1 the Fuselage AIRFRAMES and SYSTEMS

1 The Fuselage SYSTEMS AND AIRFRAMES 1.1 Introduction The contents of this book will focus on the anatomy of the aeroplane and the various • Horizontal stabiliser (tailplane), systems that enable it to operate both on Vertical stabiliser (fin), all called the ground and in the air. the Empennage. • Flight controls Typically, an aeroplane is made up of the • Landing gear following main component parts: • Powerplant (engine) (See fig. AS 1.1) • Fuselage (the central body) • Wings (mainplanes) The fuselage is the central body of the aeroplane since the powerplant, wings, empennage and landing gear are attached Rudder Vertical stabiliser Elevator Flap Aileron Fairings Horizontal Wing stabiliser Tailgear Strut Main landing gear Engine cowling Main wing Main landing gear Fuselage Fig. AS 1.1 Main parts of the aeroplane The Fuselage 1-1 Airframes and Systems E5.indb 1 13.05.2008 13:25:05 AIRFRAMES AND SYSTEMS AND AIRFRAMES to it. Fuselages may be manufactured mounted directly on the fuselage or on using various design principals. A fuselage to the vertical fin. structure is a rigid body to which the wings, empennage, engine and landing gear are This chapter will also focus on the types attached. It also contains the flight crew, of material that are commonly used in passengers, equipment and cargo. The aircraft construction. fuselage can be made from a wide range of materials which can be riveted, bolted, screwed, welded or bonded together. 1.2 Types of Aircraft Construction At the beginning of aviation development, We will examine the fuselage construction aeroplanes were made with a structure in more detail later, and will briefly describe of wood or bamboo. Problems connected to some of the stresses that act on the whole those structures were lack of strength, poor aircraft structure. Additionally, we will look at streamline shape and hence high drag. In the various methods of securing panels and the late 1920s, the aeroplane manufacturer other major structural components (wings, Lockheed developed a monocoque structure empennage, and powerplants) to the airframe. composed of moulded-plywood. This improved streamlining to improve speed Meanwhile, control surfaces are attached to and minimise drag. other main structural members such as the wings, horizontal and vertical stabilisers, The next step in aviation evolution was by means of major hinge assemblies, or an aeroplane structure of thin sheet metal attached by load path routes direct to instead of wood. This improvement reduced hydraulic or electrically operated actuators the weight and allowed mass-production of and systems. aircraft. During World War I, the Germans developed aluminium alloys by adding Engines are attached to the fuselage (single copper, manganese and magnesium, which engine aeroplanes) or wings by major sub increased the strength without increasing frame assemblies, which may hold a turbo- the weight. They called the alloy Duralumin. prop engine ahead of the wing, and are This alloy was the forerunner of the high- secured to the main or auxiliary spars and strength and lightweight alloys that the ribs in the wing. Engines mounted under aviation industry uses today. the wing are also attached by sub frames or pylons which are attached to wing spars by Two main types of aircraft construction high strength bolt/pin assemblies to enable exists: quick engine or pylon changes. • Girder framework, and • All metal stressed skin structures. Engines attached to the rear fuselage are attached by stub wing type spars. Most modern aircraft constructors use Centre mounted engines can either be various types of stressed skin construction, 1-2 The Fuselage Airframes and Systems E5.indb 2 13.05.2008 13:25:05 but some light aircraft are still constructed tubular supporting members that act as both AIRFRAMES AND SYSTEMS according to the girder framework struts and ties depending on their location. principles. Attached to this girder framework of 1.2.1 Girder Framework Construction longerons, ties and struts are attachments for the wings, empennage, powerplant This type of construction consists of and landing gear. four longitudinal or lengthwise steel tube members (termed longerons) that Fuselages of girder framework construction are supported and held in position by often result in a cross section which horizontally, vertically and diagonally is rectangular shaped and has to be mounted tie and strut members. These streamlined by the addition of fairing tie and strut members are often also of sections and a skin of either doped fabric or steel tubular construction and are attached thin plywood. Girder frameworks are only to the longerons either by bolting or used today in a limited range of light aircraft see fig. AS 1.2. welding, (Examples: Piper Cub, de Havilland Tiger Moth and Pitts Special) see fig. AS 1.3. The longerons are the main strength members of the fuselage and are designed to withstand the main bending and torsional 1.2.2 Stressed Skin Construction (twisting) loads and their generated stresses. Modern