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Russian views on the future of civil aeronautics

HYPERSONIC A computer model of the planned Hexafly technology demonstrator

PROF SERGEY CHERNYSHEV: We are working to make aviation safer, greener and more comfortable for people

Photo by CSIR

AERODYNAMICS CENTRE A model of a twin turboprop airliner set up in one of TsAGI’s wind tunnels

Photo by TsAGI

CONCEPTION: An artist’s impression of a future Russian regional jet airliner with high aspect ratio braced wings and turbofan engines mounted above the rear fuselage

Photo by TsAGI

16th February 2018

By: Rebecca Campbell

Creamer Media Senior Deputy Editor

     

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People are concerned about noise, emissions and safety. We are working to make aviation safer, greener and more comfortable for people,” highlighted Professor Sergey Chernyshev, general director of Russia’s renowned Central Aerohydrodynamic Institute (much better known in English by the transliteration of its Russian acronym, TsAGI).

He was delivering one of the keynote addresses at the 2017 Conference of the Aeronautical Society of South Africa (AeSSA), hosted by the Council for Scientific and Industrial Research (CSIR). “I like the idea of seamless travel. We need to do something to make travel faster.” He pointed out that it takes about 11 hours to fly from the far west of Russia to the country’s far east, a fact that emphasises the importance of aviation to Russia.

TsAGI is heavily involved in international aeronautical research projects, as well as national ones. It has been and is involved in a number of projects under the European Commission’s (EC’s) Framework Programmes for Research and Technological Development, the current (eighth) iteration of which is desig- nated Horizon 2020.

“In the last 70 years, the number of passengers transported by air annually has increased by almost 400 times,” he highlighted. “More than 27 000 commercial aircraft are in service.” What of the future? The Russian view of what will be required is incorporated in the country’s ‘Aviation Science and Technology Foresight 2030’ study, which was approved in 2014. Chernyshev summarised them as being new aircraft configurations and concepts; new engines and airframe-engine integration; materials and structures; systems; and enabling technologies, such as flight demonstrators and computational fluid dynamics.


It’s a Drag

“The main enemy of flight is drag,” he pointed out. Drag is composed of wave drag (“very strong when you fly supersonically”), induced drag and friction drag. In subsonic flight, induced drag and friction drag are the main components of drag. Induced drag is actually created by the passage of an aerofoil – wing or tailplane – through the air and is an unavoidable consequence of the very lift that allows an aircraft to fly. Wave drag is caused by shock waves created around an aircraft at supersonic speeds, or around some surfaces of an aeroplane at transonic speeds. Friction drag is the result of friction of the atmosphere against the whole surface of the aircraft flying through it: it is proportional to the surface area and increases with the square of the aircraft’s velocity.

Thus, a lot of research in airframe design has been and remains concerned with reducing drag. For example, the late 1970s saw significant advances in the design of supercritical aerofoils, especially wings, which increased speed and reduced wave drag. The results of such research were then applied to a number of aircraft designs, including the giant Antonov An-124 cargo aircraft (designed and developed when Russia and Ukraine were both part of the Soviet Union).

Today, a major area of research is laminar flow over wings (and tailplanes). Laminar flow is the smooth, uninterrupted flow of air over a wing – something which is very difficult to achieve in practice (because wings have seams, hinges, flaps and other features that interrupt the air flow). But, if achieved, it significantly reduces drag, meaning that an aircraft can fly further or burn less fuel. “We should work on that,” affirmed Chernyshev. Another concept for future civil airframe design is the blended wing body.

Then there is the need to reduce weight without losing airframe strength. TsAGI has been heavily involved in developing major composite structures for airframes. It has focused on using infusion as a means of producing such structures, because this technique requires less energy than the additive methods used by other countries. This has borne fruit with the Irkut MC-21 single-aisle airliner programme. The first flight test development MC-21 made its maiden flight at the end of May last year and the second one should follow this month or in March. (The Irkut Corporation incorporates the famous Yakovlev Design Bureau, now called the Yakovlev Engineering Centre, and is a subsidiary of Russia’s United Aircraft Corporation, which is 91.68% State-owned.)

Two versions of the MC-21 are being developed: the 132- to 165-seat MC-21-200 and the 163- to 211-seat MC-21-300; the Russian news agency TASS has reported that a MC-21-400 model, which could carry up to 250 passengers, is under consideration. Serial production of production aircraft should start next year. (The MC-21 is sometimes referred to as the MS-21, ‘MS’ being a transliteration into the Latin alphabet of the Cyrillic ‘MC’.)
Regarding composite structures, these account for 37.5% of the new airliner’s airframe by weight. Its wings and wing box are largely made from resin-infused composites.

TsAGI is now researching composite geodesic/isogrid integrated structures for airframes. (Geodesic structures were first applied to aeroplane design in the 1930s by British company Vickers-Armstrong; they were used in three warplanes that were manufactured for, and served with, the UK Royal Air Force and allied air forces, including the South African Air Force, during the Second World War: the Vickers Wellesley, the Vickers Wellington, and the Vickers Warwick. However, at that time, the technique required the covering of the airframe with fabric and the great increase in aircraft speed during the conflict rendered geodesic construction obsolete. The development of composites means that the concept can now be examined again. Geodesic structures have never been used in the manufacture of commercial aircraft.)

