1. Overview
Due to the light weight, high specific strength, specific modulus and good ductility, corrosion resistance, thermal conductivity, heat insulation, sound insulation, vibration reduction, high (low) temperature resistance, ablation resistance, electromagnetic wave permeability, absorbing concealment, designability, flexibility of preparation and easy processing, etc., it is an ideal material for manufacturing aircraft, rockets, space vehicles and other military weapons.
Since the introduction of advanced composites into aerospace applications, there are three achievements worth mentioning. The first is that the United States made an eight-seat commercial aircraft - Learjet 2100 - all out of carbon fiber composite materials and successfully tested it; The second is the Space Shuttle Columbia, made of a large number of advanced composite materials, which made the main cargo door 18.2 meters long and 4.6 meters wide from carbon fiber/epoxy resin, and made various pressure vessels from Kevlar fiber/epoxy resin. The space shuttle, which represents the most cutting-edge technological achievements of modern times, used resin, metal and ceramic matrix composites; The third is the use of advanced composite materials as the main load-bearing structure, the manufacture of the Boeing-767 large passenger aircraft that can carry 80 people, not only reduces weight, but also improves the aircraft's various flight performance.
The successful application of composite materials in these aircraft shows the good performance and maturity of composite materials, and is a great promotion for the application of composite materials in important engineering structures.
Figure 1 Bombardier Learjet 45XR business aircraft
Fig.2 Space shuttle Columbia (picture of the crash site in the upper right corner)
Figure 3 Boeing 767
2. Aviation field (fixed-wing aircraft, helicopters, special aircraft)
Advanced composites are used to process composite materials with primary and secondary load-bearing structures whose stiffness and strength properties are equal to or exceed those of aluminum alloys. At present, it is widely used in the manufacture of aircraft fuselage structure and the overall structure of small UAVs.
After nearly 40 years of development, composite materials for aircraft have developed from the initial non-load-bearing components to be applied to secondary and main load-bearing components, which can achieve significant results of reducing the mass by (20-30)%. At present, it has entered a mature application period, and there is no doubt about improving the technical and tactical level, reliability, durability and maintenance of aircraft, and its design, manufacturing and use experience has become increasingly rich. So far, the composite materials used in fighter jets account for about 30% of the total materials used, and the new generation of fighters will reach 40%; The amount of composite materials used in helicopters and small aircraft will reach about (70-80)%, and even all-composite aircraft will appear. 70% of the fuselage of the Comanche helicopter is made of composite materials, but it is still planned to reduce the mass of the aircraft by another 15% by reducing the mass of the front lower part of the fuselage and expanding the composite material into fittings and bearings. "Apache", in order to reduce the mass, will replace the metal fuselage with composite materials.
In the past 10 years, composite materials have also been used in domestic aircraft. For example, the composite vertical tail wall plate of a fighter aircraft jointly developed by three domestic scientific research units is 21kg lighter than the original aluminum alloy structure and 30% lighter. QY8911/HT3 developed and produced by Beijing Institute of Aeronautical Manufacturing Engineering. Bismaleimide unidirectional carbon fiber prepreg and its composite materials have been used in aircraft front fuselage section, vertical tail stabilizer, wing, resistance plate, rectifier wall plate and other components. The PEEK/AS4C thermoplastic resin unidirectional carbon fiber prepreg and its composite materials developed by Beijing Institute of Aeronautical Materials have excellent fracture toughness, water resistance, aging resistance, flame retardancy and fatigue resistance, and are suitable for manufacturing aircraft main load-bearing components, which can work for a long time at 120 °C, and have been used for the front skin of the aircraft landing gear compartment guard.
Boeing estimates that every 1kg reduction in jetliner mass can save $2,200 over the life of the aircraft.
