Schmiechen 



■^^-^^l ""' 



A, = S 



Fig. 5 - Free-discharge device 



The other possibility would be to determine the inflow momentum velocity 



"^1 = (M2 - T)/pQ (66) 



differing from the advance speed, i.e., the propeller would have to be consid- 

 ered acting in its own wake. Although nothing would be wrong with that concept, 

 it would not fit into our picture of a free -running propeller. 



As far as the intake efficiency is concerned performance data are conveni- 

 ently presented in terms of the nondimensional pressure drop 



^ = (^1 - eio)/v2^ 



(67) 



as a function of the velocity ratio 



y = v/vio . (68) 



According to the former definitions, the inlet efficiency is now 



^INL = 1 - 2^/^' 



(69) 



As it may assume very large negative values, the modified inlet efficiency 



^iNL= 1/(2- Vi^O (70) 



avoiding this inconvenience may be used as inlet performance criterion. 



5. PROPELLER-HULL INTERACTION 



5.1 Uniform Inflow 



In order to reconstruct the basic ideas concerning the interaction between a 

 propeller and the vehicle to be propelled, let us first consider the case of 



1096 



