Aircraft Material and Processes

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RECIPROCATING

ENGINE

Aircraft Construction, Repair, and Modification

AIRCRAFT MATERIALS AND PROCESSES

prepared by : Engr. Eric John Velasco

Aircraft Construction, Repair, and Modification

AIRCRAFT MATERIALS AND

PROCESSES

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Aircraft Construction,

Repair, and Modification

(15%)

Aircraft Materials and Processes; Methods

and Techniques in Repair and Modification in

Accordance With Civil Aviation Regulation;

Manufacturing, Production Processes and

Quality Assurance

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IV. AIRCRAFT CONSTRUCTION, REPAIR, AND MODIFICATION

A. Objective: To determine the basic knowledge of the Examinees on Aircraft Materials, Construction Repair,and Modification

Subject Contents:

1. Aircraft Materials and Processes

a. Physical and Chemical Properties of Ferrous Metals and Alloys, Non-Ferrous Metals and Alloys, Non-Metals (Wood, Fiberglass, others) b. Identification of Metals

c. Heat Treatment processes d. Forming/Shaping and Forging e. Joining of Metals

2. Aircraft Hardware, Cables, and Tools,Equipment a. Bolts, Nuts, Screws, Rivets, others

b. Control Cables and Cable Assemblies c. Tools and Fabrication/Repair Equipment

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Subject Contents:

3. Construction, Repair, and Modification a. Aircraft Structural Components

b. Metal Structures

c. Non-Metal Structures d. Composite Materials 4. Testing and Inspection

a. Testing of Metals - Hardness Tests b. Non-Destructive Test and Inspection

5. Corrosion Protection and Control a. Types of Corrosion

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6. Aircraft Weight and Balance a. Weighing Procedure

b. Weight and Balance Computations

c. Weight and Balance Extreme Conditions Most Forward and Rearward CG Positions

C. References:

1. Aircraft Materials and Processes - Titterton

2. Aircraft Inspection and Repair – US Printing Office

3. Maintenance and Repair of Aerospace Vehicle -McKinkey

and Bent

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Physical and Chemical Properties of



Ferrous Metals and Alloys,



Non-Ferrous Metals and



Alloys,

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5 Major Stresses to which all

Aircraft Subjected



TENSION – is the stress that resist a force tends to null

apart.



COMPRESSION – is the stress that resist a crushing

force.



TORSION – is the stress that produce twisting.



SHEAR – is the stress that resists the force tending to

cause one material to slide over an adjacent layer.



BENDING – is a combination of compression and

tension.

○ _{STRESS – is an internal force of a substance which opposes or}

resist deformation can cause strain.

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5 Major Stresses to which all

Aircraft Subjected

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5 Major Stresses to which

all Aircraft Subjected

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PROPERTIES OF MATERIALS



HARDNESS - The property of a material that enables it to resist

penetration, wear, or cutting action or permanent distortion.



BRITTLENESS – is the property of a metal which allows little

bending or deformation without shattering.



MALLEABILITY – property of metals which allows them to be bent

or permanently distorted without rupture.



STRENGTH - The ability of a material to resist deformation.



PLASTICITY - The capability of an object or material to be

stretched and to recover its size and shape after its deformation.



DUCTILITY - The property which allows metal to be drawn, bent or

twisted into various shapes without breaking.



ELASTICITY – property which enables a metal to return to its

original shapes when the forces which causes the change of shape

is removed.

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

TOUGHNESS – a material which possesses toughness will

withstand tearing or shearing and maybe stretched or otherwise

deformed without breaking.



DENSITY – the weight of a unit volume of the materials.



FUSIBILITY – the ability of a metal to become liquid by the

application of heat.



CONDUCTIVITY – the ability of a metal which enables to carry heat

or electricity



THERMAL EXPANSION

 _{Contraction – ability of metals to shrink when subjected to cooling.}  _{Expansion – expand upon the application of heat.}

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Aircraft Metals



Two Main Group of Aircraft Metals:



_{NON-FERROUS METALS – the term that}

describes metals which are have elements other

than Iron as their base. Aluminum, Copper,

Titanium, and Magnesium are some of the

common non-ferrous metals used in Aircraft

Construction and Repair.



_{FERROUS METALS – any alloy containing iron}

as its chief constituent, most common ferrous

metal in aircraft structure is steel, an alloy of iron

with a controlled amount of carbon added.

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

NON-FERROUS METALS:

1. ALUMINUM AND ITS ALLOYS

○ _{- Pure aluminum lacks sufficient strength to be used in aircraft Quenching} ○ _{construction. However, its strength increases considerably when it is}

ALLOYED, or mixed with compatible metals. TYPES OF ALUMINUM ALLOYS:

1. Cast Alloys – those suitable for casting in sand, permanent mold or die casting.

2. Wrought Alloys – those which may be shaped by rolling, drawing or

forging. These are the most widely used in aircraft construction, being used for stringers, bulkheads, skin, rivets, and extruded sections.

GENERAL CLASSES OF WROUGHT ALUMINUM ALLOYS:

1. Non-Heat Treatable Alloy – the mechanical properties obtained by cold

working are destroyed and any subsequent heating cannot restore it except by additional cold working.

2. Heat Treatable Alloy – alloy which responds readily to heat treatment

which results in considerable improvement of the strength characteristics. Greater strength is obtained and used for structural purposes.

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.

