“Now we need to aim higher”

Professor Rolf Henke, Executive Board Member for Aeronautics Research at the German Aerospace Center (DLR), believes that large passenger aircraft powered by solar technology and electric motors are still a utopian dream. But he looks forward to more revolutionary ideas.

05.2015 | 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.

Professor Henke, the round-the-world flight by solar airplane Solar Impulse 2 has grabbed the public’s attention. Does the future of aviation lie in solar power?

Rolf Henke: It is certainly a fascinating project, for which, incidentally, DLR’s Institute of Aeroelasticity carried out ground vibration tests. But I can’t imagine that we will see commercial flights by solar-powered aircraft seating more than ten passengers any time in the foreseeable future. However, there is an area in which solar energy can be exploited, and that’s fuel production. This idea is already being worked on.

And what about electric motors—another widely debated subject?

Henke: In the road transportation sector, the initial enthusiasm for electric cars has cooled down somewhat, because the range of these vehicles is still too limited. In the aviation sector, electric motors could be an exciting option for two- to four-seat air­planes. Airbus has already developed the world’s first motor-assisted glider with a hybrid, serially distributed power system, in a joint project with Diamond Aircraft and Siemens, as well as the two-seater E-Fan electric aircraft. But it will take not just one but several new generations of battery technology to reach the point where electric motors can be used to power large passenger jets. To illustrate this point: The thrust generated by the GE90, deployed in the Boeing 777 and currently the world’s largest engine, corresponds to a power output of around 70 megawatts. This is equivalent to the total output of the largest privately operated solar park in the United States, which Apple plans to build in Arizona. Aircraft noise is another issue that needs to be considered when de­sign­ing electric aircraft, because the main source of engine noise is the fan, a com­po­nent that is also required in electric propulsion systems.

Here at DLR, we are researching ways of making greater use of electricity to deliver power to onboard de­vices. The More Electric Aircraft recuperates energy from the engine and transforms it into electricity that can then be used to power control de­vices for various subsystems which until now have been operated using hydraulic or pneumatic controls. Typical functions include moving the wing flaps or pumping hot air from the engine and directing it over the wings to prevent ice formation. Electrically operated systems consume less energy and their low weight helps to save fuel. I see this as a worthwhile development.

“Drastic improvements in noise reduction will be needed so as not to compromise public acceptance.”

Professor Rolf Henke, Executive Board Member for Aeronautics Research at the German Aerospace Center (DLR)

At DLR, you tie together the diverse areas of aerospace research in Germany. What are your current priorities with respect to aircraft design in general?

Henke: We conduct research into all aspects of the air transportation system, which can be divided into three main areas. The first concerns the environment, where we are studying the issues of noise reduction during takeoff and landing and fuel-efficient route planning. These modified procedures have an impact on our next area of re­search, which concerns aircraft design in general, from the overall design process to the integration of specific components. This in turn gives rise to new technological requirements, which are implemented in the third step—the development of new com­ponents, technologies and materials. DLR can develop all-round solutions to meet all needs of the aerospace sector by applying a holistic approach that forges links be­tween and within these individual areas.

Professor Rolf Henke A leading light in the German aviation industry

Prof. Rolf Henke has been responsible for aeronautics research as a member of the Executive Board of the German Aerospace Center (DLR) since November 2010. After studying aerospace engineering, he embarked on an impressive career path in science and industry. From the mid-1980s onward, he conducted research for Messerschmitt-Bölkow-Blohm (now Airbus Operations GmbH), specializing in laminar technology. From 1992 to 1998 he directed all Airbus programs in this field, before taking on re­spon­si­bility for managing the ADIF Adaptive Wing project. In 2000 he took responsibility for Airbus high-lift technology, and from 2002 onward additionally directed work on the EU’s AWIATOR (Aircraft Wing with Advanced Technology Operation) technology platform for wing development.

