we 

 get with rubber. 



With alcohol we have about f { the result that is furnished by gasoline, since 

 nearly the same boiler and engine will be used in either case. Certain difficulties 

 which at first appeared to be attendant on the use of gasoline on a small scale 

 induced me to make the initial experiments with alcohol. This was continued 

 because of its convenience during a considerable time, but it was finally displaced 

 in favor of gasoline, not so much on account of the superior theoretical efficiency 

 of the latter, as for certain practical advantages, such as its maintaining its flame 

 while exposed to wind, and like considerations. 



Gunpowder 



Although there are other explosives possessing a much greater energy in 

 proportion to their weight, than gunpowder, this is the only one which could be 

 considered in relation to the present work, and the conclusion was finally reached 

 that it involved so great a weight in the containing apparatus and so much ex- 

 periment, that, although the simplicity of its action is in its favor where crude 

 means are necessary, experiments with it had better be deferred until other 

 things had been tried. 



Hot- Water Engine 



A great deal of attention was given to the hot-water engine, but it was 

 never put to practical use in the construction of an aerodrome, partly on account 

 of the necessary weight of a sufficiently strong containing vessel. 



Compressed Air 



Compressed air, like the other possible sources of power, was investigated, 

 but calculations from well-authenticated data showed that this system of pro- 

 pelling engines would probably be inadequate to sustain even the models in long 

 flights. As the chief difficulty lies in the weight, not of the air, but of the con- 

 taining vessel, numerous experiments were made in the construction of one at 

 once strong and light. The best result obtained was with a steel tube 40 mm. 

 in diameter, 428 mm. in length, closed at the ends by heads united by wires, 

 which safely contained 538 cubic cm. of air at an initial pressure of 100 atmos- 

 pheres for a weight of 521 grammes. 



