Performance Criteria of Pulse-Jet Propellers 



NO DIFFERENCE 

 IN EFFECT 



LOW SUCTION 

 AND THRUST 



Fig. 6 - Propeller-hull interaction 



system. The situation changes completely, when devices in nonuniform wake and 

 built-in devices are under consideration. 



The standard procedure of performance evaluation based on measured inte- 

 gral values as practiced in conventional propulsion where ever possible has 

 often been felt inadequate; Prohaska et al., 1966. Attempts to resolve the in- 

 herent logical difficulties of the procedure, e.g., concerning the determination 

 of the "correct" wake fraction, are neither satisfactory nor generally applica- 

 ble; Horn, 1964, In many cases, neither resistance nor free-running tests, if 

 feasible at all, furnish meaningful results. 



The evaluation according to the general definitions established does not suf- 

 fer from the drawbacks mentioned, but depends on the choice of the propeller 

 boundary and the measurement of local values, which as a standard procedure 

 is apparently not very convenient. When the wake fraction 



1 - m/V 



(85) 



and anything else has been determined, the thrust deduction may be estimated 

 according to the same relations as before, when the outflow efficiency is re- 

 placed by the ratio of the out and inflow efficiencies. 



In view of the final aim, the whole procedure is actually not very straight- 

 forward. Due to various reasons, not the least of which is the ambiguity in the 

 choice of the propeller boundary, the concept of thrust as a propulsive force and 

 a measure of performance turns out to be rather meaningless, however useful 

 and necessary it may be for design and model-test purposes, etc. For the eval- 

 uation of the propulsive efficiency, only the net thrust under service conditions 

 is of interest. 



In the present context, this magnitude may be defined as 



R = Mj - pQV - F 



(86) 



1099 



