《飛行員航空知識手冊》Chapter 3 Aircraft Structure


An aircraft is a device that is used, or intended to be used, for flight, according to the current Title 14 of the Code of Federal Regulations (14 CFR) Part 1, Definitions and Abbreviations.

Categories of aircraft for certification of airmen include airplane, rotorcraft, glider, lighter-than-air, powered-lift, powered parachute, and weight-shift control.

14 CFR part 1 also defines airplane as an engine-driven, fixed-wing aircraft that is supported in flight by the dynamic reaction of air against its wings.

Another term, not yet codified in 14 CFR part 1, is advanced avionics aircraft, which refers to an aircraft that contains a global positioning system (GPS) navigation system with a moving map display, in conjunction with another system, such as an autopilot.

This chapter provides a brief introduction to the structure of aircraft and uses an airplane for most illustrations. Light Sport Aircraft (LSA), such as weight-shift control, balloon, glider, powered parachute, and gyroplane have their own handbooks to include detailed information regarding aerodynamics and control.

abbreviation /əˌbriː.viˈeɪ.ʃən/a short form of a word or phrase縮略,縮寫
dynamic  /daɪˈnæm.ɪk/relating to forces that produce movement動力的(與產生運動的力有關的)
codify /ˈkəʊ.dɪ.faɪ/  US  /ˈkɑː-/to arrange something, such as laws or rules, into a system編成法典;編纂(法典、條例等)
avionics /ˌeɪ.viˈɒn.ɪks/the science and technology of the electronic devices used in aeronautics and astronautics航空電子學;航空電子技術
navigation /ˌnæv.ɪˈɡeɪ.ʃən/the act of directing a ship, aircraft, etc. from one place to another, or the science of finding a way from one place to another領航(術);導航(術)
in conjunction with結合;聯合
aerodynamics /ˌeə.rəʊ.daɪˈnæm.ɪks/

the science which studies the movement of gases and the way solid bodies, such as aircraft, move through them空氣動力學

2.Lift and Basic Aerodynamics 空氣動力學


In order to understand the operation of the major components and subcomponents of an aircraft, it is important to understand basic aerodynamic concepts. This chapter briefly introduces aerodynamics; a more detailed explanation can be found in Chapter 4, Aerodynamics of Flight.

平直飛行時,作用在飛機的四種力 (推.拉.重.升)
Four forces act upon an aircraft in relation to straight-and-level, unaccelerated flight. These forces are thrust,drag,lift,and weight.




Thrust is the forward force produced by the powerplant/propeller. It opposes or overcomes the force of drag. As a general rule, it is said to act parallel to the longitudinal axis. This is not always the case as explained later.

propeller /prəˈpel.ər/
parallel /ˈpær.ə.lel/
Longitudinal /ˈlɒn.dʒɪ.tjuːd/
the distance of a place east or west of an imaginary line from the top to the bottom of the Earth, measured in degrees
axis /ˈæk.sɪs/ (複數axes)


Drag is a rearward, retarding force, and is caused by disruption of airflow by the wing, fuselage, and other protruding objects. Drag opposes thrust, and acts rearward parallel to the relative wind.

rearward ˈrir-ˌwȯrd


retarding /rɪˈtɑːd/

遲滯; 減速

disruption /dɪsˈrʌp.ʃən/


fuselage /ˈfjuː.zəl.ɑːʒ/


protruding /prəˈtruːd/



Weight is the combined load of the airplane itself, the crew, the fuel, and the cargo or baggage. Weight pulls the airplane downward because of the force of gravity. It opposes lift, and acts vertically downward through the airplane’s center of gravity (CG).


Lift opposes the downward force of weight, is produced by the dynamic effect of the air acting on the wing, and acts perpendicular to the flightpath through the wing’s center of lift.

perpendicular /ˌpɜː.pənˈdɪk.jʊ.lər/




飛機三軸 (縱.橫.垂直)

An aircraft moves in three dimensions and is controlled by moving it about one or more of its axes.


The longitudinal or roll axis extends through the aircraft from nose to tail, with the line passing through the CG.



The lateral or pitch axis extends across the aircraft on a line through the wing tips, again passing through the CG.



