196 



Table 1 57 

 VELOCITY PRESSURE AT DIFFERENT AIR SPEEDS 



The resistance F of a body of fixed shape and presentation moving through a fluid may 

 be written 



F = P UV 



<m 



(1) 



in which p denotes the fluid density, m the viscosity, L a linear dimension of the body fixing 

 the scale, and V is the speed of the body relative to the fluid. The dimensionless ratio 



is termed the Reynolds Number R. Values of R are comparable only for geometrically 



M ... 



similar bodies. The quantity (i/2)pF 2 is termed the velocity pressure 5; it is the increase in 

 pressure above the static pressure set up in a tube whose open end is pointed into the 

 relative wind. The relation (1) is usually written F = CAq, A being some specifically defined 

 area as, for example, the area of the projection of the body on a plane normal to the wind. 

 C is usually termed the absolute resistance coefficient. It has the same value in any self- 

 consistent system of units and is a functionof the Reynolds Number R. The method of 

 defining A and L must in every case be explicitly stated. 



For speeds near the speed of sound, C is also a function of the ratio of the air speed to 

 the speed of sound. Values given in these Tables can not then be used. 



The table gives values of the velocity pressure q at different air speeds. In conjunction 

 with the values of C in subsequent tables, this table can be used for computation of the 

 resistance under specified conditions. It is computed for standard air density: dry air, 

 normal C0 2 content, I5°C, one atmosphere, standard gravity, 



0.12497 metriC 3 SlugS (Kf£^) = 0.002378 $E ( lbs " <™f> ) 

 m 3 \ 9.807 m 3 / ft. 3 \ 32.156 ft. 3 / 



For other densities the values must be multiplied by the ratio of the actual density to the 

 standard density. 



Smithsonian Tables 