2. MAGNESIUM AND ITS ALLOYS

 _{Magnesium alloy are used for cast and wrought form available in sheets, bars, tubing,}

and extrusions. Magnesium is one of the lightest metals having sufficient strength and suitable working characteristics for use in aircraft hardware. However, it is susceptible to corrosion and tends to crack.

3. TITANIUM AND ITS ALLOYS

 _{Titanium and its alloys are light metals with very high strength. It has an excellent}

corrosion resistance characteristics, particularly to the effects of salt water.

4. NICKEL AND ITS ALLOYS

 _{Nickel is the base element for most of the higher temperature heat-resistant alloys.}

While it is much more expensive than iron, nickel provides an austenitic structure that has greater toughness and workability than ferrous alloys of the same strength.

MONEL – contains about 68 % nickel and 29% copper, along with iron and

manganese. It works well in gears and parts that require high strength and corrosion resistance at elevated temperature.

INCONEL – high strength, high temperature alloys containing approximately

about 80% nickel, 14 % chromium, and small amounts of iron and other elements.

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5. COPPER AND ITS ALLOYS

 _{It is easily identified by its reddish color and by the green and blue colors of its oxides}

and salt. Copper has excellent electrical and thermal conductivity and it is primary metal used for electrical wiring.

BRASS – an alloy of copper and zinc. BRONZE – an alloy of copper and tin.

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

FERROUS METALS:

1. IRON

 _{Is like a chemical which is fairy soft, malleable and ductile in its pure form. It is silvery}

white in color and is quite heavy, having a density of 7.9 grams per cubic centimeter.

2. STEEL

 _{To make steel, pig iron is re-melted in a special furnace. Pure oxygen is the forced}

through the molten where it combines with carbon and burns. A control amount of carbon is then put back into the molten. The molten steel is then poured into molds where it solidifies into ingots. The ingots are then placed in a soaking pit where they are heated to a uniform temperature of about 2200 degrees F. They are then taken from the soaking pit and passed through steel rollers to form late or sheet metal.

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a. CARBON

 _{Carbon is the most common alloying element found in steel. When mixed with iron} core compounds of iron carbides called CEMETITE form. It is the carbon in steel that allows the steel to be heat treated to obtain varying degrees of hardness, strength and toughness. The greater the carbon content, the more receptive steel is to heat treatment and therefore, the higher its tensile strength, and hardness. However, higher carbon content decreases the malleability and weldability of steel. LOW CARBON STEELS – contains between 0.10 and 0.30 percent carbon. Primarily

used in safety wire, cable bushing, and threaded rod ends.

MEDIUM CARBON STEELS – contains between 0.30 and 0.50 percent carbon. HIGH CARBON STEELS – contains between 0.50 to 1.05 percent carbon and are

very hard. Primarily used in springs, files, and some cutting tools.

b. SILICON

 _{When it is alloyed with steel it acts as a hardener. When used in small quantities, it} also improves ductility.

c. PHOSPHOROUS

 _{Raises the yield strength of steel and improves low carbon steel’s resistance of} atmospheric condition. However, no more than 0.05 percent is normally used in steel, since higher amounts cause the alloy to become brittle when cold.

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d. NICKEL

 _{Adds strength and hardness to steel and increase yield strength. It also slows the}

rate of hardening when steel is heat treated, which increases the steels contains 3% nickel and 0.30% carbon, and used in producing aircraft hardwired such as bolts, nuts, rod end and pins.

e. CHROMIUM

 _{Alloyed with steel to increase strength and hardness as well as improve its wear}

and corrosion resistance. It is used in balls and rollers of anti-friction bearings.

f. STAINLESS STEEL

 _{Is a classification of CORROSION-RESISTANT STEEL (CRES) that contain large}

amount of chromium and nickel. Their strength and resistant to corrosion make than well suited for high-temperature applications such as firewalls and exhaust system components. It contains 18% chromium and 8% nickel. It is referred as 18-8.

AUSTENITIC STEELS – refers to 200 and 300 series stainless steel. Hardened only

by cold-working.

FERRITIC STEELS – contains no carbon. They do not respond to heat treatment. MARTENSITIC STEELS - the 400 series of stainless steel. These are magnetic and it

becomes extremely hard if allowed to cool rapidly by cooling from an elevated temperature.

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g. CHROME – MOLYBDENUM (chrome-moly) STEELS

 _{Commonly used alloy in aircraft. Making it an ideal choice for landing gear}

structures and engine mounts.

h. VANADIUM

 _{When combined with chromium, vanadium produces a strong, tough, ductile steel}

alloys. Most wrenches and ball bearings are made of chrome-vanadium steel.

i. TUNGSTEN

 _{Has an extremely high melting point and adds this characteristics to steel when it}

is alloyed. Typically used for breaker contacts in magnetos and for high speed cutting tools.

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WOOD STRUCTURES:



WOOD – wood structures requires a great deal of handwork and

therefore, are extremely expensive.

 _{SOLID WOOD – used for some aircraft wing spars and is made of solid pie cut from a}

log. Most solid cut by quarter sawing to prevent war page.

 _{LAMINATED WOOD – made up of two or three pieces of thin wood glued together with}

the same direction.

 _{PLY WOOD – consist of three or more layers of thin veneer glued together so the grain}

of each successive layer crosses the others at an angle of 45 degrees of 90 degrees.

