Дата публикации: 09 ноября 2021
Автор(ы): Sergei CHERNYSHEV →
Публикатор: Научная библиотека Порталус
Рубрика: ТЕХНОЛОГИИ →
Источник: (c) Science in Russia, №4, 2013, C.52-58 →
Номер публикации: №1636448294
Sergei CHERNYSHEV, (c)
by Sergei CHERNYSHEV, RAS Corresponding Member, Executive Director of the Zhukovsky Central Aerohydrodynamic Institute (Zhukovsky, Moscow Region)
The evolutionary path passed by Russian aircraft engineering from the beginning of the past century up to this day allowed to form today the most optimal arrangement of civil aircraft representing a fuselage-tube with a wing and engines of a great degree of two-circuit state located mostly under it or in its tail part. However, it is well known to the world aviation community that the traditional approaches practically are used up. The rightful question now arises: What will flying machines be replaced by in future? What will they look like? What engines will set them in motion and what fuel will they use? What materials will be used for their manufacture? It seems a very curious task to try to peep into the future and answer these and some other questions. Aviation science is the most appropriate candidate to accomplish this task as it is just working for long perspective in the system of aircraft industry thus creating research and technology for future generations of aircraft engineering.
Comparison of classical and supercritical wing profiles.
DAYS TO COME: WHAT HAVE THEY IN STORE FOR US?
In 2012, the Central Aerohydrodynamic Institute (TsAGI)* together with other leading institutes of aircraft industry implemented the project "Foresight of Aeronautical Science and Technologies" by order of the RF Ministry of Industry and Trade to forecast technological development of aircraft engineering up to 2030 with account of what the world and national civil aviation will meet in that period. The project involved about a hundred of experts from the TsAGI, the Baranov Central Institute of Aircraft Motor Engineering, the All-Russia Research Institute of Aviation Materials, the State Research Institute of Aviation Systems and other organizations. Let's have a brief look at findings of this research.
Considering the following twenty years the specialists forecast roughly twofold increase of air transportation volume in the world: in 2011 it made up 5.1 trln passenger-kilometers and by 2030 it can reach and even exceed 12 trln passenger-kilometers. Accordingly, the world aircraft park will also increase though disproportionately, i.e. not twofold but slightly less as the share of more spacious aircraft will increase.
By estimates of the American Boeing Corporation the world park of commercial aircraft with turbojet engines
* See: S. Chemyshev, "The Center of Aviation Science", Science in Russia, No. 6, 2008.--Ed.
will increase from 19,410 aircraft in 2010 to 33,500 in 2030. As the lifetime of civil aircraft technical equipment is long, 20 years and more, the future park will include mainly aircraft today already considered modern and supplied to the market (A320, Boeing 737, the national Sukhoi Superjet and others) and also aircraft entering the market in the next few years (A320Neo, Boeing 737MAX, Russian MS-21, etc).
But 20 years is quite a long period in which minimum one or two new generations of airliners can appear. After all, it is commonly acknowledged that from the time of appearance of civil jet aircraft already five generations of them were built in the world. What will future flying machines look like?* The "Foresight" project will answer this question.
It is well-known, civil aircraft technical equipment develops always under in fluence of priorities, tendencies and restrictions topical for each period of time. In the first years of its existence the main task was improvement of aircraft characteristics such as speed, flying range and passenger capacity. With a rise in air transportation volume, the problems of flight safety became an unconditional priority, and since then they are of primary importance. Promotion of flight safety was proclaimed as a main target by the International Civil Aviation Organization (ICAO) established in 1944.
* See: V. Klimov, D. Ganeev, "'Integrated Circuit' Aircraft", Science in Russia, No. 2, 2008.--Ed.
In the 1950s the world aviation community took care of negative action of civil aviation on the environment first due to increasing noise level and later because of emission of harmful agents in airport areas. When discussions on global warming started in the world, attention was drawn to greenhouse gas emissions (first of all CO2) produced by aircraft. These tendencies are eventually formalized in the ICAO standards to be observed by all its 190 member-states. For example, the standards of air ecology have alreadybeen toughened four times. The last amendment was made in February of this year in view of introduction of the new noise standards. ICAO prepares also CO2 emission limitations. After the terrorist acts in the USA on September 11, 2001, the problems of aviation safety, i.e. protection of civil aircraft from unauthorized intervention by third parties, acquire quite a different meaning.
