Investigation of carbon rod stiffeners for wing flutter mitigation on a supersonic business jet

Aeroelastic issues are a primary design consideration for any supersonic aircraft wing design. Previous design configurations have determined that flutter is a phenomenon that must be considered early in the design process due to the significant impact it can have on wing and empennage structure. This is due in part to the extremely thin airfoil cross sections required.; Flutter mitigation can be achieved by adding additional structural weight for increased stiffness to an airfoil section. However, in the case of supersonic aircraft, airframe weight not only directly impacts aircraft performance such as fuel consumption and payload capacity, but also has a direct impact on the strength of the sonic boom that is created and propagated to the ground. The ultimate goal of any supersonic aircraft wing design is a wing section that is extremely lightweight but with the stiffness required to delay the onset of flutter.; To increase the stiffness of a supersonic wing, special materials and design configurations will be required. It was theorized that carbon rod technology could be utilized to increase the bending and torsional stiffness of a wing section with a significant weight savings over conventional design techniques. This was achieved by incorporating several carbon rods into a bundle that were bonded together with an adhesive. These carbon rod bundles were then bonded to the upper and lower surface of a full-scale outer wing section of a conceptual supersonic wing to simulate stiffeners or stringers.; Two wing test articles were built incorporating the carbon rod stringer concept. The first test article oriented the carbon rod stringers parallel to the rear spar. This was similar to conventional design maximizing the wing section bending stiffness. The second test article placed the carbon rod stringers at an angle of 30° to the rear spar with the upper surface stringers opposite in direction to the lower surface stringers. By angling the carbon rod stringers, the torsional stiffness was maximized.; Vibration testing was performed on each of the test articles. First bending and first torsion natural frequencies for each test article were determined. Both vibration dwell testing and "rap" vibration tests were performed. Rap testing also determined the decay of the vibration from which the vibration damping constant was determined.; The natural frequencies of each article were scaled to the full size wing. Finite element models of each wing configuration were tuned in stiffness and mass to provide the correct mode shapes. Flutter analysis was performed for each wing configuration and compared to a baseline conventional aluminum wing design. Results indicted the angled carbon stringer design had higher critical flutter speeds followed by the conventional aluminum design and the design with the carbon rod stringers parallel to the rear spar, respectively. Weight comparisons determined the conventional design to be significantly heavier as compared to each carbon rod design.