LE BOURGET—French aerospace lab Onera has conducted further studies into its Gullhyver concept for an ultra-efficient airliner powered by hydrogen with strut-braced wing, open-fan engines and a wide-lifting fuselage.
Since hydrogen propulsion has lost momentum in the industry, Onera has focused on the open fan's noise and fuel efficiency, along with the integration of the strut and the wing. The open-fan architecture is a strong contender for future, more fuel-efficient propulsion systems, as CFM International's RISE demonstration program has gradually been convincing Airbus of the idea's relevance. Meanwhile, struts may enable higher-aspect ratio wings, reducing drag and thus also reducing fuel consumption.
“Because of the unducted configuration, noise is a major issue on an open fan engine,” says Philippe Beaumier, Onera's head of aeronautics. “So we performed more digital simulation to improve a fan blade's shape—such as changing their twist—for both quieter operations and better fuel efficiency. We factored in manufacturability.” While the noise reduction is unspecified, fuel efficiency was improved 2.5% compared to a 2023 reference design.
Meanwhile, the junction of the strut and the wing's surface has been a focus for Onera research engineers. The area may generate unwanted vortices, creating drag. Onera has thus found a shape for a smoother airflow, Beaumier says.
Under the Advanced Wing Maturation and Integration (AWATAR) project, Onera will use its low-speed F2 wind tunnel near Toulouse to test the aeroelastic behavior of the wing in 2026. The onset of flutter—an undesired vibration phenomenon in flight—on strut-braced, laminar-airflow wings has yet to be investigated, Beaumier says. AWATAR is part of Europe’s Clean Aviation public-private research program.
On June 13, RTX chief scientist Michael Winter challenged the relevance of the open fan concept, noting it can only degrade the performance of a wing designed for laminar airflow. “In any case, we are only counting on the outer part of the wing for the laminar airflow,” Beaumier replies. The modified Airbus A340 that served as a demonstrator in the Blade research and technology program in 2017 had only its outer wing modified for laminar airflow, he points out.
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