The propeller – a relic of the early days of powered flight more than a century ago – is making a comeback as an emblem of aviation’s greener future.
Rotors are proliferating in futuristic air taxis and prototype airplanes powered by hydrogen and electricity. The old-school appeal is also key to a radical new engine that could one day replace the turbofans in today’s jets, as climate change pressures the industry to innovate its way out of reliance on fossil fuels.
This project, developed by General Electric Co. and France’s Safran SA, could burn 20% to 30% less fuel with similar or lower noise than its latest offering for single-aisle jets, executives say. They are trying to get the engine, with its giant spinning propellers, on work planes in the mid-2030s.
The inventive drive generates some dizzyingly expensive and consequential gambles for some of the most prominent companies in the industry. Boeing Co., Airbus SE and engine makers like Rolls-Royce Holdings need to invest billions of dollars in producing greener planes that will fly well beyond the 2040s.
But it remains unclear which technologies will provide the best way forward or when airlines will be ready to adopt them.
The financial cost of a misstep can last for decades – or even wipe out a company – as engineering hurdles and regulatory scrutiny loom as potential hurdles.
“I wouldn’t want to be president of Boeing or Airbus,” said Steve Udvar-Hazy, an aircraft leasing pioneer who has been one of the biggest buyers of both companies for decades. The challenges they face when trying to make the right decision about what will replace today’s technology “are probably the toughest they’ve faced in my career,” he said at a conference last month.
The futuristic concept of GE and Safran’s partnership, CFM International, features scimitar-like blades that rotate exposed outside the turbine. It eliminates the casing that is seen in the turbofan engines that currently power most commercial aircraft.
The so-called open fan design means engineers can install much larger blades, which improves fuel efficiency by accelerating more air through the fan section for thrust rather than through the fuel-burning center.
And unlike the piston-powered propeller planes of yore, these massive blades are powered by a high-tech turbine made from advanced materials that CFM says can run on biofuels or hydrogen.
While they unveiled the concept last year, executives from the partnership offered new details in interviews about how they worked to overcome key technical hurdles that plagued previous open-fan projects.
Using supercomputers installed in US Department of Energy research labs, GE Aerospace vice president of engineering Mohamed Ali says the company’s engineers have figured out how to solve the trade-offs between cruising speed, fuel efficiency and noise.
Initial flight tests are planned for the mid-decade, before CFM and Airbus will power an A380 superjumbo jet engine for additional demonstration flights before 2030.
If these tests are successful, analysts say CFM’s open fan design will be a serious contender to power the aircraft that will replace Boeing’s 737 Max and Airbus A320neo jets – the duopoly’s most important cash cows.
“Until now, each new engine family has been evolutionary,” said analyst Robert Spingarn of Melius Research. “These are revolutionaries.”
In Ali’s view, climate change leaves little choice but to pursue such a dramatic reinvention.
“Can we really leave this fuel-burning advantage on the table?” he said.
Of course, propeller planes never completely disappeared from the market, even after the modern jet ushered in faster travel decades ago. These aircraft have been a mainstay of short regional jumps, though they never come close to matching the sales and speed of the turbofan-powered jets that routinely transport hundreds of people across continents and oceans.
Meanwhile, propellers feature prominently in other efforts to greener air transport. Pratt & Whitney and Collins Aerospace plan to fly-test a hybrid-electric propulsion system on a regional propeller-driven aircraft in 2024.
As the auto industry turns decisively to electric vehicles, Boeing and Airbus are taking more cautious steps to decarbonize, such as replacing petroleum-derived kerosene with biofuels that can be burned by today’s jet engines.
Hydrogen-powered planes will likely not be ready for decades, and in the meantime, betting on designs that rely on open-fan engines is risky — not least because conventional turbofans also have room for powerful improvement.
“The modern turbofan is one of the most efficient power generators people have ever created,” said Brian Yutko, vice president and chief engineer of sustainability and future mobility at Boeing.
“If you take the duct off,” he said, referring to the protective cover on a jet engine, “you don’t absolve yourself of integration challenges — you have others.”
There are other obstacles as well, such as the likelihood that regulators will pay special attention to new aircraft.
Airbus, for example, was skeptical of open fan designs launched 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 could cost $15 billion – or much more if an innovative technology goes wrong. The potential of the CFM open fan motor is likely to be factored into planemakers’ high-risk plans.
Boeing and Airbus are already charting their strategies for the next decade, when they will need to replace their most profitable jets, which have designs dating back to the 1960s and 1980s.
Updated: October 22, 2022, 5am