The use of advanced fibrous composites offers improvements in helicopter rotors due to improved aerodynamic geometry, improved dynamic tuning, good damage tolerance, and potential low cost. Weight reduction is also a potential advantage, but with an articulated rotor system, coning angle and autorotation considerations limit the potential rotor blade weight saving. The improved rotor performance, however, can provide substantial overall system weight savings for a given mission. The twin beam rotor blade derives its name from the fact that it incorporates two separate unidirectional glass fibre epoxy spar beams to carry centrifugal and bending loads. Each spar beam has its own titanium root end attachment, and the twin beams represent redundant load paths for improved reliability. The aerodynamic surface of the blade consists of ±45° graphite epoxy for torsional stiffness and strength and spanwise glass fibre epoxy for improved bending fatigue capability. The blade was designed to be fabricated in two halves for low cost manufacture. The cover and spar are cured together against a hard tool in an autoclave in order to ensure a sound laminate. Balance weights and low density core are bonded in, and the assembly is then machined to the chord line, thus eliminating the dimensional tolerance buildup. The two halves of the blade are bonded together with splices and erosion protection is added. Fatigue tests of full scale H-53-sized blade sections have verified the structural integrity of the twin beam blade construction and have indicated excellent damage tolerance. As predicted from small specimen testing, the composite blades exhibit twice the fatigue strain capacity of comparable aluminium blades. In addition, crack propagation is considerably slower and critical crack size larger in the composite blade. Although the initial cost of the composite blade is projected to be somewhat higher than that of aluminium blades, the longer fatigue life and projected lower maintenance cost should result in a lower cost of ownership.