Design and Key Technology of Polymer Matrix Composites for Drones

//Design and Key Technology of Polymer Matrix Composites for Drones

Design and Key Technology of Polymer Matrix Composites for Drones

Compared with metal materials, resin-based composite materials have many advantages such as lightweight structure, complicated structure or large structure, easy design, large design space, high specific strength and specific stiffness, and small thermal expansion coefficient.

The direct application of composite materials to the structure of the drone plays an important role in reducing the weight of the airframe, increasing the payload, improving safety and stealth. Design and key technology of polymer matrix composites for drones

Throughout the world of UAVs (including medium and high-altitude unmanned reconnaissance aircraft, unmanned combat aircraft, etc.), composite materials are used in large quantities without exception, and some are even composite structures, so the composite is the core.

Human-machine structure design/manufacturing technology is one of the key technologies affecting the development of drones.

Development status of domestic and foreign drones

The development of drones has a long history. The world’s first drone was successfully developed in the UK in 1917. According to incomplete statistics, more than 50 UAVs have been developed in more than 30 countries and regions around the world.

More than 300 UAV models are used, and 55 countries are equipped with drones, but they are the fastest growing. The highest levels are mainly the United States, Israel, and Russia.

The US military has nearly 20 models of approximately 20 drones. The aircraft mainly includes the Army’s “Hunter”, “Pointer” and “Shadow 200” drones. The Marine Corps’ “Dragon Eye” and “Pioneer” are not available.

Man-machine, Air Force’s “Global Hawk” and “Predator” unmanned reconnaissance aircraft and X-45, X-47 new unmanned attack aircraft. In addition, several other small UAV systems are included to support special operations needs.

China has developed UAVs for more than 40 years. It has successfully developed the No. 1 unmanned drone series, Changhong high-altitude high-speed unmanned reconnaissance aircraft, T-6 universal unmanned aerial vehicles, and Z-5 series unmanned reconnaissance aircraft.

BZK-002 unmanned reconnaissance aircraft, ASN series unmanned aerial vehicles, etc. Recently, the “Xianglong”, “Pterosaur” unmanned reconnaissance aircraft, WZ-2000 unmanned reconnaissance aircraft and “dark arrows” model drones have been developed.

The research institutions are mainly universities, research institutes and some enterprises, including Beijing University of Aeronautics and Astronautics, Nanjing University of Aeronautics and Astronautics, Northwestern Polytechnical University, Chengdu Aircraft Design Institute, Chengdu Aircraft Industry Group, Guihang Group and Zhuzhou UAV Company. In recent years, with the attention of the state, China has set off a climax of developing drones.

Application of composite materials on drones

Advantages of composite materials applied on drones Compared with manned aircraft, unmanned aircraft (UAV) does not need to consider the physiological tolerance of humans during maneuvering, nor does it require special emphasis on people. Special considerations for the structure and materials of stealth and ballistic resistance.

However, due to the advanced technology and high requirements of the airborne equipment of the drone, it is also required that the drone has a fairly good structural performance of the aircraft, which makes the unmanned aircraft have some new features different from those of the manned aircraft in structural selection.

The special nature of the drone’s missions has also made it an excellent platform for adopting new structural materials.

Compared with traditional metal materials, composite materials have the characteristics of high specific strength and specific stiffness, small thermal expansion coefficient, anti-fatigue ability, and anti-vibration ability.

It can be used in UAV structure to reduce weight by 25%~30%. According to statistics, the amount of composite materials of various advanced UAVs in the world generally accounts for 60% to 80% of the total weight of the body structure, and the total amount of composite materials can reach more than 90%. The benefits of using composite materials extensively on drones are manifold.

First of all, the composite material itself has designability, can be optimized according to the strength and stiffness requirements of the aircraft without changing the weight of the structure; it meets the needs of most UAVs in the high-wing body fusion structure in design and manufacturing technology.

The large area is shaped as a whole. Secondly, the polymer-based composite material has special electromagnetic properties, and it has the hope of meeting the high stealth technical requirements of the UAV structure/function.

The corrosion resistance of the composite material can meet the special requirements of long storage life in the harsh environment of the drone, and reduce the life cycle cost of use and maintenance.

Again, composite materials are easily implanted into chips or alloy conductors to form smart materials and structures.

At present, composite materials have become the main structural materials in the field of drones, such as carbon fiber composite materials, glass fiber composite materials, honeycomb sandwich composite materials and the like.

Generally, the drones are made of aluminum alloy except for the keel, beam and frame, landing gear and other structural parts of the fuselage, and the composite materials are widely used for the wing, the tail and various radomes, guards, skins and the like.

In addition, non-metallic materials such as wood materials, lightweight plastics, and plastic films are also widely used in small and medium-sized drones. The application of composite materials has played a crucial role in the lightweight, miniaturization and high performance of unmanned aircraft structures.

