Variable stiffness rotor

Claim 2

A rotor having: a. a hub mounted for rotation about an axis of rotation, b. a plurality of blades projecting from said hub for rotation therewith, c. a hinge member connecting each of said blades to said hub so that said blade is capable of articulating motion thereabout with respect to said hub, d. a variable stiffness spring mounted so as to be free of blade centrifugal loading and extending between said hub and said blade and extending across said hinge member.

Claim 3

Apparatus according to claim 1 wherein said variable stiffness spring includes a plurality of laminates of selected dimension and positioned in stacked relation to form a spring pack and with the ends thereof free to move longitudinally relative to one another.

Claim 4

Apparatus according to claim 2 wherein said variable stiffness spring comprises a plurality of metal laminates of selected height and width stacked with respect to one another to form a spring pack and so that the ends thereof are positioned on opposite sides of the axis of the hinge member and are free to move relative to one another toward or away from the hinge axis.

Claim 5

Apparatus according to claim 3 and including means to move said spring pack to a first position wherein each laminate presents a cross section of maximum stiffness and to a second position wherein each laminate presents a cross section of minimum stiffness.

Claim 6

Apparatus according to claim 4 wherein in said first position said laminates individually present a cross section of greater height than width, and wherein, in said second position, said laminates individually present a cross section of greater width than height to thereby vary the stiffness of the spring pack.

Claim 7

Apparatus according to claim 2 wherein said spring pack is of rectangular cross section.

Claim 8

Apparatus according to claim 2 wherein said spring pack is of cross section other than rectangular.

Claim 9

A helicopter rotor having: a. a hub mounted for rotation about an axis of rotation, b. a plurality of blades projecting from said hub for rotation therewith, c. a hinge member connecting said blades to said hub for articulating motion with respect to said hub thereabout, d. a variable stiffness spring member mounted so as to be free of blade centrifugal loading and including a spring pack comprising a stack of laminate members stacked in loose relation with respect to one another and extending across said hinge member axis, e. means supporting the first end of said spring pack in said hub so that said laminates are free to move longitudinally with respect to one another but are restrained from moving laterally with respect to one another, f. means to support the other end of said spring pack in said blade so that the ends of the laminates thereof are free to move longitudinally with respect to one another but are restrained from moving laterally with respect to one another, g. means to move said spring pack to a first position wherein said laminates present maximum stiffness to bending about the hinge member axis so that said rotor is operable as a rigid rotor and to a second position wherein said laminates present minimum stiffness to bending about said hinge member axis so that said rotor is operable as an articulated rotor.

Claim 10

A helicopter rotor having: a. a hub mounted for rotation about an axis of rotation, b. a plurality of blades projecting from said hub for rotation therewith, c. a hinge member connecting said blades to said hub for articulating motion with respect to said hub thereabout, d. a variable stiffness spring member mounted so as to be free of blade centrifugal loading and including a spring pack comprising a stack of laminate members stacked in loose relation with respect to one another and extending across said hinge member axis, e. means supporting the first end of said spring pack in said hub so that said laminates are free to move longitudinally with respect to one another but are restrained from moving laterally with respect to one another, f. means to support the other end of said spring pack in said blade so that the ends of the laminates thereof are free to move longitudinally with respect to one another but are restrained from moving laterally with respect to one another, g. means to move said spring pack to a first position wherein said laminates present maximum stiffness to bending about the hinge member axis so that said rotor is operable as a rigid rotor and to a second position wherein said laminates present minimum stiffness to bending about said hinge member axis so that said rotor is operable as an articulated rotor.

Claim 11

Apparatus according to claim 8 wherein said actuating means includes means to position said spring pack in intermediate positions between said first and second positions.

Claim 12

Apparatus according to claim 9 wherein said spring pack consists of a selected number of metal sheet laminates of selected cross section dimension and wherein each of said laminates presents a cross section of greater height than width when in said first position and a cross section of greater width than height when in said second position so as to constitute a spring of variable stiffness.

