PROPELLER DESIGNS 



The objective of this project dictated somewhat conflicting constraints on the 

 propeller design. On the one hand, the design should be somewhat representative of 

 recent CP propeller designs for surface combatants. These designs usually have five 

 blades and possess nonlinear radial distributions of skew and rake. The radial 

 distributions of blade thickness, chord length, and load distribution for these 

 propellers are selected from considerations of cavitation, strength, and propulsive 

 efficiency. On the other hand, the propeller geometry for the present investigation 

 must allow insertion of recessed, commercially available pressure transducers over a 

 wide area of the propeller blade,* built to a model scale which can be handled 

 readily by available facilities at DTNSRDC. This dictated relatively thick blades 

 and a total propeller diameter of 2 ft (0.61 m) . 



The propeller design was based on typical realistic CP propellers ' with 

 adjustments as necessary to meet the constraints imposed by the model experiments. 

 The adjustments are as follows: 



1. The chord-diameter ratio, c/D, and thickness-diameter ratio, t/D, at each 

 radial station were increased by a factor of 5/3. This allows sufficient thickness 

 to embed the gages in the model propeller while retaining the thickness-to-chord 

 ratio t/c, and to expand the area ratio A^/A of the five-bladed FFG-7 propeller 



on a three-bladed model propeller. 



2. A balanced distribution of skew** was used with somewhat larger magnitudes 

 of skew angle than on the FFG-7 propeller. The projected skew angle extended 

 from -10 deg at the 50 percent radius to +41 deg at the tip. 



Propeller 4679 was designed for the same advance coefficient J. and thrust 

 loading coefficient C , as the FFG-7 propeller. 



After preliminary experiments were completed on DTNSRDC Propeller 4679, a 

 second propeller, DTNSRDC Propeller 4718, was designed to investigate the surface 

 pressure on a more conventional propeller geometry. The modifications for this 

 second propeller are as follows: 



*The configurations of the pressure transducers are described in the section 

 on Instrumentation. 



**A balanced skew distribution has forward skew at the inner radii and aft skew 

 at the outer radii to keep the moment about the spindle axis as low as practical. 