Composite materials applied to high-altitude long-haul drones

As the world’s most famous high-altitude long-time unmanned reconnaissance aircraft, Global Hawk was developed by Northrop Grumman for the US Air Force and produced by Vought Aircraft Industries. It features a large aspect ratio with a single wing, a slender body, a V-shaped tail, a top three-point landing gear layout, a 5°54′ swept back 1/4 chord of the wing, and a V-shaped tail (upper 50°).

The composite wing is up to 35m long and the composite material accounts for 65% of the structural weight. Commercial composites and epoxy materials were used by Vought Aircraft Industries to produce the modified Global Hawk RQ-4B aircraft wing.

The new wing is increased to 39.9m and weighs about 1814kg. “Global Hawk” has a radius of 5,500km, a range of 26,000km, battery life of 42h, a practical ceiling of 19.8km, a total takeoff weight of 11,640kg, and a fuel weight of 6,727kg, which is more than half of the total weight.

It has taken off from the United States and is available anywhere in the world. The ability of strategic reconnaissance and tactical reconnaissance is the most advanced high-altitude long-time unmanned reconnaissance aircraft in the world.

It represents the current level and trend of high-altitude long-haul drone development.

China’s “Xianglong” drone debuted at the 2006 Zhuhai Air Show. It is manufactured by Chengdu Aircraft Industry Co., Ltd., initially adopting a metal wing, wingspan 25m, fuselage length 14.3m, cruising speed 750km/h, maximum mission load 650kg, maximum lifetime 9.3h.

It can be seen that the voyage of the “Global Hawk” drone is 3 times that of the “Xianglong”, the wingspan is 10m more than the “Xianglong”, and the mission load is 250kg.

Comparing the performance indexes of domestic and foreign high-altitude long-range UAVs, the research found that the key to the performance of UAVs in China is to design and manufacture flexible wings with large aspect ratio composite materials.

Depending on the environment of use (usually high altitude) and performance requirements (usually longer than 24h and a certain mission load), high altitude long-haul drones need to carry as much fuel as possible (which can improve range) and use large aspect ratio flexible wings. (can increase lift).

By using the advantages of low density, specific strength, specific stiffness and tailor ability of the resin-based composite material, it is possible to design a flexible wing with a large aspect ratio; with the integrated design/manufacturing technology of the composite material, an integral fuel tank can be arranged on the wing to improve the drone’s battery life and range.

It can be seen that the integrated design/manufacturing technology of the UAV’s large aspect ratio composite flexible wing is one of the key technologies to improve the performance of high-altitude long-haul UAVs in China, especially in high-altitude and long-haul performance.

Composite materials applied to attack drones

The United States has begun to develop air/navy-based unmanned combat aircraft based on the proof of X-45A and X-47A. In order to reduce the structural weight as much as possible, a remarkable feature of the unmanned combat aircraft structure is the large application of composite materials, and far exceeds the application level of manned fighters.

The Boeing X-45A has a wingspan of 10.3m, a chord length of 8m, an air weight of 3,640kg, and a payload capacity of 680kg. The composite material accounts for 45% of the weight of the X-45A structure.

The fuselage consists of a high-speed cutting aluminum alloy keel, beam, and frame covered with a composite skin. The LTM45EL long-life woven carbon/epoxy low-temperature curing prepreg developed by Advanced Advanced Composites of the United States is used to laminate skins, inlets, and hatches.

The tooling is provided by Janicki Industries. The curing of the low-temperature curing prepreg uses two of the company’s boat molds. The upper skin of the fuselage is about 9m × 3.7m, which is laid into a single piece, while the lower skin is processed into two 4.5m × 3.7m parts. The upper and lower skins of the nozzle section will be made of Cytec’s BMI-5250.4 carbon fiber/double horse resin. It has a curing temperature range of 177°C to 204°C and a temperature range of 59°C to 204°C.

Under the US Department of Defense contract, Boeing was allowed to abandon the development of the X-45B, incorporating the payload, voyage and objectives of the project into the X-45C currently under development in the J-UCAS program, X-45C chord length 11m, wingspan 14.6m, the flying weight is up to l5900kg.

The high-altitude long-endurance drone platform is a major military equipment project that China is in urgent need of development. Compared with metal materials, resin-based composite materials have many advantages such as lightweight structure, complicated structure or large structure, easy design, large design space, high specific strength and specific stiffness, and small thermal expansion coefficient.

The direct application of composite materials to the structure of the drone plays an important role in reducing the weight of the airframe, increasing the payload, improving safety and stealth.

Throughout the world of UAVs (including medium and high-altitude unmanned reconnaissance aircraft, unmanned combat aircraft, etc.), composite materials are used in large quantities without exception, and some are even composite structures, so the composite is the core. Human-machine structure design/manufacturing technology is one of the key technologies affecting the development of drones.