What priorities will determine the trend of civil aviation development in the coming decades? Let's emphasize two of them.
To begin with, flight safety remains a major task as before. Statistically the aircraft is most reliable mode of transport, and today on average about four air accidents fall on 1 mln regular flights in the world. As statistically only each twentieth of them is an air accident (i.e. fatal accidents) we can conclude: on the Earth one such accident falls on every 5 mln flights. But due to the expected twofold rise in air transportation volume in the future, the number of plane crashes will increase twofold in the next 20 years if no measures to improve flight safety are taken. Of course, this cannot be tolerated. Therefore, the aviation community faces a task at least to prevent degradation of the relative figures of passenger safety and in practice to improve them materially. For example, Europe, one of the most successful regions of the world in this respect, is eager to reach a situation when not more than 1 air accident per 10 mln regular flights will take place by 2050.
The second most important are ecological aspects of civil aviation, which cover not only aircraft exploitation but also the whole life cycle, from manufacture to utilization. Apart from the problems connected with noise and emissions, attention must be paid to the issue of global warming which the countries handle at the level of the United Nations Organization. ICAO as a UN agency also participates in this process. Though we should stress that carbon dioxide emissions of the world civil aviation makes only 2 percent of the total amount of anthropogenic emissions of this substance. However, in case of aviation such emissions take place at a high altitude where climate is formed.
The Western aviation community set a goal: by 2020 to reach the so-called carbon-neutral growth (i.e. maintenance of permanent CO2 emissions despite the passenger transportation growth) and by 2050 to reduce emissions twofold as compared to the level of 2005. Thus, the West places primary emphasis upon use of biofuels apart from upgrading the aircraft and their engines. It is planned in Europe that by 2050 the technological progress will allow 75 percent reduction of carbon dioxide emissions per a passenger-kilometer and 90 percent reduction of nitrogen oxides (NOx). Aircraft noise will decrease by 65 percent. All these improvements relate to the level of a standard new aircraft of 2000. Another leading world aircraft manufacturer, the USA, has similar targets.
Russia, still as a catching up country in civil aviation has to take account of the said plans to provide competitiveness of the national civil aircraft and their compliance with the advanced tight standards.
NONTRADITIONAL ARRANGEMENT OF FLYING MACHINES
Today the traditional arrangement of aircraft has already reached a level of perfection (aerodynamic quality makes 18-20 units), and any essential advance is possible only in cast of consideration of new configurations. Special advantages can be obtained by location of engines in the fuselage upper part. Ecological problems such as reduction of the noise level are a main motivation. The arrangement of aircraft with engines located above wings is also under consideration. After all, this idea is not new because there are such national airplanes An-72 and Be-200, which provides advantages at the expense of the supercirculation effect and some noise screening. There is also a variant of noise screening by elements of a horizontal tail assembly. Besides, aircraft models are studied, in which the engine is deeply integrated with an airframe. The question is the so-called concept of a distributed power unit when the engine's cold loop is separated from the hot loop and spaced physically, which provides an essential increase in the two-circuit power without an increase in engine sizes and thus achieve reduction of fuel consumption.
Departure from the classical models can take place in the design of subsonic aircraft of subsequent generations. Specialists pay special attention to studies of a nontraditional arrangement of flying machines whose main principle is connected with processes of integration. The latter can take place in respect of the wing (model "flying wing") or fuselage (model "bearing fuselage").
The "flying wing" possesses an increased aerodynamical quality, which can reach 22-25 units. Besides, such an arrangement allows screening of the noise of engines located on the upper surface of the "flying wing" near the trailing edge. Thus, a wider passenger compartment, as compared with the classical one, is realized, which increases the number of longitudinal aisles and improves comfort for passengers.
The model "bearing fuselage", which creates itself a certain lifting force, also provides arrangement of a
wider passenger compartment and realization of the noise screening effect if engines are installed on the upper surface of the fuselage tail part. Such model can allow manufacture of the aircraft of a regional class with practically straight laminar wing.