In 2006 he returned to his home region of Rhineland-Westphalia to take up a profes­sorship at RWTH Aachen University where he became head of the Institute of Aero­nautics and Astronautics (ILR). At RWTH, Henke established design, analysis and simu­lation facilities and built up a system for field measurements of aircraft noise. An en­thu­siastic teacher, he set up new courses in aircraft design and aircraft systems en­gin­eering, and has continued to lecture even now that he is a member of the DLR Executive Board. Since 2013 he has also served as chairman of the Deutsche Gesell­schaft für Luft- und Raumfahrt – Lilienthal-Oberth e.V. (DGLR), the scientific and technical umbrella organization and action and information forum for aerospace activities in Germany.

What areas offer the greatest prospects for advances in aerospace technology?

Henke: Progress comes from knowledge. For example, the better our understanding of the mechanisms that cause vortex trails, the more easily we will be able to calculate the required minimum distance between aircraft when leaving or approaching the run­way during takeoff and landing, which in turn will enable us to define more efficient and environmentally friendly flight control procedures. And the more we learn about the contrail-induced formation of cirrus clouds, the greater our knowledge concerning the impact of aviation on the global climate and the technical improvements needed to reduce these effects. Finally, it is obvious that a better understanding of the behavior of materials used in engine components will enable us to reduce engine weight and hence aircraft fuel consumption.

What is your realistic estimate of the reductions that can be achieved in CO2 emissions, fuel consumption, and noise levels in the near future?

Henke: The European aeronautics industry was the first to define fixed goals in its “Vision for 2020” published 15 years ago. 2020 is approaching fast, and we are well on the way to achieving a considerable number of these goals. Meanwhile, the original targets have been updated in the Flightpath 2050 initiative, in which DLR had a hand. Our aim is to reduce aircraft fuel consumption and CO2 emissions by 75 percent by 2050, compared with the 2000 baseline. Nitrogen oxide (NOx) emissions are to be re­duced by 90 percent and noise by 65 percent. In my opinion these are realistic tar­gets, provided the necessary efforts are made.

“Major advances also demand courage and above all determination, on a political level as well as on the part of companies.”

Professor Rolf Henke, Executive Board Member for Aeronautics Research at the German Aerospace Center (DLR)

You mention fuel, emissions, and noise: Which of these requires the most work?

Henke: Given the continuing growth in global air traffic, the issue that stands out is aircraft noise. Drastic improvements will be needed here so as not to compromise public acceptance. But there is also a need for action in a wide range of other areas. One of these is ground handling processes—which extend from transportation services to the airport to the flow management of passengers and cargo and maintenance ser­vices. Another important issue is the product lifecycle of aircraft. One of the Flight­path 2050 objectives concerns the recycling of aircraft. We are still a long way off from achieving this goal, especially in the case of modern aircraft in which more than half of their structural components are made of fiber-reinforced composites.

What drives progress in aviation?

Henke: As I see it, the days of simple solutions and quick progress are over. We have stripped the tree of all low-hanging fruit. Now we have to aim higher, for instance by developing innovative materials that will enable us to increase wing strength or by learn­ing more about stress and strain in engine components, which might enable us to reduce the number of engine stages. We also have to think about the resilience of the air transport system as a whole, to ensure that it doesn’t entirely collapse if a part of it fails. This was what happened in 2010, when the volcanic eruption in Iceland shut down all air traffic in Europe.

However, major advances also demand courage and above all determination, on a political level as well as on the part of companies.

What role does Germany’s research community play in this context?

Henke: It could play a central role. DLR is one of Europe’s largest research or­gan­izations, and its interdisciplinary approach to research provides the basis for assuming such a leading role. What is needed now is close collaboration between industry, gov­ern­ment and research, and the political will to take on this central role, in order to provide the technological system capability needed for the air transport system as a whole.

Do we have enough up-and-coming scientists and engineers to do this?

Henke: The decline in the birth rate in Germany is currently having more of an effect on the availability of skilled workers than on the number of engineers. University places in the relevant disciplines are still being filled, but that could change too. In­dus­trial companies will have to play their part, for instance by facilitating lifelong learning. It’s already rare today for someone to exercise the same profession for 40 years after completing their training or studies.

