Over the past half a century, composite materials have gained increasing dominance in the design and construction of aerospace structures. To Michigan doctoral candidate Tim Brooks, this trend has been nothing short of a “revolution” in the industry. As a researcher in Professor Joaquim Martins’ Multidisciplinary Design Optimization (MDO) Laboratory, Brooks has been implementing computational methods that are helping to make new optimized processes of composite manufacturing a reality, enabling lighter and more fuel-efficient aircraft.
As their name suggests, composites are composed of multiple distinct materials that, when combined, offer unique and beneficial properties. Fiberglass was one of the first composites to be integrated into aircraft in the 1950s, serving as a high-strength, low-weight option for aircraft components. Today, researchers are investigating novel manufacturing methods to allow for further increases in aerodynamic efficiency and performance.
Brooks has been working on the project “Aeroelastic Tailoring for Next Generation High Aspect Ratio Wings” (Professors Carlos Cesnik and Joaquim Martins as U-M principal investigators) with team-lead Aurora Flight Sciences as part of NASA’s Passive Aeroelastic Tailored (PAT) project, an innovative new carbon-fiber “tow-steered” wing. He explains:
“With a conventional composite, the stiff fibers [in the composite matrix] are arranged in alternating orientations – usually 0 degrees, 45 degrees and 90 degrees. However, this orientation of fibers, though easy to manufacture, is not necessarily the most ideal for distributing the loads in an aircraft wing.
With the advent of Automated Fiber Placement (AFP) machines, we now have the ability to lay the fibers in curvilinear paths, [or tow lines]. This ‘tow-steered’ method gives us a new degree of design freedom that enables smarter, lighter-weight structures.”
Though this AFP-enabled method of composite manufacturing has been executed on small scales previously, it has never been used to fabricate a full wing – until now. The PAT project will be the first showcase of this innovative process:
“Part of the unique behavior of composites (as opposed to metallic materials) is that they can be designed to experience desired coupling between bending and twist responses. PAT takes advantage of this property. During different aircraft maneuvers, such as nominal cruise and takeoff or landing, the wing is subjected to different loads. PAT is designed to passively change loading distribution during flight, making it highly efficient.”
To optimize the tow line configurations, Brooks leveraged numerical methods pioneered in Professor Joaquim Martins’ MDO Lab. He extended these methods to allow for tow-steered structures to be parametrized in terms of relevant design constraints, such as tow line turning radius and wing geometry.
Now that the wing skin has been fabricated, it is awaiting testing at the NASA Armstrong Flight Research Center. As the first large-scale aerospace structure of its kind to be load tested, it will provide important data on the accuracy of current composite models and inform future designs.
After his defense next semester, Brooks looks forward to starting full-time at Aurora Flight Sciences, where he will be implementing some of the optimization tools he has developed during his UM Aerospace Ph.D. studies.