Aircraft Structures Repair I

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    UNIVERSITI KUALA LUMPUR - MALAYSIAN INSTITUTE OF AVI ATION TECHNO LOGY

    AIRCRAFT STRUCTURES REPAIRAIRCRAFT STRUCTURES REPAIR

    AAB 31003AAB 31003

    UNIVERSITI KUALA LUMPUR

    Malaysian Institute of Aviation

    Technology

    UNIVERSITI KUALA LUMPUR - MALAYSIAN INSTITUTE OF AVI ATION TECHNO LOGY

    AIRCRAFT STRUCTURES REPAIR

    AIRCRAFT STRUCTURES REPAIRAIRCRAFT STRUCTURES REPAIR

    AAB 31003AAB 31003Chapter IChapter I

    Ir. Abu Zaid Bakar

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    Overview

    1. General Structures

    2. Construction Method

    3. Structure AssemblyTechnique & Protection

    4. Airframe Symmetry

    5. Fuselage, Door, Engine

    Mount, Nacelle & Landing

    Gear Attachment

    6. Wings & Stabilizer

    7. Window &

    Windscreen8. Inspection of

    Aircraft Structures

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    AIRCRAFT

    LIGHTER THAN AIR HEAVIER THAN AIR

    AIRSHIPS BALLONS POWER DRIVEN NON-POWER DRIVEN

    GLIDER (SAIL PLANES)AEROPLANE HELICOPTER

    LANDPLANE AMPHIBIANSEAPLANE

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    Beam A member subject to bending, where carry load at right angle to their length. A

    beam may be simply supported at the end. The support may be a little way from

    the ends or it may be supported at one end only, where it is called cantilever. Examples, I-beam, T-beam, Z-beam

    Application: Spar, Floorboard Structures

    Strut Member taking a compression load. Examples: Landing gear strut, Wing strut.

    Tie

    Member taking a tensile load Examples: Landing gear beam

    Strain x / x

    Stress Force per unit area. F/A

    General Structures

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    Torsion

    Member or circular cross section subject to twisting couples or torques. Examples: torque tube,

    Bending

    A cantilever beam having a downward force at the end. The beam is deflected downward, upper

    section of the beam is having tension and lower section of the beam is under compression

    Compression

    Any structure when under compression is when the forces in that structure are pointed towards

    the centre of the structure

    Tension

    Any structure when under compression is when the forces in that structure are pointed outwards

    from the centre of the structure

    Fatigue

    The tiredness of the structure after had undergone cyclic loading

    General Structures

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    General Structures

    Stress Riser

    Hoop Stress

    Different in pressure between inside and outside of the pressurised area

    of the aircraft. (Circumferential stress)

    Shear

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    Primary Structures

    All major components of the aircraft. The failure of which in flight or ground

    manoeuvres would likely to cause catastrophic structural collapse or loss of controlof the aircraft.

    Secondary Structures

    Includes all portions of the aircraft which would normally be regarded as primary

    structure but which unavoidably have such reserve strength over design

    requirements that appreciably weakening may be permitted without risk of failure.

    It also include structure which if damage would not impair the safety of the aircraft.

    Tertiary StructuresInclude all portions of the structure in which stresses are low, but which for various

    reasons cannot be omitted from the aircraft.

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    Wing Box

    Ribs

    Longerons

    Bulkhead

    Aft Spar

    Forward Spar

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    Damage ToleranceDamage tolerance is related to fatigue, crack propagationand fail-safe design.

    The structural engineers primary responsibility to ensurethe design to have adequate strength and rigidity atminimum weight.

    3 components to determine the fatigue life of a givenstructure are:

    i) material selectionii) stress level

    iii) number of cycle to be tolerated at various stress level

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    Damage ToleranceTo ensure aircraft will perform satisfactory, the structure is designed for the

    main four failure modes:

    Static ultimate strength (incld. Yield strength requirement)

    Fatigue life of the structure (crack initiation)

    Fatigue life of the damaged structure (inspection interval)

    Static residual strength of the damage structure

    Essential consideration to the development of the damage tolerance design

    Material Selection

    Fastener Load Distribution

    Ultimate Design Cut-off Stress

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    Fail Safe

    A structure in which failure of a particular part is

    compensated for by another part, that is able tocarry the loads, for a limit period of time.

    Is achieved through material selection, properstress levels, and multiple load path structural

    arrangements which maintain high strength inthe presence of a crack or damage

    A C A S C S AAIRCRAFT STRUCTURES REPAIR

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    Example of Fail Safe Criteria

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    Stress Cycle

    The stress cycle is the stress-time function which is repeatedperiodically and identically.

    Load Spectrum

    A collection of data of the load exposure of a structure. Examples

    are gust, maneuvers, landing impact, ground roll, climb, cruise,

    decent, etc.

    Damage Tolerance

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    Stress Cycle

    Fmax Maximum Stress

    Fmin Minimum Stress

    Fa Alternating Stress = (Fmax - Fmin)/2 Fm Mean Stress = (Fmax + Fmin)/2

    R = stress ratio = Fmin/Fmax

    Fmax

    Fa

    Fm

    Fmin

    Cycle (N)

    Stress (F)

    Stress

    Range

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    Load Spectrum

    Altitude

    Speed

    Gross Weight

    Range

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    Requirements

    BCAR has specify the safety factor for the structural

    parts in aircraft to be 1.5 ( if a part has a working loadof 100 pounds, it must be designed to carry 100 x 1.5

    = 150 pounds of load.

    FAA ?

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    THANK YOU