52 



EXPERIMENTS IN AERODYNAMICS. 



the wind, and less than sustained during tlie remaining half. Consequently, 

 this condition of electric contact half the time is taken to be the one desired, and 

 the velocity corresponding to it is taken from the chronograph and called the 

 soaring velocity for the plane and angle obtaining in the experiment. When 

 the electric bell indicates to the observer an exact soaring, the speed is main- 

 tained uniformly for a few revolutions, as requii'ed by the theory of the Recorder 

 already alluded to, as a requisite for the proper measurement of the wind pressure 

 on the plane. A brush H is attached to the inner arm of the balance for the 

 purpose of producing a regulated friction, and thereby diminishing somewhat 

 the fluctuations of the apparatus, which was found to be too sensitive to currents 

 to do work of all the accuracy it is capable of, except in calm weather. 



Some preliminary experiments were made in August, 1889, to determine the 

 relative velocities of soaring of different planes. But the first Component- Recorder 

 was shortly afterwards destroyed in an accident, and the observtitions were inter- 

 rupted until Sej)tember, 1890, Avhen they were resumed with the newly constructed 

 and improved Component- Recorder figured in the plate. i!*fine new planes were 

 made of light pine, and backed with lead so as to have the following sizes and 

 weights : 



It was found that the heavier planes, and especially the longer ones, required 

 light trussing in order to prevent them from bending when in rapid motion. 

 This was effected by inserting a transverse arm of round brass in the end of the 

 brass tube where the planes are attached, and carrying fine steel wire out to the 

 extremity of the plane. The 30-inch plane was further trussed by a post at its 

 center carrving wires to the four corners. 



Inasmuch as the center of pressure on an inclined plane is in front of the 

 center of figure (as will be shown in connection with the Counterpoised Eccentric 

 Plane), the lead backing was inserted to one side of the center, so as to bring the 

 center of gravity into approximate coincidence with the center of pressure when 

 the plane is inclined at low angles, and the plane was grasped at a similar 

 distance in front of the center. These provisions contributed to diminish the 

 twisting of the planes. These planes were used until November 2-5, when they 



