In the coming decades, new aircraft engines and production methods could make flying more sustainable. “Hybrid flying” using electrical energy has already begun and 3D printing promises higher efficiency and a cleaner production process. An article from Aloft - An Inflight Review.
It is less than a plan, but more than an idea. Engineers are envisaging how “hybrid flying” will propel a passenger aircraft in 2050. At takeoff and climb, the electricity from a gas turbine and from a battery will jointly power the turbine blades that provide the thrust. When cruising, the turbine alone secures the propulsion power, while simultaneously recharging the battery. In the first phase of descent, the turbine is turned off. The aircraft is now a glider and the power required for the onboard systems comes from the battery. During the second phase, the turbine blades are driven by the air stream and the electric motors turn into generators that again recharge the batteries. And finally for landing, the gas turbine is restarted and provides the thrust for the propulsion system at a low level, to assist the electrical landing process, if necessary.
This “hybrid flying” concept named E-Thrust, is part of a joint development by Airbus and Rolls-Royce. In collaboration with Cranfield University in the UK, the aircraft and the engine manufacturers have designed a completely new aircraft where the wings are set further back to the rear. The aircraft engine is integrated in the fuselage. Several electrically driven turbine blades, the fans, are on the wing roots. What is new is that turbines and fans are separated, enabling entirely new structures with optimization of both elements, and subsequently lower fuel consumption.
Power from gas turbine and batteries
The aerodynamic advantages are enormous compared to the turbines located under the wings that are currently used. The air flowing along the aircraft can be directed into the fans which benefits the thrust, instead of acting only as air resistance. If the peak power of an aircraft engine, which is presently only used at takeoff, is generated by both the gas turbine and batteries, the gas turbine can be significantly smaller than it is today. The aircraft will be quieter. In turn, less weight and less aerodynamic drag make it possible to reduce the size of the wings and tail unit, thus further reducing the weight and fuel consumption.
The list of reciprocal positive influences can be continued. However, the basic technologies that would enable this breakthrough are still lacking. This includes superconductivity that causes certain materials to lose their electrical resistance when they are cooled to temperatures well below minus 100 degrees Celsius. Motors and cables that transport the power of the turbines and batteries to the fans could be designed to be much lighter, smaller and more efficient. Cooling the components will then be the next challenge.
Moreover, what is commonly regarded as “better batteries” is still missing. This refers to a new generation of energy storage systems. Lithium-air batteries give rise to optimism since their energy density is more than twice as high as today’s storage systems. The aircraft and turbine manufacturers give their electrical engineering colleagues 25 years to develop the batteries to technical maturity. The amount of time the manufacturers will also need to adjust turbines, aircraft structure and aerodynamics.
The target year 2050 was not determined arbitrarily. The aviation industry has aligned its goals in environmental protection to this target, which they presented in 2011 to the European Commission in the report “Flightpath 2050 – Europe’s Vision for Aviation”. These objectives include a 75 per cent reduction of carbon emissions, a 90 per cent reduction of nitrogen oxides and a 65 per cent reduction of noise from aircraft. The basic parameters are similar to those announced by the aviation industry in its self-commitment in 2008.
A smaller aircraft, also based on a hybrid concept, is expected to be realised sooner than E-Thrust. By 2030, in less than 15 years, Airbus expects to have a regional traffic passenger jet for up to one hundred passengers ready for production.
There is still a long way to go. The machines could emerge from the small, all-electric training aircraft, which will be built in series under the name E-Fan 2.0 in the near future in southern France. It is to serve as a “proof of concept”, as a flying testbed and, a factor of enormous importance in aviation, as a model for the certification of electrical aircraft concepts. The additional engine in the fuselage of the follow-up model, 4.0, will increase the range significantly. The hybrid engine could also come from Germany. In April 2016, Airbus and the Siemens technology group agreed to develop a series of prototypes for different engine systems by 2020. Siemens has already created an electric motor for aircraft. With no change in weight, its performance has been increased fivefold within a few years.
