Additive manufacturing speeds wind tunnel model creation
A new composite material was developed to 3D-print a helicopter model that met structural needs while providing flexibility for fast reproduction.
Wind tunnel testing is a longstanding technique used by aerodynamicists to directly measure forces, moments and pressures — and to visualize air flows — of aircraft designs. Typically, small-scale models of the proposed designs are built for the tunnel test. However, producing scale models can be laborious, as aerospace companies can attest. Leonardo SpA (Rome, Italy, formerly known as Finmeccanica) had in the past made models from wood and metals, and later, traditional composites, which took considerable time and effort, particularly when engineers wanted to make changes to the design during the tunnel testing process.
Leonardo’s helicopter division (formerly known as AgustaWestland) needed a 1:8.5 scale model of its new AW609 tiltrotor aircraft for a series of dedicated low-speed tests at standard flight attitudes, to be performed at the company’s own wind tunnel as well as at a facility at the Politecnical di Milano. Further, engineers wanted the freedom to quickly change the model’s external geometries to understand its aerodynamics. To accomplish this, Leonardo turned to Metaltech Srl (Cavazzale di Monticello Conte Otto, Italy) and trademarked Windform 3D printing materials from CRP Technology (Modena, Italy).
Using Leonardo’s CAD files, Metaltech constructed an internal structure using aluminum and steel. CRP Technology used its Windform XT 2.0 material (carbon fiber-filled polyamide) in a selective laser sintering (SLS) process to produce the model’s fuselage and nose components, fairings, nacelles and spinners, empennage, wings and flaperons to fit over the metallic skeleton. Windform XT 2.0 composite material was chosen because it met Leonardo’s goals of rapid production, high stiffness and elongation at break, good dimensional tolerance and good detail reproduction. Windform materials were shown to have adequate resistance to wind load deflection, based on structural strength testing under anticipated loading conditions.
Because some components were larger than the build envelope of the 3D printing machine, they had to be made in segments, says CRP Technology. Using the CAD design files, the segment cuts were designed for the tunnel conditions and the stress that the components would have to sustain, without adding to production time and costs. Printing was completed within four days, and parts were waterproofed, painted and delivered to Metaltech for assembly and mounting on the model structure.
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