aircraft structures are of the The supporting ties are members subjected stressed skin type, where some of the to tension loads and their generated applied loads and generated stresses are stresses, and, the struts are supporting carried by the outside skin. The stressed members subjected to compression loads skin type provides a good streamline shape and their generated stresses. On some girder together with maximum internal space. framework designs, there can be some There are three types of metal stressed skin construction, namely: Longerons • Monocoque • Semi-monocoque • Reinforced structure. Monocoque Structure In a monocoque structure, the outside skin carries all the strength. The name monocoque Longerons means single shell and in fig. AS 1.4 the Struts/ties structure consists of three main parts. The thin metal skin carries the entire flight load Fig. AS 1.2 Tubular steel construction while the bulkhead and formers (or frames) The Fuselage 1-3 AIRFRAMES AND SYSTEMS AND AIRFRAMES Fairing Fabric covering Top cross strut Top longerons Sternpost Bracing strut Bottom longerons Bottom cross strut Fig. AS 1.3 Framework of the tail part of a fuselage give the structure its shape. Normally the skin is riveted to formers and bulkheads. Former Bulkhead Semi-Monocoque Structure The main problem in the design of a fuselage is to obtain adequate strength whilst keeping the structural weight within acceptable limits (a high strength Skin to weight ratio). The monocoque structure has the disadvantage that any damage deformation will decrease its ability to carry the flight loads. The development of Fig. AS 1.4 Monocoque structure the semi-monocoque structure overcomes this limitation and gives a good strength to weight ratio. A semi-monocoque fuselage depends primarily on bulkheads, formers and frames 1-4 The Fuselage Airframes and Systems E5.indb 4 13.05.2008 13:25:06 for vertical strength, and longerons and SYSTEMS AND AIRFRAMES stringers for longitudinal strength (see fig. AS 1.5). Bulkhead Bulkhead Frame Stringers Skin Fig. AS 1.5 Semi-Monocoque structure Longerons Stringers Formers Fig. AS 1.6 Reinforced structure Reinforced Structure It is the most commonly used structure in modern all-metal aircraft. As illustrated in metal skin over the structure that carries the fig. AS 1.6 the shape is provided by stringers, most part of the flight loads. formers and bulkheads, and is reinforced with longerons which will tolerate bending Where skin sheets are bolted or riveted stress. together on to stringers, formers or longerons, it may be necessary to add Longerons and stringers are joined with further strengthening to the joint. This is the bulkheads to form the desired shape. achieved by the introduction of a doubler When the skin is attached to these parts (see fig. AS 1.7), which is basically a strap the whole structure forms a rigid fuselage. that is riveted to both pieces of skin along The fuselage structure must be designed its edges. Doublers are often placed at with openings for doors, windshields and areas where stress cracks may appear. On windows. The area around the openings windshield fittings, they will prevent loss must be reinforced, thereby safely of the windshield because a crack, seeking supporting the loads that normally would the line of least resistance will find one of have been supported by material in the cut the many rivets which will prevent the crack out area. Stringers, formers, bulkheads and extending along the windshield mounting. longerons help to carry these loads. With regard to the other structures, it is the sheet- The Fuselage 1-5 Airframes and Systems E5.indb 5 13.05.2008 13:25:06 AIRFRAMES AND SYSTEMS Sheet metal • Metals • Wood • Composite materials Doubler 1.3.1 Metals At the beginning of modern aviation, welded Stringer steel tubular trusses (another name for girder framework construction) formed the primary structures of metal aircraft. Later, Rivet improvements were made with aluminium alloys. Pure aluminium is lightweight and corrosion resistant, but lacks strength for Fig. AS 1.7 Doubler use as a structural material. When mixed with other elements, its strength can be increased but becomes susceptible to Sandwich Construction corrosion. Only when it became possible to Aluminium alloy has a high enough tensile protect aluminium alloys from corrosion did strength that a very thin sheet may be strong they become popular as aircraft structural enough for a given application, but this thin material. sheet does not have enough stiffness to make it a totally adequate structural material. Most modern aircraft are made from The sandwich construction solves this by aluminium alloys, but the aviation industry using a lightweight core material which also uses a range of other base materials in is bonded between face plies of metal or alloy form, as listed below: reinforced fabric. The method is used for all types of aircraft from home built machines to Aluminium Alloys (General) high speed state of the art military aircraft.

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