The aircraft models with an articulated wing can also possess certain positive properties. Under the acceptable weight limitations they allow a marked increase in a wing span, which decreases the induced drag* of a flying machine.
The problem of transfer to alternate fuel becomes more topical for the air transport. The pollution-free liquid-hydrogen fuel is the most radical step in this regard. Certainly, its use will cause an essential change in aircraft look. The fact is that location of low density hydrogen fuel will require capacious cryogenic (isolated) tanks installed, for instance, on an upper part of the fuselage. The powerful coolant unit aboard will open an opportunity for implementation of technologies to reduce aerodynamic drag. Another direction of ultralow temperatures (20-60 °K) application implies introduction of electric motors using a superconductivity effect for a helical blower drive installed in the fuselage tail part.
Specialists consider also nontraditional arrangement for advanced transport airliners. For example, they study the layout of a twin-fuselage aircraft. It will allow essential reduction of the construction weight.
* Induced drag is an effect of the lifting force formation on an airfoil of finite span. It is a part of aerodynamic drag of an airfoil of finite span.--Ed.
In 2003, the exploitation of the famous British-French "Concord" airliner stopped, which along with the Russian Tu-144 was a representative of the first generation of supersonic passenger aircraft. These aircraft were turned down due to economy considerations (supersonic flights are more expensive than subsonic ones) and also the problems related to acoustic impact. But this class of vehicles keeps being attractive in the market. Since then scientists are well ahead on the road of reducing acoustic impact. Designs of supersonic aircraft of about 50 t mass were elaborated to reduce the said negative factor to acceptable values. At present studies of 100 t supersonic airliners is under way. It can be expected that provided the appropriate ecological standards are adopted, aircraft industry will tackle to creation of supersonic aircraft of the second generation.
Modern turbo fan engines have also reached a high level of technical perfection. The modern aircraft for transportation of one passenger for a distance of 100 km consume about 2-3 kg of fuel, which is comparable with motor transport. But it should be noted that further upgrading of the engines under consideration within the traditional arrangement is connected with increasing difficulties against relatively modest results. Therefore, designers pay more attention to power units of a nontraditional structural layout such as turbopropfan engines ("open rotor") with birotating propeller fans*, engines
* Birotating fans--use of two fans rotating in opposite directions, which increases engine efficiency and decreases the noise level.--Ed.
Share of composite materials in airframe weight.
of complex thermodynamic cycles, etc. Transfer to similar types of engines can secure marked improvement of aircraft performance indicators.
NEW MATERIALS AND STRUCTURES
Development of aircraft structures always kept pace with the development of new materials, which enabled specialists to create more efficient, strong and light aerodynamical structures. Like the appearance of durable and light aluminum alloys in the 1920s caused revolution in aircraft engineering, today also we witness radical changes, which are connected with wider use of composite materials (CM). Further upgrading of air transport efficiency is connected now both in foreign countries and Russia with introduction of new fiber CM with high specific strength characteristics in the airframe power to structure.
Already 40 years ago CM were introduced first into aircraft nonpower structures such as hatches, breechblocks, cowlings, etc. and later their sphere of application was spread to elements bearing loads. After many years of research and learning CM were used in critical power structures of fin assembly, wing and fuselage with a total volume of their application in the airframe up to 40-60 percent. The volume of CM application in the airframe of foreign and national civil aircraft was ever-increasing over the years. For example, if in national air liners of the previous generation (Tu-204 and 11-96) CM made up less than 10 percent of the airframe weight, in the modern aircraft Sukhoi Superjet they reach already 14 percent, and in the brand-new Russian aircraft MS-21 their share will exceed 37 percent.
The composite wing realized on MS-21 is an example of the potential CM possess. At the expense of laying of CM layers in the wing for the most efficient perception of design loads it became possible to increase the wing aspect ratio. It is a cumbersome process in case of a metal wing as its end part due to the large-span wing begins to excessively vibrate and intricatoly resist the flutter phenomenon. The wing aspect ratio of MS-21 is about 10 percent more than that of the modern A320, and respectively the fuel consumption is about 10 percent less.
