Application of advanced composite materials in UAV structural parts

Unmanned Aerial Vehicle (UAV) is an unmanned aircraft that uses a radio remote control device and its own program control device to operate, or is operated completely or intermittently by an onboard computer. As a new type of aircraft, unmanned aerial vehicle (UAV) has different requirements and missions compared with manned aircraft. Uavs usually have low cost, light structure, high stealth, long endurance and high storage life requirements, as well as high mobility and large overload requirements for unmanned combat aircraft.CFRTP

Because composite materials have the characteristics of high specific strength, large specific modulus, strong designability, strong fatigue resistance, can improve the stealth performance of the body, long service life, good shock absorption performance, etc., most of the UAV structures are made of composite materials, such as fuselage, wing, flat tail, vertical tail, tail brace, rudder surface and landing gear.

Composite materials applied to UAV structures can reduce weight by 20%-30%. At present, the industry believes that the amount of composite materials has become one of the important indicators to measure the advanced degree of a UAV, which generally needs to reach about 60%-80%. However, the United States has reached the full composite structure of UAVs (the amount of composite material reaches more than 90%) the application of composite structure in the field of UAVs polyacrylonitrile based carbon fiber and Nomex honeycomb materials are widely used in the body shell, wing skin and leading edge of UAVs; Foam sandwich composite made of PAN-based carbon fiber plate and foam material or polyacrylonitrile based carbon fiber tube is widely used as the main beam of UAV. Kevlar fiber materials are applied to propellers, fuselages, connectors and other parts to significantly improve fatigue strength and impact resistance. The main bearing structure of medium and large UAV is made of metal, the rest is made of composite materials, small and medium-sized UAV is made of carbon fiber, glass fiber and its hybrid materials, and unmanned fighter aircraft is made of carbon fiber composite material, aramid fiber and so on. Small, low-speed drones are made of carbon fiber, aramid fiber, paper honeycomb and wood.

Because the UAV does not need to consider the limitation of human physiological bearing capacity in the structural design, it can be more focused on the design of the maneuvering performance of the UAV, so that it has some characteristics in the selection of materials that are different from manned aircraft. The application of composite materials can greatly improve the stealth ability of the body. First, because the polymer is not conductive, it can avoid the formation of the scattering field of the probe wave. Secondly, the application of composite materials plays a very important role in the effective combination of structure and function. For example, through the application of structural stealth materials, the body's reflection of radar detection waves can be greatly reduced. Finally, the application of composite materials can achieve the integrity of the body, so as to achieve the purpose of stealth through smooth and integrated structural design, avoiding the scattering of detection waves caused by joints, nails and other non-smooth design. All in all, these designs effectively improve the stealth of drones. According to statistics, at present, countries around the world are largely using advanced composite materials based on carbon fiber composites on drones, accounting for 60%-80% of the total mass fraction of the structure; Reduce body mass by more than 25%. From the beginning of the non-bearing structure, more and more bearing structures of UAVs are designed and manufactured using carbon fiber composite structures.

Uav composite co-curing structure design In order to better reduce weight, increase mission load, and extend endurance, lightweight design of composite materials is the trend of modern UAV design, and the lightweight trend is the integrated design and manufacturing of structures. With the increase of the amount of composite materials, the complexity of the structure continues to rise, and it is very meaningful to give full play to the potential of composite materials, greatly reduce the weight, further simplify the integral structure of the assembly relationship, and shorten the production process. The UAV structure is generally formed by plate, beam and rib structure respectively, and then assembled by room temperature bonding. First, the unilateral plate and skeleton are bonded, followed by room temperature bonding with another plate, and the bonding quality cannot be monitored. This project intends to establish a co-curing molding (medium temperature curing) of wall panel and beam bonding, which has greater bonding strength, higher reliability, shorter component assembly cycle, greatly reduced cost, and can reduce the use of connecting parts. Co-curing design and manufacturing technology is advanced, which can better play the advantages of strong designability, high specific strength and high specific modulus of composite materials, and can further carry out lightweight design, so as to achieve the purpose of system weight reduction, task load increase, and battery life extension. The application parts of composite materials have been developed from non-load-bearing parts and sub-load-bearing parts to main load-bearing parts. The development direction also tends to be large-scale, integrated and low-cost, composite material integral molding technology by reducing the number of complex and large structure parts assembly and fasteners to achieve lightweight, efficient and low-cost composite parts. In the overall composite molding technology, the co-curing molding technology is preferred, and the composite parts manufactured by this technology have light structural weight and small deformation.

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