578 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1941 



curve for landplanes at a figure of just under 35 pounds per square 

 foot. It is likely that seaplane loading will continue upward 

 although both may be further increased (than shown by these 

 curves) as the result of introduction of assisted take-off means. 

 Power loadings have not decreased greatly and will probably stabilize 

 at about their present figure. 



In connection with landing speeds, figure 5 (C), the flattening-out 

 tendency of the curve is indicated, but it should be mentioned that 

 in general it can be shown that for equal safety, landing speeds can 

 legitimately increase proportionately to the sixth root of the gross 

 weight. Here again, therefore, the curve depicts the trend for the 

 largest sizes of equipment and it may be expected that for smaller 

 planes the landing speed will be less. 





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Next we consider cruising altitude, graph (Z>) of figure 5, where 

 the jumps represent for the most part changes in the power plant 

 which permitted economical flight at successively higher altitudes. 

 Starting from just over sea level, there was a jump in the DC-2 

 airplane to cruising at approximately 10,000 feet which remained 

 the case until the present time, December 1939. Equipment just 

 about to make its appearance will raise this to 20,000 feet and it is 

 my belief that eventually 35,000 feet will be utilized for certain classes 

 of equipment and service. 



