In Rolls-Royce's vision of aviation's future, the entire market will shift to electric power for propulsion in ways that will disrupt business models and even the design of gas turbine engines. Says Rolls-Royce Electrical global head Mike Mekhiche: "It's not a matter of if. It's a matter of when. The entire aerospace business is going to be electrified."

R-R has given itself a front-row seat as the transformation unfolds. When the US Defense Advanced Projects Research Agency launched the (now cancelled) Aurora Flight Sciences XV-24A Lightning Strike programme, R-R supplied the AE1107 gas turbine used to power the electric motors for the turboelectric, unmanned air systems. When Airbus launched the E-FanX demonstrator last year to replace one of the four turbofan engines on a BAe 146 with a 2MW-propulsion system, R-R signed up to adapt the Siemens-supplied electric motor to the existing nacelle and supply a turbine engine to function as a gas generator.


The company plans to continue to be an active participant as the technology develops. In a recent presentation, Mekhiche showed an image of a new technology called the Embedded Electric Starter Generator (E2SG). Such a technology presents a bridging step between today's technology and an electric future. Using an Adour engine demonstrator, an R-R team installed a power-dense E2SG into the inhospitable core of a jet engine, converting the shaft power directly into electric power. By removing the need for a bleed-air offtake from the compressor to an accessory gearbox, installing the E2SG in a future engine is another step in the electrification of current aircraft systems, Mekhiche says.

"We’re looking at a variety of architectures and systems solutions," he says. “We’re looking into critical technologies: motors and batteries and most importantly the control system that allows us to optimise the power flow between the engine and the loads. The [E2SG] is one important programme. But it is not the only one."

R-R's vision of the future is one that it largely shares with its peers. GE Aviation has already revealed details of an aggressive push to develop new megawatt-class motors and electrical systems for future military and commercial aircraft. Pratt & Whitney has also disclosed a similar effort, including a demonstration of a large electric motor driven by a turbofan engine. Honeywell had signed up to supply the 1MW-class electric motor for the XV-24A, which was to be integrated with the R-R turboshaft engine to power that aircraft.

R-R has not yet released similar details of in-house demonstrations of megawatt-class electric motors and integrated hybrid-electric propulsion systems, but the company's vision for the technology seems consistent with a large investment in research and development. In addition to electrifying current aircraft power systems, Mekhiche sees three new classes of electric-powered air vehicles for transportation.

First, a new class of on-demand mobility platforms will provide intra-urban transports for one to four passengers seeking to avoid road traffic congestion. Aurora Flight Sciences has pledged to divert the XV-24A's distributed electric propulsion system to this emerging market, with a goal of fielding a commercial product as soon as 2023.

A second category in the market is 20-40-passenger commuter aircraft with relatively short ranges, Mekhiche says. "The opportunity there is to actually take away some of the business jet or regional jet market.… It is very possible and plausible that an electrified platform offers a much more attractive value proposition than, say, a business jet or regional jet," he says.

Finally, the large transport market is also a candidate for electrification, at least on large short-range trips with hybrid-electric propulsion systems.


In the largest category, the transition will be more gradual, but in many ways has already started. By introducing new technologies such as the E2SG, R-R can make today's gas-powered aircraft produce electricity more efficiently, which allows designers to convert more onboard systems to electric power. Another upgrade exists in the rotorcraft market, with small electric motors providing back-up power in short bursts during, for example, a situation with an engine failure.

The next stage of electrification is coming soon, as suggested by Airbus's plan to fly the E-FanX demonstrator in 2020. It uses a turboelectric propulsion system, with a gas turbine generating electricity for electric motors that provide the thrust. "Your propulsion and your engine are now connected only by cables. They are not connected to mechanical structures," Mekhiche says.

A key limitation of a turboelectric system is the absence of an integrated battery for energy storage, he adds. Pushing beyond a turboelectric system with integrated batteries opens new paths to improving overall fuel efficiency.

"We’re looking at what electrification [means] to the engine design," Mekhiche says. "How does the engine design change because it is now going to be part of an electric powerplant? That is extremely relevant… to understanding our value stream and how we operate going forward in this electrified market. When we started doing electrification of cars and heavy-duty vehicles, we realised a lot of benefits. But actually, it was not until we had engines that were designed to be optimised for an electric propulsion system that we were able to realise the full capability of that type of system."

In what is called a parallel hybrid architecture, R-R envisions packaging a gas turbine and batteries to deliver thrust to an electric motor. By augmenting electric power with batteries during take-off and step climbs, the propulsion supplier is able to reduce the maximum thrust rating for the gas turbine without sacrificing performance, he says.

"There's an entire paradigm shift around what the engine does and when does it do it and how that can be realized," Mekhiche says.

Source: Cirium Dashboard