ski and wheels can be smaller and lighter than for a true water-based version or a land- 

 plane, and the airplane fuselage requires little or no hydrodynamic modification. The 

 minimum planing speeds are low compared to take-off and landing speeds, hence 

 accidents resulting from power failure would be less severe than for the equivalent 

 maneuvers on restricted land runways. 



The employment of this mode of operation could be of great military or com- 

 mercial significance since it embodies the primary advantages of land basing and water 

 basing without the serious disadvantages of either. There are, of course, many design 

 and operational problems which must be solved, but which can best be evaluated by 

 economical conversions of existing high-speed land-based equipment and operation of 

 these conversions under actual service conditions. 



VI. Hydrodynamic Research Results and Problems 



Planing Surfaces 



With trends toward higher landing speeds and the developments described, 

 experimental research on planing by the NACA has been largely directed toward 

 extensions of the ranges of available data to higher speeds, trims, and length-beam 

 ratios. At the same time, the scope of the work has included practical variations in 

 geometric parameters introduced by the new concepts and configurations (refs. [14 

 to 20]). 



Most of the previously determined and extended ranges of experimental pure 

 planing data for the classic flat plate have been satisfactorily correlated by Shuford 

 of the Langely Aeronautical Laboratory (ref. [21]) using the methods of modern low- 

 aspect-ratio airfoil theory. This investigator has recently extended his contribution to 

 include cross-section and plan-form effects as indicated in Figure 5. 



Lift. — The hydrodynamic lift coefficient based on wetted area is a simple func- 

 tion of a lifting-line airfoil term and a crossflow lift term. In this equation, A is the 



b 

 hydrodynamic aspect ratio — , where b is the maximum width and l m is the mean 



*«7, 



LIFTING LINE TERM, C L] _ 



CROSS-FLOW TERM, Ci 



m 0.57TAT cos 2 r (,- SIN £) + C Dr SIN 2 T C0S 3 T COS 

 L I + A ** 



p Qi c L[ _ + o 2 Cl c 



RECT. 



'm 



TRIANG. 



£ 



L a = ^- 



'm 



Figure 5. Pure Planing lift and center of pressure (Shuford). 



190 