2.1 Fixed-wing aircraft
1) Abroad
The use of composite materials for large aircraft in foreign countries can be shown through the following pictures:
Figure 4-7 The use of composite materials for large aircraft in foreign countries
Light sport aircraft (LSA) is an aircraft classification name proposed by the FAA in 2004. The maximum take-off weight of this type of aircraft does not exceed 600 kg (for aircraft taking off and landing on water, the maximum take-off weight does not exceed 650kg), the maximum level flight speed does not exceed 222 km/h, and the stall speed does not exceed 83 km/h, which is comparable to the stall speed of traditional general aircraft, but the fuel consumption is halved, and the performance is better than that of traditional general aircraft. Single- or two-seater, fixed landing gear, propellers with variable gear, or ground-adjustable pitch moments, limited to one electric motor, or piston engine. Light sport aircraft have few maintenance restrictions and can be repaired and inspected by traditional aircraft maintenance technicians, by individuals qualified to repair light sport aircraft, and in some cases by pilots or owners.
Compared with passenger aircraft and military aircraft, light sport aircraft are smaller in size, simple in structure, mild in environment, and more relaxed in airworthiness standards, so the application of composite materials in light sport aircraft is less limited and less expensive to manufacture. Light sport aircraft generally use more than 70% composite materials, which is an all-composite aircraft. Composite materials have the advantages of light weight, high strength, high modulus, integration of structure and function, integration of design and manufacturing, and easy to become large products.
The Lear Fan2100 aircraft developed by the United States is the world's first all-composite aircraft based on advanced composite materials, mainly CFRP and KFRP, with a structural weight reduction of 40%. In addition to the rotor blades, the EC120 light helicopter jointly developed by China, France and Singapore also uses composite materials in many structures such as the fuselage, vertical tail, tail boom, and horizontal stabilizer. The JETCRUZER500 6-seater business jet developed by AASI in the United States is made of carbon/epoxy composite materials for its entire fuselage.
Figure 8 Lear Fan 2100 aircraft
The light sport aircraft market is very large, and there are many related manufacturers and models, at present, this field is mainly concentrated in some developed countries in Europe and the United States, and the well-known manufacturing companies are Cessna Aircraft Company of the United States, Xirui Design Company (which has been acquired by CAIGF), Austrian Diamond Aircraft Company, German Flight Design Company, etc. Among them, Flight Design GmbH is the world's leading professional manufacturer of design and production of light sport aircraft, and the CT series light sport aircraft developed by the company basically use carbon fiber composite fuselage. Most of the Remos aircraft produced by the German company Remos Aircraft are made of carbon fiber composite materials, and the wings are made of all carbon fiber, which is light in weight and has sleek lines. It is probably the most advanced light sport aircraft ever manufactured. The main components such as the wing of the DA42 "Gemini" aircraft of the Austrian diamond aircraft company are made of composite materials.
Figure 9 Cessna aircraft
Fig.10 Searays aircraft
Figure 11 Austrian Diamond Aircraft DA42 Gemini light aircraft
Fig.12 German Remos aircraft
The use of composite materials in foreign military aircraft is shown in the figure below:
Fig.13 The use of composite materials in foreign military aircraft
2) Domestic
Y-10 (Y-10) is a four-engine jet transport aircraft developed by Shanghai Aircraft Factory, which is China's first self-developed and self-manufactured large jet airliner.
Figure 14: Y-10 (Y-10)
The dual-engine regional airliner ARJ21 Xiangfeng passenger aircraft developed by Commercial Aircraft Corporation of China uses domestic carbon fiber to reduce weight of wing tips and secondary structural parts.
Fig.15 ARJ21 Xiangfeng passenger aircraft
The C919 is the second domestically produced large passenger aircraft independently designed by China. The wing, horizontal tail, and central wing box of the aircraft use composite structural parts.
Figure 16 C919
Here are some charts of Boeing's subcontracting in China:
Figure 17 Subcontracting of Boeing 737 in China
Figure 18 Boeing 747 subcontracting in China
Figure 19 Boeing 787 subcontracting in China
Hafei delivers and delivers Airbus A350 and Airbus A320 series composite aircraft parts to Airbus Group members and/or Airbus' designated suppliers; Participate in the research, development, industrialization and mass production of current or future Airbus aircraft programs; Manufacture, sell, distribute and distribute composite aircraft parts to third parties appointed by Airbus. The company has signed 7 work package contracts with Airbus and its Tier 1 suppliers, including A320 elevators, rudders, flat tail booms and A350 elevators, rudders, belly fairings, service doors, etc.