The vertical, or yaw, axis passes through the aircraft vertically, intersecting the CG.


All control movements cause the aircraft to move around one or more of these axes, and allows for the control of the airplane in flight.


longitudinal ˌlɒn.dʒɪˈtjuː.dɪ.nəl/


lateral /ˈlæt̬.ɚ.əl/


pitch /pɪtʃ/


yaw /jɑː/



One of the most significant components of aircraft design is CG. It is the specific point where the mass or weight of an aircraft may be said to center; that is, a point around which, if the aircraft could be suspended or balanced, the aircraft would remain relatively level.


The position of the CG of an aircraft determines the stability of the aircraft in flight.

As the CG moves rearward (towards the tail) the aircraft becomes more and more dynamically unstable.

In aircraft with fuel tanks situated in front of the CG, it is important that the CG is set with the fuel tank empty. Otherwise, as the fuel is used, the aircraft becomes unstable. [Figure 2-3]



The CG is computed during initial design and construction, and is further affected by the installation of onboard equipment, aircraft loading, and other factors.

3.Major Components主要組成






Although airplanes are designed for a variety of purposes, most of them have the same major components. [Figure 2-4] The overall characteristics are largely determined by the original design objectives. Most airplane structures include a fuselage, wings, an empennage, landing gear, and a powerplant.


The fuselage is the central body of an airplane and is designed to accommodate the crew, passengers, and cargo. It also provides the structural connection for the wings and tail assembly(組合).
Older types of aircraft design utilized(利用) an open truss(桁架) structure constructed of wood, steel, or aluminum tubing. [Figure 2-5] The most popular types of fuselage structures used in today’s aircraft are the monocoque(單體構造) (French for “single shell”) and semimonocoque(半硬殼式機身). These structure types are discussed in more detail under aircraft construction later in the chapter.



The wings are airfoils(機翼,螺旋槳) attached to each side of the fuselage and are the main lifting surfaces that support the airplane in flight. There are numerous wing designs, sizes, and shapes used by the various manufacturers. Each fulfills a certain need with respect to the expected performance for the particular airplane. How the wing produces lift is explained in Chapter 4, Aerodynamics of Flight.


Wings may be attached at the top, middle, or lower portion of the fuselage. These designs are referred to as high-, mid-, and low-wing, respectively. The number of wings can also vary. Airplanes with a single set of wings are referred to as monoplanes(單翼機), while those with two sets are called biplanes(雙翼飛機).



Many high-wing airplanes have external braces(緊固裝置), or wing struts(支柱), which transmit the flight and landing loads through the struts to the main fuselage structure.

Since the wing struts are usually attached approximately halfway out on the wing, this type of wing structure is called semi-cantilever(半懸臂). A few high-wing and most low-wing airplanes have a full cantilever(懸臂樑) wing designed to carry the loads without external struts.


The principal structural parts of the wing are spars(翼樑), ribs(肋材構架), and stringers(縱樑). [Figure 2-7] These are reinforced by trusses(桁架), I-beams(I形金屬桁樑), tubing, or other devices, including the skin. The wing ribs determine the shape and thickness of the wing (airfoil). In most modern airplanes, the fuel tanks either are an integral part of the wing’s structure, or consist of flexible containers mounted inside of the wing.


Attached to the rear or trailing edges of the wings are two types of control surfaces referred to as ailerons(副翼) and flaps(襟翼,阻力板).


Ailerons extend from about the midpoint of each wing outward toward the tip, and move in opposite directions to create aerodynamic forces that cause the airplane to roll.

襟翼(flap)自油箱向機翼中間延伸,襟翼(flap)在cruising flight時與機翼齊平

Flaps extend outward from the fuselage to near the midpoint of each wing. The flaps are normally flush with the wing’s surface during cruising(最省油之飛行的) flight.


