More than 400 kilometres per hour – that is how fast the Rapid And Cost-Effective Rotorcraft (Racer), which was presented by Airbus Helicopters at the Paris Air Show on 20 June 2017, will fly. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is playing a key role in the aerodynamic design of the wings and the tail plane. To minimise the noise emissions, DLR researchers have analysed the acoustic properties of the new helicopter configuration, which in addition to the main rotor also has two small, so-called box-wings with extra rotors. The newly-introduced technology demonstrator is part of the Clean Sky 2 European aeronautics research programme.
"We are delighted to be part of this exciting and ground-breaking research project, which notably demonstrates the prospect for fast and cost-effective next-generation helicopters," says Rolf Henke, DLR Executive Board Member responsible for Aeronautics Research. "At the same time, it is a demonstration of the strength of European aviation research, where several partners pool their expertise under the umbrella of the EU research programme Clean Sky 2."
Double-decker wing design for extra lift
The Racer demonstrator will be built around a simple architecture, ensuring safety and cost-efficiency. An innovative 'box-wing' design, optimised for aerodynamic efficiency, will help lift in cruise mode while isolating on-ground passengers from the 'pusher' lateral rotors designed to generate thrust in forward flight. This concept will demonstrate its suitability for a wide spectrum of missions where increased speed and efficiency will bring significant added value for citizens and operators. This is especially the case for emergency medical services and search & rescue operations, as well as for public services, commercial air transport and private and business aviation. Final assembly of the demonstrator is expected to start in 2019, with the maiden flight taking place the following year.
Drawing upon the characteristic double-decker concept, DLR created various wing designs. Of these, suitable designs were selected and further optimised in close collaboration with Airbus Helicopters. "The final design fulfils all requirements and, in particular, will enable the Racer to attain exceptional flight performance over the entire flight range while maintaining low fuel consumption," says Thorsten Schwarz from the DLR Institute of Aerodynamics and Flow Technology in Braunschweig. "Our aerodynamic improvements for the tail boom focused on the tail plane to ensure good manoeuvrability and stability of the helicopter, in addition to low air resistance."
Flight profiles with minimal noise impact
Finally, the acoustic characteristics of the helicopter demonstrator were analysed under various flight conditions. "The identified low-noise flight conditions will help Airbus Helicopters and operators develop flight profiles with minimal noise impact on local residents," Schwarz continued. These activities were carried out jointly with ONERA as part of a call for tender won in the ITD AIRFRAME of the CleanSky 2 platform. ONERA contributed to the design of the propellers, and the vertical stabilisers, whilst the acoustic analysis is being carried out jointly by DLR and ONERA. The particularity of the project was to work on each component individually, taking into account the many aerodynamic interactions between wing/propeller, propeller wing, rotor/propeller/wing/tail parts, requiring numerous and frequent exchanges between the partners.
DLR's major contribution is made under the NACOR (New Innovative Aircraft COnfigurations and Related issues) project, a joint and coordinated proposal between the French and German research centres. Since 1998, the strong partnership between ONERA and DLR integrates studies in the field of helicopters in a common research programme. Naturally, the helicopter part of the NACOR project benefits from these dynamics. DLR is a long-term research partner of Airbus Helicopters for enhancing knowledge and developing advanced methods and tools. This research strengthens Airbus Helicopters in the development of leading products. DLR's know-how and in particular the TAU flow solver software installed at Airbus Helicopters have been key in designing the Racer. This project is funded under the European Horizon 2020 Research and Innovation Programme (Project number: CS2-AlR-GAM-2014-2015-01).