Performance Criteria of Pulse-Jet Propellers 



Due to the ambiguity in the choice of the reference magnitudes the parame- 

 ters so defined are in general not comparable for various propulsion devices, 

 except for those parameters not containing geometrical reference magnitudes at 

 all. Examples of comparable parameters, i.e., criteria proper, are efficiencies, 

 provided the boundaries of the systems are correctly chosen in any case. 



From the principle of reaction power we may directly define the overall 

 propeller efficiency 



^PROP = TV/P . (14) 



Taking into account the momentum and the energy principles we may write this 

 as the product 



^PROP - ^'EXT ^^INT '■ '■ ■ (15) 



of the external efficiency 



77EXT = ("^2 - Ml) V/(E2 - Ej) (16) 



and the internal efficiency 



^INT= (E2 - El)/P • (17) 



Introducing the mean mass -specific momenta 



m. = M./(pQ) , (18) 



energies 



e. . E,/(pQ) , (19) 



and energy jump 



e = P/(pQ) , (20) 



we have the external efficiency 



■^/EXT = ("^2 - "^l) ^/(^2 - ^l) (21) 



and the internal efficiency 



^iNT = (^2 - ^iVe (22) 



in terms of these magnitudes. 



It should be noted here that the mean mass-specific quantities m- and 



Ti = ^/T^ , (23) 



the momentum and energy velocities, respectively, are clearly distinct from the 

 ordinary mean mass or volume velocity 



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