NO. 5 STABILITY OF AEROPLANES HUNSAKER AND OTHERS 33 



Likewise fjiiu was obtained by oscillating the apparatus without 

 model in winds from 5 to 35 miles per hour. 



The coefficient /x,„ has the dimensions jo/'[', where p is density of 

 air. / a linear dimension, and V the velocity of the wind. To convert 

 fim to Mq for the full-size machine at full speed, multiply by the fourth 

 power of 24, the scale, and by the ratio of full speed to model speed. 



The model is mounted in such a manner that the axis of oscillation 

 through the two steel pivot points passes through the assumed center 

 of gravity location for the aero])lane. The actual center of gravity 

 of the model is not considered. 



Transverse arms carry counter weights by which the natural period 

 may be adjusted. The springs insure that the motion shall be 

 oscillatory. Knife-edged shackles bearing in notches in the trans- 

 verse arms carry the pull of the springs. The springs are not cali- 

 brated as the calculation eliminates the spring coefficient. 



Friction is kept small by careful design. All pivots are glass-hard 

 tool-steel points bearing inside polished conical depressions of tool 

 steel. A convenient period for observation is ^ second. In still air, 

 the apparatus will oscillate over 300 times before the amplitude is 

 diminished to ^ the initial displacement. The latter is about 3°. 



Numerical results for the pitching oscillation follow : 



§13. OSCILLATIONS IN PITCH 

 Inertia, model and apparatus = .03945 

 Inertia, aiijiaratus =.03680 



Apparatus 



Wind velocity, miles per hour 30 



/, seconds 94 • o 



IX 00172 



fjiw (less zero) 00018 



Apparatus and Model, Incidence of Wing, 0° 

 A^elocity, miles per hour 35 



t, seconds i5-5 



fi 0112 



Mo 0015 



fJiw 0002 



hm (net) 00950 



