Flutter of Flexible Hydrofoil Struts 



REPLY TO DISCUSSION 



Peter K. Besch 



Naval Ship Research and Development Center 

 Bethesda 3 Maryland^ U.S.A. 



The hydrodynamic analysis was not an unsteady three-dimen- 

 sional theory in the sense of a lifting -surface theory. A two-dimen- 

 sional unsteady strip theory was modified using three-dimensional 

 steady lifting -surface theory. 



The only parts of the three-dimensional loading formulation 

 that were independent of frequency were the lift slope and aerodyna- 

 mic center distributions. The reduced frequencies of the bending - 

 type struts at flutter are welle below 0.1 , so the above approximation 

 is valid for this region. Torsion-type struts have higher reduced fre- 

 quencies at flutter, but the flutter calculation is more accurate for 

 this region. 



DISCUSSION 



Reuven Leopold 



U.S. Navy Naval Ship Engineering Center 

 Hyattsviile, Mary land } U.S.A. 



If there are no other questions, as we have a few more mi- 

 nutes, perhaps you would allow some of the designer in me to come 

 out in a few comments. There are problems that come to the designer 

 many times as design changes, since that is the name of the game. 

 In the area where flutter is a consideration such changes pose difficult 

 problems. It is evident from the Paper, and from other investigations, 

 that the flutter evaluation is sensitive to small changes in the struc- 

 tural stiffness, weight distribution and geometry. During an actual 

 design and fabrication many changes take place. A typical example is 

 when skin thickness is designed to a minimum gauge, whereas in the 

 actual fabrication a standard gauge is used. While such design changes 

 are usually in the direction of lowering the static design stresses and 

 deflections, the modification in structural characteristics may result 

 in lowering the flutter speed. It is thus important to direct the flutter 

 investigation effort towards sensitivity type evaluation of the various 

 configurations to variations in the governing parameters. This will 

 assist the designer in assessing the design adequacy from the hydro- 



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