Now open to all readers.
April 6, 2015, c. Leeham Co. The next 15 years may well be the last new airplane programs of major airliners that look like today’s tube-and-wing aircraft because demands for new efficiency will require go beyond what engines can do within a reasonable size, says Alan Epstein, VP of technology and environment at Pratt & Whitney.
Major changes to the airframe will have to provide added efficiency gains in combination with new and evolving technology from today’s engines.
The next new airplane, the so-called Middle of the Market (MOM) aircraft, will look like today’s airplanes. The next plane after that, the replacements for the Airbus A320 and Boeing 737 families, will probably be the last iterations of the planes of today. After that, new designs are likely to emerge, Epstein says.
Getting more efficiency from engines means the use of more advance materials, evolving and new technology but larger fans have traditionally been a key to gains. The 81 inch fan on PW’s Geared Turbo Fan on the A320neo is pushing the engine size on the single-aisle airplane in traditional configuration, Epstein says.
“It looks like you can get one more iteration at…taxi weight limits and longer landing gear. You could go for four engines,” Epstein says—an idea that is counter-intuitive to trends since the introduction of the Boeing 757 for high-performance, 3,500nm-4,000nm aircraft, intended to replace the three-engine, mid-range Boeing 727-200A.
(Lest Airbus and its supporters weigh in on the introduction of the A300 in 1974, we’re talking about single-aisle airplanes at this point.)
The idea of a four-engine single-aisle aircraft raises immediate questions about fuel burn and maintenance costs of four vs two. While our own analysis, with respect to the Airbus A380, concludes the four-engine maintenance cost perception is overblown, Epstein points out that if an airplane needs 80,000 lbs of thrust (for example), this may be achieved with two 40k or four 20k engines. Maintenance costs for four engines can be achieved for the price of two, he says.
Different fuselage shapes can provide dramatic gains in efficiency, Epstein says. A NASA concept of a “D” with the flat side on top, with engines mounted on the flat side, cuts 6%-10% in fuel usage from the fuselage alone because it “cancels the wake” generated by today’s aircraft.
Airbus has been quite public showing futuristic designs, Boeing less so. While Boeing liked to position the 787 as revolutionary when the design was first revealed, it was in fact more evolutionary—a major evolution, to be sure, but still an evolution. The concepts on the drawing boards will be the first revolutionary advance since the jump from pistons to jets and the creation of the Boeing 747. If Epstein is right, we could see the launch of the first of these within this generation.