Composite flapping flexure

A helicopter comprising:

• a fuselage;
• a drive means carried by the fuselage for actuating a drive mast;
• a rotor yoke coupled to the drive mast;
• and
• a plurality of rotor blades coupled to the rotor yoke(s);
• wherein the rotor yoke comprises:
• an elongated member having an upper surface, a lower surface, a flexure region at each end, and a longitudinal axis;
• a plurality of laminated composite belts having composite fibers that are oriented along the longitudinal axis, the belts extending along the elongated member and being disposed only at the upper surface and the lower surface;
• and
• a plurality of laminated composite off-axis layers having composite fibers that are oriented at selected angles to the longitudinal axis, the off-axis layers extending along the elongated member and being disposed between the belts;
• wherein flapping forces generated by the rotor blades are accommodated by the flexure regions.

A method of accommodating flapping forces in a helicopter rotor system, the method comprising the steps of:

• providing a helicopter having a fuselage and a drive means carried by the fuselage for actuating a drive mast;
• forming an elongated rotor yoke having an upper surface, a lower surface, a flexure region at each end, and a longitudinal axis, the formation of the rotor yoke comprising the steps of:
• forming the upper and lower surfaces from a plurality of laminated composite belts having composite fibers that are oriented along the longitudinal axis;
• and
• disposing a plurality of laminated composite off-axis layers having composite fibers that are oriented at selected angles to the longitudinal axis between the belts;
• and
• forming the flexure regions by selectively reducing the thickness of the rotor yoke in a direction perpendicular to the plane of the belts, the reduction in thickness being from a reduction in the number of off-axis layers only;
• coupling the rotor yoke to the drive mast;
• coupling a plurality of rotor blades to the rotor yoke;
• and
• accommodating flapping forces generated by the rotor blades with the flexure regions.

A method to help prevent mid-plane delamination in a composite flapping flexure in a helicopter rotor system, the method comprising the steps of:

• providing a helicopter having a fuselage and a drive means carried by the fuselage for actuating a drive mast;
• forming an elongated rotor yoke having an upper surface, a lower surface, a flexure region at each, end, and a longitudinal axis, the formation of the rotor yoke comprising the steps of:
• forming the upper and lower surfaces from a plurality of laminated composite belts having composite fibers that are oriented along the longitudinal axis;
• and
• disposing a plurality of laminated composite off-axis layers having composite fibers that are oriented at selected angles to the longitudinal axis between the belts;
• and
• forming the flexure regions by selectively reducing the thickness of the rotor yoke in a direction perpendicular to the plane of the belts, the reduction in thickness being from a reduction in the number of off-axis layers only;
• coupling the rotor yoke to the drive shaft;
• and
• coupling a plurality of rotor blades to the rotor yoke.