During my research for the feature I've just written for Flight International on the greener engine technology under development in Europe's Clean Sky initiative, I was told more than once that the open rotor could be a game changer when it comes to reducing carbon dioxide emissions from aviation.
With the open rotor's ability to reduce CO2 emissions by up to 30% over today's commercial aircraft engines, it begs the question: Why is open rotor still such an open question?
Well, noise, for one thing. But Rolls-Royce tells me the wind tunnel tests it has carried out show that an open rotor engine "can be quieter than any engine flying today".
Size is another thing. They're big. Too big to be mounted on today's aircraft and with Airbus and Boeing remaining tight-lipped about their narrowbody replacement plans, it's anybody's guess as to whether the airframers will eventually design and build planes that can accommodate open rotor engines.
So, I'm afraid I'm no closer to answering the question posed in the title of this blog. Maybe one day engines like the open rotor CFM International is developing (pictured above) will be a common sight at airports. Or maybe they will continue to be a maybe.
PS - I now know more about thermal efficiency and bypass ratios than I ever did before, which should make me an interesting dinner party guest.