The future is geared

Dr. Frank Grauer, MTU’s Director Engineering Advanced Programs, talks about hot topics and the future at this year’s International Society of Air Breathing Engines (ISABE) conference, an opportunity for experts from around the world to discuss the field of air-breathing propulsion.

11.2017 | Text: Eleonore Fähling

Eleonore Fähling has been on the AEROREPORT editorial team since 2014 and in charge of the MTU employee magazine since 1999. As an aerospace journalist, she specializes in aviation history and market topics.


Dr. Grauer, you represented MTU Aero Engines as a keynote speaker at the 23rd ISABE conference in Manchester in September. What was your talk about?

Dr. Frank Grauer: My talk was about the fundamental challenges facing the aviation industry with respect to the ambitious targets set for 2050, and MTU’s strategy for helping achieve them. I am of course referring to our Claire roadmap, which stands for Clean Air Engine. I focused my attention on the period after 2030, because I wanted to highlight that we need to lay the technological foundations today.

Electric flight is a hot topic of conversation at the moment. But when you get into it, you quickly realize that the contribution electric propulsion systems make to achieving the 2050 climate goals will be modest, to say the least. It’s a question of coming up with alternatives. On the national and European level, there are a range of ideas out there as to how to optimize gas turbines to meet the 2050 targets. However, these ideas are not being marketed to the public as aggressively as electric flight. The reality is that bigger passenger aircraft are going to rely on gas turbines for a long time to come—either to power the aircraft or, if it proves an effective strategy, to generate electricity as part of a hybrid propulsion system. In other words, we’re still going to need air-breathing engines in 2050, and that means continuing to work on optimizing them.

With the world’s aero engine experts in research and industry all in one place for a whole week, what discussions did you have in the course of the events?

Grauer: Naturally we discussed a whole range of topics. Aside from electric flight, much of the discussion was about the same topics as are on the agenda here at MTU: digitalization, simulation in production and development, and additive manufacturing. The potential of ceramic matrix composites (CMCs) came up again and again. I was delighted to see many speakers describe the Geared Turbofan™ as an extremely innovative and leading solution. “The future is geared” is a phrase I heard many times.

Dr. Frank Grauer has been Director Engineering Advanced Programs for commercial and military propulsion systems at MTU Aero Engines since 2015. He joined MTU in 1999, working on ­various technology and development projects, including the TP400-D6 engine that powers the A400M. In 1998, he was awarded a doctorate from the Ruhr ­University Bochum for his work on active stability control in axial ­compressors.

Which of your colleagues’ talks and ideas were you the most excited about?

Grauer: Personally speaking, I was of course extremely excited to see how my MTU colleagues would get on. There were a total of three talks by other MTU representatives. The first explored the variable cycle engine with a focus on the factors to be taken into account in the preliminary design phase. Another presented a technique for factoring in erosion in the fan and compressor at an early stage of the design process. This is an important consideration if you want to think about the maintenance costs early on. And finally, the third presentation gave an excellent overview of the progress so far in the EU-sponsored ENOVAL project, which MTU coordinates. All three talks were delivered to a packed room and were followed by lively debate. Well executed and well received, in my opinion.

Apart from that, I found many of the keynotes interesting and they gave me an overview of what the competition is doing. I was struck by the fact that the excitement surrounding electric flight does seem to have receded a bit. People are slowly calming down and being realistic about the potential applications and timescale involved.

What else did I find interesting? Perhaps the fact that additive manufacturing is the term on everybody’s lips and that many people are realizing the potential offered by simulation in production. Then there were Airbus’s extremely innovative ideas for urban mobility, which have really caught the imagination. And Safran’s announcement that it will not be going ahead after all with its flight testing of the Open Rotor as part of Clean Sky as planned.

Another talk I found fascinating was EasyJet’s presentation on the airline’s selection process for the successor to the A320ceo. This was divided into two parts: First, the choice of aircraft between Boeing and Airbus, and then, once the decision had been taken to go with the A320 family, the engine selection process, which went in favor of the LEAP.