2 BASIC SPECIES OF WOOD USED IN AIRCRAFT CONSTRUCTION:

1. HARDWOOD – come from deciduous trees having broad leaves.

a. MAHOGANY – this hardwood is heavier and stronger than spruce. Primary use in

aircraft construction is for face sheets of plywood used in aircraft skin.

b. BIRCH – a heavy hardwood with very good shock resistant characteristics. It is

recommended for the face plies of plywood used as reinforcement plates on wing spars and in the construction of wooden propellers.

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2. SOFTWOOD – come from coniferous trees with needle like or

scale like leaves.

a. SITKA SPRUCE – most common wood used in aircraft structures. It is

relatively free from defects, has a high strength to weight ration and available in large size. FAA chosen Sitka Spruce as the reference wood for aircraft construction.

b. DOUGLAS FIR – the strength properties exceed those of spruce; however, it

is much heavier. Further more, it is more difficult to work than spruce, and has a tendency to split.

c. NOBLE FIR – slightly lighter than spruce and is equal or superior to spruce

in all properties except hardness and shock resistance. It is often used for structural parts that are subject to heavy bending and compression loads such as spars, spar flange, and has tendency to split.

d. BALSA – an extremely light wood. Balsa lacks of structural strength, it is

often sliced across its grain for use as a core material for sandwich-type panels that requires lightweight and rigidity.

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

QUALITY OF WOOD:

_{Some of the categories a woods quality is based on include how straight}

the grain is, the number of knots, pitch pockets, splits and presence of decay.

1. GRAIN DEVIATION – regardless of the species of wood used aircraft construction, it must

have a straight grain. This means all of the woods fiber must be oriented parallel to the materials longitudinal axis. A maximum of deviation of 1:15 is allowed. In other words, the grain must not slope more than 1 inch in 15 inches.

2. KNOTS – it identifies where a branch grew from the tree trunk.

3. PITCH POCKETS – small opening within the annual rings of a tree can fill resin and form pitch pocket. It slightly weaken the piece of wood.

4. CHECKS, SHAKE AND SPLITS

CHECKS – a crack that runs across the annual rings of a board and occurs during the

seasoning process.

SHAKE – a crack or separation that occurs when two annual rings separates along

their boundary.

SPLITS – a lengthwise separation of the wood caused by the wood fibers tearing apart.

5. STRAINS AND DECAY

STRAINS – It is caused by decay usually appears streaks in the grain. Strains that uniformly discolor the annual rings are evidence of decay.

DECAY – is caused by fungi that grow in damp wood, and is prevented by proper seasoning and dry storage. A simple way of identfying decayed wood is to pick at a suspected area with the point of a knife. Sound wood will splinter, while a knife point will bring up a chunk of

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PLASTICS OR RESINS

1. THERMOSETTING RESINS – it hardens or set when heat of the

correct value is applied. It cannot softened and reshaped after

having been solidified.

2. THERMOPLASTIC RESINS – can be soften by heat and

reshaped or reformed many times without changing composition,

provided that the heat applied is held with proper limits.



Types of Thermoplastic Material used for Aircraft Windshield

and Side Windows:

 _{1. CELLULOSE ACETATE – transparent and lightweight. It has a tendency to}

shrink and turn yellow. When applied with acetone it softens.

 _{2. ACRYLIC – identified by trade names as Lucite or Plexiglas or in Britain}

Perspex. It is stiffer than cellulose acetate. More transparent and for all purpose is colorless. It burns with a clear flame and produces a fairly pleasant odor. If acetone is applied to acrylic it leaves a white residue but remains hard.

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THERMOPLASTIC RESINS:

 _{1. CELLULOSE ACETATE}

 _{2. POLYETHYLENE – is made in low and high-density qualities.} Low-density polyethylene is made in thin, flexible sheet or film and is used for plastic bags, protective sheeting and electrical insulation. High-density polyethylene is used for containers such as fuel tanks, large drums and bottles.

 _{3. VINYLS – manufactured in a variety of types and has a wide range of} application. Their used in aircraft includes seat covering, electrical

insulation, moldings, and tubing. They are flexible and resistant to most chemical and moisture.

 _{4. ACRYLIC RESIN – a water clear plastic that has a light transmission} of 92%. This property, together with its weather and moisture resistance, makes it an excellent product for aircraft windows and windshields.

 _{5. POLYTETRAFLOUROETHYLENE (Teflon) – is encountered in} non-lubricated bearings, tubing, electrical devices and other applications.

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Composite

ABBREVIATIONS:



_{AFRP - Aramide Fibre Reinforced Plastic}



_{CFRP - Carbon Fibre Reinforced Plastic}



_{GFRP - Glass Fibre Reinforced Plastic}



_{HOBE - Honeycomb before Expansion}



_{MSDS - Material Safety Data Sheet}



_{NDT - Non Destructive Testing}



_{NTM - Non Destructive Testing Manual}



_{Prepeg - Pre impregnated Fabric}

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

Advantage

 _{Composite materials are mainly used to reduce weight, that means if} weight can be saved, more cargo, fuel or passengers can be carried. More advantages are:

 _{high strength to weight ratio}  _{reducing of parts and fasteners}  _{reducing wear}

 _{corrosion resistance}



Disadvantage

Disadvantages are:  _{general expensive}

 _{not easy to repair; that means you need well trained staff, tools,} equipment and facilities to repair composite components

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Elements of Composite Structure



Reinforcing Materials



Core Materials

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Aircraft Fabric Covering



Aircraft fabric covering is a term used for both

the material used and the process of covering

aircraft open structures. It is also used for

reinforcing closed plywood structures



Early aircraft used organic materials such as

cotton and cellulose dope, modern fabric

covered designs usually use synthetic materials

such as Nylon and butyrate dope for adhesive,

this method is often used in the restoration of

older types that were originally covered using

traditional methods.

