Inertial vibration isolator spring for helicopter

A vibration isolator assembly adapted for rotation about an axis, said assembly comprising:

• an inner hub adaptable for mounting on said axis;
• an outer hub having a predetermined inertial mass;
• and
• a plurality of spiral shaped spring arms, each said arm having a body with a first retention portion connected to said inner hub and a second retention portion connected to said outer hub;
• at least one pad disposed on at least one of said first retention portion or said second retention portion;
• each said first retention portion and said second retention portion include an essentially rectangular cross-section having a thickness h;
• each said first retention portion and said second retention portion having at least one external surface;
• said at least one pad being disposed on one of said at least one external surface of said first retention portion or of said second retention portion;
• each of said at least one external surface being perpendicular to its respective said rectangular cross-section;
• said at least one pad being recessed at least a distance h from a top edge and a bottom edge of said external surface;
• and
• said at least one pad is of a uniform thickness tN and where tN has a magnitude less than h.

A vibration isolator assembly adapted for rotation about an axis, said assembly comprising:

• an inner hub adaptable for mounting on said axis;
• an outer hub having a predetermined inertial mass;
• and
• a plurality of spiral shaped spring arms, each said arm having a body with a first retention portion connected to said inner hub and a second retention portion connected to said outer hub;
• at least one pad disposed on at least one of said first retention portion or said second retention portion;
• each said first retention portion and said second retention portion include an essentially rectangular cross-section having a thickness h;
• each said first retention portion and said second retention portion having at least one external surface;
• said at least one pad being disposed on one of said at least one external surface of said first retention portion or of said second retention portion;
• each of said at least one external surface being perpendicular to its respective said rectangular cross-section;
• said at least one pad being recessed at least a distance h from a top edge and a bottom edge of said external surface;
• said retention portion has at least two said external surfaces;
• each said external surface of each said retention portion having at least one of said at least one pad disposed on said each said external surface;
• each said pad having an interior chord-wise edge, said edges being parallel and aligned in a span-wise manner;
• at least one through-hole passing from one of said at least two said external surfaces to the other in each of said retention portions;
• said at least one through-hole passing through each said pad disposed on its respective said external surface;
• and
• each of said at least one through-holes located at least a distance C from its respective said interior chord-wise edge;
• wherein said distance C is greater than a distance l which is the location of the peak interlaminar shear load in said retention portions from said interior chord-wise edge.

A method for determining a retention configuration for a spring arm for use in a vibration isolator, said method comprising:

• optimizing a composite spring arm from equations K = E 0.3 × bh 3 12 ⁢ R 3
• and ϵ = α ⁢ ⁢ h 0.3 ⁢ π ⁢ ⁢ R 2 ;
• and
• calculating the design moment at the retention area as M = bh 3 ⁢ E ⁢ ⁢ α 1.8 ⁢ π ⁢ ⁢ R 2 .