When extended, the flaps move simultaneously downward to increase the lifting force of the wing for takeoffs and landings. [Figure 2-8]



Alternate Types of Wings

With the Federal Aviation Administration’s (FAA) recent addition of the LSA category, various methods are employed to control flight and to produce lift. These methods are discussed in Chapter 4, Aerodynamics of Flight, which provides information on the effect controls have on lifting surfaces from traditional wings to wings that use both flexing (due to billowing) and shifting (through the change of the aircraft’s CG). Handbooks specific to each category of LSA are available for the interested pilot. LSA illustrate various lifting surfaces and control methods. For example, the wing of the weight-shift control aircraft is highly swept, and the shifting of weight to provide controlled flight. [Figure 2-9]


水平尾翼(Horizontal Stabilizer),簡稱平尾

垂直尾翼(Vertical Stabilizer),簡稱垂尾

The empennage includes the entire tail group and consists of fixed surfaces such as the vertical stabilizer(垂尾) and the horizontal stabilizer(平尾).

The movable surfaces include the rudder(方向舵), the elevator(升降舵), and one or more trim tabs(配平片). [Figure 2-10]


The rudder is attached to the back of the vertical stabilizer. During flight, it is used to move the airplane’s nose left and right.


The elevator, which is attached to the back of the horizontal stabilizer, is used to move the nose of the airplane up and down during flight.

配平片(Trim tabs)

Trim tabs(配平片) are small, movable portions of the trailing edge of the control surface. These movable trim tabs, which are controlled from the flight deck, reduce control pressures. Trim tabs may be installed on the ailerons, the rudder, and/or the elevator.

配平片(Trim Tab)是飛機三個操縱平面上的一種片狀裝置。藉由空氣動力學的原理,可幫助飛行員減輕對各操縱翼面的操控量,或保持操縱面於指定的適當位置。一般小型飛機,經常在水平舵面(升降舵)及垂直舵面(方向舵)可見到Trim Tab的裝置。簡單配平片的調整,有機械手動與點動微調兩種方式。


A second type of empennage design does not require an elevator. Instead, it incorporates a one-piece horizontal stabilizer that pivots(置於樞軸上) from a central hinge(樞紐) point. This type of design is called a tabilator(全動平尾), and is moved using the control wheel, just as the elevator is moved.

For example, when a pilot pulls back on the control wheel, the stabilator(全動平尾) pivots so the trailing edge moves up. This increases the aerodynamic tail load and causes the nose of the airplane to move up. Stabilators have an antiservo tab(反補償片) extending across their trailing edge. [Figure 2-11]The antiservo tab moves in the same direction as the trailing edge of the stabilator and helps make the stabilator less sensitive. The antiservo tab also functions as a trim tab to relieve control pressures and helps maintain the stabilator in the desired position.

Anti-Servo Tab會給飛行員帶來操縱時的阻力手感,最終得到防止操作過度(over control)的作用。

比如當飛行員壓杆,Stabilator向上傾斜,平尾仰角變大,造成機體後部升力變大,於是機首向下傾斜(nose down)。
但是往往升降舵的效果非常明顯,反映到杆力就是力量非常輕,如果沒有Anti-Servo Tab的話,得不到足夠的力量反饋,飛行員很有可能操作過量。

Landing Gear起落架

The landing gear is the principal support of the airplane when parked, taxiing, taking off, or landing. The most common type of landing gear consists of wheels, but airplanes can also be equipped with floats for water operations, or skis for landing on snow. [Figure 2-12] The landing gear consists of three wheels—two main wheels and a third wheel positioned either at the front or rear of the airplane. Landing gear with a rear mounted wheel is called conventional landing gear.


Airplanes with conventional landing gear are sometimes referred to as tailwheel(尾輪) airplanes. When the third wheel is located on the nose, it is called a nosewheel, and the design is referred to as a tricycle gear.
A steerable nosewheel or tailwheel permits the airplane to be controlled throughout all operations while on the ground. Most aircraft are steered(駕駛) by moving the rudder(方向舵) pedals(方向舵腳蹬), whether nosewheel or tailwheel. Additionally, some aircraft are steered by differential braking.

