AEROTOPICS QUIZ 4 (AIRMATCON) Reviewer

Welding in Aircraft

Joins metals permanently by fusion (melting edges together).

Used in structural assemblies, engine mounts, exhaust systems, and repairs.

Must ensure strength, reliability, and minimal distortion

Gas Welding (Oxy-Acetylene)

Flame melts base metal + filler rod.

Used for thin steel tubing, repairs.

Advantage: portable, inexpensive.

Limitation: slower, less control on high-strength alloys

Arc Welding (Electric Arc)

Heat from electric arc between electrode and workpiece.

Types: SMAW (Shielded Metal Arc Welding)

GTAW (Gas Tungsten Arc Welding / TIG)

GMAW (Gas Metal Arc Welding / MIG)

SMAW (Shielded Metal Arc Welding)

stick electrode, general use.

GTAW (Gas Tungsten Arc Welding / TIG)

tungsten electrode, inert gas shield, precise, used for aluminum, stainless steel, titanium.

GMAW (Gas Metal Arc Welding / MIG)

continuous wire electrode, fast, used for production

Spot Welding (Resistance Welding)

Current passes between electrodes, fuses sheets at contact points.

Common for thin sheet metal (skins, ducts).

Fast, clean, but limited to lap joints

Aluminum

Welded mainly with TIG (GTAW).

Issues: oxide film must be removed, high thermal conductivity - distortion risk

Magnesium

Welded with inert gas shield (TIG).

Highly flammable - special precautions

Titanium

Requires inert gas shielding (argon) to prevent contamination

Steel (Chromoly, Stainless)

Oxy-acetylene or TIG commonly used.

Must control cooling to avoid brittleness

Welding Safety

Protective gear: helmet, gloves, apron.

Ventilation: prevent inhalation of fumes (esp. magnesium, cadmium).

Fire safety: magnesium sparks, acetylene handling.

Avoid welding near fuel tanks or flammable materials

Visual testing

smooth bead, no cracks, uniform penetration.

Non-destructive testing (NDT)

Dye penetrant (surface cracks), Radiography (X-ray for internal defects), Ultrasonic (detect subsurface flaws).

Destructive testing (sample coupons) - tensile, bend, impact tests

Common Welding Defects

Porosity, Cracks, Incomplete fusion, Undercutting, Overlap

Porosity - gas pockets, weak weld.

Cracks - due to cooling stress or contamination.

Incomplete fusion - poor penetration.

Undercutting - groove melted along base metal edge.

Overlap - excess metal without fusion

Corrosion

Chemical/electrochemical attack that converts metal back to a compound (oxide, salt).

Corrosive agents

acids, salts, moisture, exhaust gases. Can occur internally or externally

Direct Chemical Corrosion

Direct exposure to caustic liquids/gases.

Examples: battery acid, flux residues, trapped cleaning solutions

Electrochemical Corrosion

Most common in aircraft.

Requires anode, cathode, electrolyte, electrical contact (rivets, bolts, joints)

Factors Influencing Corrosion

1. Pure metals unsuitable - alloys used.

2. High temperature - faster reactions.

3. Electrolytes form with condensation, salt spray, dirt, exhaust gases.

4. Crevices/faying surfaces trap electrolytes - rapid corrosion.

5. Biological growth keeps surfaces damp.

6. Residual stresses from machining/welding - cracking in corrosive environment

General Surface (Uniform Attack)

most common, direct chemical attack.

Pitting

powdery deposits, tiny pits that penetrate deeply.

Concentration Cell (Crevice)

corrosion in joints, under deposits.

Active-Passive Cell

breakdown of protective oxide film.

Filiform

worm-like traces under paint, severe in aluminum.

Intergranular

attack at grain boundaries.

Exfoliation

advanced intergranular, lifting of surface grains (extrusions).

Galvanic

dissimilar metals in contact with electrolyte.

Stress Corrosion

constant/cyclic stress + corrosive environment.

Fatigue Corrosion

cyclic stress + corrosion, below endurance limit.

Fretting Corrosion

vibration causes rubbing at loaded joints (smoking rivets).

General Treatment

1. Remove corrosion (mechanical/chemical).

2. Neutralize residual material.

3. Restore protective film (coating, plating, painting)

Treatment of Aluminum Alloys

1. Mechanical removal (abrasives, aluminum wool, wire brush).

2. Chemical neutralization (5% chromic acid, Alodine).

3. Protective coatings (cladding, anodizing, alodizing, organic finishes)

Cladding

pure aluminum layer.

