Panel Discussion 



high aspect ratio. Calculations by these methods, for an elliptic loading give a 

 parabolic shape and linear down wash. For high aspect ratio and camber ap- 

 parently numerical discrepancies arrive. Next problem regards the flow be- 

 hind the blade, for according to D. Cummins the wake rolls up quite rapidly and 

 within the framework of linear theory it is possible to predict this rolling up. 

 But the next blade will meet this rolled up vortex sheet, which gives rise to a 

 correction. For sails the leading edge vortex, as mentioned by Dr. Laitone, the 

 separation from the top surface will be accompanied by separation from the 

 bottom surface which gives a low lift, while the lift slope is very high. 



Pien remarks that for a sail the camber is caused by the loading, because 

 the sail is flexible the camber is different for different angles of attack. 



Thieme refers to a thesis of Dr. Feltz (Braunschweig), with Prof. Schlichting. 

 Here a flexible plate is considered between two small cylinders and the pressure 

 distribution is calculated on the plate for several values of the parameters. 

 This problem is similar to the problem mentioned. (Z JV.M.M.). 



Barakat remarks that essentially the determination of the shape of the sail 

 is essentially an eigenvalue value problem. (Thwaites, Nielson) The sail can 

 assume different shapes under similar circumstances. For a porous sail the 

 problem is changed somewhat. 



Weissinger remarks that for a swept delta wing the downwash cannot be ex- 

 pected to be linear because of three-dimensional effects. 



(Admirally) wrote a program for the design of propellors by lifting- surface 

 theory. 



A number of features are still lacking: the difference of the hub, there is 

 not only an effect due to contraction due to nonlinear effects, there is also a 

 contraction due to the absence of the hub. 



Moreover boundary -layer effects are not included. For a section with large 

 boundary -layer development the sheet would be wrong. The design by lifting- 

 surface theory cannot yet compete with the design by an experienced designer in 

 particular with respect to cost. 



Pien remarks that at NSRDC Dr. Morgan's group is developing a program 

 for taking account of the hub. 



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