THE DYNAMOMETER-CHRONOGRAPH. 85 



NOVEJIBER 4, 1890. 



Continuation of experiments with 80-inch (diameter) two-bladed aluminum propeller to determine ratio 



ofpoioerput out to return in end-thrust obtained. 



Dynamometer-Chronofiraph with attached propeller is placed on outer arm of the Component- 

 Recorder and driven by an electric motor placed in the center of the Recorder. The electric motor 

 is run by a dynamo, the current from which is carried to the heavy brush contact B (plate II) of 

 the turn-table, and thence along the arm to the electric motor, and the dynamo itself is run by 

 the steam-engine which drives the turn-table. 



In the manner already described, the pencil P" of the Dynamometer-Chronograph registers the 

 power p ut out ; P' registers seconds from the mean time-clock, and P registers the end-thrust of 

 the propeller. A fourth pencil is fixed to the frame of the Recorder and registers on the dyna- 

 m ometer cylinder the forward motion of the Recorder arm about its vertical axis against the ten- 

 sion of a horizontal spring, the spring being disposed so as to be extended by the forward motion 

 of the outer arm. Thus, when the propeller is driven at such a velocity as just to exceed the 

 velocity of the turn-table, the outer arm bearing the Dynamometer moves forward, the horizontal 

 spring begins to extend, and its extension is recorded on the Dynamometer sheet, together with the 

 power put out, the amount of end-thrust obtained, and the time trace from the mean time-clock. 



Preliminary to the experiments the surface of the inner arm of the balance was increased so 

 that the resistance of the Drjnamomcter on the outer arm to the wind of advance should be largely 

 counterbalanced. This was accomplished by adding a surface of 17 square inches at a distance 

 of 4 inches (104 centimeters) from the axis of rotation. 



At 2 12 Casella air-meter reads 1,779,600. 

 At 5 39 " " " 1,881,900. 



Toward end of experiments, wind almost entirely died away. 



Dynamometer-Chronograph sheet No. 3 — notes and measurements: 

 Propeller blades set at angle of 75° with axis. Horizontal spring No. 3. 

 Pulley cord of Dynamometer running on 4-inch pulley. 



Chronograph cylinder geared so as to make 1 revolution to 2,000 revolutions of propeller. 

 Set screw of Dynamometer in " " hole. 



Turn-table driven so as to give linear speed of approximately 2,000 feet per minute, 

 (a) Dynamo = 1,170 revolutions per minute. 



Qi) Propeller = = 1,032 revolutions per mmute. 



(c) Extension of power pencil P" = 0.65 inches. 



(d) Extension of end-thrust pencil P = 0.20 inches (varying). 



(c) Horizontal spring: no appreciable extension, except occasional j uraps produced by wind. 

 (/) Speed of turn-table (from sheet of stationary chronograph in office) = 5.41 seconds in one 

 revolution = 1,865 feet per minute. 



The above entries, taken from the original note-book, will be readily under- 

 stood in connection with the following explanations : 



{a) The 1,170 revolutions of dynamo refer to the revoUitions of the dynamo- 

 electric machine, and are read oif by means of a Buss-Sombart Tachometer. 