One of the concepts of 2020 might be of relevance to the jet of 2030. But Airbus and Siemens could also work on hybrid helicopters, unmanned aerial vehicles with electric and hybrid engine systems, as well as drones. The two companies have already pooled 200 employees for this project; the investment in the next five years is expected to exceed 100 million euros.
Climate protection is not the sole concern at the centre of all this research and development. It is also about technological leadership in the global aircraft market, as the EU openly stated in its Flightpath report. With its regional jet, Airbus would enter a market in which two companies from the American continent are striving to become the world’s third largest aircraft manufacturer after Airbus and Boeing: Embraer from Brazil and Bombardier from Canada. Conversely, both are pushing heavily into the “higher” segment of short-haul aircraft that is dominated by Airbus and Boeing.
Yet another competitor has appeared on the scene – Comac from China, a state-owned enterprise founded in Shanghai in 2008. A twin-propeller regional jet, equipped with engines from General Electric, was delivered as early as 2015, and a Comac short-haul aircraft should be ready for serial production by the end of 2018. More-over, Comac and Bombardier signed a long-term cooperation agreement in 2011 to develop alternatives to Airbus and Boeing. In this dynamic environment, a technological leader in hybrid flying with regional and short-haul jets could keep a number of competitors at bay.
The electrical engineers working on today’s E-Fan two-seater are also focused on tomorrow’s 100-seater and the prospective 300-seater aircraft. And the same applies to process engineers. Specialising in carbon fiber composites, they have done a good part of their homework, as more than 50 per cent of the A350 consists of stable and lightweight CFRP. The next step is just around the corner. The use of 3D printers has also gained ground in the aviation industry. Manufacturing moulds has been eliminated and there is less material loss because cutting, turning and drilling have become unnecessary.
Airplane from 3D printer?
The days in which the common layer printers with their command of simple geometries stood in factory workshops are gone. Today, laser printers can create complex structures, for example, overhanging shapes. Acceleration of the process has been enormous. What previously took 15 hours to layer-print, can now be accomplished in two to three hours.
But once the production extends beyond prototypes and individual pieces, the calculation begins. Even if the method is resource efficient, if it only constitutes a technological stand-alone solution, the investment costs will be too high and the printing will not be cheaper than the previous methods. In order to optimise the use of the printer, more and more segments of the production process have to be aligned to it. Mechanical engineering last experienced such a development in the 1980s, when Computer Integrated Manufacturing (CIM) led to the end-to-end interconnections of entire design and manufacturing workflows.
A change of strategy at Airbus is already on the agenda. Until now, prefabricated parts and components were bought from suppliers. But the Airbus plant in Varel, in northern Germany, has already started printing its own components. In future, up to ten per cent of the components and spare parts will be produced on site in the facilities. There are even dreams of complete aircraft coming out of the printer. Select the model, specify the number of seats, press the button, and the next morning the rough body of the Airbus rolls out of the printing hangar.
The first steps have already been taken. Airbus has printed the first mini airplane “Thor” in Hamburg. Only the two electric engines and the steering controls are classical fixtures. The unmanned aerial vehicle, with a length and wingspan of four metres, is already being tested. It was assembled from nearly 50 parts because the largest printer available could only print pieces under 2.10 metres in length. The assembly took four to six weeks. But the industry is working on the development of more powerful systems. To enable the Airbus developers to become familiar with the technological possibilities, the group has bought a stake in the US car manufacturer, Local Motors, which is planning to print cars. Dozens of Airbus engineers are now being trained in 3D printing.
The “Thor” parts were melted from the powder of plastic polyamide. In the next two years they will be made from titanium, stainless steel and aluminum. In 2025, the first cargo plane could be printed. The rough body would still be assembled from individual parts, but maybe even that will change when the E-Thrust takes-off in 2050.