AIRPLANE PERFORMANCES — HAMLIN AND SPENCELEY 447 



in high parasite drag coeflicients. The airplane drag coefficient for the 

 propeller should be increased to 0.015 to allow for cooling drag at high 

 speeds. 



Of the utmost importance is the effect of compressibility on drag 

 above the critical speed, which depends upon body shape and altitude. 

 Ballistic data have been useless to the airplane designer because of 

 the complete neglect of aerodynamic characteristics as such, the blunt 

 projectile trailing edge shapes, and generally the extremely high Mach 

 Number regimes of projectile flight. 



Figure 14. — Compressibility drag multiplication factor. 



Reference 2 provides the basis for the compressibility drag multi- 

 plication factor used for wings. This factor is multiplied directly 

 times the airplane drag calculated on the above basis neglecting shock 

 wave effects. These factors, assumed to vary directly as wing thick- 

 ness as shown in jBgure 14, are 15.6, 12.0, and 9.6 for 13, 10, and 8 

 percent thick laminar flow airfoils at M= 1.0. In the case of a fuselage, 

 representing a more compact three-dimensional body, a corresponding 

 value of 6.0 has been assumed. 



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