Figure 20 The first delivery ceremony of Hafei's A320 elevator (picture from the Internet)
Figure 21 The first delivery ceremony of Hafei's A320 elevator (picture from the Internet)
Xifei manufactures the entire wing of the A320 aircraft for Airbus and becomes a Tier 1 supplier.
Fig.22 The first pair of Airbus A320 wings produced by AVIC West are fitted to the fuselage
In China, civil aircraft can use international procurement to make up for the technological gap, such as aircraft engines, some airborne equipment, parts and materials. However, there are still many things in civil aircraft manufacturing that cannot be bought with money, such as the overall design capability of the aircraft, especially the integration ability, which depends on the accumulation of experience. Another example is fly-by-wire operation, which is the core technology, Airbus has been relatively mature in this aspect, and the Boeing 777 also uses fly-by-wire technology, some of which are still fly-by-wire technology, which will not be sold to us, only by their own research and development.
In recent years, many domestic units have also gradually carried out the research and development of light sport aircraft, and have achieved certain results. In September 2011, Shenfei signed a cooperation agreement with Cessna Aircraft Company of the United States to develop and produce the first Cessna 162 light sport aircraft based on aluminum alloy fuselage in mainland China, and successfully made its first flight.
In 2012, Nanchang Hangkong University and Zhuhai Qiangen FRP Products Co., Ltd. jointly developed the "Red Mouth Europe" sports aircraft, the aircraft structure is made of carbon fiber, glass fiber, epoxy resin, sandwich materials, etc., the main structure of the fuselage wing is made of carbon fiber composite materials, and part of the partition is glass fiber composite materials. The sandwich structure is partially adopted, and the outer part is covered with carbon fiber reinforced epoxy resin matrix composite surface plate, and 90% of the aircraft structure is composite material, which makes the aircraft light in weight and good in strength.
图23红嘴鸥 Black Headed Gull
Bodongfeng Aircraft Co., Ltd. independently developed the DF2 composite two-seater light sport aircraft (as shown in Figure 24), which was tested in July 2008. The main load-bearing structure of DF2 aircraft is made of carbon fiber material, and the design starting point is relatively high, but it still needs further improvement.
Fig.24 Domestic DF2 all-composite light sport aircraft
In June 2013, the electric two-seater light sport aircraft independently developed by Shenyang University of Aeronautics and Astronautics successfully made its first flight at Shenyang Faku Caihu Airport. This new clean energy aircraft uses lithium batteries as energy and uses all-carbon fiber composite material structure to build a fuselage, which has the characteristics of low cost, energy saving, environmental protection, safety and practicality compared with traditional gasoline aircraft. Liaoning Pacific Aviation Industry Co., Ltd. introduced the United States design KIS-2, KIS-4 are composite materials of 2-seat and 4-seat light aircraft, its structure is mainly FRP, such as wing beams, flat tail and other places on the use of carbon fiber composite materials.
Fig.25 Blue Eagle AD200 aircraft
At present, composite sandwich structures are the most widely used in light aircraft. The sandwich structure is usually made of relatively thin plates as panels, and thicker materials with low density are glued together as cores, such as honeycomb sandwich structure or foam sandwich structure.
The use of composite materials for domestic military aircraft is shown in the figure below:
Fig.26 The use of composite materials in domestic military aircraft
2.2 Helicopters
1) Helicopter landing gear
The skid-type helicopter landing gear has a simple structure, light weight, reliable performance, and is not easy to be damaged, mainly relying on the elastic deformation of the structure to absorb the landing energy. It can be installed with pontoons for take-off and landing on the surface or other special sites, which has great advantages in the civil field where the aircraft speed is slow, the take-off weight is light, the site is easy to guarantee, and the logistics is weak.
At present, metal matrix composites are mostly used. Like all fiber-reinforced composites, metal matrix composites can be designed to achieve a certain characteristic by using different fibers, matrices, and adjusting fiber capacities.
However, at present, the biggest disadvantages of metal matrix composites are their low fiber toughness, high process production cost, immature process, difficult to achieve mass production, and expensive. In addition, the design of metal matrix composites must be carefully considered in connection methods, load transfer paths, and fragile areas to estimate the potential for weight savings, thus making the design more difficult. The metal matrix composite material has poor shock absorption performance, and the use of this material as a landing gear must be equipped with complex shock absorption devices, which increases the weight and cost of the fuselage.
