580 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



Table 2. — Airplane cruising speeds: factors causing increases of the past 10 years 

 and possibilities of the neat 10 Years 



Note.— Further, but more remote possibilities are: Cooling drag reduetions or elimination; very high wing 

 loadings using assisted take-off; greater than normal power-plant improvements; complete laminar flow by 

 section change combined with small chord or boundary layer control. 



190 miles an hour. My prognostication of increases to 266 miles an 

 hour cruising speeds in the next 10 years will be effected by the same 

 items but with a different relative proportion for each as shown in 

 the second column of table 2. The importance played by flying at 

 still higher altitudes should be noted together with important im- 

 provements in drag reduction, although of only one-quarter the 

 magnitude that maintained for the last 10 years. The reason for 

 this is shown in table 3 where it will be observed that horsepower 

 "wasted" in overcoming unnecessary drag is now but 20 percent of 

 the total as against 66 percent 10 years ago. At that time, speeds 



Table 3. — 10 years advance in aerodynamic cleanness 



I "Wasted horsepower" is horsepower consumed in overcoming the drag of unnecessarily exposed parts or 

 of nonstreamllne shapes. 



» "Streamline speed"' is the speed the airplane would make at a given altitude If its only drag were smooth 

 flat plute skin friotion; drag caused by efficient cooling of the engine; and induced drag due to lift. 



Figures are obtained by using the method of £. Melvlll Jones. 



