l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 62 



facilitate the starting of the vehicles. At the terminus a slope of half this 

 amount, but extending over about 490 feet, is provided to facilitate the arrest 

 and return of the carriage. On each side of the line and extending along its 

 full length is laid an electrical conductor, whereby current is fed to the motor 

 of the carriage. The return circuit is made by way of the rails. For the last 

 300 feet or so of the track an additional pair of rails is laid down alongside the 

 running rails. On these additional rails, slippers carried by the vehicle bear 

 so that over this distance, or at least a portion of it, the carriage skates instead 

 of rolling. This facilitates stopping, and in addition furnishes a safety device 

 in case of emergency. 



It is intended ultimately to have four electric carriages to work on tlic line 

 described above. One has already been constructed, and has been used for a 

 number of experiments. The employment of four carriages has been adopted 

 in view of the fact that each series of experiments requires a different equip- 

 ment of the carriage and different registering apparatus. If only one were 

 used the time lost in dismantling and remounting it with each series of experi- 

 ments would be very considerable. It is essential also that each vehicle should 

 be specially designed to meet the conditions of the particular class of experi- 

 ment for which it is intended. According to present intentions the first 

 carriage will be used to measure the horizontal and vertical components and 

 the resultant of the air pressure on surfaces of sustentation, whether plane 

 or curved, simple or compound. The determination of the direction of the 

 resultant, the center of pressure, its displacement when the angle of incidence 

 is changed and the '" angle of attack " will also be undertaken with this 

 carriage. The second and third vehicles are intended for experiments on 

 propellers or tractors, one being used for the large screws employed for 

 dirigible balloons and the other for the smaller aeroplane screws. The 

 tractive effort, the power absorbed and the mechanical efficiency of each type 

 of propeller will be determined at all speeds. A further important subject 

 of study with these two carriages will be the effect of the translational motion 

 on the output and efficiency of the propellers. A comparison will be instituted 

 between the efficiency, etc.. of a propeller when rotating on a fixed axis and 

 when moving with the same speed of rotation, but with various different speeds 

 of translation. The fourth carriage will be specially equipped for measuring 

 the resistance or "'drift" of the various parts of a flying machine. 



The weight of the first carriage is aliout three and three-fourths tons, ex- 

 cluding the motor, and a little less than five tons with the motor. The body 

 of the carriage is built up of steel plates stiffened with angle irons and 

 measures twenty feet in length and six feet six inches between the longitudinal 

 members of the frame. Current is supplied to the motor by means of two 

 pairs of sliding contacts carried in the side of the truck. The movement of 

 the carriage is controlled from a lookout-post commanding the whole line. 



.All the carriages will be furnished with appropriate measuring instruments. 

 A chronograph will register the number of revolutions of the wheels in a 

 given time, from which the speed will be deduced. In addition there will be 

 a direct speed recorder registering the value of ds/dt at each instant of the 

 travel. A recording watt meter will register the power furnished to the motor 

 either on a time or a distance basis. One or more recording dynamometers 

 will also be carried whereby the particular data being determined will be 

 measured. The efficiency of tlie wliolc plant at all speeds, tlie frictional 