“The benefits of these new [geodesic] structures are up to a 10% to 12% weight reduction; long life; and reliable FOD (foreign object damage) protection,” he explained. This programme was started as part of the EC’s Seventh Framework Programme. Today, TsAGI has a composite geodesic fuselage barrel section and a test rig on which to evaluate it. These were both developed to validate the structural modelling of the concept.

Another area of research for future airframes is the so-called bionic designs, that is, designs more closely modelled on forms found in nature, such as in birds.


Fast and Frugal

A further research priority is new architecture power plants. One such technology is distributed electric power plants. “We’re working on this concept,” he stated. This involves using a ‘kerosene’ (gas turbine) engine to generate electricity, which then powers electric motors which, in turn, drive aircraft propellers. A design concept TsAGI is looking at is for a regional aircraft which would have four propellers mounted at the wing tips in two push/pull pairs, which would be driven by electric motors. The concept includes an ability to tilt the wing slightly, which would give the aircraft a short takeoff and landing capability, which would be valuable for operations to and from many small airports and airfields in remote areas of Russia.

From 2005 to 2012, TsAGI was involved with companies and research institutes from across Europe in the EC Sixth and Seventh Framework Programmes studying another alternative engine architecture: the open rotor turbofan. Open rotor turbofans offer reduced fuel consumption and lower carbon dioxide emissions, but are noisier than high bypass ratio conventional turbofan engines. “Open rotor engines provide very good economic efficiency, with fuel savings of 18% . . . 20%” he observed. “But they increase, a little bit, the noise.” To deal with this, the research consortium came up with a “green aircraft concept” design which used two open rotor engines mounted on pylons above the rear fuselage, within an H-shaped tail structure (a tailplane with vertical fins and rudders at each end); the tailplane would deflect the noise of the open rotor engines upwards and so not disturb people on the ground.

In terms of national projects, TsAGI is looking at a number of design options for future regional aircraft for Russia. One is a high-aspect-ratio braced wing turboprop. Aspect ratio is the span to mean chord ratio; the longer, the narrower the wing, the higher the aspect ratio. The higher the aspect ratio of the wings, the lower the induced drag. A second design is for a regional jet, with the turbofan engines mounted over the wing. The third design also features a high-aspect- ratio braced wing, but with turbofan engines mounted on top of the rear fuselage.

In sharp contrast to regional air transport is high-speed air transport. “My favourite topic – the sonic boom!” quipped Chernyshev. The Institute, with European partners, is doing research into a low sonic boom civilian jet, initially for the business aviation market. “The main issue in the world is: What is the acceptable level for the sonic boom?” This is probably around 65 decibels, which is the level of noise generated by a city during daytime. TsAGI has been developing, refining and revising designs for such an aircraft for some ten years and has evolved the concept over this period.

“Moving beyond the supersonic regime of flight, we have, with our European partners, the concept of Hexafly – a hypersonic civil aircraft,” he adds. This project was started under the seventh Framework Programmes and, in addition to TsAGI, involves three other Russian research institutions, three Australian universities and research institutes, universities and companies in Belgium, France, Germany, Italy, and the UK, as well as the European Space Agency (ESA – which is not an agency of the European Union). A hypersonic aircraft would, ESA has pointed out, be able to fly from Brussels, in Belgium, to Tokyo, in Japan, in less than two-and-a-quarter hours.

Hexafly stands for High-Speed Experimental Fly Vehicles. Strictly speaking, its abbreviation is Hexafly-Int, the suffix -Int standing for International. Hypersonic speeds are speeds in excess of Mach 5.0, that is, five times the speed of sound. Computer modelling and simulations have been carried out, and wind tunnel models built and tested. The partners in the programme are aiming at flying an unpowered demonstrator in 2019: this would be accelerated to hypersonic speeds by a rocket and then released to fly, unpowered, on its own.

Aerotown

TsAGI was founded in Moscow in 1918 and is one of the oldest, perhaps the oldest, continuously existing aeronautical research institutions in the world. It constructed its first large wind tunnel in 1925. (The original building and wind tunnel are now preserved.) Today, it has more than 60 wind tunnels and gas dynamics facilities, ranging enormously in size and in terms of the wind velocities they can generate. It also has a comprehensive array of other test facilities.

In addition to studying the aerodynamics of aircraft and spacecraft, the institute also studies the effect of air flows on fixed structures such as buildings and bridges. Additionally, it carries out hydrodynamics research and has the necessary test facilities to do so, including large water tanks.

“Our campus is like a small town, with real town infrastructure,” he observed. “We consume about 1 000 MW of electricity a year. We spend $1-million every three months [on electricity]. About half of our funding comes from the Ministry of Industry and the Ministry of Science. About half we make in a commercial context.”

• Chernyshev also attended the Summit International Forum for Aviation Research, also hosted by the CSIR in Pretoria, in October, which immediately preceded the AeSSA conference.

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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