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Aeroelastic Flutter Suppression

24 June 2019

CRP Technology has played a key role in a joint project with the Politecnico di Milano (PoliMi) and the University of Washington in the construction of parts for the aeroelastic wind tunnel demonstrators for ‘Aeroelastic Flutter Suppression’.

Through the know-how earned in over 20 years of activity serving the most demanding and performing industrial sectors, CRP Technology was able to assist PoliMi in choosing the best technology and material to guarantee the success of the project. Selective laser sintering and the Windform XT 2.0 carbon-composite material, which replaced the previous formula of Windform XT in the Windform TOP-LINE family of composite materials, saw improvements in its mechanical properties. This included +8% increase in tensile strength, +22% in tensile modulus, and a +46% increase in elongation at break. These mechanical properties guaranteed the achievement of the required characteristics of stiffness, lightness as well as a very smooth external surface.

The net result was that the PoliMi team was able to transfer resources from the construction to the design phase, obtaining better optimised components. The wing components had to be light and stiff with parts characterised by thin layers to obtain the lightest possible components. Often the CAD design of the aerodynamic sectors is pushed to the limits and with a smooth external surface.

The net result was that the PoliMi team was able to transfer resources from the construction to the design phase, obtaining better optimised components. The wing components had to be light and stiff with parts characterised by thin layers to obtain the lightest possible components. Often the CAD design of the aerodynamic sectors is pushed to the limits and with a smooth external surface.

During the test phase, the aerodynamic sections are not usually subjected to high stress since they do not form the primary structure of the aircraft. However, they perform a very important task as they efficiently transmit the aerodynamic forces to the flexible spar, acting as the interface structure between the fluid (incoming air) and the internal structure of the wing. It was therefore fundamental that a good surface finish was achieved on the parts exposed to the incoming wind. The components were of reduced weight and were able to transmit the aerodynamic loads on the wing’s longitudinal spar.

CRP Technology was also involved with another related project. The focus of Gust Load Alleviation techcniques assessment on wind tUnnel MOdel of advanced Regional aircraft (GLAMOUR) is on technological optimisation and experimental validation of Gust Load Alleviation (GLA) control systems for an advanced Green Regional Aircraft manufactured by Leonardo Aircraft Division. The expected benefits of such technologies are mainly the mitigation of gust load responses, the reduction of peak stresses so to potentially decrease sizing loads and consequently increase the weight saving. Most generally, the capability to control the load distribution spanwise could contribute to other global targets such as fatigue lifetime as well aeroelastic and aerodynamic performances. Thanks to Windform 2.0’s carbon fibres, the combination of the vibration frequency targets together with the forced mass constraints is allowed.

CRP Technology was involved in the manufacturing of the external aerodynamic segments of the two wind tunnel demonstrators for both projects using selective laser sintering technology and carbon-composite Windform XT 2.0. Prior to professional 3D printing, the aerodynamic sections of the wings were produced by carbon or glass fibre fabrics dry lamination, which were wrapped Styrofoam blocks suitably cut to match the wing’s shape. This manufacturing process required much longer times and yielded lower quality surface finish.

Professional 3D printing has revolutionised the entire process of construction and verification of the parts allowing faster production speed and the possibility of optimising the internal shape of these aerodynamic sections to make them as light weight and stiff as possible.

3D printed aerodynamic sectors, assembly phase
Aerodynamic sector of the wing (detail) – GLAMOUR project. Courtesy of PoliMi

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