Using composites to create 3D printed wind tunnel model

4 Mar 2019

A 3D printed aircraft model has been created for wind tunnel testing using high-performance Windform composites and selective laser sintering. Shardell Joseph reports. 

A 3D-printed aircraft model has been created for wind tunnel testing using high-performance composites and selective laser sintering (SLS).

Italian developer of additive manufacturing materials, CRP Technology, has printed components for the LEONARDO tiltrotor AW609 aircraft model, made for low-speed wind tunnel testing, using its Windform XT 2.0 carbon-composite material.

Enlisted by LEONARDO HD – a Rome-based helicopter manufacturer for the aerospace, defence and security industries – Windform’s high-performing mechanical and aerodynamic properties combined with CRP’s selective laser sintering techniques have proven capable of fast wind tunnel testing while withstanding the aerodynamic loads simulated.

In the past, LEONARDO used more conventional materials, such as wood and metal, for its wind tunnel models, but has recently started using a mixed solution of wood and composite fibre materials. The helicopter manufacturer now uses a computer-aided design (CAD) and computer-aided manufacturing approach for all its models, which involves milling the structural aluminium and steel frame, and printing the external parts.

In the case of the LEONARDO tiltrotor AW609 aircraft model, CRP printed various components, including the nose, cockpit, rear fuselage, external fuel tanks and fairings, using its Windform XT 2.0 material.

This carbon-fibre composite also has high heat deflection, high stiffness, good tensile strength, as well as other beneficial properties.

Composites and laser sintering  

Windform XT 2.0 replaces the previous formula, Windform XT created in 2005, which was originally designed for the manufacture of wind tunnel models for motorsports customers.

The new material has improved mechanical properties, including an 8% increase in tensile strength, 22% in tensile modulus, and a 46% increase in elongation at break.

Using SLS additive manufacturing to 3D print the parts, the material enables accurate, reliable and durable prototypes and functional applications.

The SLS technique uses a laser as the power source to sinter powdered material by automatically aiming the laser at points in space – defined by a 3D model –  which binds the material together to create a solid structure.

This technology combined with the mechanical and thermal properties of the Windform materials allows for the creation of functional prototypes and end-use parts that meet the specifications for high-performance products, such as race cars.

‘In regards to AW609, CRP Technology has been able to produce, via laser sintering and using Windform XT 2.0, most of the external parts of the wind tunnel model with greater complexity and functionality in a fraction of time over traditional methods, and with high-performance mechanical and aerodynamic properties,’ says CPR Technology Chief Technology Officer and Vice President Franco Cevolini.

The process

As the whole parts are bigger than the job area size, it is necessary to split them into portions, build them separately and bond them with structural adhesive.

Identifying the best areas to split that wouldn’t impact performance was an operation undertaken with CAD, evaluating the functional measures of the working volume but also the possibility to optimise volume – tightly packing the print area leaving only minimal clearance between parts – simultaneously minimising production time and costs.

The last step was the complete model surface finishing, directly mounting it onto the rig assembly to address any small imperfections from joining the components.

The surface of the whole model was flattened and then treated with a liquid – which CRP declined to disclose – that has a double function to make it waterproof and to prime the surface before painting.

The AW609 was tested at the LEONARDO HD wind tunnel facility in Milan, Italy, using low speeds to simulate a standard range of flight attitudes.

Cevolini says the team is already working on further developments to improve the properties of the composite materials.