The computed values of thrust deduction and the measured result ob- 

 tained from model resistance and self-propulsion experiments are shown in 

 Table 3. Since no correction for increased frictional drag has been includ- 

 ed, the potential flow prediction of (1-t) should be higher than the 

 measured value*. The agreement between the two calculated values (pressure 

 integration and Lagally theorem) indicates good numerical accuracy. Also 

 note that the correction to body singularity strengths changes the thrust 

 deduction fraction by less than 3 percent. The comparison between lifting- 

 line and lifting-surface predictions shows that the influence of blade 

 thickness and chordwise loading reduces the thrust deduction fraction by 

 only 4 percent. The agreement between theory and experiment is quite en- 

 couraging and is considered to be within experimental accuracy. 



It is believed that the discrepancy between Beveridge's result and the 

 current work lies in the derivation of the propeller sink-disk strength. 

 Beveridge used the induced axial velocity at a lifting line . The present 

 method (equation 27) properly averages the velocity field at the disk plane, 

 resulting in a lower sink strength, as shown in Figure 10. 



It is also of interest to examine the distribution of the interaction 

 force over the afterbody. This is a function of both the body sectional- 

 area distribution and the breadth and intensity of the propeller disturb- 

 ance field. The longitudinal distribution of the thrust deduction, 

 (dt(x)/dx), acting on the body only, is shown in Figure II. The signifi- 

 cant contribution is over the last 25 percent of the body length with 50 

 percent concentrated in the last 6 percent of the length. 



EXAMPLE 2: COMPARISON OF THEORETICAL AND EXPERIMENTAL PRESSURE 

 DISTRIBUTIONS ON THREE BODIES OF REVOLUTION 



Wind-tunnel experiments were recently conducted to determine the flow 



9 

 characteristics of three streamlined bodies of revolution. Measurements 



of the afterbody pressure distribution with and without a stern propeller 



in operation were obtained for comparison with analytical predictions. The 



profile of the parent body (DTNSRDC Model 5225-1) is shown in Figure 12 



*The added frictional resistance is expected to increase the value of t 

 by no more than 5 percent, based on Reference 9. 



32 