Anodizing

electrolytic oxide film.

Alodizing

chemical oxide film (field use).

Organic finishes

paint, primers (zinc chromate, wash primer, epoxy primer).

Treatment of Ferrous Metals

1. Mechanical removal (abrasive blasting).

2. Surface treatments (chrome plating, cadmium plating, galvanizing, metal spraying, organic coatings)

Chrome plating

decorative or hard (wear resistance).

Cadmium plating

sacrificial corrosion protection (common in hardware).

Galvanizing

zinc coating, sacrificial protection.

Metal spraying

molten aluminum sprayed on steel (sacrificial).

Organic coatings

paint over properly prepared surfaces.

Testing of Metals

determine mechanical properties, suitability for aircraft use. Common tests: tensile, hardness, impact, fatigue, creep, shear, compression

Tensile Test

measures strength, yield point, elongation.

Hardness Test

resistance to indentation (Brinell, Rockwell, Vickers).

Impact Test

toughness under sudden loads (Charpy, Izod).

Fatigue Test

resistance to repeated cyclic stresses.

Creep Test

deformation under constant stress at high temperature.

Shear Test

resistance to sliding forces.

Compression Test

resistance to crushing loads.

Inspection

detect defects, ensure safety and reliability. it is continuous during manufacturing, maintenance, and service. Types: visual, dimensional, surface, internal

Visual Inspection

first line of defense; look for cracks, corrosion, deformation.

Dimensional Inspection : check tolerances, fits, alignments.

Surface Inspection

scratches, dents, wear.

Internal Inspection

hidden flaws, requires NDT methods.

Nondestructive Testing (NDT)

Methods to inspect materials/structures without damaging them. Importance: detect flaws early, preserve component integrity, reduce costs

Visual (VT)

simplest, aided by magnifiers, borescopes.

Liquid Penetrant (PT)

dye penetrant reveals surface cracks.

Magnetic Particle (MT)

magnetic field + iron particles show cracks in ferromagnetic materials.

Ultrasonic (UT)

high-frequency sound waves detect internal flaws.

Radiographic (RT)

X-rays or gamma rays reveal internal defects.

Eddy Current (ET)

electromagnetic induction detects surface/subsurface flaws in conductive materials.

Thermography

infrared imaging shows heat patterns, hidden defects.

Acoustic Emission

detects sound waves from crack growth or stress.

Tensile/Hardness Tests

material qualification.

Visual Inspection

daily checks.

Liquid Penetrant

cracks in aluminum skins.

Magnetic Particle

steel landing gear.

Ultrasonic

composites, bonded joints.

Radiography

welds, castings.

Eddy Current

cracks around rivet holes

Arm (moment arm) - distance (inches) from datum to CG of item (+ aft, - forward).

Datum - reference plane/line chosen by manufacturer (all arms measured from here).

CG (Center of Gravity) - point where aircraft balances; expressed in inches from datum or %MAC.

CG Limits - forward & aft allowable CG positions.

CG Range

distance between forward & aft limits.

Moment

weight × arm (lb-in).

Moment Index

moment ÷ constant (100, 1,000, etc.) to simplify numbers.

Basic Empty Weight (GAMA)

standard empty + optional/special equipment.

Useful Load (GA)

max gross - empty weight (pilot, pax, baggage, fuel, oil).

Payload (GAMA)

occupants, cargo, baggage.

Zero Fuel Weight (GAMA)

max weight excluding usable fuel.

Ramp Weight

total loaded weight incl. fuel; > takeoff weight (taxi fuel).

Takeoff Weight

max allowable for takeoff.

Landing Weight

max allowable at landing.

MAC (Mean Aerodynamic Chord)

average wing chord; CG often expressed as %MAC.

Gasoline

6 lb/gal

Jet A

6.8 lb/gal

Jet B

6.5 lb/gal

Oil

7.5 lb/gal

Water

8.35 lb/gal

Transport Aircraft

Weight Relationships

Empty + Operating = Basic Operating Weight.

Payload = Zero Fuel Weight.

Fuel = Ramp Weight -> Taxi -> Takeoff - Enroute Burn - Landing

General Aviation

Weight Relationships

Empty + Useful Load = Takeoff -> Enroute Burn -> Landing

Effects of Excess Weight

Higher takeoff speed/run.

Reduced climb rate.

Lower max altitude.

Shorter range.

Reduced cruise speed/maneuverability.

Higher stall speed.

Higher landing speed/roll.

Excess nosewheel load

Balance and CG controld

etermines stability.