The Powerplant發動機:包含引擎、螺旋槳

The powerplant usually includes both the engine and the propeller. The primary function of the engine is to provide the power to turn the propeller. It also generates electrical power, provides a vacuum source for some flight instruments, and in most single-engine airplanes, provides a source of heat for the pilot and passengers. [Figure 2-13] The engine is covered by a cowling(整流罩), or a nacelle(引擎艙), which are both types of covered housings. The purpose of the cowling(整流罩) or nacelle(引擎艙) is to streamline the flow of air around the engine and to help cool the engine by ducting(管道) air around the cylinders(汽缸).



The propeller, mounted(架設好的) on the front of the engine, translates the rotating force of the engine into thrust, a forward acting force that helps move the airplane through the air. The propeller may also be mounted(架設好的) on the rear(後面) of the engine as in a pusher-type aircraft.
A propeller is a rotating airfoils(機翼,螺旋槳) that produces thrust through aerodynamic action.


A low pressure area is formed at the back of the propeller’s airfoil, and high pressure is produced at the face of the propeller, similar to the way lift is generated by an airfoil used as a lifting surface or wing. This pressure differential pulls air through the propeller, which in turn pulls the airplane forward.


There are two significant factors involved in the design of a propeller which impact its effectiveness.


The angle of a propeller blade(槳葉角, 槳葉安裝角, 槳葉傾斜角), as measured against the hub(旋翼葉轂ㄍㄨˇ) of the propeller, keeps the angle of attack relatively constant along the span of the propeller blade, reducing or eliminating the possibility of a stall(失速).


The pitch(槳距) is defined as the distance a propeller would travel in one revolution(旋轉) if it were turning in a solid(完整的).

These two factors combine to allow a measurement of the propeller’s efficiency. Propellers are usually matched to a specific aircraft/powerplant combination to achieve the best efficiency at a particular power setting, and they pull or push depending on how the engine is mounted.

參考資料:關於螺旋槳的指標 槳距和槳葉角 propeller pitch & blade angle

  1. Fuselage座艙機身部分。
  2. Wings機翼部分,其中Aileron副翼與Flaps襟翼又是最重要的兩個組成部分。
  3. Empennage機尾部分,其中Vertical(垂直)和Horizontal(水平)、Stabilizers(安定面)又是最具代表性的部分。眾所皆知的Rudder方向舵,就是Vertical Stabilizers(垂直安定面)的一部分。而Elevator(升降舵),就是Horizontal Stabilizers(水平安定面)的一部分。
  4. Landing Gear起落架。一般又簡單分成:固定式(Fixed)與可收放式(Retractable)兩種。
  5. Powerplant動力部分,其中引擎(Engine)也就是整架飛機的心臟。當然,在它前面少不了那隻產生推力的螺旋槳(噴射機不在此列)。



The subcomponents of an airplane include the airframe(機身), electrical system, flight controls, and brakes(制動器).


The airframe is the basic structure of an aircraft and is designed to withstand all aerodynamic forces, as well as the stresses imposed by the weight of the fuel, crew, and payload(淨載重量).


The primary function of an aircraft electrical system is to generate, regulate, and distribute electrical power throughout the aircraft. There are several different power sources on aircraft to power the aircraft electrical systems. These power sources include: engine-driven alternating current (AC) generators, auxiliary(輔助的) power units (APUs), and external power. The aircraft’s electrical power system is used to operate the flight instruments, essential systems such as anti-icing, etc., and passenger services, such as cabin lighting.


The flight controls are the devices and systems which govern the attitude(飛行姿態) of an aircraft and, as a result, the flightpath followed by the aircraft. In the case of many conventional airplanes, the primary flight controls utilize hinged(有鉸鏈的), trailing-edge surfaces called elevators for pitch, ailerons for roll, and the rudder for yaw. These surfaces are operated by the pilot in the flight deck or by an automatic pilot.


Airplane brakes consist of multiple pads(墊片) (called caliper(卡鉗) pads) that are hydraulically(液壓)squeezed toward each other with a rotating disk (called a rotor轉子) between them. The pads place pressure on the rotor which is turning with the wheels. As a result of the increased friction(摩擦) on the rotor, the wheels inherently(自然地) slow down and stop turning. The disks and brake pads are made either from steel, like those in a car, or from a carbon material that weighs less and can absorb more energy. Because airplane brakes are used principally during landings and must absorb enormous amounts of energy, their life is measured in landings rather than miles.

