Why GE thinks Dowty’s cutting-edge blade technology could lift RISE

UK propeller manufacturer’s expertise is seen as critical to informing design of open-fan demonstrator.

GE Aerospace has highlighted the growing involvement of UK subsidiary Dowty in the CFM International RISE open-fan technology demonstrator programme, with the propeller maker’s design and industrial know-how seen as increasingly critical to the effort.

Arjan Hegeman, vice-president of future flight engineering at the US propulsion specialist, says Dowty was recruited after it became apparent the open-fan architecture would need to draw on expertise from both the turboprop and turbofan worlds.

While the RISE’s compact core is essentially a classical turbofan based on GE’s existing turbine capabilities, “what we are adding in front of it is a turboprop”, he told journalists during a briefing at Dowty’s Gloucester, UK factory on 30 June.

In particular, as the roughly 4m (13ft)-diameter fan spins at around 1,000rpm – much slower than the 3,000-4,000rpm of a typical ducted fan – a different engineering approach is required.

“If you construct that slow-moving blade like we would do with a turbofan blade, you are not doing it right – you get a non-optimised solution,” says Hegeman.

Additionally, the requirement for variable-pitch blades also plays to Dowty’s traditional strengths, he says. “It is all built and designed on RISE on Dowty’s experience and Dowty’s legacy.”

Jonathan Chestney, technical director at Dowty, points to the firm’s long history of producing composite propeller blades since its first such product entered service on the Saab 340 in 1984.

“We are used to the open configuration while the broader CFM joint-venture has got all that turbofan experience.

“We are bringing the deep understanding of propeller technology to inform the open-fan design,” he says.

Besides the ability to make light, strong and reliable blades, Dowty’s expertise includes research into automated resin transfer moulding (RTM) technologies that will enable higher-rate production.

Chestney confirms that Dowty’s participation in the RISE effort has grown in recent years. “We are now making it a lot clearer about the influence we are having and how we are contributing,” he says.

Dowty has already performed initial tests of the blade-retention technology intended for the RISE, a system based on a long-running design incorporated on turboprop propellers.

“We are taking that fan element and making sure all the learnings we have had from the last 40 years can be applied to ensure we have a maintainable and effective system for the open-fan,” Chestney adds.

“As we move from the regional transport segment into the narrowbody space, reliability is going to be essential. This is the expertise we are providing to the broader CFM RISE programme.”

Dowty is not currently working on any active commercial aircraft programme – the mothballed De Havilland Canada Dash 8-400 is the most recent – but continues to build propellers for military types, notably the Lockheed Martin C-130J.

But should the RISE move from a demonstrator to a full production engine, incorporating Dowty into the industrial set-up would require a significant reallocation of workshare.

On the current Leap-series engines, CFM partner Safran Aircraft Engines is responsible for the entire low-pressure system including the fan and its RTM-produced fan blades.

Last June, Safran detailed testing it had performed on three different RTM fan-blade configurations for RISE as part of a French government-funded research and technology project. Evaluation of the blades has continued this year.

While Safran will likely build the blades for the initial demonstrator engine expected to fly in 2029, Hegeman hints that these could be swapped out for Dowty-produced parts if required.

But he stresses that at this stage the RISE is a demonstrator programme and no decision has been made to launch serial development or the industrial composition of such a product.

“GE and Safran are both involved in the demonstrator – it’s about combining the best of both companies,” he says.

Stung by the reliability issues experienced by all latest generation of turbofans including the Leap, CFM continues to promise that the RISE will offer better durability levels and consequently greater time-on-wing.

In fact, Hegeman argues that the better propulsive efficiency of the open-fan architecture versus a ducted configuration will allow it to lower stress on the core, running at a lower temperature, for instance, and improving longevity of hot-section parts.

“Now I have a stack that still far exceeds what a ducted fan can do – so I have better performance – but I also blow it away from a durability perspective.

“And if there’s one thing we have learned over the last years is that durability matters as much, if not more, than fuel efficiency.”

Hegeman concedes that although at the start of the RISE project “we were all on the fuel burn”, this has since shifted.

“We are getting more and more focussed on the durability and unlocking the advantages of this architecture.”

Despite promising “revolutionary” fuel-burn savings from the RISE engine, Hegeman insists the architecture is “nothing new”.

He points to GE’s development of its UDF demonstrator in the 1980s, allied to the maturity of the individual turboprop and turbofan elements.

“It looks very different, which can be perceived as ‘oh this is risky, it’s all new’, but it really isn’t.”