Engineering plastics are extensively applied in aircraft due to their lightweight nature, impact resistance, high strength, excellent electrical insulation, corrosion resistance, wear resistance, and ease of molding. Nearly all types of engineering plastics and their reinforced composites can find suitable applications and play vital roles in an aircraft structure. The applications of engineering plastics in aircraft can generally be categorized into electrical components, structural parts, interior trim, and transparent components.
Plastic Electrical Components
Their superior electrical insulation properties drove the initial use of engineering plastics in aviation. They are primarily used in motors, electrical appliances, instrumentation, and power distribution systems to manufacture coil bobbins, terminal blocks, sockets, connectors, switches, as well as insulation layers and protective sleeving for wiring. For example:
- ABS, Polycarbonate (PC), PBT, and Polyamide (PA): Used for manufacturing electrical conduits, regulators, connectors, and various switches.
- Polyetheretherketone (PEEK): Utilized for radar components and radomes.
- Pyromellitic Polyimide (PI) Film: Used for insulation and protective layers of aviation wires and cables due to its exceptional heat resistance and dielectric properties.
Plastic Structural Parts
Replacing metal with engineering plastics for structural parts in aircraft engines and various accessories is a significant trend for expanding their application. These parts include self-lubricating bearings, bushings, seals, retaining rings, fasteners, instrument housings, cams, pulleys, gears, clamps, and various gaskets. Examples include:
- Polyetheretherketone (PEEK): Used for manufacturing various engine components.
- Polyamide (PA) and Polyoxymethylene (POM): Used for pulleys, cams, retaining rings, clamps, and gears.
- Polytetrafluoroethylene (PTFE): Utilized for bearings due to its excellent self-lubricating properties.
- Polyimide Molding Compounds: Used to replace bronze for wear-resistant bushings in engine front frames.
- Glass Fiber Reinforced Polyimide: Used for jet engine tail nozzles and flap seals (fish scales).
Plastic Interior Trim
Interior trim represents another critical area of plastic application. For instance, in a Boeing 727 with a gross weight of 77,180 kg, plastics account for 2,730 kg, of which 908 kg are used for interior trim. These components include luggage racks, flooring, liners, seats, window frames, acoustic/thermal insulation, and decorative adhesives. Large-surface panels such as decorative side walls, ceilings, storage bins, and partitions are often surfaced with Polyvinyl Fluoride (PVF) film, which offers both aesthetic appeal and flame retardancy.
| Material | Processing method | Sun visors, lamp covers, food boxes, lavatory tissue boxes, magazine racks, and projector housings |
| Polycarbonate (PC) | Rotational molding, Injection | Sun visors, lamp covers, food boxes, lavatory tissue boxes, magazine racks, and projector housings |
| Polycarbonate (PC) | Rotational molding, Injection | Window frames, magazine racks, waste bins, seats, passenger service units (PSU), meal trays, carpet edging |
| ABS | Injection, Extrusion | Seat armrests, door inner panels, door trim |
| Polyamide (PA) | Injection, Extrusion | Seat backs, elastic cushions, wall panels, carry-cots |
| Polysulfone (PSU) | Rotational molding, Thermoforming | Ventilation and drainage pipes |
| PVF Film | Casting or Extrusion | Surface laminates for wall panels, ceilings, etc. |
| Polyethersulfone (PES) | Injection | Window frame channels, sunshade rails, door handles, latches, oxygen mask housings, telephones, knobs |
| Polyethersulfone (PES) | Extrusion | Decorative panels, ejection seat covers |
| Polyethersulfone (PES) | Vacuum forming, Thermoforming | Sun visors, lamp covers, food boxes, lavatory tissue boxes, magazine racks, projector housings |
Transparent Plastic Components
Transparent components refer to materials used for observation and lighting, including windshields, canopy covers, nose cones, various-shaped cabin windows, transparent partitions, instrument panels, passenger lighting covers, and navigation light covers. Since these are part of the airframe structure, they must maintain an aerodynamic profile and withstand aerodynamic loads, pressurization, and kinetic heating during flight. Consequently, they serve as both structural and functional members.
