NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 115 



Leading from the valve to the main cylinder are 3mm. wide and 34mm. apart 

 over their openings. It will thus be seen that when the valve is in its central 

 position, as it should be at the beginning of the piston stroke, both ports are 

 covered witli a lap of 0.5mm. inside and out, so that the valve has to move 

 0.5 mm. before suction or discharge can take place. As the valve is moving most 

 rapidly at this point, it opens and both functions begin before the piston has ad- 

 vanced perceptibly. The delivery is made at the ends of the valve cylinder 

 through two copper pipes of 1 cm. diameter that unite into a single pipe before 

 reaching the boiler. The throw of the valve is 14 nun. so that the ports are un- 

 covered and held wide open for the greater portion of the stroke of the piston, 

 and begin to close only when the latter approaches the end of its stroke. In this 

 way perfect freedom is given to the flow of the water and all choking is avoided. 

 As the engine has been run at a speed of more than 688 revolutions per minute, 

 the pump must have made at least 344 strokes in the same time, thus displa- 

 cing 166.2 cc. of water. The diameter of the piston rod and valve stem is .'! mm. 

 and they pass through stuffing boxes with glands of the ordinary type for pack- 

 ing. This pump served its purpose admirably, and with it it was possible to 

 maintain a continuous circulation of water through the two coils of the boiler. 



The third element in the steam-generating system is the '.toiler proper 2 

 ( Plates 25 and 26A), which consists of two coils of copper pipe, having an out- 

 side diameter of 10 mm., each coil being formed of 21 turns each 75 mm. in di- 

 ameter upon the outside and spaced 7.5 mm. apart, so that the total axial length 

 of each coil is 36 cm. 



The water is delivered to the front end of the right-hand coil, and, first 

 passing through this, crosses over at the rear of the boiler to the left-hand 

 coil, returning through it to the front whence it is led to and delivered into the 

 top of the separator. Here the steam and water are separated, the former 

 going through the separator and thence to the engine, while the unevaporated 

 water falls to the bottom to be again taken into the pumps and sent through the 

 coils. 



In order that the draft of the burner and the gases of combustion might not 

 be dissipated, it was necessary to sheathe the boiler. The method of doing this 

 is shown in Plate 25. It will be seen that the front half of the boiler is wrapped 

 in a sheet of mica through which the coils can be faintly seen. This, in turn, is 

 held at the extreme front end by a strip of thin sheet-iron, 0. Over the back 

 end the stack Q, made of very thin sheet-iron, is slipped. This has an oblong 

 cross-section at the lower end where it goes over the boiler; it is provided with 

 a hole through which the midrod passes, and terminates in a circular opening of 

 about 10 cm. diameter. 



-The reader who may care to note the evolution of this boiler, by trial and error, will find a 

 portion of the many discarded types shown in Plate 13. 



