Currently, composite materials have become one of the four major material systems alongside metallic materials, polymer materials, and inorganic non-metallic materials. The level of a nation's composite materials industry has become a key indicator of its scientific, technological, and economic strength. Advanced composite materials are a source of competitive advantage for national security and the economy. It is predicted that by 2020, only composite materials will have the potential to achieve a 20%–25% performance improvement.
1. Applications in Aircraft Fuselage Structures
Advanced composite materials are used to manufacture primary load-bearing structures and secondary load-bearing structures, offering stiffness and strength comparable to or exceeding those of aluminum alloys. These materials are now widely applied in the manufacturing of aircraft fuselage structures and small unmanned aerial vehicle (UAV) integrated structures. The United States has extensively adopted composites in fighter jets and combat aircraft.In the 1960s, the U.S. first utilized carbon fiber-reinforced plastics (CFRP) in military aircraft for components such as cabin doors, access panels, fairings, and control surfaces (e.g., ailerons and rudders) with low or non-load-bearing requirements. By the early 1980s, composites advanced to tail components like vertical and horizontal stabilizers (secondary load-bearing structures), as seen in aircraft such as the F-15, F-16, F-18, Mirage 2000, and Mirage 4000. During this phase, composite usage remained limited.By the late 1980s, fourth-generation fighters like the F-22 and F-35 JSF began incorporating composites into major load-bearing structures such as wings and fuselages, accelerating the integration of composites into military aircraft. The usage of composite materials has continued to increase (Table 1-2), now accounting for 20%–50% of the structural mass in modern military aircraft.
British company ICI used GF/PA (likely glass fiber-reinforced polyamide) to produce valves for fighter aircraft, ensuring that these valves maintain performance and dimensional stability even after prolonged exposure to fuel across a wide temperature range. Du Pont also employed materials such as GF, KF/PA, and PPS (polyphenylene sulfide) to manufacture components for military aircraft.
Taking the fourth-generation F/A-22 fighter as an example, composites account for 24.2% of its structural materials. Among these, thermosetting composites make up 23.8%, while thermoplastic composites constitute approximately 0.4%. Around 70% of the thermosetting composites are based on bismaleimide (BMI) resin, used to produce over 200 types of complex components. The remaining thermosetting materials primarily consist of epoxy resin-based composites, with additional use of cyanate ester and thermoplastic resin-based composites. Key application areas include wings, mid-fuselage skins, frames, and tail sections.
Military rotorcraft also extensively utilize composites. For instance, the V-22 Osprey tiltrotor aircraft employs composites for over 40% of its structural mass, including the fuselage, wings, tail, and rotational mechanisms, totaling more than 3,000 kg of composite materials. The latest European Eurocopter Tiger attack helicopter features composite materials in 80% of its structural components, nearing a fully composite airframe. In contrast, military transport aircraft use fewer composites-C-17 at 8% and C-130J at just 2%-though the Airbus A400M military transport incorporates an all-composite wing, with composites representing 35% of its structural mass when empty.
In civil aviation, the early 1980s U.S.-built single-pilot Star舟 light aircraft had a structural mass of around 1,800 kg, with composites exceeding 1,200 kg. The 1986 Voyager light aircraft, with over 90% of its structure made of carbon fiber composites, set a world record for a non-stop, nine-day continuous around-the-world flight. Today, the rivalry between aerospace giants Boeing and Airbus has intensified, with a key focus on increasing composite material usage (Figure 1-2).
To produce the first all-composite 787 aircraft fuselage, Boeing adopted a fiber placement method similar to that used by Raytheon. The process created a composite fuselage component measuring 7 meters in length and 6 meters in width. This structure was manufactured using Automatic Fiber Placement (AFP) technology on a massive rotating mandrel. The mandrel was pre-machined with grooves matching the shape and dimensions of the fuselage stringers and longerons. Preformed stringers and beams (made from carbon fiber prepreg layers and pressure-cured) were placed into these grooves before winding. During production, the mandrel rotated along its axis, allowing continuous fiber winding onto the mold to form the fuselage shell, with window openings left unlaid. The fuselage shell, along with the beams and stringers, was then autoclave-cured to create a monolithic composite fuselage section, which was later demolded as the final product.
The Boeing 787's composite fuselage section is not only the world's largest filament-wound fuselage component but also recognized as the largest carbon fiber pressure vessel ever produced. The composite material's exceptional tensile/hoop strength enables it to withstand higher cabin pressure, maintaining an internal pressure equivalent to an altitude of 6,000 feet (1,830 meters)-compared to the typical 7,000–9,000 feet in conventional aircraft-significantly improving passenger comfort. Additionally, composites resist corrosion (a major weakness of metal airframes), allowing cabin humidity to remain stable at 10–15% (versus 5–10% in metal fuselages), further enhancing comfort.
Under the growing influence of composite technology, Airbus completely redesigned the A-350, renaming it the A-350 XWB (Extra Wide Body). The aircraft increased its composite material usage from the original 40% to 52%. The A-350 XWB's fuselage is 13 cm wider than the 787's, enabling a 9-abreast seating configuration in high-density layouts (compared to the 787's maximum of 8-abreast). Like the 787, the A-350 XWB will maintain cabin pressure at an altitude-equivalent of 6,000 feet.
