When a large airplane manufacturer encountered Highland Composites and learned about the possibilities available with its proprietary braiding processes, a project was born to reimagine a key structural component to support a jet fuselage – the T-stiffener.
The customer is best known for its mid-sized commercial jets that carry 80-120 passengers on regional routes directly from airport-to-airport, bypassing hubs. The company also makes military, executive, and agricultural aircraft.
The customer was interested to explore competing in the next-largest class of regional jets that carry 120-160 passengers—a category long dominated by Boeing’s 737 and Airbus’s A319 programs.
The customer was interested to explore potential competitive and business advantages of fuselage support structures created from composite materials using braiding or over-braiding technology. Possible benefits included a need for fewer stiffeners to provide the same structural reinforcement at lower aggregate weight, thereby lowering costs for parts to manufacture and maintain a jet as well as lower fuel costs due to lighter weight.
The customer engaged Highland Composites in the co-development of a reimagined T-stiffener based upon the unique capabilities of its proprietary braiding processes and the strength and inventiveness of its R&D team.
Existing composite T-stiffeners were constructed from four separate components made from pre-preg composite material: three planar legs or blades and one long small cylinder placed at the point where the three legs come together to form a T-shape. The cylinder, called the noodle, originated as a thin, flat piece of pre-preg composite material that was rolled up into a cylinder in a hand-layup process. The three legs would then be joined to the noodle using a mold to hold them in place while the structure was hardened in a curing process to form a single structure.
The Highland Composites team began its reimagination of the structure guided by the principle that a component that is closer to near-net-shape as a direct result of its manufacturing process would perform better. A braid architecture was designed to produce a triangular braided noodle with a tri-axial fiber orientation in a single, automated process that reduced touch-labor when compared to the hand-rolled cylindrical noodle with its uni-axial fiber orientation.
Next the team reconsidered the three legs as potential braided parts, guided by the principle of near-net-shape desirability but also by the goal to automate the process where possible to reduce touch-labor for the sake of consistency, repeatability, and lower costs. The result was a truly innovative design of both product and process in which an open cylindrical braided structure was formed, then run through a die assembly designed by Highland Composites to collapse the open cylinder down around the triangular braided noodle into a preform in the shape of a T-stiffener.
The resulting preform of three exterior legs in a T-shape with the triangular braided noodle at its center axis was then placed into a mold assembly for a Resin Transfer Molding process and curing process. The result is a T-stiffener made from two braided components fused into a single structure.
Highland Composites designed the die assembly and pre-form, the mold, the RTM process and — most notably – reimagined the structure using two braided components rather than four components, while eliminating the need for a touch-labor step to create the noodle.
Highland designed the braid architecture to manufacture the noodle in a form closer to the near-net-shape most ideal for the structure, as well as the open cylindrical braid. The R&D team also created the pre-form, and developed the Resin Transfer Molding process to infuse the structure with resin and harden it.
The finished part exceeded performance criteria and far outperformed other competing technologies.