Composite Material and Automated Lay-up
Very little information is available to the public about the creation of the Berkut wing. Meanwhile, for this project, the scientists of ORPE Technologiya named after A.G. Romashin and VIAM developed the technology of manufacturing composite material with the specified properties, the basic design principles of carbon yarn reinforced unidirectional prepregs. It was done in a uniquely short time. The first experimental panels made of the new materials were produced and tested as early as 1986 as part of a wing box model about four metres long, successfully passing all the required tests. For the first time in the USSR, the forward-swept wing was manufactured using the automated lay-up method to maximise the materials' properties. Why was automatisation so important? The point is that the automated lay-up ensured the most precise application of the prepreg tapes (carbon tapes impregnated with a binder) on the tooling, thus forming the layers of the carbon fibre panel. In some places, the number of such layers in the future wing was up to 120, so the slightest inaccuracy would make a complex and expensive part unusable.
"The theory of the forward swept wing dates back to the 1930s, but the material is only available nowadays. The aircraft's original design with a forward-swept wing was called the C-22. The console panels were created for testing new materials. At that time, we had the only installation in Russia for the automated prepreg lay-up. But even its capabilities were insufficient to solve the task of creating the composite wing. The fact is that its programs provided lay-up only in two coordinates. So, we manually set up the machine for two more coordinates. It was simple but painstaking work: as soon as the spring-loaded "head", which was rolling along the tooling, "landed" on the limit switch, we started to adjust coordinates so that it would move further, as we needed. The emotions were unforgettable! I had been working for a month without a day off. We then had an idea of developing the equipment software that would allow us to get control programmes for four axes simultaneously. We wrote technical specifications for NIAT, and then, based on our experience, a group of software engineers developed the necessary system for CNC code. Later we used this system to develop programs for the Su-47 wing project," recalls Valery Ternovoi, head of the Process Automation Department at ORPE Technologiya.
The Wing's Trial
The "black wing" has indeed become a completely non-abstract global challenge. Almost every solution found was implemented for the first time in the country. The specialists of Technologiya, together with their colleagues from Sukhoi and VIAM, had to solve in a short time the problems related to the organisation of control of raw materials, calculate temperature deformations during autoclave moulding as well as the effective modes of thermal exposure and force impact depending on the binder characteristics, as also do many things that nobody had done before them in the USSR and Russia. They also developed a methodology for designing thick-walled asymmetrically reinforced wing panels, solved the seemingly impossible task of non-destructive testing of thick panels containing metal sheet reinforcements and created test methods for thick-walled witness samples, ensuring high reliability and realisation of carbon plastic characteristics in the completed panels.
"It was a difficult time. Plants were closing down, and the overall situation was difficult. And we received an order to produce a forward-swept wing for the Su-47. The work was stressful but exciting because we were making a wing using the automated lay-up method for the first time. Now, you start the machine, set the coordinates, and it does what it needs to do, so you have to watch. At that time, you had to improvise because of new equipment that no one else in the country had, because of the new material. We adjusted all parameters to the installation, tried and tested the best way. Sometimes because of binder problems, we had to remove layers and put new ones on, but we did everything just right. Manufacturing the wing for the Berkut was a great experience that was a breakthrough not only for aviation but also for production. We introduced the method of automated lay-up of aviation articles, improved the quality of the materials, and it was an outstanding experience for the workers," recalls Alexander Konashenkov, a CNC machine operator at ORPE Technologiya.
The Composites Were Rated High
The strength tests of the wing were carried out in the static test hall of the Sukhoi Design Bureau. Both consoles were loaded at once. It was the first CFRP wing in our country, so everyone involved in the project was very nervous. The load was increased gradually. We listened attentively to the slightest clicking sound each time the new load was announced. There was no talking. Particularly nervous excitement started with the first sonorous clicks, which meant that the internal stresses were approaching the strength limit of the composite. Seeing the wing deflecting heavily but easily holding the load was astonishing. The carbon fibre-reinforced plastic wing withstood the calculated test with a margin of safety.
The specialists of ORPE Technologiya were not worried about the Su-47 flight test, as they were confident in the reliability of the carbon fibre-reinforced plastic panels. But everyone was proud of the result achieved in the close cooperation of material scientists, strength engineers, designers, product engineers, testers, workers and foremen from Sukhoi Design Bureau, TsAGI, VIAM and ORPE Technologiya.
The Berkut has become a milestone in developing the national aviation industry. In combat and civil aviation, the technologies developed and adjusted in those years are embodied in the tail fins and wings of the MC-21. For ORPE Technologiya, work on the "black wing" has also become the basis for successfully implementing the serial production of structural elements of the future T-50 (Su-57) fighter, which is now being supplied to the troops.