Propeller is making a comeback as air travel seeks greener future

The old-school feature is central to a radical new engine that could replace turbofans on jetliners, as climate change pushes aviation to innovate

This handout computer-generated image released on September 21, 2020 by the European multinational aeronautics company Airbus shows a prototype of zero-emission hydrogen-powered aircraft. RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / AIRBUS" - NO MARKETING - NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS
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The propeller — a relic from the dawn of powered flight more than a century ago — is making a comeback as an emblem of aviation’s greener future.

Rotors are proliferating on futuristic air taxis and plane prototypes powered by hydrogen and electricity. The old-school feature is also central to a radical new engine that could one day replace the turbofans on today’s jetliners as climate change pushes the industry to innovate its way out of fossil fuel dependence.

That design, developed by General Electric Co. and France’s Safran SA, could burn 20 per cent to 30 per cent less fuel with similar or less noise than their latest offering for single-aisle jets, executives say. They’re angling to put the engine, with its giant whirling propellers, on workhorse planes by the mid-2030s.

The invention push makes for some dizzyingly expensive and consequential wagers for some of the sector’s most prominent companies. Boeing Co., Airbus SE and engine makers such as Rolls-Royce Holdings need to plough billions of dollars into producing more environmentally friendly planes that will fly well past the 2040s.

But it’s not clear yet which technologies will provide the best path forward, or when airlines will be ready to embrace them.

The financial toll of a misstep could linger for decades — or even wipe out a company — while engineering hurdles and regulatory scrutiny loom as potential roadblocks.

“I wouldn’t want to be a president of Boeing or Airbus,” said Steve Udvar-Hazy, the pioneer of aircraft leasing who’s been one of both companies’ biggest buyers for decades. The challenges they face in trying to make the right call about what will replace today’s technology “are probably the most difficult they’ve faced in my career,” he told a conference last month.

The futuristic concept from GE and Safran’s partnership, CFM International, features scimitar-like blades that spin exposed outside the turbine. It eliminates the casing that is seen on turbofan engines that currently power most commercial aircraft.

That so-called open-fan design means engineers can install much bigger blades, which improves fuel efficiency by accelerating more air through the fan section for thrust instead of through the fuel-burning centre.

And unlike piston-driven propeller planes of yore, those huge blades are driven by a high-tech turbine made with advanced materials that CFM says can run on biofuels or hydrogen.

While they unveiled the concept last year, executives of the partnership offered new details in interviews about how they’ve worked to overcome key technical hurdles that bedevilled earlier open-fan designs.

Using supercomputers housed in research labs at the US Department of Energy, GE Aerospace’s vice president of engineering Mohamed Ali says company engineers have unlocked how to resolve trade-offs between cruise speed, fuel efficiency and noise.

Initial flight tests are planned for mid-decade before CFM and Airbus rig the engine to an A380 superjumbo jet for additional demonstration flights before 2030.

If those trials are successful, analysts say CFM’s open-fan design will be a serious contender to power the aircraft that will eventually replace Boeing’s 737 Max and Airbus A320neo jetliners — the duopoly’s most important cash cows.

“Up until now, each new engine family has been evolutionary,” said analyst Robert Spingarn of Melius Research. “These are revolutionary.”

As Ali sees it, climate change leaves little choice but to pursue such dramatic reinvention.

“Can we really afford to leave that fuel-burn advantage on the table?” he said.

Of course, propeller planes have never completely vanished from the market, even after the modern jet ushered in faster travel decades ago. Such aircraft have been a mainstay of short, regional hops, though never coming close to matching the sales and speed of the turbofan-powered jets that routinely fly hundreds of people across continents and oceans.

Meanwhile, propellers figure prominently in other efforts to make air transport greener. Pratt & Whitney and Collins Aerospace plan to flight-test in 2024 a hybrid-electric propulsion system on a regional, propeller-driven aircraft.

An illustration of Sweden's Heart Aerospace's ES-30 electric-hybrid aircraft.  (Photo by Handout  /  Heart Aerospace  /  AFP)  /

While the car industry decisively pivots to electric vehicles, Boeing and Airbus are taking more cautious steps to decarbonise, like replacing petroleum-derived kerosene with biofuels that can be burnt by today’s jet engines.

Hydrogen-powered airliners likely won’t be ready for decades, and in the meantime, going all-in on designs that rely on open-fan engines is risky — not least because conventional turbofans also have room for powerful improvements.

“The modern turbofan is one of the most efficient power generators that people have ever created,” said Brian Yutko, vice president and chief engineer for sustainability and future mobility at Boeing.

“If you take the duct away,” he said, referring to a jet engine’s protective covering, “you don’t absolve yourselves of integration challenges — you have different ones.”

There are other obstacles, too, such as the likelihood that regulators would pay new aircraft special attention.

Airbus, for example, was sceptical of open-fan designs pitched by CFM about 15 years ago as it considered engines for what became the A320neo, people familiar with the matter said.

Developing a new aircraft can cost $15 billion — or far more if a groundbreaking technology goes awry. The potential of the CFM open-fan engine is likely to factor into plane makers’ high-stakes plans.

Boeing and Airbus are already plotting their strategies into the next decade, when they’ll need to replace their most profitable jets, which have designs that date to the 1960s and 1980s.

Updated: October 22, 2022, 5:00 AM
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