Evaluation of Rapid Prototyping Technologies for Use in Wind Tunnel Model Fabrication

Abstract

Current manufacturing techniques used for manufacturing metal wind tunnel models are slow and costly. Reliance on these traditional methods creates a delay in validating the analytical model’s predicted results with results from testing the physical model. Rapid Prototyping (RP) may prove to be the fastest means to create a bridge between these Computational Fluid Dynamic (CFD) and experimental ground testing databases. This project demonstrates that stereo lithography and selective laser sintering can be used successfully to rapidly fabricate vi able wind tunnel models. Two models, the UCAV X-45A and a Strike Tanker, were designed and manufactured using these RP technologies. Several design requirements and procedures for each model are addressed within this report. These requirements include the fabrication of the exterior surface using low cost rapid prototyping technologies, minimization of wing deflection, allowing access to the balance block and pressure scanning module, placement of pressure tap instrumentation, and a device for detecting sting/model contact under load. The UCAV X-45A and Strike Tanker models were manufactured and installed in wind tunnels at the Air Force Research Laboratory and the Air Force Institute of Technology. I. Introduction APID Prototyping (RP) is a robust, accurate, and affordable method to support aerospace research and development. Rapid Prototyping serves as the link between Computational Fluid Dynamic (CFD) simulations and experimental ground testing correlations. In the past, it took months to manufacture mo dels for ground testing. With the seamless merging of computational models and recent innovations in RP technologies, inexpensive models can be fabricated literally overnight and tests performed immediately thereafter. Rapid fabrication results in a faster and better response to the designer’s needs by permitting concurrent study of new concepts in the wind tunnel and via computer simulation. Testing of RP models early in the design cycle serves as a vital verification of system performance. Should the tes ting indicate a need for design changes, the changes can be made early in the design cycle where the cost and schedule impacts are less severe. The electronic model of the geometry defines the outer surface of the air vehicle concept, but it is not sufficient to immediately begin fabrication of the wind tunnel model. A wind tunnel model design effort must be performed to address a number of factors including mounting, instrumentation, and rapid prototyping fabrication technique. While current RP manufactur ing processes include stereo lithography, selective laser sintering, laser engineered net-shaping, and fused deposition modeling, among many others, two techniques were implemented under the direction of the Air Force Research Laboratory Air Vehicles Directorate: stereo lithography (SLA) and selective laser sintering (SLS). SLA is a layered manufacturing method that utilizes a photo -curable liquid resin in combination with an ultraviolet laser. 1 A vat of the resin sits underneath the laser, and the laser “draws” on the top layer of liquid. When the ultraviolet laser beam hits the liquid it hardens a small amount of the resin under the beam point. By drawing and then filling the outline of a layer, a solid layer of material is created. This layer is