(importing) resistance of ski-body combinations, resistance due to spray, and the 

 transition resistance of land-water skis have been investigated. 



Other continuing problems include that of separated flows with negative pres- 

 sure regions ventilated to the atmosphere, the increase in wave impact effects with 

 landing speed and their alleviation, and high aspect-ratio hydrofoil configurations for 

 modern aircraft. The need for higher-speed hydrodynamic test facilities to keep pace 

 with the increasing minimum flight speeds associated with transonic and supersonic 

 airplanes has been recognized. 



II. Introduction 



The last fifteen years have seen many revolutionary changes in the power plants, 

 performance, and geometry of aircraft, and in their missions and modes of operation. 

 At the same time there has been an almost complete disappearance of the seaplane 

 from the aeronautical scene. History has begun to repeat itself, however, in that some 

 of the original reasons for water-basing are again becoming valid and some cogent new 

 ones are emerging. Without dwelling on these reasons, it may be said that the present 

 military interest in the use of water as a landing and take-off medium lies in its still 

 unexploited potentialities for aerial warfare from advance bases and its unequaled 

 invulnerability to conventional or high-energy bombing. 



The term "high-speed" in aeronautics is typical rather than restrictive since the 

 trend has always been toward higher powers in smaller packages and higher useful 

 speeds. The jet engine has greatly accelerated the curve of attainable speed against time 

 so that high speeds are now transonic and even supersonic. It has also brought with it 

 for water-based aircraft a liberation from the propeller-clearance dimension and a 

 true size parity with other aircraft. This fact leads for the first time to water-based 

 airplanes having mission capabilities comparable to those of the best landplanes, and 

 greatly encourages a new utilization of the water-basing concept. 



This paper reviews briefly the basic considerations involved in the design of 

 water-based aircraft as influenced by the present era of high-speed flight, the new con- 

 cepts for water operation that have arisen, and some of the associated hydrodynamic 

 problems that have been investigated or formulated. The contents for the most part 

 represent the activities and views of the author and his associates in the National 

 Advisory Committee for Aeronautics, which, in cooperation with the military services 

 and the aircraft industry, has continued to devote a substantial research effort to this 

 area. 



III. Symbols and Definitions 



Planing and Submerged Surfaces 



_ L 



C L planing lift coefficient, — 



qS 



M 

 C m planing trimming-moment coefficient about trailing edge, 



"t.e. 



C L lifting-line component of C L 



C L cross-flow component of C L 



b 

 A planing aspect ratio, — 



r trim or angle of attack with respect to still-water surface. 



/? angle of dead rise from keel to chine 



182 



qSl n 



