China is developing a UAV with an asymmetric variable-sweep wing
Hypersonic UAV from SZPU in hypersonic configuration with folded wing, left-bottom view. Graphics SZPU / SCMP
Chinese science seeks new paths of development aviation technologies that will improve all its main characteristics and expand its operating capabilities. For example, it became known about the development of a hypersonic unmanned aerial vehicle with an asymmetrically variable sweep wing. Such a design will allow it to demonstrate high performance at all speeds and flight modes.
At the level of theory
Another study in the field of heavy-duty UAVs was conducted by specialists from the Northwestern Polytechnical University (Xi'an). The work was led by Professor Ma Yiyuan.
The main goal of the unnamed project was to improve the UAV's performance in all expected flight modes, from takeoff and landing to cruising hypersonic speed. To this end, the project used an unusual technical solution - the so-called rotary wing with asymmetrically variable sweep.
In recent years, Chinese science has been actively studying unusual designs and layouts of aircraft. The asymmetric or "oblique" wing has not gone unnoticed either - several similar studies are known. However, before SZPU and Ma Yiyuan's team, no one had tried to use such a bearing plane on a hypersonic aircraft.
Chinese specialists worked out the main aspects of such a project and formed an optimal design of the UAV. This design was carefully studied at the theoretical level and using mathematical and computer models as an example. Based on the results of such studies, amendments were made to the original project.
By now, SZPU has conducted all the necessary research and determined the prospects of the original UAV design. A report on the work done was published in July in the scientific journal Advances in Aeronautical Science and Engineering. The unusual nature of the project soon attracted the attention of Chinese and foreign media.
The publication provides basic information about the design of a hypothetical UAV and the characteristics achieved. It also shows the appearance of the device in different flight modes. The achieved advantages and expected difficulties of various kinds are listed.
In general, so far we are only talking about the theoretical development of an unusual design. Further development of the research project is apparently not planned. However, certain ideas and developments of this project may find application in the creation of real models of aviation equipment. However, complete copying of the proposed ideas and solutions seems extremely unlikely due to their overall complexity.
Hypersonic carrier
The SZPU project proposes a hypersonic UAV of unusual design. It should be of medium size and takeoff weight of several tons. Such a device is considered as a carrier of various loads. First of all, these could be medium and light Drones different purposes. A large apparatus will be able to deliver them to a designated drop zone, where they will have to act independently.
Experimental aircraft with an oblique wing AD-1 of American design, 1980. Photo NASA
A streamlined fuselage with a bottom capable of generating lift has been developed for the heavy UAV. A variable geometry rotary wing is placed on top of the fuselage. A small-area front horizontal tail and a full-size stabilizer in the tail are also provided.
The wing of the device is structurally straight. Its span does not exceed the length of the fuselage. The plane is installed on top of the glider using a hinge and must rotate around a vertical axis. The position of the wing, as well as the sweep of its halves, depends on the current flight speed.
The drone has a power plant based on two engines, providing flight in all modes. These can be combined engines with a turbojet and ramjet circuit. Details of this kind and the required level of performance are not specified.
The composition of the onboard equipment is also unknown and probably was not worked out in detail. The research project had other goals, and avionics issues were not important. However, the need for autonomous control in some modes is mentioned.
It is proposed to organize a payload compartment inside the fuselage. The new UAV should carry up to 2 tons of cargo. First of all, it is proposed to make it a carrier of light and medium drones. It will be able to break through to a given area and perform the release of its load. The UAVs being transported will have to solve specific tasks.
Flight modes
According to the authors of the project, the hypersonic UAV should take off from an airfield. For takeoff, the wing is set to zero sweep angle. This achieves an aerodynamic quality of 9,1, which is quite sufficient for stable flight. In this configuration, the drone can develop high subsonic speeds.
When approaching the speed of sound, it is proposed to turn the wing at an angle of 45°. In this case, one half of it acquires a normal sweep, and the other - a reverse sweep. Despite the asymmetry, the wing in this configuration gives an aerodynamic quality of up to 5,6. With an "oblique" wing, the UAV should develop high supersonic speed. As the speed increases, the lift created by the fuselage and its contribution to the overall result increase.
At high supersonic speeds and when reaching hypersonic speeds, the UAV must turn its wing along the fuselage, and it is turned off. After this, 67% of the lift is created by the fuselage, and the remaining load falls on the large-area stabilizer.
A UAV with such modes will be able to develop a speed of at least 5 M and rise to a height of up to 30 km. The possible flight range, combat radius and other important parameters have not yet been disclosed.
The Switchblade UAV, developed in the 2010s by Northrop Grumman
Desired benefits
Chinese scientists note that the proposed UAV has a number of important advantages and benefits. These include several design features, theoretically achievable flight characteristics, operational capabilities, etc.
An asymmetric wing allows for a certain simplification of the design. In essence, such a plane is a single unit that requires only one hinge. A variable-sweep wing of a traditional design is much more complex - it consists of two separate planes, each of which receives its own hinge and drive. In addition, a single wing is characterized by increased strength and is more resistant to loads.
The rotating wing has several positions for different speeds. At hypersonic speeds, there is no need for it, and the wing is folded onto the fuselage. At the same time, the wing and its mechanisms are not subjected to increased aerodynamic and thermal loads. A wing of traditional design does not allow for all this.
However, this is only a limited simplification of the design. Hypersonic flight places special demands on the aircraft, and they require specific technical measures. Probably, Chinese specialists took this into account in their new project, but it is unclear how this affected the complexity of the design.
It is obvious that the airframe of a prospective UAV, including a movable wing, should be made of heat-resistant alloys and composites. There are also high requirements for the hinge and wing drives, which must withstand high loads in all flight modes. There are also other specific points related to the main task of the project.
Modern solutions
It should be recalled that the idea of an asymmetric variable-sweep wing appeared quite a long time ago. Such aircraft architecture was studied theoretically and on models, and full-fledged experimental aircraft were built and tested. However, not a single such project has progressed beyond testing.
The first projects of such equipment were developed in Germany during the Second World War and did not reach the stage of construction and testing of experimental equipment. The first full-fledged aircraft with an "oblique" wing took to the air only in 1979. It was the AD-1 product from the American agency NASA. The tests continued for several years and provided the collection of a lot of data. Then new projects were created, but they were again limited to design only.
All the experiments showed that the unusual wing design allows for a reduction in frontal and wave resistance in different flight modes, as well as improving other parameters. Obvious advantages over a fixed wing and symmetrical variable-sweep planes were demonstrated. At the same time, difficulties arose with the development of a hinge that had to demonstrate sufficient strength and reliability.
All previous projects of similar equipment were closed due to the complexity and lack of fundamental advantages over aircraft of traditional design. However, now SZPU decided to return to the old idea and implement it using modern materials and solutions. Moreover, Chinese specialists decided to use an unusual design in hypersonic technology.
At the level of research and modeling, it was possible to demonstrate the viability of the new project and its strengths. Whether it will be developed is still unknown. It is quite possible that in the near future they will move from theoretical development to practical measures.
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