The propeller is making a comeback in the pursuit of greener air travel

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 and France’s Safran, could burn 20% to 30% 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, Airbus and enginemakers such as Rolls-Royce Holdings Plc need to plow 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.<br/>