How will open fan engines stay safe from blade-out situations?
November 30, 2025
An engine blade-out situation occurs when one or more fan blades break away during operation. Whether resulting from a foreign object impact or metal fatigue, blade-out events can have a significant effect on flight safety.
A failed blade from an engine rotating at high speed must be contained to prevent structural damage to the aircraft. Unlike traditional engines, the open fan design poses greater design and safety challenges.
Fan blade containment issues on current and future turbofan designs
The constant pursuit of enhancing propulsive efficiency has pushed engine manufacturers to explore alternative designs and technologies. Fan blades on conventional turbofan engines are enclosed within a large duct, which serves as protection against failed blade events.
The containment casing is made of multiple layers of fiber mesh and epoxy, offering maximum impact strength and reliability. Removing the outer casing in the open fan design allows the installation of a much larger fan. However, researchers face a variety of design and operational challenges, including containment of failed blades.
Protection against breakaway events in the open fan design
Open fans are designed to rotate at considerably lower RPM than conventional ducted fans. GE Aerospace demonstrates that a modern large ducted engine fan achieves speeds greater than 2,500 RPM.
Conversely, an open fan design, such as the CFM RISE, achieves fan speeds in the range of 1,000 RPM, minimizing risks during blade separation events. The low-velocity, low-weight design of the open fan has approximately six times lower energy than comparable ducted fans.
Despite the extent of risk, the nacelle and fuselage areas around the fan are reinforced with high-strength materials for protection. The armouring used in fan cases on conventional ducted engines can be applied to the local area next to the engine in the open fan design.
The NASA Glenn Research Center and the Naval Air Warfare Center (NAWC) are collaborating with the FAA to design lightweight composite ply shields to protect against released blades during operation. In order to prevent breakaway blades from rupturing the fuselage, composite shields of varying thickness are tested.
Full-scale verification tests on a “simulated released” blade showed that it caused a large crack on the 24-ply composite test shield without penetration. The blade used for the test was similar in design, materials, and operating conditions (release velocity and angle) to that used for open rotor engines.
Testing of material technologies
Safran Aircraft Engines is testing a range of fan blade configurations to demonstrate the structural integrity of the open fan architecture. With over 175 ingestion and endurance tests conducted on the large-diameter fan blades, the manufacturer has recorded aerodynamic and acoustic improvements.
The VP Engineering and R&T for Safran Aircraft Engines, Pierre Cottenceau, stated,
“In the last few months, we have conducted numerous test campaigns with full-scale fan blades at our Villaroche facility. The highly promising results from these tests are enabling us to expand our technology portfolio and help define the next generation of engines in line with our decarbonization objectives.”
Moreover, wind tunnel tests on a scaled-down Open Fan model have shown impressive strength and durability during operation. Experimental analyses like these demonstrate the importance of shielding and reinforcement in the areas closer to the open fan engine.
Featured Image: NASA
