Su-57 Felon - Materials

According to Russian data, the proportions of Su 57?s structural manufacturing materials are 18% titanium alloy, 40-44% aluminum alloy, 22-26% composite material, 10% steel, and 4% others-usually said to include rubber, surface coatings and so on. When measuring the advancement of fighter aircraft materials, the ratio of titanium alloys and composite materials is usually used as an intuitive indicator-the more you use, the more you are willing to pay for the aircraft and the more you are willing to pursue high performance.

Observing the selection of the material ratio of the Su 57, combined with the development history of Soviet Russian fighter jets, it is obviously in line with Russia's value orientation in the Su 57 development project: cost control first. Among the fighter materials, steel is the heaviest, but it can provide the greatest absolute strength and higher temperature resistance than titanium alloys; therefore, steel is still an irreplaceable material for some key components such as landing gear. The aluminum alloy is lightweight, and its strength can meet most of the body structure requirements, so it is suitable as the main body material.

For the classic metal structure fighter, the steel and aluminum structure can provide good overall performance at the lowest design and manufacturing cost. Titanium alloy is somewhere in between. Although heavier than aluminum, it is much lighter than steel, but it is stronger than aluminum, more resistant to high temperatures, and occupies a smaller volume; therefore, titanium alloy is used in structural design, it can effectively avoid some embarrassing situations that are beyond the tolerance of aluminum alloy and can only be replaced by steel.

The most typical examples are SR-71 and MiG-25. Because aluminum alloy has a very severe degradation in strength performance at high temperatures, it is generally believed that high-speed aircraft that need to continue flying more than 2.5 times and the fuselage structure will be friction with air at high speed for a long time, and the surface temperature of the fuselage will exceed the tolerance limit of aluminum alloy.

The Soviets used steel to manufacture the main structure of the MiG-25, which was cheaper and less difficult, but the aircraft was heavier and had lower flight performance. The SR-71 titanium alloy is the opposite, lightweight, but technically difficult, and extremely expensive. Because the smelting and processing of titanium alloys are very difficult, the design and manufacturing costs of titanium alloy structural parts are quite high, which has not changed until now.

This makes the application of titanium alloys have a strong marginal effect - the investment is high, but the absolute benefits that can be brought (weight reduction, reduction of internal structure space occupation) are not high; therefore, only when the performance requirements are very high, a particularly high proportion of titanium alloys will be used when a performance improvement is worth spending a lot of money.

When the F22 was developed in the United States, the overall structure plan believed that, on the premise of meeting the basic performance requirements, for a fighter flying at twice the speed of sound, 25% of the titanium alloy has the lowest cost, and 45% of the titanium alloy can achieve the lightest weight? -But whether it is 24% of YF22 or 41% of mass-produced F22, they have not reached the lightest weight requirement. This is also a compromise to cost.

The proportion of Su 57's titanium alloy is only 18%, which is roughly the same as Su 27, which is much lower than F15's 26% and F22's 41%-not to mention that compared with F22, it is almost half lower than F15. This shows that the structural manufacturing cost of Su 57 is controlled quite strictly. In order to inherit the layout of the Su-27?s engine pod-style lifting body, the mid-body thickness of the Su 57 is seriously insufficient, and the large opening design that severely damages the overall structural rigidity and strength runs through. The structural layout form itself is very undesirable.

This kind of large opening area itself is the key area of fighter titanium reinforcement. With only 18%, the Su 57 has the least chance to compensate for structural layout defects through material properties.