NO. 3 LANGLEY MEMOIR ON MECHANICAL PLIGHT 33 



have been carried on the front rod, but, as subsequent experience has shown, 

 these wings would have been inadequate to the work, both from their insuffi 

 cienl size and their lack of rigidity. 



The propellers, which were to be 80 cm. in diameter, 1.25 pitch-ratio, and 

 which were expected to make from five to six hundred revolutions a minute, were 

 carried on the end of long tubular shafts, not parallel, but making with each 

 other an angle of 25 degrees, and united by gears near the bow of the vessel in 

 the manner shown in Plate 10. 



The first engines were of the oscillating type, with the piston-rod connected 

 directly to the crank; were very light, and were unprovided with many of the 

 usual fittings belonging to a steam engine, such as rod or piston packing; and 

 their construction was crude in comparison with their successors. They were 

 tested with the Prony brake and found to be deficient in power, for with a steam 

 pressure of 80 pounds to the square inch, they ran at the rale of 1170 revolu- 

 tions per minute, and developed only .3(13 horse-power. It soon became evident 

 that they were too light for the work that it was intended that they should do, 

 and steps were taken, even before the completion of these tests, for the construc- 

 tion of a pair of more powerful cylinders, which should also be provided with a 

 special boiler for the generation of the steam. Acting upon the supposition, 

 which, as the sequel showed, was unwarranted, that compounding would result 

 in a saving of steam, it was decided to work with compounded cylinders. As two 

 propellers were to be used, they were each fitted with a distinct pair of cylinders 

 working directly upon the shaft, but so connected by gearing that they were 

 compelled to turn at the same rate of speed. 



The cylinders were of the inverted oscillating type, like the first pair of 

 engines, but, unlike them, they were single-acting. The dimensions were: di- 

 ameter of high-pressure cylinder 1.25 inches; low pressure, 1.94 inches, with a 

 common stroke of 2 inches, and with cranks set opposite to each other so that 

 one cylinder was always at work. The cylinders were held at their upper ends 

 by a strap passing around a hollow conical trunk, which served the double pur- 

 pose of a support for the cylinders and an intermediate receiver between them. 

 This receiver had a mean inside diameter of 1.25 inches, with a length of 4.75 

 inches, so that it had about twice the cubical capacity of the high-pressure cyl- 

 inder, while the displacement of the low-pressure cylinder was about 2.5 times 

 that of the high; ratios that would have given satisfactory results, perhaps, had 

 the steam pressure and other conditions been favorable to the use of the com- 

 pound principle in this place. There were no valves for the admission of the 

 steam, for, inasmuch as the engines were single-acting, it was possible to make 

 ports in the cydinder-head act as the admission and exhaust ports as the cylinder 

 oscillated, and thus avoid the complication and weight of eccentric and valves. 



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