Maximizing aircraft fuel efficiency: Engines matter

Posted Tuesday, 8 August 2017, 16:31

Part 4 in a series featuring interviews with experts 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 highlight the potential fuel efficiency improvements 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.

“An aircraft without engines is a glider”, says professor Meyer (Mike) J. Benzakein, assistant vice president of aerospace and aviation research at Ohio State University.

We agree. No conversation about aircraft technology would be complete without discussing engine technologies, and no one has quite the experience that Dr. Benzakein has with the engine development. During his three-decades career with General Electric, he was responsible for the engineering development of CFM56—the most popular powerplant in civil aviation history —as well as the GE90 engine used in Boeing’s 777 family. We interviewed him on March 2, 2017, about the importance of developing fuel efficient engines. A transcript of our conversation is below, edited for length and clarity.

ICCT: This blog series focuses on the fuel efficiency potential of clean-sheet aircraft. But we don’t hear much about clean-sheet engines. Why not?

Mike Benzakein (MB): As a matter of fact, there are many more clean sheet engines than clean sheet aircraft. It goes this way: Normally, when Boeing makes a new airplane, we—GE, or Pratt & Whitney, or whoever—put new engines on. It seldom goes the other way. Let’s take Boeing right now. Boeing is doing an airplane that they call the Boeing 777x, and it’s a derivative airplane. But GE is going to put an engine on it and it’s a brand new, clean-sheet engine. Same experience with Airbus airplanes. If you look at today, the best example is the A320neo—you may have heard about it. The A320 is an airplane that was first put into service 25 years ago, and when they needed to really upgrade the line, guess what they did. They got the engine people to give them new, clean-sheet engines [(this one and this one)], and called it the A320neo: New Engine Option. So normally you do have many more clean-sheet designs for engines than airplanes.

ICCT: How are clean-sheet engines different than derivative engines?

MB: A derivative is normally taking an engine that you already have, and you decide to make, let’s say, a better fan. So I change one component of the engine and I improve the engine that way. Or you say okay, I’m going to put a new combustor for lower emissions, or I put a new turbine for better performance. That’s a derivative. A clean sheet is where, in principle, every part of the engine is new. It’s a much more expensive proposition. I mean, budget-wise today, derivative engines can cost between, let’s say, $100 million and $200 million, to develop. A brand-new engine costs more like $1 billion. So there’s a big difference. The engine people try not to make too many new clean-sheet engines.

ICCT: Other than demands from the airframe manufacturers, do other factors influence an engine manufacturer’s decision to create a new clean-sheet engine?

MB: It seldom does because I told you the price tag of a new engine. On the other hand, if we make an engine and we don’t have an airplane to put it on, it’s a waste of energy and money. So we normally respond to airframers. And they’re pushing us hard because they are normally in competition. So you have a Boeing airplane—let’s take the new 737 MAX, which is in competition with the A320neo. They both would like to have the best performance they can get so they can compete and get the majority of the sales. They’re going to do the best they can on their own but, on the other hand, it’s in their interest to get the latest and most efficient engines. They don’t care if it costs General Electric $100 million or $500 million to develop. They want to have something that will give them a bigger part of the market. It’s true on performance. It’s even true on thrust. You know, when you start a new airplane, the airframer tells you, for instance, “I will never need more than 100,000 pounds of thrust.” But as the airplane is developed, it gets heavier and it wants to go further. So guess what? All of a sudden, the 100,000 pounds of thrust they needed has become 120,000! And they don’t care whether the engine manufacturer has to make a new engine to do that. This is what the free market is all about—you need to be able to compete. And, honestly, for the engine manufacturers, while the ultimate customer is the airline, the internal customer is the airframer. So we need to do what the airframer wants—within reason, of course. We need to stay competitive. And both Airbus and Boeing, I talked about these two guys, are very good at it. They like to play one engine manufacturer versus the other in terms of performance, in terms of concessions, in terms of price, and so on.

ICCT: You were highly involved in the CFM56 engine development. What triggered the program?

