Performance Criteria of Pulse-Jet Propellers 



In the following, the ideal efficiency will be chosen as advance criterion, 

 while the hydraulic efficiency 



"^HYD " "^PROP ' "^ I DEAL 



(32) 



will be considered as performance criterion proper, i.e., the propeller perform- 

 ance will be characterized by the function 



^HYD " '^(^■^IDEAl) 



(33) 



see Fig. 3. 



■•'' "ffj. 



The advantage of this presentation of per- 

 formance data, as compared with the older one 



IDEAL 



^/PROP - g (^To) 



(34) 



(Gutsche, 1937), is due to the facts that, on the 

 one hand the ideal efficiency, contrary to the 

 load factor, is restricted to values between 

 zero, for the towing condition, and unity, for the 

 idling condition, and on the other hand the hy- 

 draulic efficiency, i.e., the degree of approxi- 

 mation towards the ideal is, contrary to the 

 propeller efficiency, a reasonable performance 

 criterion over the whole range of working con- 

 ditions including the towing condition. 



I 'IDEAL 



IDLING CONDITION 



Fig. 3 - Performance 

 characteristic 



Concerning the detailed analysis of the hydraulic efficiency, we may write 



^HYD " ^JET ^INT . ' (35) 



the jet efficiency accounting for the nonuniformities of the inflow and outflow in 

 space and time. Introducing the inflow and outflow efficiencies 



1^ /2e 



'1/2^ ^^ 1/2 



"^INF/OUTF 



we have for the jet efficiency 



T/jET = (1 - /^^)/(1/T)ouTF " ^^/"^'iNf) 



or, in terms of the energy ratio, 



•■ ;j'" ■■ ■ . i. ■ 



■^JET = ("^OUTF - ■^INF ^)/(l - ^) ■ 



(36) 



(37) 



(38) 

 (39) 



This efficiency may apparently not be split up into factors accounting for the in- 

 flow and outflow separately. 



1091 



