Modern civil aircraft intended for commercial air carriers must not only show high performance characteristics, but also be distinguished by low operating costs. When creating new samples of such equipment, the need to reduce all basic costs is taken into account, and new options for reducing the cost of maintenance and flights are constantly emerging. An interesting version of the liner, capable of showing special efficiency, was proposed this year by NASA and DLR organizations. A promising concept project is called eRay.
The US National Aeronautics and Space Administration (NASA) and the German Center for Aeronautics and Space (DLR) make significant contributions to the development of aviation in all major categories, including commercial aviation, which is responsible for transporting people and goods. The specialists of these organizations are constantly searching for new ideas, coming up with new proposals and testing them. In the summer of this year, the two organizations presented the concept of a promising aircraft capable of showing high performance characteristics with increased economic indicators.
The new project with the tentative title eRay was being worked out with a reserve for the future. When formulating the requirements for it, forecasts regarding the development of commercial aviation until 2045 were taken into account. Current forecasts show that by this time in developed and developing countries, passenger and freight traffic will grow significantly. In this regard, the development of the airfield network and the solution of various organizational issues will be required. In addition, new aviation technology with characteristic capabilities will be required to support transportation. In terms of its characteristics, it should surpass the existing samples.
NASA and DLR believe the commercial aircraft of the future should be 60% more economical than current ones. It should be able to operate at small aerodromes, as well as be characterized by reduced noise and ease of operation. In their research and report on it, the authors of the new project used the existing production aircraft Airbus A321-200 as a kind of reference. A promising eRay was supposed to have similar parameters of capacity and carrying capacity, but at the same time show advantages in all other areas.
The eRay concept is not yet intended for a full-fledged design with the subsequent launch of production and operation of equipment. In this regard, the specialists of scientific organizations were able not to limit themselves and use the most daring ideas, which are not yet ready for implementation in practice. It was the use of such solutions that made it possible to solve the assigned tasks and "create" a new version of the aircraft of the future.
According to the most optimistic forecasts, the eRay aircraft will be 30% lighter than the production A321. The efficiency of the power plant is increased by 48%. The overall energy efficiency of the board increases by 64%. It should be noted that in order to obtain such results, scientists and designers had to not only introduce new ideas, but also abandon their usual solutions. As a result, the proposed liner differs markedly from modern representatives of its class.
The eRay project proposes the construction of a cantilever low-wing aircraft with a swept wing. A tail unit is provided, including only a stabilizer with a large transverse V. There is no keel. In an original way, due to the need to improve efficiency, the problem of arranging the elements of the power plant was solved. Its individual units are placed in different parts of the wing, as well as in the tail of the fuselage.
The fuselage of the aircraft, in general, resembles the units of existing machines. The construction of an all-metal structure of high elongation with aerodynamic shape is proposed. The bow part is given under the cockpit and technical rooms, behind which there is a large salon with passenger seats. A volume for cargo is provided under the passenger compartment - first of all, for luggage. The tail compartment must accommodate one of the power plant engines.
It is proposed to dock swept planes with the fuselage. The wing obtains an optimal profile, and on most of its surface there are no elements that can disturb the flow. On the leading and trailing edges of the wing, mechanization of the traditional type is provided. At the ends, the designers placed a pair of by-pass turbojet engines with the necessary equipment.
Instead of the traditional empennage, the eRay project uses an unusual system. At the tail end of the fuselage, a conical annular channel is installed for the pushing propeller of the power plant. On the sides of this channel, the designers placed two stabilizer planes installed with a significant transverse V. There is no keel. Yaw control should be carried out by changing the thrust of the wing motors or by means of wing mechanization.
According to NASA and DLR calculations, three-quarters of the energy efficiency gains can be achieved only through aerodynamics. For example, 13% of the overall increase in efficiency is provided by laminar flow around the fuselage. Bringing the wingspan to 45 m gives an increase of another 6%. Abandoning the keel shortens the airframe surface, reducing air resistance.
However, the task of reducing the "extra" waste of energy is solved not only due to aerodynamics. So, the possibility of removing the side windows of the passenger compartment was considered. In this case, the design of the fuselage is greatly simplified, which leads to its lighter weight and a corresponding reduction in the requirements for the engines. However, such an innovation is not considered mandatory, since passengers may not like it. It is unlikely that a carrier wants to get energy efficiency, but be left without customers.
The eRay project envisages equipping the aircraft with a hybrid power plant. The wing should be equipped with turbojet engines that generate thrust from gases, as well as drive a pair of electric generators. Electricity through the necessary converters must be supplied to the batteries, as well as to the tail motor. The main advantage of such a power plant is the ability to flexibly change the general parameters of thrust to obtain the optimal fuel consumption corresponding to the current flight regime.
