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Apparatus and methods are disclosed for designing and manufacturing a composite structure, such as a composite rotor blade spar or composite rotor blade. A first mold may define a first mold surface and a second mold may include a rigid layer and a heated layer secured to the rigid layer and definin

Apparatus and methods are disclosed for designing and manufacturing a composite structure, such as a composite rotor blade spar or composite rotor blade. A first mold may define a first mold surface and a second mold may include a rigid layer and a heated layer secured to the rigid layer and defining a second mold surface. A plurality of heating elements embedded in the second mold may be activated according to different temperature progressions to cure portions of the uncured composite rotor blade positioned coextensive therewith. In some embodiments, the second mold defines a root portion and first and second branch portions. A shear web may be placed between the branch portions during curing. The blade spar may define a complete airfoil contour or have fairings secured thereto having lines extending therethrough to a tip jet. A tip jet mounting structure and blade root attachment apparatus are also disclosed.

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1. A rotor system for a rotorcraft comprising: a hub;a composite blade spar defining proximal and distal ends and a blade duct, the composite blade spar mounted to the hub at the proximal end thereof;a tip jet mounted proximate the distal end of the composite blade spar in fluid communication with t

1. A rotor system for a rotorcraft comprising: a hub;a composite blade spar defining proximal and distal ends and a blade duct, the composite blade spar mounted to the hub at the proximal end thereof;a tip jet mounted proximate the distal end of the composite blade spar in fluid communication with the blade duct; anda compressed air source in fluid communication with the blade duct. 2. The rotor system of claim 1, wherein: the composite blade spar defines a longitudinal axis extending between the proximal and distal ends;the composite blade spar comprises a plurality of plies each having a plurality of fibers parallel to one another and having an orientation angle with respect to the longitudinal axis; andthe orientation angles of a portion of the plurality of plies are between 46 and 90 degrees. 3. The rotor system of claim 1, wherein: the composite blade spar defines a longitudinal axis extending between the proximal and distal ends;the composite blade spar comprises a plurality of plies each having a plurality of fibers parallel to one another and having an orientation angle with respect to the longitudinal axis; andthe orientation angles of a portion of the plurality of plies are between 0 and 44 degrees. 4. The rotor system of claim 1, further comprising a mounting structure defining a fluid path in fluid communication with the blade duct, the mounting structure having upper and lower surfaces and wherein: the tip jet is secured to the mounting structure in fluid communication with the fluid path;the composite blade spar defines upper and lower surfaces;the composite blade spar and mounting structure abut one another at a joint and wherein the upper surface of the composite blade spar;the upper surface of the mounting structure lie on a common airfoil contour extending across the joint; andthe lower surface of the blade spar and the lower surface of the mounting structure lie on the common airfoil contour. 5. The rotor system of claim 4, wherein the mounting structure comprises a composite material. 6. The rotor system of claim 5, wherein the mounting structure comprises first and second portions and wherein a portion of the composite blade spar is captured between the first and second portions. 7. The rotor system of claim 1, wherein the composite blade spar comprises a resin having an operating temperature at least as high as about 300° Fahrenheit. 8. The rotor system of claim 7, wherein the resin has an operating temperature at least as high as about 400° Fahrenheit. 9. The rotor system of claim 8, wherein the resin has an operating temperature at least as low as about −60° Fahrenheit. 10. The rotor system of claim 1, wherein: the composite blade spar defines a plurality of bolt apertures extending from the proximal end into the composite blade spar along the longitudinal axis, the bolt apertures distributed circumferentially around the proximal end;the composite blade spar further defines a plurality of nut apertures extending from the proximal end through the composite blade spar perpendicular to the longitudinal axis, each nut aperture intercepting a bolt aperture; andbolts extend from the hub through the bolt apertures and engage nuts positioned in the nut aperture. 11. The rotor system of claim 10, wherein the nuts positioned in the nut aperture are barrel nuts. 12. The rotor system of claim 10, wherein the bolts have a plurality of different tensions. 13. The rotor system of claim 10, further comprising a retention ring positioned within the hub and resisting movement of the bolts along the longitudinal axis with respect to the hub. 14. The rotor system of claim 13, wherein a pitch control arm is mounted to the retention ring. 15. A method for designing a blade for a rotor system, the method comprising: specifying design constraints including two or more of flapping stiffness, rotational stiffness, frequency response, and lead-lag stiffness along the length of a blade;specifying a length of the blade and an aerodynamic contour for a distal portion of the blade;specifying a ply sequence approximating the aerodynamic contour;evaluating expected performance of the ply sequence with respect to the design constraints; andif the design constraints are not satisfied within a tolerance, performing one or more of the following until the design constraints are satisfied within a tolerance adjusting a contour of one or more end portions of one or more plies of the ply sequence effective to closer conform the expected performance of the ply sequence to the design constraints, andadjusting a fiber orientation of one or more plies of the ply sequence effective to closer conform the expected performance of the ply sequence to the design constraints. 16. The method of claim 15, wherein: the ply sequence defines a longitudinal axis; andadjusting the fiber orientation of one or more of the plies comprises adjusting the fiber orientation of one or more plies to an angle one of between 0 and 44 degrees relative to the longitudinal axis and between 46 and 90 degrees relative to the longitudinal axis. 17. The method of claim 15, wherein the ply sequence defines a hollow blade having a blade duct extending therethrough along a longitudinal axis thereof. 18. The method of claim 15, wherein: the ply sequence defines a longitudinal axis and each ply comprises a proximal boundary and distal boundary defining an extent of the ply along the longitudinal axis; andadjusting a contour of one or more end portions of one or more plies comprises adjusting a contour of one or more of the proximal boundary and distal boundary. 19. The method of claim 18, wherein adjusting the contour of one or more of the proximal boundary and distal boundary comprises adjusting an extent along the longitudinal axis of one or more of the proximal boundary and distal boundary. 20. A computer system comprising: a processor operable to execute executable data and operate upon operational data; anda memory storing executable and operational data effective to cause the processor to receive design constraints including two or more of flapping stiffness, rotational stiffness, frequency response, and lead-lag stiffness along the length of a blade,receive a length of the blade and an aerodynamic contour for a distal portion of the blade,receive a ply sequence approximating the aerodynamic contour,evaluate expected performance of the ply sequence with respect to the design constraints, andif the design constraints are not satisfied within a tolerance, perform until the design constraints are satisfied within a tolerance one or more of adjust a contour of one or more end portions of one or more plies of the ply sequence effective to closer conform the expected performance of the ply sequence to the design constraints, andadjust a fiber orientation of one or more plies of the ply sequence effective to closer conform the expected performance of the ply sequence to the design constraints.