Claim 13

Apparatus according to claim 10 and including a layer of low-friction material sandwiched between adjacent laminates of said spring pack.

Claim 14

Apparatus according to claim 11 wherein each of said laminates is of the same cross-sectional shape and is of the same height and width and of selected number to produce a variable spring of selected stiffness ratio when in said first and said second positions.

Claim 15

Apparatus according to claim 12 wherein said laminates are of different cross-sectional dimension so that the cross section of the spring pack is of selected shape and constitutes a spring of desired stiffness when in said first position and to constitute a spring of desired stiffness when in said second position.

Claim 16

Apparatus according to claim 8 wherein said hinge member is a flapping hinge.

Claim 17

Apparatus according to claim 8 wherein each of said laminate members is identical and is of rectangular shape and of rectangular cross section and wherein said spring pack is of rectangular cross section.

Claim 18

Apparatus according to claim 8 and including means joining said laminate members of said spring pack.

Claim 19

Apparatus according to claim 8 wherein said variable stiffness spring member is the same for each of said blades and including: a. means to cause said variable stiffness spring members to vary in stiffness simultaneously and to the same degree.

Claim 20

A helicopter rotor having: a. a hub member mounted for rotation about an axis of rotation, b. a plurality of blades projecting radially from said hub member and having a root end, c. a blade-cuff supporting said blades for pitch change motion about a blade feathering axis, d. a hinge member connecting said cuff to said hub so that said blade and cuff are supported for pivot motion about the hinge member axis from said hub member, e. a variable stiffness spring mounted so as to be free of blade centrifugal loading and extending across said hinge member axis and supported at its opposite ends in said hub member and said cuff.

Claim 21

A helicopter rotor having: a. a hub member mounted for rotation about an axis of rotation, b. a plurality of blades projecting radially from said hub member and having a root end, c. a blade-cuff supporting said blades for pitch change motion about a blade feathering axis, d. a hinge member connecting said cuff to said hub so that said blade and cuff are supported for pivot motion about the hinge member axis from said hub member, e. a variable stiffness spring mounted so as to be free of blade centrifugal loading and extending across said hinge member axis and supported at its opposite ends in said hub member and said cuff.

Claim 22

Apparatus according to claim 18 wherein said variable stiffness spring includes a plurality of metal sheets of selected cross-sectional shape and positioned in stacked relation with respect to one another.

Claim 23

Apparatus according to claim 19 and including means to support one end of said sheets in said hub so that said sheets are free to move longitudinally with respect to one another but are substantially restrained from lateral motion with respect to one another and means to support the other end of said sheets in said cuff so that said sheets are free to move longitudinally with respect to one another but are restrained from moving laterally with respect to one another and means to pivot said sheets so stacked between a first position wherein each of said sheets presents a cross section of maximum height and minimum width with respect to said hinge axis so as to constitute a spring of maximum stiffness extending across said axis between said hub and said cuff and a second position wherein each of said sheets presents a cross section of minimum height and maximum width with respect to said hinge axis so that said sheets so stacked constitute a spring of minimum stiffness between said hub and said cuff across said hinge axis.

Claim 24

Apparatus according to claim 20 and wherein said hinge member is a flapping hinge.

Claim 25

Apparatus according to claim 18 and including means to support said variable stiffness spring in said hub and said cuff so that blade centrifugal loading is not imparted thereto but passes through said cuff and hinge member to said hub member.

Claim 26

A helicopter rotor having: a. a hub mounted for rotation about an axis of rotation, b. a plurality of blades projecting from said hub for rotation therewith, and having a flexible section therein, c. a variable stiffness spring mounted so as to be free of blade centrifugal loading and extending across said flexible section and mounted for flexing motion therewith.

Claim 27

A helicopter rotor having: a. a hub mounted for rotation about an axis of rotation, b. a plurality of blades projecting from said hub for rotation therewith, and having a flexible section therein, c. a variable stiffness spring mounted so as to be free of blade centrifugal loading and extending across said flexible section and mounted for flexing motion therewith.