On June 14, 2013, Airbus successfully conducted the maiden flight of its new wide-body A350 XWB aircraft, marking another milestone in the global aviation industry following Boeing's B-787 "Dreamliner." The A350 XWB and B-787 use 52% and 50% composite materials, respectively, signifying a new era in aerospace composite development.
The 555-seat A-380, the world's largest aircraft, achieved groundbreaking feats in aviation history by extensively utilizing carbon fiber-reinforced plastic (CFRP). Composite materials constitute 25% of the aircraft's mass, with 22% being CFRP and 3% being GLARE fiber-metal laminate (a layered hybrid of aluminum and glass fiber composites), the latter's first use in civil aircraft. CFRP components include: speed brakes, vertical and horizontal stabilizers (doubling as fuel tanks), elevators, ailerons, flap spoilers, landing gear doors, fairings, vertical tail fin boxes, upper cabin floor beams, rear pressure bulkheads, rear fuselage sections, horizontal stabilizers, and ailerons.
Following the A-340's pioneering use of carbon fiber for the keel beam and composite rear pressure bulkheads-breaking traditional design barriers-the A-380 further challenged engineering norms by adopting CFRP for its central wing box (connecting the wings to the fuselage). This innovation alone reduced weight by 1.5 metric tons compared to advanced aluminum alloys. CFRP's weight savings, combined with fatigue and corrosion resistance, improved fuel efficiency by 13% over competing models and reduced emissions. The A-380 became the first long-haul aircraft to achieve under 3 liters of fuel per passenger per 100 km, with operating costs 15–20% lower than the most efficient aircraft of its time.
Dassault Aviation's Falcon 7X business jet, capable of cruising at 12,000 meters with a max speed of Mach 0.8, accommodates 8 passengers and boasts a range of 10,560 km (5,700 nautical miles). Raytheon's Beechcraft Premier 1 light jet reaches a cruising speed of 835 km/h with a range of 2,759 km-both featuring advanced all-composite fuselages.
Japan's new transport aircraft, ALELEX, also incorporates significant carbon fiber composites.
China has also extensively utilized composite materials in aircraft design and production. For instance, the QY8911/HT3 bismaleimide unidirectional carbon fiber prepreg and composite material developed and manufactured by the Beijing Aeronautical Manufacturing Technology Research Institute have been applied to components such as the forward fuselage section, vertical tail stabilizer, outer wing panels, spoilers, and streamlined fairings of aircraft. The PEEK/AS4C thermoplastic resin unidirectional carbon fiber prepreg and composite material developed by the Beijing Institute of Aeronautical Materials exhibit exceptional fracture toughness, water resistance, aging resistance, flame retardancy, and fatigue resistance. Suitable for manufacturing primary load-bearing aircraft structures, these materials can operate long-term at 120°C and have been used in the front skins of aircraft landing gear bay panels.
The Chinese military aircraft "Flying Leopard," which incorporates significant carbon fiber composite components, has an overall length of approximately 22.3 meters, a wingspan of 12.7 meters, a maximum takeoff weight of 28.4 tons, a maximum external payload capacity of 6.5 tons, a top speed of Mach 1.70, and a ferry range of around 3,600 kilometers. With combat capabilities surpassing those of the Jaguar, Tornado, and Su-24 aircraft, the Flying Leopard demonstrates characteristics consistent with third-generation fighter jets.
2. Application of Composite Materials in Aircraft Stealth
In recent decades, significant progress has been made in the research of stealth composite materials, which are evolving toward characteristics of "thinness, lightness, broadband (spectral) absorption, and strength (impact resistance, high-temperature resistance)." Carbon fiber-reinforced composites are not only lightweight and high-strength structural materials but also possess critical stealth functionality. For example, CF/PEEK or CF/PPS exhibit excellent broadband absorption performance, effectively absorbing radar waves. The United States pioneered the use of stealth materials in aircraft, with the F-117 and F-22 being the most heavily coated. The stealth coating on the F-117 was highly complex, incorporating up to seven different materials.
The primary structure of the U.S. F-22 supersonic fighter utilizes medium-modulus carbon fiber-reinforced specialty engineering plastics. Similarly, the Mirage III fighter's deceleration parachute covers and ejection seat components are made from such materials, which have been successfully applied to radar-absorbing parts like aircraft ribs, skins, connectors, and fasteners. The Tomahawk cruise missile casing, the airframe substrate of the B-2 stealth bomber, and sections of the F-117A stealth aircraft also employ carbon fiber-modified polymer radar-absorbing materials.
In 2000, the U.S. Air Force upgraded the F-117's stealth materials, replacing the original seven-layer coating with a single material. This change standardized maintenance procedures and radar-absorbing materials across all F-117s, reducing technical specifications by approximately 50%. Post-upgrade, the maintenance time per flight hour for the F-117 was cut by over half, and annual maintenance costs for all 52 F-117s dropped from 14.5million,6.9million. Unlike the F-117, the F-22 avoids full-body radar-absorbing coatings but applies ferrite radar-absorbing coatings to all internal and external metal components. This coating is durable, wear-resistant, and easier to apply compared to the F-117's system.
Experts predict that by the 2030s, advanced composites such as conductive polymer electrochromic materials, hybrid semiconductor materials, nanocomposites, and intelligent stealth technologies will be practically implemented in aircraft. These innovations could fundamentally transform avionics systems and aircraft control methodologies.
Source: Aviation Composite Materials and Their Mechanical Analysis by Haitao Cui and Zhigang Sun (Eds.)