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Aircraft Dope



Aircraft dope is a plasticised lacquer that is

applied to fabric-coated aircraft. It tautens

and stiffens fabric stretched over airframes

and adheres and protects fabric applied to

other skin material.



Typical doping agents include nitrocellulose,

cellulose acetate and cellulose acetate

butyrate. Liquid dopes are highly flammable;

nitrocellulose, for instance, is also known as

the explosive propellant "guncotton". Dopes

will often include colouring pigments to

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Problem Areas

a.) Deterioration

Fabric deteriorates only by exposure

to ultraviolet radiation as used in an

aircraft covering environment

b.) Tension

Most Fabrics obtains maximum

tension on an airframe at 350 degrees

Fahrenheit and will not be excessive on

aircraft originally covered and doped

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Aircraft Fabric Synthetic

a.) STC approved covering material

Difference in fabric may be denier, tenacity,

thread count, weight, shrink, tension and

weave style

*tenacity- customary measure of strength of a

fiber or yarn.

* denier is a measure of the linear density, the

tenacity works out to be not a measure of force

per unit area, but rather a quasi-dimensionless

measure analogous to specific strength

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b.) Polyester Filaments

Manufactured by polymerization of various

select acids and alcohols, then extruding the

resulting molten polymers through spinnerets

to form filaments

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c.) Covering Procedures

Coating types, covering accessories and

covering procedures also may vary;

therefore, the covering procedures given in

the pertinent manuals must be followed to

comply with the STC.

d,.) Installation

Initial installation of polyester fabric is

similar to natural fabric. The fabric is installed

with as little slack as possible, considering

fittings and other protrusions. *slack-not

using due diligence, care, or dispatch

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Aircraft Fabric-Natural



Physical Specifications and minimum

strength requirements for natural fabric

fiber, cotton and linen, used to recover

or repair components of an aircraft.

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Recovering Aircraft



Recover or repair aircraft with a fabric of equal

quality and strength to that used by the original

aircraft manufacturer

*note:

recovering or repairing aircraft with any type fabric

and/or coating other than the type used by the

original aircraft manufacturer is considered a major

alteration. Obtain approval form from then FAA on

fabric and installation data. Cotton and linen rib

lacing cord, machine and hand sewing thread, and

finishing tapes should not be used with polyester

and glass fabric covering

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Reinforcing tape



Reinforcing tape should have a

minimum 40 lbs. resistance without

failure when static tested in shear

against a single rib lace, or a pull

through resistance when tested against

a single wire clip, rivet screw, or any

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Finishing tape



Sometimes referred as surface tape, should have

the same properties as the fabric used to cover

the aircraft

Using the 2" Dacron straight finishing tape, measure and cut

strips of the tape to be long enough to overlap both the leading and

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Lacing Cord



Should have a minimum breaking

strength of 40 lbs.. Rib lace cord should

have a micro-crystalline fungicidal wax,

paraffin free wax, or beeswax coating, or

other approved treatment to prevent

wearing and fraying when pulling

through the structure

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Machine Thread and Hand

sewing Thread



Machine Thread-Shall have a minimum breaking

strength of 5 lbs



Hand sewing Thread-Shall have a minimum breaking

strength of 14 lbs

Hand Sewing Thread (FAA approved)

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Flutter Precautions



When recovering or repairing control

surfaces, especially on high performance

airplanes, make sure that dynamic and

static balances are not adversely

affected. Weight distribution and mass

balance must be considered to preclude

to possibility of induced flutter

*flutter- To wave or flap rapidly in an

irregular manner:

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Preparation of the structure for

covering

a.) Battery Box Treatment

An Asphaltic, rubber based acid-proof coating

should be applied to the structure in the area of a

battery by box, by brush, for additional protection

from battery acid

b.) Worn holes

Oversized screw holes or worn size 4 self tapping

screw holes through ribs and other structures

used to attach fabric may be redrilled a minimum

1-1/2 hole diameter distance from the original

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Fairing Precautions



Aluminum leading edge replacement fairings

installed in short sections may telescope

during normal spar bending loads or from

thermal expansion and contraction. This

action may cause a wrinkle to form in the

fabric, at the edge of the lap joint. Trailing

edges should be adequately secured to

prevent movement and wrinkles.

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Dope Protection



Solvents found in nitrate and butyrate dope

will penetrate, wrinkle, lift, or dissolve

most-one part wood varnishes and most-one-part metal

primers. All wood surfaces that come in

contact with doped fabric should be treated

with a protective coating such as aluminum

foil, cellulose tape, or dope proof paint to

protect them against the action of the

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SEALANT COMPOUND

SEALANTS – used to contain fuel, maintain cabin

pressure, reduce fire hazards, exclude moisture,

prevent corrosion, and fill gaps and smooth

discontinuities on the aircraft exterior.

SEALING – is a process that confines liquids and

gases within a given area or prevents them from

entering areas from which they must be excluded.

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Categories of Compounds

Sealing compounds are divided into two categories, silicone and nonsilicone.

 1.Silicone compounds – are usually white, red, or grey in colour and are used in general where heat resistance is required.