MB: The world looked like it needed an engine with 20,000 pounds of thrust. Boeing wanted to do a new airplane, a derivative airplane beyond a 737 which was flying around as the 737-200 [and had a low bypass ratio engine]. They wanted to do a 737-300. At that moment McDonnell Douglas also needed a new engine for their DC-8s. And what happened is Pratt & Whitney, who at that time had cornered 75% to 80% of the commercial market, thought they could do that with a derivative engine, which is called a JT-8D ReFan. But Boeing wanted to have a new engine, and Pratt & Whitney started to develop one called a JT10D and decided they didn’t want to go through the investment into a new engine. They never thought that some little outfit called CFM that nobody knew anything about could come in and compete. In the meantime, between France and the United States, at a pretty high level, in fact—really at the president level of both countries, they decided to collaborate on a new engine. The reason we needed the presidents [of the nations] was because [GE] were using a military core, which goes inside of the F110 engine. So it was decided to cooperate and do a clean-sheet engine. And it was a real adventure because we had never worked together, so it was [a] learning [process]. The learning helped because it really became the strongest collaboration in the world.

ICCT: Let’s talk about open-rotor engines. It’s a technology that’s been in the works for a while but never went into service. Why is that?

MB: They’re too big. It never materialized, and honestly, I don’t know that it will. The open rotor is good for fuel efficiency—we all know that. It has some negatives on noise, and maybe you can really make up for a difference in noise, but they’re very big, and with the size comes drag and weight. And it’s very difficult to justify it. Now, you can say, “What happens when fuel price goes up?” Maybe there’d be more pressure to do that. There are the ways to compensate for that. We might talk about electric engines, for instance. Electrical propulsion is the wave of the future. I think open rotors are not. Some people are still working on open rotors, but I really don’t see them getting it to product for a long time.

ICCT: How long is a long time?

MB: Really, ever. I really mean it. I don’t see open rotor coming in. To put it in perspective, on a 737, the size of the rotors would be bigger than the GE90 thrust engines, which are huge for a small airplane. It’s a very big deal. The drag that goes with it is really very difficult to cover. Now, this is my opinion. The only thing that I can offer as proof—nobody did them. Nobody’s ever done them. If there were, they would put more effort into it.

ICCT: You mentioned electric propulsion—can you tell me more?

MB: To me, this is the future. It is the future because it can bring with it some real reductions in fuel burn. It’s not tomorrow, but, for larger planes, probably 20 years from now. And it’s more difficult to execute, but it’s real, and more and more people are working on both sides of the Atlantic—I should say that there are people working on the Pacific side also—but it’s probably mainly between the U.S. and Europe. It is on everybody’s agenda; it’s just a question of what it takes to get it done. For the same reason, there is a hybrid electric conference that takes place in Germany in the November time period in the last couple of years. You’ve got a thousand people going to these conferences. When you really look at it, what has happened on the ground… We have Tesla running around, and you look at how much the whole ground vehicles have electrified. We should be able to do it on airplanes. And it’s going to pay off. It’s more complicated than just putting batteries on, but it is what’s going to change.

Now, for very little airplanes, you’ll be able to use batteries. We call it an all-electric airplane, so you don’t put any fuel anywhere. It’s a Tesla. But then as you move to bigger airplanes, the ability of large batteries to power these airplanes is going to take… we cannot forecast how long it’s going to take. I’m serious about that. I was part of a National Academy study that took a year, and when we looked at what would be available 20 years from now, it still would not get a Gulfstream G150 business jet off the ground. So we need to rely on other things, which is what we call turbo[electric] propulsion, which really combines normal turboshafts with regular fans and really get very high bypass ratio. We’re looking at 20% to 25% in fuel burn by putting that on, which is much better than what we can do improving conventional engines.

ICCT: Electric propulsion aircraft does sound good. How do you think the government can take part in ensuring this technology flies in the not-so-distant future?

MB: There will be a push for fuel taxes. There will be a push for low-carbon. That’s the regulation part. And as for the technology itself, the government needs to support it financially by funding work, not necessarily at the universities alone, but into industry also. We talked about the GE90 engine, which was developed 20 years ago. It came from programs from NASA that were done 10 years or 15 years before that. So I think it takes the government to really support this effort. And it is being done today by NASA, primarily on the commercial side. NASA is putting a big facility west of Cleveland just to test electrical engines, and it’s a great investment. It’s ahead of time, which is great for a government facility, and it’s going to be a great play for a number of us.

ICCT: And what about the private sector?

MB: Obviously the private sector drives things. They all will be there and you know why? They’ll be there because they want to be number one. And they will not let somebody else win. Whether you talk about GE, Pratt & Whitney, Rolls Royce, everybody’s doing it. They’re in different things because nobody knows what exactly the solution is, so they’re all hedging their bets and doing some serious development, and they’re doing some of them with the aircraft manufacturers. All this is going to play itself out in the next ten years because by then, there will be a roadmap for what products you need when. We need them to drive, but we need the governments here, the governments in Europe, and we need the universities involved, too.


*Audio interview transcription by Stephen Naimoli

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