5.Types of Aircraft Construction飛機架構的種類


The construction of aircraft fuselages evolved from the early wood truss(桁架) structural arrangements to monocoque(硬殼式結構) shell structures to the current semimonocoque(半單殼式結構) shell structures.


半單殼式結構除硬殼式機身交有之圖形隔框外,其內部結構有縱樑、骨架、加強內弦板、帽狀繫樑等,以構成架構且可以增加強度,此種類型飛機結構之優點是可以承受較大的應力,且可以承受擁有較寬敞之空間,以容納旅客、貨貨和飛機上的其他裝備, 目前的飛機結構,大部分均採用此種型式。



Monocoque construction uses stressed skin to support almost all loads much like an aluminum beverage can.
Although very strong, monocoque construction is not highly tolerant to deformation(變形) of the surface. For example, an aluminum beverage can supports considerable forces at the ends of the can, but if the side of the can is deformed slightly while supporting a load, it collapses easily.


Because most twisting and bending(彎曲) stresses are carried by the external skin rather than by an open framework, the need for internal bracing(支撐) was eliminated or reduced, saving weight and maximizing space.

One of the notable and innovative methods for using monocoque construction was employed by Jack Northrop. In 1918, he devised(發明) a new way to construct a monocoque fuselage used for the Lockheed S-1 Racer. The technique utilized two molded plywood(三夾板)half-shells that were glued together around wooden hoops or stringers.

To construct the half shells, rather than gluing many strips(長條)of plywood over a form, three large sets of spruce strips were soaked(浸透的)with glue and laid in a semi-circular concrete mold that looked like a bathtub. Then, under a tightly(緊緊地) clamped lid, a rubber(橡膠)balloon was inflated in the cavity(空隙) to press the plywood against the mold(黴菌).

Twenty-four hours later, the smooth half-shell was ready to be joined to another to create the fuselage. The two halves were each less than a quarter inch thick.

Although employed in the early aviation period, monocoque construction would not reemerge for several decades due to the complexities involved. Every day examples of monocoque construction can be found in automobile manufacturing where the unibody is considered standard in manufacturing.


Semimonocoque construction, partial or one-half, uses a substructure to which the airplane’s skin is attached. The substructure, which consists of bulkheads(隔板) and/or formers of various sizes and stringers, reinforces the stressed skin by taking some of the bending stress from the fuselage.

The main section of the fuselage also includes wing attachment points and a firewall. On single-engine airplanes, the engine is usually attached to the front of the fuselage. There is a fireproof partition between the rear(後面的) of the engine and the flight deck or cabin to protect the pilot and passengers from accidental engine fires.

This partition(隔板) is called a firewall and is usually made of heat-resistant material such as stainless steel. However, a new emerging process of construction is the integration of composites or aircraft made entirely of composites.

Composite Construction複合結構


The use of composites(複合材料) in aircraft construction can be dated to World War II aircraft when soft fiberglass(玻璃纖維) insulation(絕緣材料) was used in B-29 fuselages. By the late 1950s, European high performance sailplane(滑翔機)manufacturers were using fiberglass as primary structures.

In 1965, the FAA type certified the first all-fiberglass aircraft in the normal category, a Swiss sailplane called a Diamant HBV. Four years later, the FAA certified a four-seat single-engine Windecker Eagle in the normal category. By 2005, over 35 percent of new aircraft were constructed of composite materials.

Composite is a broad term and can mean materials such as fiberglass, carbon fiber cloth, Kevlar(克維拉纖維)© cloth, and mixtures of all of the above.

Composite construction offers two advantages: extremely smooth skins and the ability to easily form complex curved or streamlined structures. [Figure 2-15]

Composite Materials in Aircraft複合結構於飛機之應用

Composite materials are fiber-reinforced matrix systems. The matrix is the “glue” used to hold the fibers together and, when cured, gives the part its shape, but the fibers carry most of the load. There are many different types of fibers and matrix systems.

