GE Aviation has broken a two-year silence on a major research project in hybrid electric propulsion with a new white paper that discloses several major advances demonstrated in two experiments since 2015 and that confirms the company is in talks with several potential aircraft makers about using the new technology.
Among traditional propulsion suppliers, Honeywell and Rolls-Royce have been most outspoken about efforts to develop new hybrid propulsion technology. Both companies have partnered to develop a 1MW-class hybrid propulsion system for the Aurora Flight Sciences XV-24A, a demonstrator for the US Defense Advanced Research Projects Agency.
But GE has been working quietly behind the scenes to build the foundational technology for a similar 1MW-sized powerplant with broad applications across military, commercial, business and general aviation markets, according to a white paper published by the company on 25 August.
During two events staged since 2015, GE demonstrated major advances in two key ingredients of any hybrid propulsion system: power generation and electric motors, the document shows.
In the area of power generation, GE modified an F110 engine, a propulsion option for the Boeing F-15 and Lockheed Martin F-16, to generate 1MW of electric power. By siphoning compressed air from the core, GE extracted 250kW from the high-pressure turbine and – in and industry first for a two-shaft engine – 750kW from the low-pressure turbine, according to the white paper.
As a megawatt of electric power is equivalent to 1,341hp, the F110 still has plenty of thrust to continue powering even in a single-engined aircraft. A single F110 can generate up to 32,000lb-thrust, which is equivalent to 44,300hp.
By extracting electric power from both modules of the turbine section, GE has created an architecture with a broad array of potential future applications, including military programmes with an interest in laser weapons.
After generating the electric power, GE also has demonstrated an advanced electric motor designed by the company’s research centre in a separate project, according to GE’s white paper. The 1MW motor drove a propeller designed by Dowty, another GE subsidiary. When coupled with a gas generator, such a hybrid propulsion system could produce the same thrust as a large version of the Pratt & Whitney Canada PT6A turboshaft engine.
The motor itself represents the state of the art in efficiently converting electricity into power. Whereas most aviation motors are designed to achieve 90% efficiency, the new motor demonstrated by GE is 98% efficient, the white paper claims. Importantly, such efficiency means a 1MW motor produces only 20kW of waste heat, rather than at least 100kW if a conventional aviation motor is used. GE has not revealed the size or weight of the device.
“With these two tests over the past two years, GE engineers have set a new benchmark for the aviation industry by extracting a megawatt of power from a modern jet engine while also generating thrust – and also by extracting a megawatt of power from an electric motor in order to drive a propeller,” the white paper says.
By comparison, the Boeing 787 uses six generators to produce a maximum load of 1.4MW of electric power, which the aircraft uses to provide power for de-icing the wing and engine nacelles and pressurising the cabin.
In the future, the aviation industry is contemplating the feasibility of hybrid-electric power systems for a broad range of aircraft, including up to about 150 seats. Airbus has outlined a technology roadmap that leads to a narrowbody-sized hybrid electric demonstrator in about 20 years. Meanwhile, Boeing has teamed up with JetBlue Technology Ventures to fund Zunum Aero, which is designing a hybrid-electric business aircraft and 50-seat regional jet to fly in the early 2020s.
“GE Aviation is currently engaging with several prospective companies on hybrid electric aircraft concepts,” the company says in the white paper.
Meanwhile, GE in 2013 opened a $51 million Electrical Power Integrated System Center (EpisCenter) in Dayton, Ohio. The facility is sized to test electric power systems ranging in size from 500kW to 2.5MW.
“This allows customers to transfer risk and cost to GE, while working to minimise both at entry into service,” the document says.