CFM International RISE

The CFM International RISE ("Revolutionary Innovation for Sustainable Engines") is an open rotor engine currently under development by CFM International, a 50–50 joint venture between American GE Aerospace and French Safran Aircraft Engines. The engine is planned to support both hydrogen and sustainable aviation fuels, and it plans to achieve a 20% reduction in fuel burn and in carbon dioxide emissions compared to its predecessors.

Background
The 1973 oil crisis increased oil prices in the 1970s, which caused engine manufacturers to research new technologies to reduce fuel burn, including open rotor (also known as propfan) engines. However, none of those designs made it to production aircraft, mostly due to decreasing oil prices and concerns over the high noise footprint of those engines.

Both Safran and GE Aviation had experimented with open rotor based engine designs in the years before the RISE project was announced. Safran had performed ground tests for an open rotor engine in 2019 as a part of the European Union's Clean Sky project, while GE had performed wind tunnel tests on a derivative of the GE36 engine at the start of the 2010s in collaboration with the Federal Aviation Administration.

Program announcement
CFM International announced the RISE program in June 2021 as an intended successor of the CFM LEAP turbofan engine, with plans to enter service in the mid-2030s. At the 2022 Farnborough Airshow in July of that year, CFM International and Airbus announced plans to start flight tests for the RISE engine on an Airbus A380-based testbed in 2026.

In June 2023, General Electric tested the first rotating components of the new engine, mating the first high-speed, low-pressure turbine stage to a GE F110 military test engine. As of late 2023, GE was producing test parts toward the goal of producing a demonstrator engine for flight testing. The demonstrator would pair an open fan set with a GE Passport gas generator.

Design
Unlike the GE36 and PW-Allison 578-DX contra-rotating engines that were proposed in the 1980s and Safran's open rotor engine in the 2010s, the RISE has only a single-stage open rotor. The open rotor stage is followed by a non-rotating stage of stator vanes. The two stages have variable pitch control. The RISE has a tractor configuration that pulls the aircraft into motion, unlike the pusher configuration of those other engines. The single-rotating design had previously been validated by the IRON project as part of the Clean Sky 2 program, and GE had dubbed the concept as the Unducted Single Fan (USF) engine. The fixed stator vanes vary their pitch to deswirl the flow, and they close almost completely together to act as an air brake, avoiding the need for a thrust reverser. The RISE will also use a recuperator, which captures waste heat from the exhaust gas to pre-heat the air that exits the compressor before it enters the combustor.

Applications

 * Boeing X-66A (planned)