Thermoplastic sandwich structures as the key to sustainable rudders in aircraft construction

Fiber composite sandwich construction has been established in aircraft construction for decades and is used, among other applications, for control surfaces such as rudders. It enables extremely lightweight yet highly rigid structural components. Until now, however, almost exclusively thermoset fiber composites have been used in combination with honeycomb cores made of aramid folded paper forming a hexagonal core cell structure. These materials are complex to manufacture, heavily manual, and only recyclable to a limited extent. In view of rising production figures, stricter environmental requirements, and the need for greater automation, thermoplastic fiber composites are increasingly becoming the focus of research.

As part of the Airbus lead Horizon Europe "Clean Aviation" research and development project "Faster-H2", the "EcoRudder" project work package activity investigated the use of thermoplastic honeycomb core sandwich structures for the rudder of a typical commercial aircraft. "We wanted to show that thermoplastic sandwich structures are not only more sustainable, but can also meet the high mechanical requirements in aircraft construction," explains Dr.-Ing. Ralf Schlimper, project responsible at Fraunhofer IMWS. In the project consortium, the partners Fraunhofer IMWS, Airbus, Technical University of Denmark (DTU), and honeycomb core developer EconCore analyzed the use of a honeycomb core made of the high-temperature plastic PEI with a special hexagonal cell geometry. The honeycomb core is produced in a continuous process and combined with carbon fiber-reinforced thermoplastic cover layers. These pre-consolidated sandwich semi-finished products form the basis for further, highly productive component manufacturing.

Thermoplastic sandwich molding: forming, joining, and functional integration in a single process

The sandwich panels were further processed using the Thermoplastic Sandwich Molding Technology (TSM) developed at Fraunhofer IMWS. This technology enables thermoplastic sandwich structures to be formed three-dimensionally in a single-stage process while simultaneously creating functionally relevant areas in a targeted manner. In contrast to conventional manufacturing routes, which require several process steps and manual reworking, TSM allows for largely automated processing with short cycle times.

In the TSM process, the thermoplastic sandwich material is heated above the melting temperature of the matrix and then thermoformed three-dimensionally according to the component contour. The honeycomb core remains structurally intact in the load-bearing areas, so that the high stiffness and load-bearing capacity of the sandwich is retained. In defined edge and connection areas, however, the honeycomb core can be selectively melted down. In this way, tapered ramps, edge reinforcements, or solid zones can be integrated for later joining and fastening points – an essential prerequisite for use in complex aerospace structures such as rudder shells.

"The combination of continuously produced honeycomb core, thermoplastic cover layers, and sandwich thermoforming technology opens up completely new possibilities for automated and scalable production. Especially for aerospace sandwich parts, this is a decisive step toward economical and sustainable production processes," says Jochen Pflug, CEO of EconCore and ThermHex.

Demonstrator confirms potential

A prototype component segment of a rudder manufactured as part of the EcoRudder project demonstrates the potential of the developed technology. The demonstrator shows thermoplastic sandwich shells integrated into a segment of an original, load-bearing carbon fiber-reinforced plastic spar. As future aircraft programs require materials that combine lightweight construction, sustainability, and industrial manufacturability the project has provided important technological building blocks for this.

The prototype component segment was furthermore mechanically tested with realistic in-service loading with both bending and torsional loading cases, using a special multi-axial built test rig in DTU Structural Lab. Failure mechanisms of the thermoplastic rudder materials were additionally investigated thoroughly through an associated PhD project at DTU, where also resistance against impact damage was evaluated. Prof. Christian Berggreen at DTU says that “the new thermoplastic sandwich rudder concept showed throughout testing and analysis considerable potential for utilization in both rudders as well as in other aircraft control surfaces, when comparing the performance versus weight with traditional thermoset based sandwich configurations currently in use in the aircraft industry”.

The results of the research project and the demonstrator will be presented from March 10 to 12, 2026, at the JEC Composites Show at the EconCore (booth 6P108) and Fraunhofer IMWS (booth 5L142) exhibition stands. An in-depth technical exchange on novel composite sandwich technologies will take place at the Composite Sandwich Conference on May 5 and 6, 2026, in Halle (Saale).

The project FASTER-H2 (project number: 101101978) is supported by the Clean Aviation Joint Undertaking and its members. 

( February 26, 2026)