Third, the key technology of composite material design/manufacturing for drones

The design criteria for composite materials for drones do not need to consider human physiological tolerance. In order to give full play to the performance advantages of composite materials, it is possible to design a lower safety factor than manned machines, in order to achieve higher flexibility.

Performance, the drone can design a large over-load factor, reaching 15~20g; also because the drone can have more design space and adopt a more advanced aerodynamic configuration, so it is necessary to study Develop some new design specifications and calculation guidelines to guide the design, calculation, testing, and acceptance of the UAV composite structure.

Pneumatic and structural design difficulties of the composite wing are based on high-altitude long-endurance drones. Domestic research has been carried out on large aspect ratio flexible composite wing, but these studies are still lacking for the flexible composite wing.

Sufficient understanding has not effectively uncovered the strong coupling relationship between structure, strength, aerodynamics, and control, let alone the effective use of the flexibility of the large aspect ratio composite wing to improve the performance of the aircraft.

At high altitude and super high altitude long-haul unmanned reconnaissance aircraft working at a height of 20~30km, the air is thin and the air density is less than 8.4% of the sea level air density. Therefore, the relationship between the aerodynamic characteristics and the lift of the low Reynolds number is studied. It is one of the ways to improve the lift of the wing.

A large aspect ratio composite flexible wing, under the action of flight load, when there is an external excitation, a nonlinear structural deformation will be produced, and the nonlinear deformation of the structure will affect the aerodynamic force, forming a structural and aerodynamic Coupling, this coupling effect is easy to cause the aerodynamic divergence of the UAV during high altitude long-haul, which can not converge and cause wing failure. Therefore, high-altitude drones with large aspect ratio wings must address the flight control issues of such flexible wings.

The large aspect ratio composite flexible wing has a light structure. To meet the minimum weight and maximum efficiency requirements of the structure, it is often necessary to rely on the comprehensive structure optimization design technology.

Due to the complexity of the large aspect ratio composite flexible wing design, this comprehensive optimization design requires optimization design at multiple levels, such as topology shape optimization and size optimization.

Moreover, this optimization considers complex aeroelastic problems. A comprehensive optimization design technique with multiple objectives, multiple constraints, and multiple multi-level design variables.

Large-scale composite material complex structure integrated manufacturing deformation

A prominent problem in the manufacture of composite materials is that they cannot be obtained with precise geometric or configuration dimensions similar to metal components, especially for large integrated complex composite structures, which may often be deformed due to a smaller local structure, ultimately resulting in Large integrated complex structures are highly deformed and cannot be used for component assembly.

Typical large-scale composite materials have high-altitude long-endurance UAV large aspect ratio flexible composite wing, unmanned attack wing body fusion large composite monolithic components.

In the study of the manufacturing process of these structures, attention is paid to the effects of uneven temperature distribution, uneven pressure distribution, structural asymmetry and other factors on deformation and determining the key factors affecting deformation, proposing deformation control methods and providing various measures to compensate for deformation. In order to solve the deformation problem of large and complex structures reasonably and effectively.

Stealth composite material structure design/manufacturing technology

Stealth is a high-tech technology required by modern warplanes. Due to the frequent occurrence of enemy air defense and radar surveillance, drones put forward higher requirements for stealth. Modern stealth technology mainly includes material stealth, coating stealth, plasma stealth, structural detail design, and stealth.

The structure of the UAV is mostly a composite sandwich structure. On the basis of the structural detail design stealth, the author believes that the research on the stealth design and manufacturing technology of the composite foam or honeycomb sandwich structure can be given priority, and the detail design and structural design and manufacturing level can be solved. UAV composite stealth technology.

RTM and RFI molding composite structural parts mechanical properties evaluation technology

Low cost and high efficiency are the distinguishing features of drones. The use of integrated forming technology plays an important role in reducing the number of composite parts, reducing the use and maintenance costs, saving costs, and improving efficiency. In recent years, RTM and RFI molding processes have been used to manufacture composite components.

However, this molding process has not been applied to specific models in batches. The reason is that the author believes that the relationship between the design, mechanical properties, configuration and mechanical properties of RTM and RFI molded composite structural members (such as woven composite components) has not been clearly understood.

Although some studies have been conducted on the mechanical properties of RTM and RFI molded composite components, this research is not systematic and incomplete.

Therefore, further research and evaluation of the mechanical properties of RTM and RFI molded composite structural members is a powerful guarantee for the design/manufacturing of low-cost, high-efficiency and cost-effective UAV structural platforms.

In addition, there are low-cost manufacturing technologies (low-cost materials, automated manufacturing, structural connection technology, etc.), rapid composite non-destructive testing technology, and intelligent material design/manufacturing technology.

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By |2019-05-13T03:16:16+00:00November 26th, 2018|uav technology|0 Comments
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