Joints in a helicopter structure.

Composite Materials, Joints, Strength

Airbus Helicopters Rapid And Cost-Effective Rotorcraft RACER (Source: Airbus Helicopters)

In the EU research project Clean Sky 2, Airbus Helicopters collaborates with international partners to develop an airworthy demonstrator of an exceptionally fast helicopter, called RACER. Fraunhofer LBF contributes to the Project Pre-Development Review by analyzing the strength of structural joints of the forward fuselage.

European collaboration

Within the Clean Sky 2 Joint Undertaking (JU), which is a major EU research project organized as a Public Private Partnership, one of the objectives is to realize the Rapid And Cost-Effective Rotorcraft (RACER) as a demonstrator of a novel high-speed helicopter. To this end, Airbus Helicopter coordinates development partners from all over Europe. The Project Pre-Development Review (PDVR) serves to assess the overall feasibility of the structural design and represents an important milestone of the development process.

Contribution to the Project Pre-Development Review

The high envisioned airspeed of the RACER results in increased aerodynamic loading of the fuselage structure. Additional loads may result from special events such as collisions with birds (bird-strike). As a contribution to the Project Pre-Development Review conducted by Airbus Helicopters, Fraunhofer LBF is tasked with assessing the general feasibility of the preliminary joint design of the forward fuselage with respect to these loads. Based on results of bird-strike simulations performed by colleagues of Fraunhofer EMI, LBF analyses the strength of the joints. Reaction loads resulting from the bird-strike as well as the aerodynamic pressure distribution on the surface are considered.

Specific modifications of the existing computational model are required to make the joint analysis possible. The loads transferred at the part interfaces which are designed as riveted joints are determined via Finite Element analysis. The shear- and tensile loads acting on the individual rivets are then derived using geometric transformations and subsequently compared to the Design Allowables for the respective materials and fasteners.

The joint-loads at all locations thus considered are below the allowable values. No critical stresses due to the scenario described above are identified. As an example, a more detailed analysis of a rivet joint on the right hand side of the fuselage considers the influence of local bending and demonstrates that no rivet pull-out is to be expected for the design concept under investigation.


In the EU research project Clean Sky 2 Airbus Helicopters is collaborating with international partners to develop and investigate an airworthy demonstrator of a new fast rotorcraft. Fraunhofer LBF contributes to the Project Pre-Development Review by evaluating the loading of structural joints in the forward fuselage region. None of the investigated joints is critically loaded according to the analysis.

Finite element analysis of the forward fuselage.

Finite element analysis of the forward fuselage.

Sponsors and partners

This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No AIR-GAM-2016-2017-05.

“As part of the Clean Sky 2 project, Airbus Helicopters together with partners within the European Union is researching ways to make helicopters more environmentally friendly and faster. The speed aspect, which is supposed to be up to 50% higher than in conventional helicopters, also provides a fresh challenge to the structure and design. Fraunhofer LBF’s excellent cooperation and timely results enabled us to review and protect the design concept of our helicopter. Thank you for the precise, fast and constructive support. We look forward to conducting joint research with you in the future.” Michael Wegmann, Airbus Helicopters Germany.