Performance of Transparent Plastics
Transparent materials are categorized into two types:
- Polymethyl Methacrylate (PMMA), this is a general-purpose plastic.
- Polycarbonate (PC), this is an engineering plastic.
These materials are used for monolithic transparent parts or as structural layers in glass-plastic composite systems. Structures include single-layer, double-layer, and laminated forms. Laminated structures are further classified by material combinations: glass-glass, glass-acrylic, glass-polycarbonate, and acrylic-polycarbonate.
| Structure | Material | Connection Types | Features | Applications |
| Single-layer | Monolithic acrylic or PC board | Various rigid or flexible connections | Easy to process and manufacture | Windows for small/medium aircraft and helicopters; fighter canopies and windshields; bomber nose cones and observation windows |
| Double-layer | Two acrylic sheets with a rubber/plastic spacer; air or nitrogen-filled cavity | Clamping frame or plate | Fail-safe structure; excellent thermal and acoustic insulation | Passenger windows and door windows for large/medium aircraft; some cockpit side windows |
| Laminated | Multiple layers of glass, acrylic, or PC bonded with transparent interlayers; may include heating elements | Clamping frame (glass); clamping plate or bolts (plastic) | Bird-strike resistance or bulletproof capability | Bird-strike resistant windshields and bulletproof glass for military/civil aircraft and some helicopters; some fighter canopies |
Aviation-grade Polycarbonate (PC) sheet is extruded from specific Bisphenol A type PC resin and then calendered. Compared to acrylic, its primary advantage is superior impact resistance (falling-weight impact strength is 20 times that of oriented acrylic) and higher heat resistance (heat deflection temperature is ~30°C higher). However, it has poor abrasion resistance, is prone to stress cracking under solvent exposure, and is UV-sensitive, usually requiring a hard coating for protection. In aviation, it is rarely used alone but serves as the load-bearing structural layer in laminated transparent panels.
Requirements for Transparent Materials
Transparent components must possess excellent optical properties, sufficient structural strength, wear resistance, a long service life, high reliability, and ease of maintenance.
| Item | Requirements |
| Shape | Streamlined to reduce drag; stealth aircraft require special shapes for low radar cross-section (RCS) |
| Field of View | Excellent visibility and clarity; fighters require wide front and side views, as well as downward, upward, and rear visibility |
| Optical Properties | High light transmittance, minimal haze; critical windows must meet strict optical distortion and angular deviation standards; thick parts must account for binocular parallax and ghosting |
| Load Capacity | Static: withstand aerodynamic and pressurization loads; Dynamic: meet fatigue life requirements; Concentrated: bird-strike resistance for front sections and bulletproof requirements for combat aircraft |
| Thermal Resistance | Standard: -55 to 60°C; supersonic aircraft must withstand kinetic heating above 95°C |
| Environmental | Resistance to aging, humidity, heat, and salt spray |
| Flame Retardancy | Horizontal burn rate not exceeding 64 mm/min |
| Processability | Easy to thermoform and machine; decomposition temperature must be significantly higher than molding temperature |
| Maintainability | Easy to repair with high component interchangeability |
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Typical transparent components differed by plane type:
| Type | Name |
| Attack Aircraft | Front windshield (bulletproof), side windshield, movable canopy |
| Bomber | Bombing sight window, cockpit central/main windshields, nose cone, navigation windows, observation covers, rear gunner windows (side/front-bulletproof) |
| Passenger Aircraft | Central/main windshields, eyebrow windows (upper fixed), clear-view windows (movable), side fixed windows, entry door windows, passenger cabin windows |
| Helicopter | Green filter glass, windshields, lower-view glass, pilot door windows (upper/lower), sliding glass, front/rear cabin door glass |
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