 2.Nonsilicone compounds – can be any colour and are used where heat resistance is not required.

Specification / Classification

The classification system for sealants in Boeing material specifications (BMS.s) is as follows:

 Class A – Brushcoat Sealant. (Thinned with solvent to provide viscosity suitable for brushing).

 Class B – Filleting Sealant. (Relatively heavy consistency with good thixotropic (low-slump) properties).

 Class C – Faying Surface Sealant. (Medium consistency for good spreadability).

 Class D – Hole-Filling Sealant. (Similar to Class B but with very low slump).  Classes E and F – Sprayable sealant

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Basic Designation for Wrought

and Cast Aluminum Alloys

(AA-Numbering System)

Wrought Alloys

Alloy Number Major Identifying Elements



_{1XXX Pure Aluminum (99.00% minimum aluminum)}



_{2XXX Copper}



_{3XXX Manganese}



_{4XXX Silicon}



_{5XXX Magnesium}



_{6XXX Magnesium and Silicon}



_{7XXX Zinc}



_{8XXX Other elements}



_{9XXX Unused series}

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Cast Alloys

Alloy Number Major Identifying Elements



_{1XXX 99.00 % minimum aluminium}



_{2XXX Copper}



_{3XXX Silicon with added copper and/or magnesium}



_{4XXX Silicon}



_{5XXX Magnesium}



_{6XXX Unused series}



_{7XXX Zinc}



_{8XXX Tin}



_{9XXX Other elements}

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Aluminum Alloys

Type of Alloy Classification

Pure (99% above) 1xxx Copper 2xxx Manganese 3xxx Silicon 4xxx Magnesium 5xxx Magnesium Silicon 6xxx Zinc 7xxx Other Element 8xxx

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Temper Designation for Heat Treatable

Alloys

 T1 – Cooled from an elevated temperature shaping process and naturally aged to a substantially stable condition

 T2 – Annealed

 T3 – Solution heat treated and cold worked.  T4 – Solution heat treated and naturally aged.

 T42 – Solution heat treated from 0 temper to demonstrate response to heat treatment by the user, and naturally aged to a substantially stable condition

 T5 – Cooled from an elevated temperature shaping process and artificially aged

 T6 – Solution heat treated and artificially aged.

 T62 – Solution heat treated from 0 F temper to demonstrate response to heat treatment by the user, and artificially aged

 T7 – Solution heat treated and stabilized

 T8 – Solution heat treated, cold worked, and artificially aged  T9 – Solution heat treated, artificially aged, and cold worked

 T10 – Cooled from an elevated temperature shaping process, cold worked, and artificially aged

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Aluminum Association Numbering

System

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Aluminum Cladding

 Several aluminium alloys as for example 2024 and 7075 are very susceptible tocorrosion. Sheets of such material are clad with a thin layer of pure aluminium with 1 % zinc on both sides as a means of corrosion protection. These layers are permanently welded to the base material in a rolling process at high temperature. Other than electroplated stock, clad material can be formed. The thickness of the clad layers is about 3 or 5 % of the material thickness. An

ink print on US sheet metal that reads ALclad, Clad or ALC indicates that such sheet is clad.

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Steel Numbering

System

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Steel Numbering

System

_{Type of Steel} _{Classification}

Carbon 1xxx Nickel 2xxx Nickel Chromium 3xxx Molybdenum 4xxx Chromium 5xxx Chromium Vanadium 6xxx Tungsten 7xxx Silicon Manganese 8xxx

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Temper Designation System

 Basic Temper Designation

 F – As fabricated  O – Annealed

 H – Strain hardened (Non heat treatable products only)  W – Solution heat treated

 T – Heat treated to produce stable tempers other than F, O, or H  Temper Designation for Non Heat Treatable Alloys

 _{H 1 – Strain hardened produced by cold working the metal to the desired}

dimension.

 H2 – Strain hardened, then partially annealed to remove some of the hardness.  H3 – Strain hardened, then stabilized.

 The degree of hardening is indicated by a second digit following one of the

above designations:  2 - 1/4 hard  4 - 1/2 hard  6 - 3/4 hard  8 - full hard  9 - extra hard

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Temper Designation System

Fabricated (F) – Denotes that the metal has been

fabricated to ordered dimensions without any attempt

on the part of the producer to control the results of

either strain hardening operations or the thermal

treatments. There are no mechanical property limit,

and the strength levels may vary.

Annealed (O)- Applies to wrought that have undergone a

thermal treatment to reduce their mechanical property

levels to their minimum. Often describe as soft dead

metal.

Strain Hardened (H)- applies to those wrought products

which have had an increase in strength by reduction

through strain hardening or cold working operations.

H is followed by two or more digits

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Temper Designation System

Thermally Treated ( T) – Produce temper other

than F,O, H. Applies to those products which

have had an increase in strength due to

thermal treatments, with or without

supplementary strain hardening operations. T

is always followed by two or more digits.

Solution Heat Treated ( W) – An unstable

temper applying to the certain of the (7xxx)

heat treatable alloys that, after heat

treatment spontaneously age harden at room

temperature. Only when the period of natural

aging is indicated

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Materials

Carbon Content

Wrought iron

Trace to 0.08%

Low carbon steel

0.08% to 0.30%

Medium carbon

steel

0.30% to 0.60%

High carbon steel

0.60% to 2.2%

(72)

(73)

Heat Treatment

Processes

METALWORKING PROCESSES



_Hot-working

○ _Forging ○ _Rolling 

_Pressing



_Hammering



_{Cold Working}

○ _{Cold Rolling} 

_{Cold Drawing}



_Extrusions

(74)

Heat Treatment Processes for

Aluminum

 HEAT TREATMENT – is a series of operations involving the heating and cooling of metals in their solid state. Its purpose is to make the metal more useful, serviceable and safe for a definite purpose.