NASA and DLR see a pair of bypass turbojets as the basis for the power plant for eRay. Products with sufficient performance and reduced dimensions are proposed to be placed in the wingtips. Within the framework of the project, the application of engines with a system of heat exchangers, heating the incoming atmospheric air due to gases behind the turbine, was studied. In some modes, this allows you to reduce fuel consumption by 20%.
Experts from the two organizations reviewed existing electrical devices of the required types and made certain conclusions. It turned out that the existing generators, batteries and motors allow building a power plant for eRay, but its characteristics will be far from desired. To obtain optimal parameters, new technologies and solutions are required. In particular, the possibility of using the effect of superconductivity, which can affect the parameters of an electric motor, is being considered.
The existing storage batteries also do not allow creating an aircraft with the desired parameters. Technologies of 2010 level provide an energy density of the order of 335 W * h / kg. By 2040, this parameter is expected to grow to 2500 W * h / kg. However, in the short term, one has to rely on batteries with more modest characteristics of about 1500 W * h / kg. According to calculations, the combined power plant with electric and turbojet engines will provide a flight duration of at least 6-7 hours and a range of more than 6,000 km.
The report on the eRay concept project provides interesting figures showing the potential of such a technique. The designers calculated the main performance indicators of different equipment while solving the same problem. The A321 aircraft, when performing a "reference" flight at a range of 4,200 km, should consume a total of just under 84.5 MW of energy. To do this, he needs 15881 kg of fuel. The plane spends 2.36 liters of fuel to transport one passenger per 100 km. For the promising eRay aircraft, according to calculations, the total energy consumption reaches 39.57 MW - this is 5782 kg of fuel. To transport a passenger per 100 km, you need only 0.82 liters of fuel. Thus, under the given conditions, the promising machine turns out to be 65.3% more efficient than the serial model.
One of the ways to improve energy efficiency is to use the space in the passenger compartment wisely. NASA and DLR offer three options for the liner cockpit with different capacities. First of all, we consider the economy class cabin, created on the basis of the A321 cabin. In this case, the seats are installed in rows of 3 + 3 with a central aisle. In this configuration, the aircraft carries 200 people. In the Premium Economy configuration, the seating capacity is increased to 222 passengers, for which different seats are used and the distribution of available volumes is optimized. A variant with salons of three classes has also been worked out. Business class accommodates 8 seats, while Economy and Economy Slim seats 87 and 105 passengers, respectively.
In the proposed form, the eRay aircraft has a length of 43.7 m. The wingspan is 38 m in the basic configuration or 45 m in the advanced one, which gives some increase in energy efficiency. The weight of the empty aircraft is determined at 36.5 tons. The maximum take-off weight is 67 tons. The payload is about 25 tons, including 21 tons of passengers and 4 tons of luggage. Flight performance depends on the elements of the power plant used. In general, they should be at the level of existing models of commercial aviation.
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The eRay concept, unveiled this year by leading research organizations in the United States and Germany, is in fact another attempt to find ways to further develop passenger aviation. As rightly noted in the project report, in the future there will be new requirements for commercial aviation, and carriers will need new models of equipment with special capabilities. The search for solutions to this problem does not stop, and the eRay project once again offers original ideas of one kind or another.
In the NASA and DLR project, the main goals were to increase energy efficiency and improve aerodynamics, which should positively affect the overall efficiency of the aircraft. To obtain such characteristics, a special airframe design is proposed, combining well-mastered and new solutions, as well as an unusual hybrid power plant based on dissimilar components. Calculations show that the optimal consumption of fuel energy in combination with improved aerodynamics should increase both the flight and economic performance of the equipment.
However, so far all these results remain “on paper”. The eRay liner concept, like other developments of its kind, has a serious flaw, and its authors are well aware of this. At the present time and in the near future, designers will not be able to realize all the advantages of the proposed concept. Achievement of the set goals is hampered by the lack of necessary technologies. Thus, the idea of a turbojet engine with heat exchangers and power delivery to a generator needs further elaboration and practical testing. Batteries with the desired characteristics are not yet available, and the characteristic aerodynamic appearance of the aircraft must confirm its capabilities in the course of various studies.
The development of the technology required to build a real eRay aircraft is costly and time-consuming. The authors of the project are well aware of this, and therefore they are considering a promising aircraft in the context of aviation development in the next decades - up to 2040-45. They believe that by this time science will create the necessary components and conduct all the required research, which will allow the implementation of new concepts: either eRay or other projects.
The NASA / DLR eRay concept project - due to its specific purpose - cannot be considered a success or a failure. Its goal was to determine the paths for the development of civil commercial aviation and find the optimal design that meets the requirements of the future. Scientists and engineers of the two countries have carefully studied the current question and presented their own version of the answer. It is quite possible that in the late thirties, aircraft similar to the current eRay will actually take off. However, the development of aviation can go in other ways, and therefore future airliners will have similarities with other concepts of our time.
