Ian Tonkin

At PERRINN we’re of course major advocates of open access and firmly believe that businesses will have more to gain from sharing and collaborating versus the traditional don’t-you-even-dare-copy-my-homework sort of way. “So, go on then, show me!” I hear you say, well, to give you some brief context first, our story begins in Brazil…

The Instituto Tecnológico de Aeronáutica (ITA)(Aeronautics Institute of Technology), is a higher education institution located a 90-minute drive north east of São Paulo in São José dos Campos, Brazil.

This renowned institution was first established in 1950 as part of Brazil’s national Institute of Aeronautics and Space (IAE) – see also the links to Embraer here – and today, boasts the largest research wind tunnels in Latin America.

It’s this very wind tunnel where PERRINN’s project 424 Le Mans prototype design finds itself at the centre of a study into the suitability and accuracy of using 3D printed parts in wind tunnel prototyping simulations.

With the sheer geographic size of Brazil, shipping traditional aluminium test rigs and prototypes to the wind tunnel was quickly becoming too expensive and time consuming.

As part of his M.Sc. thesis, Bruno Ricardo Massucatto Padilha looked into addressing these problems by using wind tunnel models that could instead be 3D printed on site. Padilha’s first problem to overcome was evaluating the suitability and smoothness of 3D printed materials in testing and development. In a nutshell, the smoother the surface, the more accurate and informed one’s results are and 3D printed parts were as yet unproven. (For the super-tecchies among us, aluminium has an average roughness of 0.83microns whereas a 3D printed part in 10.55microns).

Using the open access designs of Project 424, Bruno Padilha and the team at the ITA, including Guiding Professor Roberto Gil Annes da Silva, collaborating students and technicians Guilherme Barufaldi, César Duarte, Newton Vicente and Marcos Souza constructed a 3D printed scale model of the all-electric race car, rigged it up with sensors and set about testing it in the wind tunnel.

Padilha explains: “When I saw Nic Perrin’s project, it came at the perfect time as we could utilise his design to inform our academic and commercial research. The Project 424 design is thoroughly modern and the high-performance prototype enabled us to reach our goals in a much shorter time than it would have otherwise. This collaborative approach to design and engineering is definitely the way forward and the transfer of knowledge from motorsport to aerospace has been of incredible benefit to us.

“To correct the surface of 3D printed parts, the solution was to apply of a layer of epoxy resin with low viscosity and with self-levelling properties. In the sequence, a mix of sand and water is applied in a gentle manner in order to remove only the vitrification of the resin. Finally, a layer of spray PU paint is applied to block ultraviolet interference for an optical reading. The result of the final roughness was 0.52 microns, that is, less rough than the aluminium wing. The model was submitted to a laser scanner, and the result of the obtained volume is 95.4% of geometric fidelity, with the total material cost amounting to just US$750 (c.£585), which worked out to an average of just 5% of an identical aluminium equivalent.”

Many congratulations from all of us at Project 424 to Bruno and the team on developing such a timely, cost-effective and brilliant solution.