Maximizing aircraft fuel efficiency: Back to the drawing board

Part 2 in a series featuring interviews with members of the technical advisory group who worked with the ICCT on our cost assessment of near- and mid-term technologies to improve new aircraft fuel efficiency. The aim of the series is to illuminate the potential fuel-burn benefits of “clean-sheet” aircraft designs, to give a sense of how they influence the fuel efficiency trends in general, the risks that come with them, and, most importantly, what might be done to encourage them.

Dr. Juan Alonso, professor of aeronautics and astronautics at Stanford University, was one of the group of experts assembled by the International Civil Aviation Organization (ICAO) in 2010 to help that organization develop mid- and long-term fuel burn technology goals for aircraft designs. We turned to him for insights into why real-world aircraft fuel efficiency improvement fell short of those goals, and what can be done to get us closer to achieving them. We visited him in his office on February 15, 2017. Our conversation is captured in the video below. Some highlights:

As we’ve noted, there’s been limited improvement in aircraft fuel efficiency over the past 15 years, and one of the reasons is the lack of new technologies deployed on airplanes (02:07) and “clean sheet” design. Dr. Alonso gives an excellent explanation, with examples, of what a clean-sheet design aircraft is (04:40) and why they have the potential to achieve much larger improvements in fuel efficiency than derivatives of existing types (06:46). His nominee for the best clean-sheet design aircraft of all time: the Douglas DC-3 (07:45).

Starting at 09:22 the conversation turned to comparing the level of fuel efficiency improvement we see on cars and trucks with that of aircraft. The bottom line: while it is “probably not technologically possible to improve [aircraft fuel efficiency] at rates of eight percent per year,” the current rate of improvement—about one percent per year—is unacceptable and could be increased.

At 10:40 the discussion turns to predictions for the future: “radically new and different aircraft configurations,” not tube-and-wing architecture like all aircraft we fly in today, and much more integrated, to the point that the engines may be “embedded into the airframe.” Alonso also expects that we will see electric powerplants, and a combination of standard and alternative fuels (12:04). However, in the meantime, advanced propulsion, laminar flow technology and composite materials will become more common (12:52).

The role of government in advancing aircraft technology and efficiency is a key question. Dr. Alonso offered two answers: one, providing “the seed funding and carrying it to a point where industry can begin to see the value of that technology and introduce it into a product” (16:32); two, setting performance targets. “Judiciously, government institutions . . . have to set the bar high enough such that the standards . . . are forcing the adoption of some technologies in a responsible way” (17:22). (It comes as no surprise that he’s “disappointed” by the CO₂ standard that ICAO adopted [19:37]).

Finally, he left us with a piece of the puzzle: “The key is in ensuring that we can minimize the risk of introducing these technologies and that at the same time we could reduce the cost of putting these new technologies on aircraft. If we can figure out how to do those two things, we will find the rate of improvement of fuel burn in the commercial aircraft fleet accelerate, rather than decelerate in the next few years” (21:52).

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