 SOLUTION HEAT TREATMENT – is the process of heating certain aluminum alloys to allow the alloying elements to mix with the base metal.

 QUENCHING – rapid cooling by means of water, oil, brine, etc.  SOAKING or HOLDING – held the temperature within about plus

or minus 10 degrees Fahrenheit of this temperature and the base metal until the alloying elements is uniform throughout.

 NATURAL AGING – when an alloy is allowed to cool at room temperature and can take several hours or weeks.

 ARTIFICIAL AGING – accelerating the aging process by cooling at an elevated temperature.

 ANNEALING – is the process that softens a metal and decrease internal stresses.

 STRAIN HARDENING – also referred to as COLD WORKING or WORK HARDENING. This requires mechanically working of metal

(75)

Steps of Heat Treatment

The heat treatment takes place in three steps.

Step 1: Solution heat treat, that is heating of the material to

a specified temperature and holding it there for a specified

time.

Step 2: Quenching

Step 3: Age hardening (precipitation) at room temperature

or elevated temperature

The quenching must occur rapidly. After quenching the material

initially is soft and ductile.

(76)

Methods of Heat

Treatment

(77)

HEAT TREATMENT FOR STEELS:

 ANNEALING – is a form of heat treatment that softens steel and

relieves internal stress. It is heated about 50 degrees F above its critical temperature, soaked for specified time then cooled.

 NORMALIZING – the process of forging, welding, or machining

usually leave stresses to the steel that could lead to failure. To normalize, it is heated about 100 degrees F above its critical

temperature and held there until the metal is uniformly heat soaked, then removed from the furnace and allowed to cool in still air.

 HARDENING – is heated above its critical temperature so carbon can

disperse uniformly in the iron matrix.

 TEMPERING – reduces the undesirable qualities of martensitic steel.

It is heated to a level considerable below its critical temperature and held there until it becomes heat soaked, then allowed to cool to room temperature in still air.

(78)

CASE HARDENING TREATMENTS:

1. CARBURIZING – forms a thin layer of high carbon steel on

the exterior of low carbon steel.

 _{PACK CARBURIZING – is done by enclosing the metal in a fire-clay}

container and packing it with a carbon-rich material such as charcoal. The container is then sealed, placed in furnace, and heated.

 _{GAS CARBURIZING – is similar to pack carburizing except the carbon}

monoxide gas combines with gamma iron and forms a high-carbon surface.

 _{LIQUID CARBURIZING – produces a high-carbon surface when a part is}

heated in a molten salt bath of sodium cyanide or barium cyanide.

2. NITRIDING – differs from carburizing in that a part is first

hardened, tempered and then ground to its finished

dimensions before it is case hardened.

3. CYANIDING – is a fast method of producing surface

(79)

(80)

(81)

Forming/Shaping and

Forging

(82)

(83)

(84)

(85)

Aircraft Welding

Fusion welding is the blending of compati ble molten

metals into one common part or joint. Fusing of

metals is accomplished by producing suf ficient heat

for the metals to melt, flow together and mix. The

heat is then removed to allow the fused joint to

solidify.

Non-fusion welding is the joining of metals by

adhesion of one metal to another. The most

prominent non-fusion welding processes used on

aircraft are brazing and soldering, which are cov ered

in detail later in this section.

(86)

FUSION WELDING PROCESSES

The three principal methods of fusion welding are

gas, electric arc, and electrical resistance

. Fusion

welding results in superior strength joints because

the metal parts are melted together into a single

solid object. Since fusion-welded joints are used

extensively in high-stress applications, their failure

is likely to have catastrophic consequences. To

fully appreciate the level of detail that must be

exercised when inspecting welded components,

you must be aware of the characteristics that

define a quality fusion-welded joint.

(87)



OXYACETYLENE WELDING

Oxyacetylene welding, often referred to as gas

weld ing, gets its name from the two gases, oxygen and

acetylene, that are used to produce a flame. Acetylene

is the fuel for the flame and oxygen sup ports

combustion and makes the flame hotter. The

combination of these two gases results in sufficient

heat to produce molten metal. The temperature of the

oxyacetylene flame ranges from 5,600 to 6,300 F

(88)



ELECTRIC ARC WELDING

Electric arc welding includes shielded metal arc

welding, gas metal arc welding, and tungsten inert

gas [TIG) arc welding. Although TIG welding is the

method that is predominantly used in aircraft fabri

cation and repair, a technician is also required to

understand the other methods.

