Fabrication Of Boron-Hybrid Swashplates

This paper describes Boeing Vertol IR&D prototype production and subsequent programs for the development of a fabrication method for high modulus advanced composite rings, to be used to reinforce the stationary and rotating swashplate assemblies of the Boeing Vertol Heavy Lift Helicopter (HLH). The fundamental design requirement was to fabricate four sizes of boron-epoxy (AVCO 5505/4 Rigidite) rings, having a thickness ranging from 0.160 in. to 0.200 in. and outside diameters varying from approximately 44 in. to 58 in., which were adhesively bonded to a 7075-T73 aluminum alloy swashplate. An initial investigation was designed to produce half-scale hardware. The purpose of this study was to develop a machine where critical parameters such as resin content, winding rate, compaction loads, tape tension, guides and tracking were determined. Five experimental subscale rings were wound and match mold cured in a platen press. Elastic moduli progressed from 15 x 106 psi to 27 x 106 psi, ultimately exceeding the design requirement by 12%. The second part of the investigation was to translate the experimental data into the design and fabrication of a production machine. Production operating parameters were developed to the extent that composite rings having an elastic modulus of 36 x 106 psi (50% greater than required) were fabricated. The final portion of this investigation involved the joining of the boron epoxy composite to the 7075-T73 aluminum alloy substructure. Because of the large difference in the thermal expansion characteristics of the two components, thermosetting adhesive systems were ruled out. A new room temperature curing acrylic based adhesive system, B.F. Goodrich, TAME 200 PB-2, which has properties exceeding the epoxy hot-cured materials, was used.