518 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1939 



istic of an airplane shows more clearly the advance during the quarter 

 century than does this figure. Twenty or 25 years ago each square 

 foot of wing area was expected to lift some 8 to 10, perhaps 12 

 pounds. But with improved form and increased speed, these figures 

 have been raised to 30 and 40 and above in recent designs. It may be 

 of interest to note that for flying birds, this ratio is of the order of 

 2 to 4. This is due, in part at least, to the lower speed at which the 

 bird flies, especially as compared with the modern trend in airplane 

 speeds. 



This brings us to the question of speed. A quarter of a century 

 ago, airplane speeds were of the order of 50 to 80 miles per hour, and 

 airplanes were chiefly for military or naval use. Today, cruising 

 speeds of 150 to 200 miles per hour are the accepted normal, with 

 top speeds considerably higher. What then is the outlook for the 

 future? Is there a limit to the speed of the airplane? Here again, 

 no one can safely predict. Suppose, however, we put the question a 

 little differently, in this way. Assuming available the present con- 

 tent of the domain of science, engineering, and technology, with 

 everything sacrificed to the one feature of speed, and supposing all of 

 the factors affecting speed combined in the optimum manner and 

 degree; what speed might we then expect? With the question put 

 in this manner, it is possible to give at least an approximate answer 

 and it works out to be somewhere about 500 miles per hour. How 

 closely has this figure been approached? What is the present speed 

 record ? Here the answer is 424 miles per hour ^ held by an Italian 

 seaplane. It should be noted, however, that such a plane has no 

 commercial value. Everything has been sacrificed to speed. Almost 

 the entire useful load has been given over to engine weight, leaving 

 only a small margin for a few gallons of fuel and the pilot. The 

 course is 2 kilometers or about a mile and a quarter. And thus, 

 by a tour de force, as we may term it, with everything made sub- 

 servient to this special purpose, this speed of 424 miles per hour has 

 been attained, and speeds closely approaching 500 miles per hour 

 appear to be quite within the framework of possible modern achieve- 

 ment, if we are willing to pay the price. 



At the same time we should perhaps remember that outside the 

 possibilities of commercial stratosphere flight, which are as yet un- 

 proven, it does not appear probable, in any near future and with the 

 present content of science, engineering, and teclmology, that we shall 

 much exceed 300 miles per hour for commercial planes and perhaps 

 400 miles per hour for the fastest military or naval fighting planes. 

 In planes for actual service, the margin between total lift and the 

 weight of the structure cannot be almost entirely given over to power 



' Considerably higher speeds have been attained since the date of writing this paper. 



