Weissinger and Maass 



radial velocity component was lost, when the ring vortices representing the pro- 

 peller slipstream were placed along cylinders with constant radii and not along 

 the real streamtubes. Since the constant-radii assumption influences the 

 propeller-induced axial velocities only in a slight degree, we now prefer to use 

 the continuity law, when we determine the shape of the duct. 



Figure D-1 shows that the difference between the two methods can be con- 

 siderable. The four ducted propellers in Fig. D-1 all have the same design total 

 thrust Cj s 4, while the duct thrust is varied systematically between and 45%. 



Duct D4 



Continuity- law method 

 Boundary ^condition method 



Simplified boundary- condition 



method drjdy - Uf^jv. 



0.5 y/R 



Duct D5 



— - ->jP5 y/R 



0.5 y/R 



05 y/R 



Fig. D-1 - The shape of the duct calculated 

 by different methods 



1262 



