One of my favourite songs as a child was “It’s not easy being green” as sung by Kermit the Frog. Can you blame me? I was taller than everyone else in my class, including the teacher. I stood out like a sore thumb.
If you’re an engine manufacturer today, you just might find yourself humming that tune as you stare at the face of one very tall order - airlines want a new narrowbody aircraft that is ultra-fuel efficient, dramatically cuts emissions AND offers big gains in economics (and doesn't split your eardrums). Oh yes, and they’d like to have it in about seven years (some even earlier). It’s a lofty request. And even the biggest Boeing 737 operator in the world, Southwest Airlines, has expressed the difficulty that proposition entails.
“Some of these goals like super-low emissions and super-low noise and super-low NOx and super-low CO2 are diametrically opposed to each other when you get down to the basic chemistry and physics of it,” says Southwest senior director of engineering and maintenance programs Dale Stolzer, noting that “you can design an engine that’s fuel efficient, and lower NOx” but you will have to compromise elsewhere, such as on noise.
Southwest was one of the first carriers to call for the start of work on a new aircraft to counter the rising cost of fuel. I remember a luncheon in DC two years ago during which Southwest co-founder Herb Kelleher said Boeing should incorporate 787 technology into a new 737 design. Unlike other airlines that have shown open preference for open rotor engine technology, however, Southwest has been relatively quiet on this point.
Stolzer says that an ideal 737 replacement for Southwest would be a next generation narrowbody that offers the purported operational efficiencies over current designs but has “a common type rating” with the 737. Check out my article here.
Whether such a replacement will include open rotor technology remains to be seen. To be sure, engine makers are pushing ahead with new designs. During the recent Singapore Airshow, CFM International - the joint venture between Snecma and GE – reiterated that it is “actively pursing counter-rotating fan technology, as well as open rotor designs that build on the experience of the unducted fan from the late 1980s”. Two potential open rotor designs are being validated for an engine in the 25,000-pound (111 kN) thrust class that could provide a 35:1 bypass ratio.
I think Kermit would approve. As he says, green is “beautiful and I think it’s what I want to be”.