Aircraft Construction and Materials

download Aircraft Construction and Materials

of 4

Transcript of Aircraft Construction and Materials

  • 8/13/2019 Aircraft Construction and Materials

    1/4

    AIRCRAFT CONSTRUCTION AND MATERIALS

    Chapter Objective: Upon completion of this chapter, you will have a basic working knowledge ofaircraft construction, structural stress, and materials used on both fixed- and rotary-wing airfraft.

    One of the requirements of an Aviation Structural Mechanic is to be familiar with the various termsrelated to aircraft construction. Aircraft maintenance is the primary responsibility of the AviationStructural Mechanic H (AMH) and Aviation Structural Mechanic S (AMS) ratings. Therefore, youshould be familiar with the principal aircraft structural units and flight control systems of fixed androtary-wing aircraft. While the maintenance of the airframe is primarily the respon-sibility of theAMS rating, the information presented in this chapter also applies to the AMH rating. The purpose,locations, and construction features of each unit are described in this chapter.

    Each naval aircraft is built to meet certain specified requirements. These requirements must beselected in such a way that they can be built into one machine. It is not possible for one aircraft tohave all characteristics. The type and class of an aircraft determine how strong it will be built. A

    Navy fighter, for example, must be fast, maneuverable, and equipped for both attack and defense. Tomeet these requirements, the aircraft is highly powered and has a very strong structure.

    The airframe of a fixed-wing aircraft consists of five principal units. These units include the fuselage,wings, stabilizers, flight control surfaces, and landing gear. A rotary-wing aircraft consists of thefuselage, landing gear, main rotor assembly, and tail rotor. A furtherbreakdown of these units ismade in this chapter. This chapter also describes the purpose, location, and construction features ofeach unit.

    FIXED-WING AIRCRAFT

    Learning Objective: Identify the principal structural units of fixed-wing and rotary-wing aircraft.

    There are nine principal structural units of a fixed-wing (conventional) aircraft: the fuselage,engine mount, nacelle, wings, stabilizers, flight control surfaces, landing gear, arresting gear, andcatapult equipment.

    FUSELAGE

    The fuselage is the main structure or body of the aircraft to which all other units attach. It providesspare for the crew, passengers, cargo, most of the accessories, and other equipment.

    Fuselages of naval aircraft have much in common from the standpoint of construction and design.They vary mainly in size and arrangement of the different compartments. Designs vary with themanufacturers and the requirements for the types of service the aircraft must perform.

    The fuselage of most naval aircraft are of all-metal construction assembled in a modification ofthe monocoque design. The monocoque design relies largely on the strength of the skin or shell(covering) to carry the various loads. This design may be divided into three classes: monocoque,

    semimonocoque, and longitudinal members, that is, stringers and longerons, but has no diagonal web

  • 8/13/2019 Aircraft Construction and Materials

    2/4

    members. The reinforced shell has the shell reinforced by a complete framework of structuralmembers. The cross sectional shape is derived from bulkheads, station webs, and rings. The longi-tudinal contour is developed with longerons, formers, and stringers. The skin (covering) which isfastened to all these members carries primarily the shear load and, together with the longitudinalmembers, the loads of tension and bending stresses. Station webs are built up assemblies located at

    intervals to carry concentrated loads and at points where fittings are used to attach external partssuch as wings alighting gear, and engine mounts. Formers and stringers may be single piecesof built-up sections.

    Figure 1-1.-Semimonocoque fuselage construction.

    The semimonocoque fuselage is constructed primarily of aluminum alloy; however, on neweraircraft graphite epoxy composite material is often used. Steel and titanium are found in areas subjectto high temperatures. Primary bending loads are absorbed by the "longerons," which usuallyextend across several points of support. The longerons are supplemented by other longitudinalmembers, called "stringers." Stringers are lighter in weight and are used more extensivelythan longerons. The vertical structural members are referred to as "bulkheads, frames,and formers." These vertical members are grouped at intervals to carry concentrated loadsand at points where fittings are used to attach other units, such as the wings, engines, andstabilizers. Figure 1-1 shows a modified form of the monocoque design used in combat aircraft.

    The skin is attached to the longerons, bulkheads, and other structural members and carriespart of the load. Skin thickness varies with the loads carried and the stresses supported.

    There are many advantages in the use of the semimonocoque fuselage. The bulkheads,frames, stringers, and longerons aid in the construction of a streamlined fuselage. They also add tothe strength and rigidity of the structure. The main advantage of this design is that it does not dependonly on a few members for strength and rigidity. All structural members aid in the strength of thefuselage. This means that a semimonocoque fuselage may withstand considerable damage and stillremain strong enough to hold together. On fighters and other small aircraft, fuselages are usuallyconstructed in two or more sections. Larger aircraft may be constructed in as many as six sections.

