NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 27 



under consideration for driving the models. I assumed that the longest Audit of 

 the model would he less than five minutes. Any weight of battery, then, that the 

 model carried in consumable parts lasting beyond this five minutes would be 

 lost, and hence it was proposed to build a battery, the whole active life of which 

 would be comprised in this time, to actuate a motor or motors driving one or. 

 two propellers. 



According to Daniell, when energy is stored in secondary batteries, over 

 300,000 megergs per kilogramme of weight can be recovered and utilized if 

 freshly charged. 



300,000 megergs = 0.696 horse-power for 1 min. 

 300,000 megergs =0.139 horse-power for 5 min. 



In a zinc and copper primary battery with sulphuric acid and water, one 

 kilogramme of zinc, oxidized, furnishes at least 1200 calories as against 8000 

 for one kilogramme of carbon, but it is stated that the zinc energy comes in so 

 much more utilizable a form that the zinc, weight for weight, gives practically, 

 that is in work, 40 per cent that of carbon. The kilogramme of carbon gives 

 about 8000 heat units, each equal to 107 kilogrammetres, or about 6,176,000 foot- 

 pounds. Of this, in light engines, from 5 to 10 per cent, or at least 308,800 

 foot-pounds, is utilized, and f of this, or about 124,000 foot-pounds, would seem 

 to be what the kilogramme of zinc would give in actual work. But to form the 

 battery, we must have a larger weight of fluid than of zinc, and something must 

 be allowed for copper. If we suppose these to bring the weight up to 1 kilo- 

 gramme, we might still hope to have 50,000 foot-pounds or 1.5 horse-power for 

 one minute, or 0.3 horse-power for 5 minutes. 



Storage batteries were offered with a capacity of .25 horse-power for 5 min- 

 utes per kilogramme, but according to Daniell one cannot expect to get more 

 than 0.139 horse-power from a freshly charged battery of that weight for the 

 same time. 



The plan of constructing a battery of a long roll of extremely thin zinc or 

 magnesium, winding it up with a narrower roll of copper or platinized silver, in- 

 sulating the two metals and then pouring over enough acid to consume the major 

 portion of the zinc in 5 minutes, was carefully considered, but the difficulties were 

 so discouraging, that the work was not undertaken. 



The lightest motors of 1 horse-power capacity of which any trace could be 

 found weighed 25 pounds, and a prominent electrician stated that he would not 

 attempt to construct one of that weight. 



In trials witli a ^ horse-power motor driving an 80 cm. propeller of 1.00 

 pitch-ratio, I apparently obtained a development of 0.56 indicated horse-power 

 at 1265 revolutions ; hut at lower speeds when tried with the Prony brake, the 

 brake horse-power fell to 0.10 at 546 revolutions, and even at 1650 revolutions 



