December 20, 2016 the Deputy of Prime Minister Dmitry Rogozin held meeting in TSAGI, dedicated to the activities of the program of the creation of passenger aircraft MC-21. The meeting was attended by the leadership of the Ministry of Industry and Trade of Russian Federation, the Research Center Institute named N.E. Zhukovsky, FSUE TSAGI, PJSC KLA, PJSC Irkut Corporation, the representatives of the leading Russian aircraft construction enterprises and organisations.

A distinctive feature of the new aircraft has been widely used in the airframe design of polymer composite materials. This solution is intended to ensure MC-21 advantage in the flight performance. At the same time the introduction of composites has required a large amount of unprecedented strength tests. The testing of a number of composite structures is completed. Special attention is given to isolated test of innovative lengthened wing, coffer and mechanisation which are made with composites.  For the first time there was created and tested the design propulsion of this size with composite materials in Russia.

In a direct line to the Deputy of the Prime Minister information was provided of the Irkutsk Aviation Plant - branch of PJSC Irkut Corporation on preparations for the first flight test of the MC-21-300 aircraft . Participants also examined the TSAGI section of the static tests where the assembly of MC-21-300-0002 aircraft designed for static testing is completed.

As you know, there are two groups of strength tests: Static and Resource. Static tests - a test to determine the level of static strength of the aircraft structure. In other words the ability of the aircraft structure to withstand one-time high load. These tests are needed to determine the strength characteristics of the design, limits of possible load in operation - abrupt manoeuvres, air gusts, turbulence, system failures, etc..Thus, during the test verified the ability of MC-21 aircraft structure to perceive append designed loads, not to break down and do not receive unacceptable residual deformations.

Lifetime tests (or - re-static) - a set of tests aimed at determining the fatigue strength and operational survivability of the aircraft structure. Fatigue strength is the ability of construction to withstand repetitive loads and operational vitality is the ability of construction to resist the development of cracks and other defects. On the basis of these tests, the decision of assigned resource - the number of flights that can take an aircraft before it becomes a used aircraf. Also, these characteristics affect the value of the period between inspections - the number of flights, after which the aircraft should be carefully checked for the absence of dangerous cracks, corrosion and so on.

The МС-21-300-0003 wing manufactured at Aerocomposite-Ulyanovsk

At this stage, in order to ensure the strength of the structure of MC-21 and preparations for the first flight, already tested nose section of the fuselage, air brake, rudders and flippers, landing gear struts, a number of field units, made of composite materials, also dozens of constructive samples, reflecting the work of the major structural elements of power. At the finish line out the static tests of wing spar boxes and the keel. Based on the results of these tests, as well as supporting their of calculations will be concluded on the static strength of the airframe construction of the aircraft for the first stage of flight tests.

The decision to start the flight tests will make the Methodological Council, formed on the basis of LII. Gromov, which considers all aspects of the aircraft readiness for the first flight, including in the part of durability, based on the expert opinion of the FSUE Central Aero-Hydrodynamic Institute named of professor N.E. Zhukovsky, which held the main volume of the strength tests on the MC-21 program.

As it is known, a feature of MC-21 aircraft is a large amount of innovation in airframe design. The world's first wing of a large passenger aircraft will be produced with composite materials based on carbon composites using vacuum infusion (non-autoclave) technology that provides its benefits, but also has certain risks, including those in terms of the strength characteristics and resource of the wing. Therefore,  the special attention is given to the testing of elements from composites.

The ultimate goal is to "break" the wing console (wing box) made of composite materials. According the experts terminology, "design bearing capacity will be determined." Currently, this MC-21 wing console passes the static tests in TSAGI. These tests are known as isolated because it is tested separately from the glider. Today the test results meet the forecasts.

Considering the novelty of the materials and manufacturing techniques of details, within the MC-21 program unprecedentedly a large volume of research works is carried out. Tens of thousands of elementary and structurally-similar samples were researched and tested. Among them, in particular, four prototypes of a the wing box caissons of keel and the stabiliser. The carried-out testing showed correctness of technical solutions and confirmed the efficiency of the techniques of designing applied by designers.

The tests allowed to determine not only the strength characteristics of the parts and components of the composite, but also the behaviour of composites under the influence of climatic and operational factors. So, damages which can be received during operation of the aircraft were applied on all tested composites. In particular, tat he stand of CIAM in Turaevo the resistance of a design was tested to external influences, such as a collision with birds at maximum speed.

The basis of the conclusion of specialists of TSAGI will be formed not only by results of the carried-out static testing. At the same time there are held endurance tests, the interim results of which are also considered in the preparation for the first flight. Thus, within the MC-21 program, endurance tests were carried out already since 2010. In particular, a regular slot of the fuselage of the MC-21 aircraft in TSAGI withstood 47,000 cycles, each of which corresponds approximately to the same real flight. Tail section of the fuselage withstood 240 thousand similar cycles.

Works on ensuring the static durability of the MC-21-300 to the initial stage of flight tests are under way. According to world practice, the total amount of this work will be less than a full range of strength tests. The fact that the first phase of flight tests of the aircraft will be subjected to significant stresses and will fly with the "Restriction Settings". In particular, the flight will be carried out in normal weather conditions and flight mission will not include complicated manoeuvres.

After impregnation binder design in a special oven, it is processed on a milling machine, a robot, which cuts off the edges from the given templates and drills the necessary holes.

After the beginning of flight tests static testing will be continued. The main units of the aircraft will be subjected to the maximum settlement loads. I This will consistently expand the range of conditions of flight prototypes. And at the final stage of static tests units will be subjected to ultimate loads.

The "baton" of justification of durability of the design will be picked up by static tests of a glider which are prepared to be conducted in TSAGI. The results will allow to lift further limits from flight tests, allowing the prototypes to enter the limits of flight regimes.

Static test results processing will identify and eliminate potential design flaws, will show the way to further improve the design of the aircraft. Elements, the strength of which was lower than estimated, will be developed further. On the other hand, the items shown above the required strength can be facilitated in order to improve the performance characteristics of the aircraft.

Element of a design of a wing MS-21 collected from three components after the impregnation in a vacuum bag and scraps.

The test results will also be used for verification and validation of the applied calculation methods. This will further reduce the number of field tests, replacing them with "virtual" experiments conducted by computer simulation. Also, the results of the static tests will continue to be studied by the Russian and foreign authorities upon the receiption of the type certificate of MC-21 aircraft.

MC-21 aircraft, delivered to endurance tests in TSAGI will never rise into the air, but its "raid" will always be significantly ahead of the raid of a real aircraft in the airlines. Therefore, any potential hazards associated with strength will be revealed in the course of modifications and eliminated earlier so there is no opportunity to create a real threat to passengers.

Assembling the wing of MC-21-300-0003 at Aerocomposite-Ulyanovsk