CHAPTER VII. 



WATER PERFORMANCE. 



General. The seaplane or flying boat is at an advantage rela- 

 tive to her sister of the land in that the sea is an aerodrome that 

 is always large enough either for run to get off or for run after 

 alighting : there is, therefore, no need to calculate these lengths. 



Again, when a seaplane is launched from the deck of a ship 

 she is fitted with a wheel chassis for the purpose, and therefore 

 in this case reference can be made to the work of the previous 

 chapter, pages 6 1 and 64. 



On the other hand, while it is true that any aeroplane that 

 can fly can get off the ground, it is not true that any seaplane 

 that can fly can get off the water. We must therefore investi- 

 gate, for a seaplane or flying boat, the criterion that she can get 

 off in a calm getting off head to a wind need not be considered 

 as it is an easier condition than getting off in a calm. 



Model Tests. Let L be any fixed linear dimension (say the 

 overall length) of a flying boat hull, or of the complete float 

 system of a seaplane, and let / be the corresponding dimension of 

 a geometrically similar small model of it. 



Let W w be the portion of the weight of the seaplane that is 

 water-borne and let w w be the corresponding quantity for the 

 model. 



Let V be the speed of the seaplane at the time in question 

 and let v be that of the model. 



Further, let the model be run at the same angle as the full 

 scale machine. 



Let F be the resistance due to the water for the full scale 

 machine and /that for the model. 



Then 



F J^_ 

 V*P = z/7 2 



V 2 v z 

 provided that T~ = T ' ' ^ 



W w w w 

 and - - - - (3) 