(89)

SHIELDED METAL ARC WELDING

In SMAW welding, a metal wire rod, which is com posed

of approximately the same chemical compo sition as the

metal to be welded, is clamped in an electrode holder. This

holder, in turn, is connected to one terminal of the TR power

supply by a heavy gauge electrical cable. The metal to be

welded is attached to the other terminal of the power supply

through another electrical cable usually equipped with a

(90)



GAS METAL ARC WELDING

Gas metal arc welding (GMAW), formerly called Metal Inert Gas (MIG) welding, is used primarily in large volume production work. An advantage of GMAW over stick welding is that no slag is deposited on the weld bead. An uncoated filler wire acts as the electrode. It is connected to one terminal on the power supply, and fed into the torch. An inert gas such as argon, helium or carbon dioxide flows out around the wire to protect the weld zone from oxygen. The metal to be welded is connected to the other terminal of the power supply. When power is supplied to the electrode, and it is brought into contact with the work, it produces an arc, which

(91)



TUNGSTEN INERT GAS WELDING

Tungsten inert gas welding (TIG) is the form of elec tric arc welding that is used most in aircraft mainte nance. TIG welding uses a tungsten electrode that does not act as filler rod. The electrode is con nected to an AC or DC electrical power supply to form an arc with the metal being welded. The arc is

concentrated on a small area of the metal, raising its

temperature to as high as 11,000 F, without exces sively heating the surrounding metal. The base metal melts in the area of the arc and forms a pud dle into which the filler rod is added.

(92)



ELECTRIC RESISTANCE WELDING

Many thin sheet metal parts for aircraft, especially stainless steel parts, are joined by one of the forms of electric resistance welding; either spot welding or seam welding.

SPOT WELDING

When spot welding, two copper electrodes are held in the jaws of a vise-like machine and the pieces of metal to be welded are clamped between them. Pressure is applied to hold the electrodes tightly

together while electrical current passes between the electrodes. SEAM WELDING

While it would be possible to create a seam with a series of closely spaced spot welds, a better method is to use a seam welder. This equipment is com monly used to manufacture fuel tanks and other components where a continuous weld is needed.

(93)

(94)

Weld inspection



~ A good weld is uniform in width, with

even ripples that taper off smoothly into

the base metal. There should be no burn

marks or signs of overheating, and no

oxide should form on the base metal

more than 1/2 inch from the weld.

Furthermore, a good weld must be free

of gas pockets, porosity, and inclusions

(95)

Weld inspection



Penetration is the depth of fusion in a

weld, and is the most important

characteristic of a good weld. Penetration

depends on the thickness of the material

to be joined, the size of the filler rod, and

welding technique. A typical butt weld

should penetrate 100 percent of the

thickness of the base metal, while a fil let

weld must penetrate 25 to 50 percent

(96)

Weld inspection

 ~Poor welds display certain telltale characteristics. For example, too much acetylene makes the molten metal boil, causing bumps along the center and craters along the weld's edge. A cold weld has irreg ular edges and considerable variation in depth of penetration, while excessive heat produces a weld with pitting along its edges and long, pointed rip ples. If a part is cooled too quickly after being welded, cracks often appear adjacent to the weld. Whenever a welded joint displays any of these defects, all of the old weld must be removed and the joint rewelded

(97)

(98)

Aircraft Hardware, Cables,

and Tools, Equipment

(99)

AIRCRAFT RIVETS, BOLTS,

NUT, SCREWS AND

(100)

(101)

(102)

(103)

(104)

C = 1.5 D

N = 0.5 D

NOTE:

As a rule of thumb, to determine fastener diameter to be used will be 3x the thickness of the thickest

(105)

426 – Countersunk Head

(100 degrees) 470 – Universal Head

(106)



The 2117-T rivet is designated as an

“AD” rivet, and has a dimple on the

head. A “B” designation is given to a

rivet of 5056 material and is marked

with a raised cross on the rivet head.

Each type of rivet is identified by a part

number to allow the user to select the

correct rivet. The numbers are in series

and each series represents a particular

type of head.

(107)



Countersunk head rivets (MS20426

supersedes AN426 100-degree) are used where

a smooth finish is desired. The 100-degree

countersunk head has been adopted as the

standard in the United States. The universal

head rivet (AN470 superseded by MS20470) has

been adopted as the standard for protruding-

head rivets, and may be used as a replacement

for the roundhead, flathead, and brazier head

rivet. These rivets can also be purchased in half

sizes by designating a “0.5” after the main length

(i.e., MS20470 AD4-3.5).

(108)

Identification marking of

rivet

MS 20470AD3-5 Complete part number

MS Military standard number

20470 Universal head rivet

AD 2117-T aluminum alloy

3 3/32nds in diameter

(109)

(110)

(111)

(112)

Bulbed Cherrylock

Rivets.

One of the earlier types of mechanical-lock

rivets developed were Bulbed Cherrylock blind

rivets.

These blind rivets have as their main

advantage

the ability to replace a solid shank rivet

size for size.

(113)

(114)

(115)

(116)

The CherryMax

•It uses one tool to install three standard rivet

diameters and their oversize counterparts.

•This makes the use of CherryMax rivets very

popular with many small general aviation repair

shops.

•The CherryMax rivets consists of five parts;

bulbed blind header, hollow rivet shell, locking

(foil) collar, driving anvil, and pulling stem.

(117)

(118)

An Olympic-Lok

•is a light three-piece mechanically

locked,

spindle-type blind rivet. It carries its stem

lock

(119)

(120)

Huck rivets

The Huck rivet has the ability to tightly

draw-up two or more sheets of metal

together while being installed.

(121)

(122)

Common pull-type Pop rivets

Produced for nonaircraft related

applications, are not approved for use on

certificated aircraft

(123)

AIRCRAFT BOLTS

( Threaded fasteners)

GENERAL PURPOSE BOLTS

The hex head AN 3 THROUGH AN 20 is an all

purpose structural bolt used for general

applications involving tension and shear

loads where a light drive fit is permissible.