In aircraft, the most common matrix is epoxy resin(環氧樹脂), which is a type of thermosetting(熱固) plastic. Compared to other choices such as polyester resin(聚酯樹脂), epoxy is stronger and has good high-temperature properties. There are many different types of epoxies available, with a wide range of structural properties, cure times and temperatures, and costs.

The most common reinforcing fibers used in aircraft construction are fiberglass and carbon fiber.

Fiberglass has good tensile(有延展性的) and compressive(壓縮的) strength, good impact resistance, is easy to work with, and is relatively inexpensive and readily available. Its main disadvantage is that it is relatively heavy, and it is difficult to make a fiberglass load-carrying structure lighter than a well designed equivalent aluminum structure.

Carbon fiber is generally stronger in tensile(可拉長的) and compressive strength than fiberglass, and has much higher bending stiffness(堅實). It is also considerably lighter than fiberglass. However, it is relatively poor in impact resistance; the fibers are brittle(脆的) and tend to shatter under sharp impact. This can be greatly improved with a “toughened” epoxy resin system, as used in the Boeing 787 horizontal and vertical stabilizers. Carbon fiber is more expensive than fiberglass, but the price has dropped due to innovations driven by the B-2 program in the 1980s, and Boeing 777 work in the 1990s. Very well-designed carbon fiber structures can be significantly lighter than an equivalent aluminum structure, sometimes by 30 percent or so.

Advantages of Composites 複合材料的優勢


Composite construction offers several advantages over metal, wood, or fabric, with its lighter weight being the most frequently cited(表彰). Lighter weight is not always automatic. It must be remembered that building an aircraft structure out of composites does not guarantee it will be lighter, it depends on the structure, as well as the type of composite being used.


A more important advantage is that a very smooth, compound curved, aerodynamic structure made from composites reduces drag. This is the main reason sailplane designers switched from metal and wood to composites in the 1960s.


In aircraft, the use of composites reduces drag for the Cirrus and Columbia line of production aircraft, leading to their high performance despite their fixed landing gear. Composites also help mask the radar signature of “stealth”(不聲張的活動) aircraft designs, such as the B-2 and the F-22.


Today, composites can be found in aircraft as varied as gliders to most new helicopters.
Lack of corrosion(腐蝕) is a third advantage of composites.

Boeing is designing the 787, with its all-composite fuselage, to have both a higher pressure differential and higher humidity in the cabin than previous airliners. Engineers are no longer as concerned about corrosion from moisture condensation(冷凝) on the hidden areas of the fuselage skins, such as behind insulation(絕緣) blankets. This should lead to lower long-term maintenance costs for the airlines.

Another advantage of composites is their good performance in a flexing environment, such as in helicopter rotor blades. Composites do not suffer from metal fatigue and crack growth as do metals. While it takes careful engineering, composite rotor blades can have considerably higher design lives than metal blades, and most new large helicopter designs have all composite blades, and in many cases, composite rotor hubs.

Disadvantages of Composites 複合材料的劣勢

Composite construction comes with its own set of disadvantages, the most important of which is the lack of visual proof of damage. Composites respond differently from other structural materials to impact, and there is often no obvious sign of damage.

For example, if a car backs into an aluminum fuselage, it might dent(撞凹) the fuselage. If the fuselage is not dented, there is no damage. If the fuselage is dented, the damage is visible and repairs are made.

In a composite structure, a low energy impact, such as a bump or a tool drop, may not leave any visible sign of the impact on the surface. Underneath the impact site there may be extensive delaminations(剝離), spreading in a cone-shaped area from the impact location. The damage on the backside of the structure can be significant and extensive, but it may be hidden from view. Anytime one has reason to think there may have been an impact, even a minor one, it is best to get an inspector familiar with composites to examine the structure to determine underlying damage. The appearance of “whitish” areas in a fiberglass structure is a good tip-off that delaminations of fiber fracture has occurred.

A medium energy impact (perhaps the car backing into the structure) results in local crushing of the surface, which should be visible to the eye. The damaged area is larger than the visible crushed area, and will need to be repaired. A high energy impact, such as a bird strike or hail while in flight, results in a puncture(小孔) and a severely damaged structure. In medium and high energy impacts, the damage is visible to the eye, but low energy impact is difficult to detect. [Figure 2-16]


If an impact results in delaminations(剝離), crushing of the surface, or a puncture(小孔), then a repair is mandatory(必須履行的).


