Performance of Partially Submerged Propellers 



The actual calibrations are then 

 performed by applying a known force 

 (weight) at a given point simultane- 

 ously with a pure moment. The force 

 and moments are varied independ- 

 ently. Outputs of all four gages are 

 recorded as various weights are im- 

 posed on the systems. The same 

 range of weights is then calibrated 

 with different moments to assure that 

 there are no coupling effects. A typi- 

 cal calibration curve is shown as Fig. 

 A5. The line has a slope which is the 

 arithmetic average of the data over 

 the range of interest. The error of 

 any reading is within 1.5%; hence, 

 data acquisition with this dynamom- 

 eter is considered to be about 3%. 



Since the dimension b enters into 

 the calculation of the moment, it is 

 necessary to establish the point of 

 application of the transverse forces 

 in the plane of the propeller. For 

 Propeller 3768 the design reference 

 plane, located at the mid-chord length, 

 was used ( b= 3.31 in.). The center 



of lift on the blade varies depending ^. . . ^, , , r _> 



., „, . A 1- 1 j-i. Fib. A4 - Photograph of dyna- 



upon the flow regime. A check on the mometer calibrations 



error introduced by inaccuracy in de- 

 termination of the magnitude of b 



shows that if the error was as large as 1.0 in. there would be less than 1% 

 error introduced into the determination of the eccentricity. 



NOMENCLATURE 

 A Area 



Aq Disc area (7rDV4) 



Aq Submerged disc area 



B^P Blade thickness fraction 



Cq Drag coefficient fOp/- ^Av^ j 



Cl Lift coefficient [hi- pAvA 



e^ Loading coefficient h/- pk^V'^ 



C| Loading coefficient il — pk'^v"^ 



1489 



