Fast, lightweight and fuel-efficient: The RACER high-speed helicopter can reach flying speeds of up to 400 kilometres per hour. Its outer shell components are manufactured using an innovative, highly automated process. The innovative, sustainable method was developed by a research team at the Fraunhofer Institute for Casting, Composite and Processing Technology IGCV in collaboration with Airbus Helicopters.
At over 400 kilometres per hour, RACER — short for ‘Rapid and Cost-Effective Rotorcraft’ — moves through the air much faster than conventional helicopters, which travel at around 230 to 260 kilometres per hour. However, this is not the only feature that sets the helicopter apart. The top layers of its side shells are made of carbon fibre-reinforced plastic (CFRP) and the sandwich core is made of phenolic resin honeycombs. Until now, these large sandwich shells were produced manually using a time-consuming and expensive process called hand lay-up.
In collaboration with Airbus, researchers at Fraunhofer IGCV in Augsburg have developed a highly automated process for manufacturing the CFRP shell components. This development is funded as part of the Clean Sky 2 programme of the European Union. The demonstrator platform is a prime example of European coordination and integration, uniting over 25 consortia of industry and science organisations from 13 countries, supported by a large-scale ecosystem of SMEs, in the EU’s endeavour to promote cleaner air travel.
Photo credit: Airbus Helicopters GmbH
The 3.4 x 1.5 metre shell segments manufactured by this automated process form the rear right and left parts of the outer skin. They connect the rear tail boom to the cockpit. ‘Until now, the shells were made using carbon fibre-reinforced lightweight materials, but we have advanced the production process. It is now based on the Automated Fiber Placement process,” says Thomas Zenker, a scientist at IGCV. A robot places continuous fibre-reinforced pre-impregnated materials in an automated fashion. This process uses unidirectional tapes that have better mechanical properties and generate less waste than web-based plastic composites. The sandwich core, made up of phenolic resin honeycombs, increases the structure’s stiffness; its strength comes from the fibre-reinforced skin layers. An adhesive film ensures the transmission of force between the core and the skin layers.
‘Before the material is cured, the robot places the high-quality fibres in a tool. It does this by following a specially developed programming methodology. The tool concept was developed specifically for this process. Its surface defines the shape of the fibres during the AFP process. The complex geometries of the variably formed sandwich pockets are taken into account. In other words, the tapes are placed precisely where the structure of the finished component requires,” says the engineer, summarising the process.
RACER holds huge sustainability potential
Depending on the stacking sequence and the fibres used, a carbon fibre reinforced plastic (CFRP) component manufactured using the automated fibre placement (AFP) process can be more resilient than a steel element, while weighing significantly less. ‘This is an important aspect of aviation, where every kilogramme saved helps reduce fuel consumption,’ says the researcher. Using this material reduces the weight of the shell segments by five percent.
Depending on the energy mix used during production, this can improve the ecological footprint by up to 15 percent per shell segment.
Automated Fiber Placement for low-waste processes
The advanced production processes offer additional benefits, too. For example, thanks to the more efficient process, Zenker and his team have been able to reduce production waste from 45 to 20 per cent. Depending on the number of helicopters produced, the automated process can also achieve production cost savings compared to the conventional manual lay-up method. At a production rate of 65 helicopters per year, for instance, this saving amounts to 20 per cent.
The two side parts for the helicopter prototype were completed in August 2020. Airbus then took care of the curing process and non-destructive material testing, which uses ultrasound to examine components for potential defects. New material and production process combinations require close scrutiny, especially in safety-critical sectors such as aviation. Additional characteristics of the material samples were determined and evaluated as part of the Permit-to-Fly procedures. These mechanical tests are a prerequisite for the demonstrator to be cleared to fly.
The components from Fraunhofer IGCV passed the tests and are currently being assembled into a prototype. The sustainable helicopter is scheduled for completion in early 2022 and will take its first test flight shortly afterwards.
Its high speed makes it especially suitable for use in all types of emergency situation. However, it could also potentially be used as an air taxi to transport passengers between urban centres, bypassing traffic altogether.
Photo credit: Airbus Helicopters GmbH