While waiting for the repair, the damaged area should be covered and protected from rain. Many composite parts are composed of thin skins over a honeycomb core, creating a “sandwich” structure. While excellent for structural stiffness reasons, such a structure is an easy target for water ingress(進入) (entering), leading to further problems later. A piece of “speed tape” over the puncture is a good way to protect it from water, but is not a structural repair. The use of a paste filler to cover up the damage, while acceptable for cosmetic purposes, is not a structural repair, either.


The potential for heat damage to the resin(樹脂) is another disadvantage of using composites. While “too hot” depends on the particular resin system chosen, many epoxies begin to weaken over 150° F. White paint on composites is often used to minimize this issue. For example, the bottom of a wing that is painted black facing a black asphalt(柏油) ramp on a hot, sunny day, can get as hot as 220 °F. The same structure, painted white, rarely exceeds 140 °F.

As a result, composite airplanes often have specific recommendations on allowable paint colors. If the airplane is repainted, these recommendations must be followed.

Heat damage can also occur due to a fire. Even a quickly extinguished small brake fire can damage bottom wing skins, composite landing gear legs, or wheel pants.

Also, chemical paint strippers are very harmful to composites, and must not be used on them. If paint needs to be removed from composites, only mechanical methods are allowed, such as gentle grit blasting or sanding. Many expensive composite parts have been ruined by the use of paint stripper, and such damage is generally not repairable.

Fluid Spills on Composites

Some owners are concerned about fuel, oil, or hydraulic(液壓的) fluid spills(溢出量) on composite surfaces. These are generally not a problem with modern composites using epoxy resin(環氧樹脂). Usually, if the spill doesn’t attack the paint, it won’t hurt the underlying composite.

Some aircraft use fiberglass fuel tanks, for example, in which the fuel rides directly against the composite surface with no sealant(密封劑) being used. If the fiberglass structure is made with some of the more inexpensive types of polyester resin(聚酯樹脂), there can be a problem when using auto gas with ethanol blended into the mixture. The more expensive types of polyester resin, as well as epoxy resin, can be used with auto gas, as well as 100 octane(辛烷) aviation gas (avgas) and jet fuel.

Lightning Strike Protection


Lightning strike protection is an important consideration in aircraft design. When an aircraft is hit by lightning, a very large amount of energy is delivered to the structure. Whether flying a light general aviation (GA) airplane or a large airliner, the basic principle of lightning strike protection is the same. For any size aircraft, the energy from the strike must be spread over a large surface area to lower the “amps per square inch” to a harmless level.

If lightning strikes an aluminum airplane, the electrical energy naturally conducts easily through the aluminum structure. The challenge is to keep the energy out of avionics(航空電子技術), fuel systems, etc., until it can be safely conducted overboard. The outer skin of the aircraft is the path of least resistance.


In a composite aircraft, fiberglass is an excellent electrical insulator(絕緣體), while carbon fiber conducts electricity, but not as easily as aluminum. Therefore, additional electrical conductivity needs to be added to the outside layer of composite skin. This is done typically with fine metal meshes(網) bonded to the skin surfaces. Aluminum and copper(銅) mesh are the two most common types, with aluminum used on fiberglass and copper on carbon fiber. Any structural repairs on lightning-strike protected areas must also include the mesh as well as the underlying structure.

For composite aircraft with internal radio antennas(天線), there must be “windows” in the lightning strike mesh in the area of the antenna. Internal radio antennas may be found in fiberglass composites because fiberglass is transparent to radio frequencies, where as carbon fiber is not.

The Future of Composites

In the decades since World War II, composites have earned an important role in aircraft structure design. Their design flexibility and corrosion(鏽蝕) resistance, as well as the high strength-to-weight ratios possible, will undoubtedly continue to lead to more innovative aircraft designs in the future. From the Cirrus SR-20 to the Boeing 787, it is obvious that composites have found a home in aircraft construction and are here to stay. [Figure 2-17]


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