Carbon fiber/epoxy composite materials have excellent combined properties and are more suitable for use as helicopter landing gear materials. The carbon fiber/epoxy resin composite material can be designed according to the different requirements of the landing gear, and the molding process, material grade, and reinforcing material can be reasonably selected according to the force situation, so as to achieve the purpose of saving costs and reducing quality.
Fig.27 Composite helicopter landing gear (picture from the Internet)
2) Helicopter blades
The rapid development of helicopter technology, especially rotor technology, is largely due to the use of composite materials. The advantages of composite materials have been fully exerted in the rotor blade, which provides the possibility for the improvement and optimization of the aerodynamic shape of the rotor blade and the optimization of the dynamic characteristics of the rotor blade. More importantly, the composite material greatly improves the rotor life under the action of alternating load, and can achieve "maintenance according to the situation". This not only improves the safety of the helicopter, but also greatly reduces the cost of propeller manufacturing, which brings considerable economic benefits.
Fig.28. Planing view of the helicopter rotor
3) Helicopter paddle hubs
Compared with propellers, the composite of propeller hubs is relatively difficult, but breakthroughs have been made. The star-shaped flexible propeller hub successfully developed by the French aerospace company in the late 70s is the first breakthrough in the application of composite materials in the rotor propeller hub, and then countries have begun to research and test composite bearingless propeller hubs, making it possible to make the rotor structure fully composite. This is a revolution in the development of helicopter technology.
Fig.29. Articulated composite viscoelastic bearing hub of a Boeing-360 helicopter
4) Helicopter transmission system
The application of composite materials in the transmission system has also been put on the agenda, Boeing, McDonnell Douglas, Kaman Helicopter Company has carried out a lot of research work, Boeing has used graphite fiber and glass fiber mixed winding rotor shaft, reducer housing, etc. on its 360 helicopter to achieve success, its life is unlimited, while the weight is reduced by 25%.
Fig.30 Composite rotor shaft for Boeing-360 helicopter
5) Helicopter fuselage
In recent years, the application of composite materials in the fuselage has also made great progress, the first test flight of the all-composite fuselage is the S275 helicopter of Sikorsky Company, followed by the test flight of the D2292 helicopter of the all-composite fuselage of Bell Company and the Boeing-360 helicopter of Boeing Helicopter Company. These helicopters offer considerable benefits in terms of airframe weight, production costs, reliability and maintainability compared to the original aircraft.
Fig.31 The vertical tail of the domestic straight-9 all-composite culvert
2.3 Special aircraft (due to the large number and variety, only UAVs are used as an example here)
The composite structure of the UAV mainly includes laminate structure and sandwich structure, due to its strong designability, the number of parts and components of the UAV can be greatly reduced in the overall design of structural components, and the typical application is the wing-body fusion structure, see Figure 32-Figure 33.
Figure 32 U.S. X-48B UAV
Fig.33 European "Barracuda" UAV (fuselage is full carbon fiber composite material)
The structure used on the UAV has a sandwich structure and a laminate structure, such as the fuselage structure is composed of a longitudinal beam flange, a skin and a transverse frame, as shown in Figure 34; Among them, the skin is a honeycomb sandwich structure, and the beam flange is mostly a composite laminate structure. The wing surface is mostly sandwich panel beam structure, sandwich wall structure, full-height foam sandwich structure, skin cavity structure and sandwich box structure, as shown in Figure 35:
Fig.34 Typical structure of UAV fuselage
Fig.35. Typical structure of UAV wing surface
The reinforcing materials used in the structural parts of UAV composite materials mainly include carbon fiber, glass fiber, etc., while the resin system mainly includes epoxy resin system and bismaleimide resin system, the former has better manufacturability, and the latter has better temperature resistance.
The manufacturing methods of UAV composite structural parts mainly include autoclave molding, vacuum bag forming and compression molding.
Fig.36 Bagging of auxiliary materials for autoclave forming process
Source: Advanced Materials Industry Expo
Reprint: Material PLUS