Conuduction Heating for Adhesive Bonding of Rotorcraft Primary Structure

A final stage in the manufacturing of a rotorcraft structural article is presented. A single-part composite skin is stiffened with a series of pre-cured composite frames. Legacy designs feature either mechanically fastened metallic skin and frames, or longitudinally split composite skin bonded and fastened to composite frames. In the new design, all frames are simultaneously bonded using a high-performance, thermally-activated film adhesive. No fasteners are used. This approach improved the load transfer, damage tolerance, and part count. The success of this complex bonding operation is highly dependent on the control of the process parameters, mainly the bondline temperature. Required temperature uniformity across all bondlines was achieved by independently controlled conductive Heat Transfer Tiles (HTT's) dedicated to each frame. The National Research Council's HTT technology delivers non-uniform heat flux based on variable thermal boundary conditions which results in improved temperature uniformity compared to traditional heater blankets. Custom HTTs, control system and fixturing were evaluated and used to manufacture seven test articles. The success of the exercise was confirmed by process data, non-destructive, destructive, and full-scale testing.