Propeller -Induced Appendage Forces 



v^ ' ^-'■'///..•/f.>:0:. 



Fig. 1 - Tunnel 



The BT-2 propellers had a 100% increase in blade section thickness over BT-1, 

 together with a pitch reduction of 7.5%. Detailed characteristics of the propel- 

 lers are shown in Fig. 2. The four-bladed propellers are shown in Fig. 3. All 

 test propellers had a diameter of 8 in. 



APPENDAGE- BALANCE SYSTEM . .. i. . 



The success of an experiment involving dynamic measurement involves a 

 satisfactory sensing or balance system, a stiff (high- resonant- frequency) 

 balance- appendage system, and an adequate dynamic calibration technique. For 

 completeness, each of these components will be discussed in some detail. 



Dynamic Balances '-'' ' ; ; 



The basic balance element consists of a strain- gaged force unit designed on 

 the flexure plate principle with one balance unit mounted on each end of the ap- 

 pendage. The use of flexure plates is a common approach in instrumentation 

 design wherein sensitivity to forces in only one direction are desired. The 

 flexure plate unit consists of extremely stiff top and bottom plates separated by 

 two very thin side members. The upper and lower plates can move parallel to 



171 



