TABLE 1 1 9. 



AERODYNAMICS. 



On the basis of the results given in Table 118 Langley states the following condition for the 

 soaring of an aeroplane 76.2 centimetres long and 12.2 centimetres broad, weighing 500 grammes, 

 that is, a plane one square foot in area, weighing i.i pounds. It is supposed to soar in a 

 horizontal direction, with aspect 6. 



TABLE 119. - Data for the Soaring of Planes 76.2 X 12.2 cms. weighing 500 Grammes, Aspect 6. 



In general, if p = - 

 area 



Soaring speed v\ - 



V k Fg. cos a 



Activity per unit of weight =v tan a 



The following data for curved surfaces are due to Wellner (Zeits. fur Luftschifffahrt, x., Oct. 

 1893). 



Let the surface be so curved that its intersection with a vertical plane parallel to the line of 

 motion is a parabola whose height is about ^ the subtending chord, and let the surface be 

 bounded by an elliptic outline symmetrical with the line of motion. Also, let the angle of incli- 

 nation of the chord of the surface be a, and the angle between the direction of resultant air 

 pressure and the normal to the direction of motion be )8. Then ft < a, and the soaring speed is 



-, while the activity per unit of weight =z>tan /3. 



k />a cos j3' 



The following series of values were obtained from experiments on moving trains and in the 

 wind. 



Angle of inclination a = 3 o +3 6 9 12 



Inclination factor F a = 0.20 0.50 0.75 0.90 i.oo 1.05 



tanj8= o.o i 0.02 0.03 0.04 o.io 0.17 



Thus a curved surface shows finite soaring speeds when the angle of inclination a is zero or even 

 slightly negative. Above a= 12 curved surfaces rapidly lose any advantage they may have for 

 small inclinations. 



SMITHSONIAN TABLES. 



109 



