trials are not yet complete but so far the comparative results do not seem to differ 

 significantly from those obtained in model tests. 



A matter of great importance is the pressure and acceleration which the hulls of 

 fast patrol boats have to sustain at sea. Pressures have been recorded up to 25 lbs. per 

 square inch with maximum accelerations ranging from about 2g to 3g. The latter are 

 of course well below the figure of 50g mentioned by the last speaker in another connec- 

 tion. The seas to which the fast patrol boats were subject are probably more severe 

 than those for flying boats and in the particular trial for which results are quoted the 

 waves were 3 to 4 feet high and about 70 to 80 feet long. The large pressures build 

 quickly in the fast patrol boats and generally in about a thirtieth of a second. My im- 

 pression is that impact stresses develop at a slower rate in aircraft. 



It would be most useful if Mr. Parkinson could add to the value of his most 

 instructive paper by giving some complementary information from his wide experience 

 with flying boats regarding the various points mentioned. 



J. D. Pier son 



Mr. Parkinson has presented an excellent, comprehensive review of the trends in 

 seaplane design particularly with regard to high speed aircraft. I have only a few com- 

 ments to add with regard to the water loads imposed in take-off and landing. 



It appears that the trend towards longer and thinner hulls required for high 

 speed flight is consistent with the improvement in seaworthiness in rough water ship 

 designs. Unfortunately, the aircraft trend includes an increasing speed for take-off and 

 landing. 



In a more descriptive sense the aircraft speeds on the water are approaching the 

 conditions at the bottom of a great waterfall such as Yosemite Falls. From a height of 

 over 1500 feet the free fall velocity would be over 300 feet per second. It is in such a 

 relative stream that the thin-skinned, lightly built seaplane must be successfully landed. 

 And not only must this be accomplished many times in calm conditions but also in 

 waves. 



Many ways of doing this have been noted. On wheeled aircraft the tire and oleo 

 strut provide the energy absorbing stroke. For the hull the deadrise of the bottom effec- 

 tively provides this stroke, and devices such as skis and hydrofoils may be extended 

 below the keel to extend further the effective stroke. 



The actual application of these configurations to seaplane designs requires the 

 detailed calculation of loads for structural design. Because of the trend towards the 

 longer, slimmer hull forms these loads calculations have been made more complex by 

 the interaction of the body flexibility and the dynamic water forces. It has only been 

 in the past few years that the development of the rapid automatic computation systems 

 has made such combined solutions possible. 



The water loads problem is treated by dividing the hull into a number of trans- 

 verse slices which are acted upon by the water forces and react according to the overall 

 motion of the aircraft and the major bending modes. The water forces on each slice 

 are determined on the basis of the local hull shape and water conditions (including 

 waves) and the dynamical motion of the slice. The summation of all slices gives the 

 net effect on the body. 



Even for a very limited number of divisions of the hull, manual calculation of 

 this loads problem is well-nigh impossible. However, with the large computers such as 

 the IBM 701 and then the 704 a large number of sections may be handled simultane- 

 ously for the required solution. 



So far in the computational work, uniform waves of trochoidal form, have been 

 used to represent the sea as a matter of convenience. Other wave shapes and combina- 

 tions of water conditions are within the capability of the computational machinery, and 

 we look forward to a greater combination of the results of oceanographic studies and 

 practical seaplane design. 



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