“For us, that means that we will continue to work with our partner Pratt & Whitney to improve the Geared Turbofan™. We want to work with aircraft manufacturers to achieve even better bypass ratios so that we can make more use of the theoretical advantages offered by the GTF concept.”

Dr. Frank Grauer, Director Engineering Advanced Programs for commercial and military propulsion systems at MTU Aero Engines

What engine technologies for the future are researchers exploring at the moment?

Grauer: If we’re talking about the next generation of aircraft, for instance a successor to the A320 around 2030, it’s primarily a case of making developments that build on current concepts. For us, that means that we will continue to work with our partner Pratt & Whitney to improve the Geared Turbofan™. We want to work with aircraft manufacturers to achieve even better bypass ratios so that we can make more use of the theoretical advantages offered by the GTF concept. Here, the way the engine is integrated into the aircraft plays a significant role.

As far as our competitors are concerned, they should see this as a sign that “the future is geared” and make their own efforts to embrace the GTF and gather their own experience in this area.

Dr. Frank Grauer Aircraft engines that are to meet the 2050 climate goals need revolutionary concepts, he says.

Composite Cycle Engine

Engines with a high bypass ratio are to connect modern turbo components with piston engines.

What about the period up to 2050?

Grauer: That’s still a very open question. Clearly, thinking is tending towards disruptive concepts that will improve engines’ thermal efficiency. Currently, there are a wide range of national and European projects examining and evaluating enhancements to cycle processes. One of the most popular concepts is what is known as a composite cycle engine, in which the thermodynamic cycle can be significantly optimized using an additional piston engine component. Incidentally, that idea can be traced back to an MTU patent and is currently being examined by numerous universities and research institutes.

All of these ideas give rise to the question of whether the potential that is undoubtedly there can be effectively harnessed. For instance, weight and reliability will always play a critical role in aviation. We are only in the early stages in this regard, and still need to come up with some good ideas. We are directly involved in the important studies so that we can fulfill our role as drivers of innovation in the aviation sector and, at the same time, identify future development trends and technology demands.

Video: Answers from MTU experts: Will we soon fly using electrical power only? Article with video

Answers from MTU experts: Will we soon fly using electrical power only?

Dr. Jörg Sieber provides his opinion on the matter: Will we soon fly using electrical power only? He furthermore touches upon hybrid-electric flying and the possibilities to further develop conventional gas turbines. To the video

What’s new with regard to electric engine concepts?

Grauer: It is becoming increasingly obvious that all-electric engines, that is to say fan engines powered solely by batteries, will remain, at best, restricted to small-scale applications and short-range journeys for the foreseeable future. These are exactly the applications being targeted by Airbus with its ideas for urban mobility, for instance.

As far as high-volume passenger flights are concerned, the community is focusing on turbo-electric systems. Here, a gas turbine generates electricity that is distributed to multiple fan engines around the aircraft via a smart system of on-board electronics. The key concern is the impact that this has on the whole. On the plus side, we can expect benefits resulting from boundary layer suction, improvements to wing aerodynamics, and even perhaps the omission of control surfaces. On the other hand, these sorts of systems add complexity and weight. It’s something we will have to look at in depth. We are working on these studies with a range of partners such as Airbus, Siemens, and Bauhaus Luftfahrt, for instance in the EU-sponsored CENTRELINE project, so that we can build on our understanding in this area and spot any trends at the earliest opportunity.

What does the industry need?

Grauer: Innovative and creative minds with the ability to develop key mainstream technologies such as heat-resistant, lightweight materials as well as industrialize new production techniques such as additive manufacturing. Expanding on simulation techniques is also a part of the puzzle.

Has the next generation’s time come, then, within the aero engine industry?

Grauer: Certainly, we have a lot of exciting topics for young engineers to get their teeth into. There is a huge opportunity for them over the coming years. After all, if we are to build aero engines that can meet the 2050 climate targets, we are going to have to move away from our traditional evolutionary approach and find completely new, revolutionary concepts.

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