152 



Tables 140-142. 



AERODYNAMICS. 

 TABLE 140. — Effect of Aspect Ratio upon Normal Plane Pressure (Eiffel). 



The mean pressure on a rectangular plane varies with the "aspect ratio," a name introduced 

 by Langley to denote the ratio of the length of the leading edge to the chord length. The effect 

 of aspect ratio on normally moving rectangular plates is given in the following table, derived 

 from Eiffel's experiments. 



Aspect ratio 



Pressure on rectangle 

 Pressure on square 



I .CO 



i.oo 



1-5 

 1.04 



3.00 

 1.07 



6.00 

 1 . 10 



10.000 

 I -145 



14.60 

 1.25 



20.00 

 1-34 



30.00 

 1.40 



41 • 500 

 1-435 



50.0c 

 1-47 



TABLE 141. — Ratio of Pressures on Inclined and Normal Planes. 



The pressure on a slightly inclined plane is proportional to the angle of incidence a, and 

 is given by the formula Pa = c- P90 • a. The value of c, which is constant for incidences up to about 

 12°, is given for various aspect ratios. The angle of incidence is taken in degrees. 



Aspect ratio. 

 Value of c. . . 



0.036 



0.043 



3 

 0.050 



4 

 •053 



5 

 0.057 



6 

 0.061 



7 

 0.065 



0.070 



9 



0.075 



10 

 0.08c 



TABLE 142. — Skin Friction. 



The skin friction on an even rectangular plate moving edgewise through ordinary air is given 

 by Zahm's equation, 



F(kg/m^) = o. 00030 {^(m^) jo^j F(km/hr.) }i-«6 in metric units 

 or F(pds./ft.2) = 0.0000082 U(ft.2))o-»3{F(ft./sec.)j':S6, 



where A is the surface area and V the speed of the plane. The following table gives the friction 

 per unit area on one side of a plate. 



Smithsonian Tables. 



