Fiber reinforced composite spar for a rotary wing aircraft and method of manufacture thereof

A method for manufacturing a composite spar (10) for a helicopter rotor blade (6), the composite spar being composed of composite laminates (60, 70) having a combination of high and low modulus composite fibers disposed in a binding matrix, the composite spar (10), furthermore, having upper and lower wall regions (40, 42), forward and aft conic regions (45, 47) and a longitudinal axis (25), wherein the method is characterized by the steps of:

• providing at least two molds (90, 100), each of the molds including complementary mold halves (90a, 90b, 101a, 100b) having mold surfaces (94a, 94b, 104a, 104b) defining the upper and lower wall regions (40, 42) and the forward and aft conic regions (45, 47), the mold surfaces (94a, 94b, 104a, 104b) being of progressively larger dimensions from an innermost mold (90) to an outermost mold (100), the outermost mold (100) defining the outer mold line contour of the composite spar 10);
• laying-up crossply laminates (60) in each of the upper and lower wall regions (40, 42) of the molds, said crossply laminates (60) having end portions (62e) extending into the forward and aft conic regions (45, 47), the end portions (62e) furthermore extending beyond one of the mold surfaces associated with one of the complementary mold halves of each mold, the crossply laminates (60), furthermore, being composed of high modulus composite fibers,
• laying-up at least one unidirectional laminate (70) in each of the upper and lower wall regions (40, 42) of one of the molds, said unidirectional laminate (70) composed of a combination of high and low modulus composite fibers;
• assembling the crossply and unidirectional laminates (60, 70) over an inflatable mandrel assembly (110) to form a preform assembly (120) having the unidirectional laminate (70) interposed between the crossply laminates (60) comprising the steps of:
• sequentially placing the inflatable mandrel assembly (110) into the complimentary mold halves (90a, 90b, 100a, 100b) of the molds (90, 100);
• and
• joining the end portions 62e of the crossply laminates (60) to form structural joints (68) and slip planes (66) in the forward and aft conic regions (45, 47);
• closing the outermost mold (100) over the preform assembly (120);
• pressurizing the inflatable mandrel assembly (110) for urging the crossply and unidirectional laminates (60, 70) against the mold surfaces (100a, 100b) of the outermost mold (100) to compact the laminates (60, 70);
• and,
• curing the crossply and unidirectional laminates (60, 70), whereby the forming of structural joints (68) and slip planes (66) in the conics regions (45, 47) facilitates uniform compaction of the crossply and unidirectional laminates (60, 70).

A composite spar (10) for a helicopter rotor blade (6), the composite spar (10) having upper and lower wall regions (40, 42) connected by a forward and aft conic regions (45, 47), the composite spar (10) tapering in vertical thickness dimension along the longitudinal axis (25) thereof and having an outer mold line contour along which a peripheral dimension is measured, the composite spar (10) being characterized by:

• crossply laminates (60) in each of the upper and lower wall regions (40, 42) having end portions (62e.sub.a, 62e.sub.b) extending into the forward and aft conic regions (45, 47), respectively, said end portions (62e.sub.a) of said crossply laminates (60) in said upper wall region (40) overlaping said end portions (62e.sub.b) of said crossply laminates (60) in said lower wall region (42) to form structural joints (68) in the forward and aft conic regions (45, 47), said structural joints operative to integrate said crossply laminates (60);
• said crossply laminates (60) including a plurality of individual crossplies (62) having a constant chordwise width dimension along the longitudinal axis (25);
• and
• at least one unidirectional laminate (70) in each of the upper and lower wall regions (40, 42) interposed between said crossply laminates (60), said unidirectional laminate (70) including a plurality of individual unidirectional plies (72) having a constant chordwise width dimension along the longitudinal axis (25);
• said constant width dimension crossplies and unidirectional plies (62, 72) forming a constant peripheral dimension;
• whereby said constant peripheral dimension increases the inertial mass of the composite spar (10) at the tip end (4) thereof.