Composite materials allow implementation of brand-new structural power patterns also for the fuselage. We have launched work on application of grid composite structures for this part of the aircraft. The weight reduction factor plays an important role here. For example, application of the respective grid structure for rockets allows to reduce the weight by 25-40 percent and for civil aircraft, as expected, by 15-20 percent.
In distant perspective new materials can help pursue a long-standing dream of aircraft manufacturers about the so-called morphous (or adaptive) aircraft, which changes its shape depending on regimes of flow.
It is no secret that the arrangement of modern civil aircraft is a compromise between different regimes and is oriented to a cruising flight. The high-lift devices are used for securing safe speeds on takeoff and landing. By way of development of systems of mechanization the scientists consider the variants of "seamless" smooth mechanization of the front and rear edges and even the jet flap system, where control is effected at the expense of blowing-out of high energy jets.
The designers are trying to find possibilities of optimal control of aircraft forms so that the latter accommo-
dates itself continuously to the flight regimes like a bird, for example, by using an adaptive wing, in which the form of a profile and a wing changes in plan.
Such attempt gave rise to a variable swept wing already used in aircraft engineering, for example, in the national fighter MIG-23. It is true that in this case the wing structure was heavy and complex. New materials and structures made of them can open up possibilities unknown before to aircraft engineers.
Another perspective line of aircraft aerodynamic perfection is airflow control (its laminarization), which will reduce essentially friction resistance and increase flight lift-drag ratio. Considered are both passive variants, requiring no extra energy and also active ones, for example, the boundary layer suction/blowing-out and plasma discharge influence.
COMMON AIRCRAFT EQUIPMENT
The main development trends of aeroplane equipment consist in turning down of hydraulic systems as main energy carriers and further development of integrated modular avionics*. The world aircraft engineering implements the concept of a "more electrical" or "fully electrical" aircraft, promising weight loss, simplification of maintenance and reliability improvement. All drives and boosters** in such aircraft will be electrical, and aircraft will be controlled by electrical signals. Such system can be easily transferred to a fully automated regime.
The crew error in flight has to be ruled out in the air transport of the future. This means that automated control systems will play increasingly important role. The so-called "clever board" will become a practice, which will accept control responsibility, and the crew role will be to observe and insure the work of automatic machines.
AIR TRAFFIC MANAGEMENT
Aircraft is a part of a large air transport system, in which air traffic management is the most important component. As we noted above, the air transport flow would increase many times in the following decades. For example, by 2050 in Europe up to 25 mln commercial air flights will be carried out annually as com-
* Avionics (from aviation and electronics) is a set of radioelectronic systems designed for application as airborne radioelectronics.--Ed.
** Booster is an element of a system (in aviation) which allows operation of control blades, ailerons, propellers and other airborne equipment without great efforts.--Ed.
pared with 9.4 mln flights in 2011. Under the circumstances, the world system of air transport will face revolutionary changes connected with introduction of new management technologies, which should be supported by on-board and ground structures. In particular, such technologies will include transfer to trajectories of the four-dimensional format (4-D) with the accuracy of penetration to the specified space point within several minutes.
In conclusion we must point out that in December of 2012 the Russian government adopted the program "Development of Aircraft Industry for 2013-2025". It will become a basis for economic support of national aircraft engineering for more than a decade. This program includes several subprograms including aircraft manufacture, helicopter industry, aircraft engine-building, aircraft instrument making, small-scale aviation, aeronautical science and technologies.
With reference to the subprogram devoted to aeronautical science and technologies one may note with satisfaction that in recent years the government has allocated again for aeronautical science considerable funds comparable with amounts of financing of aeronautical research organizations in such countries as Germany and France. It is reasonable to expect that the said funds will result in significant scientific findings securing creation of a new competitive national aircraft engineering. This subprogram envisages drawing up of a "National Plan of Scientific and Technological Development in Aircraft Engineering for a Period Until 2025 and Future Trends". The plan will become a long-term research program for aeronautical research institutes in cooperation with design offices of the industry, institutes of the Russian Academy of Sciences and higher educational institutions. It will be directed to the elaboration and perfection of breakthrough technologies, which will become a guarantee of progress in aircraft engineering and secure competitiveness of national aircraft equipment.
Опубликовано на Порталусе 09 ноября 2021 года
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