Russian attack drone S-70 will become invisible to the enemy
Percussion prototype drone S-70 "Hunter", Photo: wikipedia.org
Drone aviation over the past decades it has been proving its significance and consistency. Recent conflicts, especially in Nagorno-Karabakh, prove that modern attack UAVs can have a serious impact on the course of hostilities on the ground. The main hope of the Russian strike aviation is rightly considered the heavy strike UAV S-70 "Okhotnik", the developer of which is the company "Sukhoi".
News about the new Russian strike-reconnaissance drone, which can operate in conjunction with the fifth-generation fighter Su-57, appear quite dosed. So, recently the TV channel "Zvezda" in its program confirmed the version that the attack drone will receive "stealth" nozzles for the engines.
It's worth noting that this is not really news. For a long time at exhibitions "Okhotnik" in the form of a model has been demonstrated with just such a design of the engine nozzle. In this regard, the layout really differs from the currently flying prototype of the technology demonstrator, which was previously the hero of the videos of the Russian Ministry of Defense.
Attack drone S-70 "Okhotnik" will receive a flat nozzle
A distinctive feature of the new Russian attack drone of the Sukhoi company should be a nozzle design that is new for domestic aviation. Unlike the usual round ones, it will become rectangular (flat). Until recently, this design feature was not used in Russian aviation.
Previously, such a move was implemented only on the world's first serial fifth-generation fighter - the American F-22 Raptor. Following him, the American supersonic heavy stealth strategic bomber Northrop B-2 Spirit received the same nozzles. This design makes it possible to increase the stealth of aircraft and their survivability.
A mock-up of the Okhotnik strike drone, Photo: Mikhail Zherdev
According to Sergei Kuzmin, who holds the position of Deputy General Designer of the Motor Design Bureau of UEC UMPO, the new version of the S-70 Okhotnik strike UAV will receive a flat nozzle, which will provide the drone with less visibility. According to Kuzmin, the new product will allow more efficient dissipation of the heat trace from the engine operation. Thanks to this, it will become much more difficult to hit the "Okhotnik" with the help of guided missiles with infrared and thermal homing heads.
According to Kuzmin, this innovation is unique for the domestic aircraft industry. The specialist noted that such a technical solution is not currently used on any domestic fighter. At the same time, Kuzmin emphasized that the introduction of such a nozzle shape has been a worldwide trend since the end of the XNUMXth century. This makes it possible to provide a set of necessary special characteristics in the rear hemisphere of the aircraft, first of all, invisibility.
According to the designer, the new flat nozzle, which was developed in Ufa, will be almost completely hidden in the design of the S-70 Okhotnik strike drone, which will reduce the visible flame from a running engine, effectively dissipating it. For additional camouflage from guided missiles, the developers, during constructive measures in the inner part of the nozzle, cover the hot parts of the engine with cold elements. Due to the cover of the nozzle in the airframe design, the radar signature of the aircraft is also reduced.
The specialist also said that the nozzle for an impact drone is assembled using additive technology, in which parts and structural elements are produced on a 3D printer, after which they are assembled and tested at a stand where more than 200 different sensors are installed.
It should be noted that in Ufa, at the Motor enterprise, a rectangular (flat) nozzle was studied back in the early 1990s. It is known that one of the Su-27UB fighters was specially converted into a flying laboratory. The left engine (AL-31F) of the fighter was equipped with a flat nozzle developed by the Ufa enterprise. In this case, the nozzle had the ability to change the reverse and direction of the thrust vector.
A prototype of the S-70 "Okhotnik" drone in flight, video frame of the Ministry of Defense of the Russian Federation
As part of the experiments, about 20 flights were made, which were accompanied by good test results. Among other things, it was noted that the IR signature of a running engine with a new nozzle design was significantly reduced (several times). However, the lack of the necessary funding in the 1990s became the reason for the stoppage of this kind of work.
What are the advantages and disadvantages of a rectangular nozzle
The greatest interest of engineers and designers in rectangular nozzles arose in the early 1970s. At the same time, the interest was initially based solely on the military application of such technology. This sectional shape promised advantages only for combat aircraft. Most of all, researchers were attracted by two possibilities: a decrease in infrared and radar signature and a change in the direction of the thrust vector, which could increase the maneuverability of the aircraft.
Radar signature decreased due to the maximum possible matching of the contours of the engine nozzle with other elements of the aircraft structure. It is practically impossible to do this when using a nozzle with a regular (round) cross-section.
In addition, special radio-absorbing materials were subsequently used in the design of the nozzle elements, as was done on the fifth-generation F-22 fighter. Infrared visibility was reduced due to the correct formation of the ratio of the width to the height of the nozzle and the outgoing jet in order to reduce its temperature.
Fighter of the fifth generation F-22 Raptor, photo: wikimedia.org
The first combat aircraft to take off with new engine nozzles was the American experimental F-15 STOL / MTD fighter. This happened at the end of 1988. The development and generalization of the results of the tests obtained formed the basis for the creation of a flat nozzle for the Pratt & Whitney F119-PW-100 engines, which were installed on the F-22 Raptor fighter.
Besides the obvious advantages, the flat nozzle also has disadvantages. Structurally, the thrust vector on such a nozzle is controlled only in the vertical plane. And this lack of all-aspect ratio, which can be critical for combat fighters, which are focused on maneuverable combat. At the same time, this drawback plays practically no role for shock and reconnaissance UAVs.
Another drawback of this design, which some experts call the main one, is the mass of such a nozzle. In addition to tensile loads, flat nozzles also experience bending loads. Providing for them the required level of rigidity and strength inevitably entails an increase in the mass of the entire structure. It is known that on the experimental F-15 STOL / MTD fighter the increase in weight for each of the two engines was 180 kg.
The rectangular nozzle has an alternative
In any case, today we can say that a flat nozzle is not an uncontested solution for military aviation. The axisymmetric (circular) thrust vectoring nozzle is a serious competitor. In favor of greater maneuverability and to the detriment of radar visibility in the rear hemisphere, the domestic Su-57 and the Chinese fifth-generation fighter J-20 were chosen.
It is not known, however, which nozzles will be installed on the Su-57 fighters with the second stage engines, but now China and Russia are not alone in their choice. The Americans also opted for a traditional axisymmetric nozzle for their fifth-generation F-35 fighter-bomber.
It turns out that the developers of the F-35 preferred increased maneuverability and reduced weight to the detriment of the ideas of stealth technology. At the same time, an interesting feature of the F-35 engine nozzle is the serrated edges, which helps to reduce radar signature, but not as effectively as it would be with a rectangular nozzle.
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