Methods for creating consistent large scale blade deflections

Abstract

Methods are disclosed to design resilient hydrofoils ( 164 ) which are capable of having substantially similar large scale blade deflections under significantly varying loads. The methods permit the hydrofoil ( 164 ) to experience significantly large-scale deflections to a significantly reduced angle of attack under a relatively light load while avoiding excessive degrees of deflection under increased loading conditions. A predetermined compression range on the lee portion of said hydrofoil ( 164 ) permits the hydrofoil ( 164 ) to deflect to a predetermined reduced angle of attack with significantly low bending resistance. This predetermined compression range is significantly used up during the deflection to the predetermined angle of attack in an amount effective to create a sufficiently large leeward shift in the neutral bending surface with the load bearing portions of the hydrofoil ( 164 ) to permit the hydrofoil ( 164 ) to experience a significantly large increase in bending resistance as increased loads deflect the hydrofoil ( 164 ) beyond the predetermined reduced angle of attack. The shift in the neutral bending surface causes a significant increase in the elongation range required along an attacking portion of the hydrofoil ( 164 ) after the predetermined angle of attack is exceed. Methods are also disclosed for designing the hydrofoil ( 164 ) so that it has a natural resonant frequency that is sufficiently close the frequency of the reciprocating strokes used to attain propulsion in an amount sufficient to create harmonic wave addition that creates an amplified oscillation in the free end of the reciprocating hydrofoil ( 164 ).

1 . A method for improving the performance of a swim fin, comprising: 
 (a) providing a foot attachment member having a toe portion;    (b) providing a blade member connected to said foot attachment member and forming a forward extension of said foot attachment member, said blade member having opposing surfaces, outer side edges, a root portion adjacent said toe portion of said foot attachment member and a free end portion spaced from said root portion and said foot attachment member, said blade member having a predetermined length between said root portion and said free end portion, said blade member having a longitudinal midpoint between said root portion and said free end portion, said blade member having a first half portion between said root portion and said longitudinal midpoint and a second half portion between said longitudinal midpoint and said free end portion;    (c) providing said blade member with sufficient root portion flexibility adjacent said root portion to permit a root pivotal node to form during use within said blade member adjacent said root portion, said root portion flexibility being arranged to permit said first half of said blade member to experience a first half deflection of at least 10 degrees during a relatively light kicking stroke such as used to reach a relatively relaxed cruising speed,    (d) providing said blade member with sufficient midpoint flexibility adjacent to said longitudinal midpoint to permit a midpoint bending node to form during an inversion portion of said relatively light kicking stroke within said blade member adjacent said longitudinal midpoint, said midpoint bending node forming a second half deflection adjacent to said second half of said blade member during said inversion portion of said relatively light kicking stroke, said first half deflection and said second half deflection forming an S-shaped wave along said predetermined length of said swim fin during said inversion portion.    
   
   
       2 . (canceled)