The aviation and aerospace industries have always been a place for innovation, constantly engineering better, more efficient technology. The Unducted Fan (UDF) or Propfan engine, is making a comeback after decades of suspension of the project.
First conceptualized in the 1970s, after a peak in fuel prices, UDF engines presented a revolutionary design, completely different from traditional jet engines (enclosed in a "case"). These engines had a distinct appearance due to the exposed fan blades, used in order to achieve fuel efficiency by combining the best of turboprop and turbofan technologies. However, the goal was not only to maximize fuel efficiency, but also to maintain the same capabilities of jet engines (speed and altitude) (Cross, 2022).
In the late 1980s, when fuel prices plummeted, priorities shifted away from fuel efficiency, leading to the shelving of promising UDF engine prototypes like the GE36 UDF, despite successful testing phases. The project was simply no more needed.
Fast forward to today, rising fuel prices and the urgent need for carbon emission reduction (Hemmerdinger, 2021) have re-directed interest back to Propfan engines. GE Aerospace, in collaboration with Safran Aircraft Engines (through their 50/50 joint company called "CFM"), introduced the latest prototype of UDF engines in 2021. This engine, named "Rise," promises a staggering 20% fuel savings compared to conventional turbojet engines (RISE - CFM International, 2023).
These groundbreaking engines have been showcased at industry events, like the famous "Paris Air Show" in the Le Bourget airport, and through partnerships with major aircraft manufacturers, like Airbus. CFM Rise aims to demonstrate a working prototype by the mid-2020s and ground tests and simulations are already underway.
The advantages of UDF engines lie, as previously mentioned, in their superior fuel efficiency, offering potential environmental benefits by reducing carbon emissions, which is a big concern in the aviation sector. These engines are also adaptable: they are mountable in various aircraft positions, and have a future for commercial airlines. However, noise emissions have been a concern with earlier UDF designs. Yet, manufacturers like CFM assure that the "Rise" engine is being rigorously tested to meet stringent noise emission standards.
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The return of UDF engines propels the aviation industry closer to its ambitious carbon reduction goals. While electric and hydrogen-powered aircraft are on the horizon, UDF engines present a crucial interim solution, enhancing fuel efficiency and potentially reducing emissions by up to 20%, as mentioned above. Moreover, as the aviation sector races towards achieving net-zero emissions by 2050, the return of unducted fan engines represents a significant step forward in propulsion technology. Their unmatched fuel efficiency could pave the way for revolutionizing future aircraft design and potentially ushering in a new era of eco-friendly aviation before the transition to new types of fuels and energies.
by Camilla Pasetti
Sources Cited:
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McFadden, C. (2023) 'Resurrected GE propfan offers a 20% boost to aircraft fuel efficiency,' Interesting Engineering, 19 June. https://interestingengineering.com/innovation/new-general-electric-propfan-engine (Accessed: December 9, 2023).
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Hemmerdinger, J. (2021) Cheap fuel killed propfan concepts decades ago. Can CFM’s revived concept endure? https://www.flightglobal.com/engines/cheap-fuel-killed-propfan-concepts-decades-ago-can-cfms-revived-concept-endure/144167.article (Accessed: December 12, 2023).
RISE - CFM International (2023). https://www.cfmaeroengines.com/rise/Â (Accessed: December 12, 2023).
Reed, J. and Reed, J. (2022) FADEC Alliance to provide electronic Control System for sustainable engine Demo. https://www.aviationtoday.com/2022/12/19/fadec-alliance-provide-electronic-control-system-sustainable-engine-demo/Â (Accessed: December 12, 2023).
Sweetman, B. (2013) 'The short, happy life of the prop-fan,' Smithsonian Magazine, 15 November. https://www.smithsonianmag.com/air-space-magazine/the-short-happy-life-of-the-prop-fan-7856180/Â (Accessed: December 12, 2023).
GE continues testing of Sub-Scale blade configurations for the open rotor engine | GE Aerospace (no date). https://www.geaerospace.com/press-release/other-news-information/ge-continues-testing-sub-scale-blade-configurations-open-rotor (Accessed: December 9, 2023).