  • 8/13/2019 Aircraft Construction and Materials

    3/4

    Various points on the fuselage are heated by station number. Station 0 (zero) is usually located at ornear the nose of the aircraft. The other fuselage stations (FS) are located at distances measured ininches aft of station 0. A typical station diagram is shown in figure 1-2. On this particular aircraft,station 0 is located 93.0 inches forward of the nose.

    Quick access to the accessories and other equipment carried in the fuselage is through numerousdoors, inspection panels, wheel wells, and other openings. Servicing diagrams showing thearrangement of equipment and the location of access doors are supplied by the manufacturer in themaintenance instruction manuals and maintenance requirement cards for each model or type ofaircraft. Figure 1-3 shows the access doors and inspection panels for a typical aircraft.

    In aircraft construction, a longeron , or stringer or stiffener ,[1] is a thin strip of material to which the skinof the aircraft is fastened. In the fuselage, stringers are attached to formers (also called frames) and runin the longitudinal direction of the aircraft. They are primarily responsible for transferring the aerodynamicloads acting on the skin onto the frames and formers. In the wings or horizontal stabilizer, longerons runspanwise and attach between the ribs . The primary function here also is to transfer the bending loadsacting on the wings onto the ribs and spar.

    Sometimes the terms "longeron" and "stringer" are used interchangeably. Historically, though, there is asubtle difference between the two terms. If the longitudinal members in a fuselage are few in number andrun all along the fuselage length (usually 4 to 8), then they are called "longerons". The longeron systemalso requires that the fuselage frames be closely spaced (about every 4 to 6 in or 10 to 15 cm). If thelongitudinal members are numerous (usually 50 to 100) and are placed just between two formers/frames,then they are called "stringers". In the stringer system the longitudinal members are smaller and theframes are spaced farther apart (about 15 to 20 in or 38 to 51 cm). Generally, longerons are of largercross-section when compared to stringers. On large modern aircraft the stringer system is more commonbecause it is more weight-efficient, despite being more complex to construct and analyze. Some aircraftuse a combination of both stringers and longerons . [2]

    Longerons often carry larger loads than stringers and also help to transfer skin loads to internal structure.Longerons nearly always attach to frames or ribs . Stringers often are not attached to anything butthe skin , where they carry a portion of the fuselage bending moment through axial loading .[3] It is notuncommon to have a mixture of longerons and stringers in the same major structural component.

    http://en.wikipedia.org/wiki/Aircrafthttp://en.wikipedia.org/wiki/Aircrafthttp://en.wikipedia.org/wiki/Aircrafthttp://en.wikipedia.org/wiki/Longeron#cite_note-1http://en.wikipedia.org/wiki/Longeron#cite_note-1http://en.wikipedia.org/wiki/Longeron#cite_note-1http://en.wikipedia.org/wiki/Formerhttp://en.wikipedia.org/wiki/Formerhttp://en.wikipedia.org/wiki/Formerhttp://en.wikipedia.org/wiki/Rib_(aircraft)http://en.wikipedia.org/wiki/Rib_(aircraft)http://en.wikipedia.org/wiki/Rib_(aircraft)http://en.wikipedia.org/wiki/Longeron#cite_note-2http://en.wikipedia.org/wiki/Longeron#cite_note-2http://en.wikipedia.org/wiki/Longeron#cite_note-2http://en.wikipedia.org/wiki/Rib_(aircraft)http://en.wikipedia.org/wiki/Rib_(aircraft)http://en.wikipedia.org/wiki/Rib_(aircraft)http://en.wikipedia.org/wiki/Stressed_skinhttp://en.wikipedia.org/wiki/Stressed_skinhttp://en.wikipedia.org/wiki/Stressed_skinhttp://en.wikipedia.org/wiki/Longeron#cite_note-3http://en.wikipedia.org/wiki/Longeron#cite_note-3http://en.wikipedia.org/wiki/Longeron#cite_note-3http://en.wikipedia.org/wiki/Longeron#cite_note-3http://en.wikipedia.org/wiki/Stressed_skinhttp://en.wikipedia.org/wiki/Rib_(aircraft)http://en.wikipedia.org/wiki/Longeron#cite_note-2http://en.wikipedia.org/wiki/Rib_(aircraft)http://en.wikipedia.org/wiki/Formerhttp://en.wikipedia.org/wiki/Longeron#cite_note-1http://en.wikipedia.org/wiki/Aircraft
  • 8/13/2019 Aircraft Construction and Materials

    4/4