As I see it, experience is the most problematic issue. During my time at Airbus, I got to see the final development phase of the A320, then the work on the A330 and A340 as well as the A380 and the beginning of the A350 program. This most recent Airbus off­spring is now also already in scheduled service. If Airbus starts developing a com­plete­ly new aircraft in five or ten years’ time, it is possible that the people working on the project will never have done this sort of thing before, even though they left school or university 20 years before.

Will it always be necessary to invest so much time in developing new technologies to the point where they start earning money?

Henke: Yes, the development phase in the aviation industry will always be relatively long compared with other sectors. By the time a new engine or aircraft is placed in service, it will have gone through around ten years of design studies and development, and another five years to produce a prototype, including one or two years of flight test­ing. This requires billions of euros in up-front investments that will take years to amort­ize, owing to the relatively low number of units produced. But these investments are still very worthwhile, as can be seen from the manufacturers’ order books, which are full for many years ahead. Nonetheless, researchers are looking into ways of re­ducing development lead times and hence the level of investments. An example is the “Virtual Product” project currently in progress at DLR.

What effect does progress in space technology have on commercial aviation?

Henke: It has a huge effect. Just look at the Apollo program, where engineers and tech­ni­cians introduced systematic project management for the first time. Or the sat­ellites that provide support for air traffic control. One day in the very distant future, our descendants might fly in hypersonic aircraft, combining aviation and space travel. At DLR, researchers in aeronautics and space technology often work hand in hand.

You brought up the subject of hypersonic aircraft. What changes in air travel can we expect to see generally in the second half of this century?

Henke: For one thing it will hopefully be quieter, more comfortable and more sus­tain­able. There will probably also be an increase in the use of unmanned systems, for transporting cargo for instance. However, most of the changes in the foreseeable fu­ture will be evolutionary, not revolutionary. In the near future, I don’t see anything like a supersonic aircraft that can take you from Europe to the States and back on the same day—unless it is demanded (and paid for) by one of the new billionaires, that’s to say mega-businesses such as Google or Alibaba.

And what will change for me as a passenger in the next 40 years?

Henke: When I think back to my first flight in 1970, nothing much has changed from the passenger’s point of view. Airplanes are quieter, the cabins more comfortable, but the major technological developments in recent years with regard to fuel con­sump­tion, emissions, and maintenance processes don’t really affect the passengers on­board. One area where improvements could be made is ground handling pro­cesses­—such as all those time-consuming security checks. There is also plenty of room for improvement in the networking of different modes of transportation, for instance from road to rail and from there to the airplane. This calls for clever solutions—and the cour­age and determination to implement them.

German Aerospace Center (DLR)

  • The German Aerospace Center (DLR) is the national aeronautics and space research center of the Federal Republic of Germany. Approximately 8,000 employees work at its headquarters in Cologne and 15 other locations in Germany. DLR has its own flight facilities in Braunschweig and Oberpfaffenhofen near Munich.
  • Four offices in Brussels, Paris, Tokyo and Washington D.C. are responsible for or­gan­izing cooperative ventures with international partners.
  • DLR’s 32 institutes work on numerous projects concerning the future of aviation and spaceflight, and develop environmentally friendly technologies for applications in energy supply, mobility, communications and security.
  • DLR operates the largest civilian fleet of research airplanes and helicopters in Europe—ranging from the A320ATRA to the Cessna 208B and including one aircraft powered exclusively by fuel cells.
  • DLR has been given responsibility by the federal government for the coordination and implementation of the German space program, and also takes part in joint inter­nation­al missions.
  • DLR has a long history. Its earliest predecessor, the “Modellversuchsanstalt für Aero­dynamik der Motorluftschiff-Studiengesellschaft” (institute for aerodynamic model testing of the society of studies for motorized dirigibles), was created in Göttingen in 1907.
  • The German Aerospace Center in its present form was created in 1969, initially as the Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (German institute of aerospace research and testing, DFVLR), which brought together Germany’s hith­erto widely dispersed aeronautics and space research activities under one roof.
  • In 1997, this organization was merged with the Deutsche Agentur für Raum­fahrt­an­gelegen­heiten (German agency for space affairs, DARA), creating the German Aero­space Center (DLR) as it is today.

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