Fabricated from SAE 2330 nickel steel and

cadmium plated. Identified by a cross or

asterisk

(124)

AN BOLT HEAD

IDENTIFICATION

GENERAL PURPOSE - CROSS OR ASTERISK

AIRCRAFT BOLTS

( Threaded fasteners)

(125)

AIRCRAFT BOLTS

( Threaded fasteners)

GENERAL PURPOSE BOLTS

The AN 73 - AN 81 (MS20073-MS20074) drilled

head bolt is similar to the standard hex bolt,

but has a deeper head that is drilled to receive

wire for safetying. The AN3-AN20 and

(126)

AIRCRAFT BOLTS

( Threaded fasteners)

CLOSE TOLERANCE BOLTS

This type of bolt is machined more accurately

than the general purpose bolt. They can be

Hex headed - (AN173-AN186) or have a

Countersunk head- (NAS80-NAS86) they are

used in applications where a tight drive fit is

required (the bolt will only move into position

only when struck with a 12-14 ounce hammer)

(127)

AN BOLT HEAD IDENTIFICATION

AIRCRAFT BOLTS

( Threaded fasteners)

AN BOLT HEAD IDENTIFICATION

CLOSE TOLERANCE - CROSS OR ASTERISK INSIDE

A TRIANGLE

(128)

AIRCRAFT BOLTS

( Threaded fasteners)

CLASSIFICATION OF THREADS

NC – American national coarse

NF – American national fine

UNC – American standard unified coarse

UNF – American standard unified fine

(129)

AIRCRAFT BOLTS

( Threaded fasteners)

THREAD designation

Threads are designated by the number of times

the incline (threads) rotates around a 1 inch

length of given diameter bolt or screw.

EX. 4-28 thread indicates that a ¼” dia. Bolt

has 28 threads in 1” of its thread length.

(130)

AIRCRAFT BOLTS

( Threaded fasteners)

THREAD designation

Threads are designated by the Class fit

(tolerance allowed in manufacturing).

Class 1 – Loose fit

(Easily turned by the fingers)

Class 2 – Free fit

(Aircraft Screws)

Class 3 – Medium fit

(Aircraft Bolts)

Class 4 – Close fit

(Requires a wrench to turn the nut onto

a bolt)

(131)

Limits and Fits

 _{Clearance Fit – in this assembly there is a space between the two parts. The shaft is}

always smaller than the part it fits into.

 _{Interference Fit – in this assembly there is no space between the parts. The shaft is}

always larger than the part it fits into. This means that force is required to assemble the parts.

 Transition Fit – this is a range of fits which can be either clearance or interference. The

(132)

AN4-8A

• AN

means the bolt is manufactured according to

Air Force-Navy specs.

•

4 identifies the diameter of the bolt shank in 1/16"

increments

•

8 identifies the length of the shank in 1/8"

increments

• A

means the shank of the bolt is un-drilled (no

letter here means a drilled shank)

AIRCRAFT BOLTS

( Threaded fasteners)

(133)

AN4-H8A

• _AN

means the bolt is manufactured according to Air

Force-Navy specs.

• ₄

identifies the diameter of the bolt shank in 1/16"

increments

• H

identifies the head is drilled

•

8 identifies the length of the shank in 1/8" increments

• A

means the shank of the bolt is un-drilled (no letter here

means a drilled shank)

AIRCRAFT BOLTS

( Threaded fasteners)

(134)

Within a given diameter (i.e. 1/4, 3/8, 1/2, etc.) of any AN/MS/NAS series, all bolts will have the same thread length, no matter how long the bolt.

The thread lengths for each series bolt are on the specification prints and in a chart under the "Aerospace Bolt Interchange" heading under Tech Info

In all MS and NAS series bolts, the dash number is the grip in 1/16" (0.0625") increments, e.g. -18 = 18 x 0.0625" = 1.125" = 18/16".

Thus, to determine the overall length of a bolt, simply add the thread length for that series and diameter to the grip length you desire, e.g. NAS 1306-24: grip is 1.50" + threads: 0.578" = 2.078" overall length.

In AN series bolts, you must have a chart or bolt gauge to determine lengths, grips or part numbers. THE DASH NUMBERS DO NOT INDICATE EITHER GRIPS OR OVERALL LENGTHS.

AIRCRAFT BOLTS ( Threaded fasteners)

(135)

(136)

BOLT GRIP LENGTH CORRECT

BOLT GRIP LENGTH TOO SHORT

BOLT GRIP LENGTH TOO LONG

(137)

COUNTERSUNK HEAD BOLT

INTERNAL WRENCHING BOLT

DRILLED HEX HEAD BOLT

CLEVIS BOLT Types of Bolts

(138)

CLOSE TOLERANCE (STEEL OR ALUMINUM ALLOY) ALUMINUM ALLOY (62,000 P.S.I.) CORROSION RESISTANT STEEL (125,000 P.S.I.)

STEEL 125,000 P.S.I STEEL 150,000 P.S.I HEAD MARKINGS

(139)

MACHINE SCREW

STRUCTURAL SCREW

SELF-TAPPING SCREW

CAUTION

Self-tapping Screws should never be

used to replace standard screws, nuts, or rivets originally used in the

structure.

CAUTION

Self-tapping Screws should never be

used to replace standard screws, nuts, or rivets originally used in the

structure. COUNTERSUNK HEAD ROUND HEAD BRAZIER HEAD grip length grip length grip length