ETRIOLLA designed and tested an elastic, natural laminar flow (NLF) transonic wing with active load control and alleviation systems. IBK coordinated the project and led model design and aeroelastic simulation.

ETRIOLLA (Experimental Transonic Investigations on Laminar Flow and Load Alleviation) was a Clean Sky Joint Undertaking (FP7) project dedicated to developing and testing a large-scale elastic NLF wing model under transonic and off-design conditions. The goal was to validate aerodynamic performance, laminar flow robustness and load control strategies for future “greener” aircraft configurations, supporting the ACARE 2020 vision for sustainable aviation.

Natural Laminar Flow (NLF) technology aims to maintain laminar boundary layer flow over as much of the wing surface as possible, minimizing drag and noise. Achieving this in realistic conditions requires both high Reynolds numbers and precise surface quality. To replicate flight-relevant aerodynamic behavior, the ETRIOLLA model was built at a scale of 1:3.05 with a span of 5.6 m, designed to operate at cruise Mach numbers (~0.74) in the ONERA S1 transonic wind tunnel (France).

Due to the extreme sensitivity of laminar flow to surface imperfections, the model’s aerodynamic surface was manufactured to exceptionally tight tolerances, and elastic deformation under aerodynamic load was intentionally included in the design process. The so-called “hot shape” design ensured that the model would achieve the correct aeroelastic twist under load, resulting in realistic flow conditions during testing.

To maximize test flexibility, the ETRIOLLA wing featured five remotely actuated movable devices, each equipped with real-time position and force sensing. These devices allowed optimization of Load Control & Alleviation (LC&A) settings during wind tunnel runs. IBK Innovation developed and validated these systems through a dedicated flap demonstrator in the company’s laboratory, simulating bending and torsion effects on the hinge mechanisms prior to model integration.

Parallel to the design and manufacturing, extensive aerodynamic and structural simulations were conducted to predict loads, deformations and dynamic behavior. Before the wind tunnel tests, the University of Bristol (UOB) performed static load and ground vibration tests (GVT) to verify stiffness and dynamic characteristics and to assess flutter and divergence safety.

• Project coordination and system-level management (2013–2016)
• Elastic NLF wind tunnel model design and simulation (2014–2015)
• Actuation demonstrator and lab validation of LC&A systems (2015)
• Successful transonic WT campaign and laminar flow validation at ONERA (2016)

• Funding body: Clean Sky Joint Undertaking (EU FP7)
• Grant number: 323460
• “This project has received funding from the Clean Sky Joint Undertaking under the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement No 323460.”

01/2013 – 12/2016

Phases: model design and actuation system development (2013–2014), manufacturing and validation

(2015), wind tunnel testing and optimization (2016).

• https://cordis.europa.eu/article/id/169963-realistic-nextgeneration-wing-model-for-testing/de
• https://cordis.europa.eu/project/id/323460
• https://www.onera.fr/fr
• https://www.bristol.ac.uk
• https://www.foi.se
• https://www.refraschini.it