Aviation Maintenance: Metallic Structures

Inspect riveted joints, looking for chipped or cracked paint that may indicate shifted or loose rivets. Smoking around rivets indicates movement, or fretting rivets. Check for cracked rivets and missing shop and manufactured heads. Look for cracks near rivets or stressed areas. Inspect for corrosion.

Brinelling, burnishing, burr, corrosion, crack, cut, dent, erosion, chattering, galling, gouge, inclusion, nick, pitting, scratch, score, stain, upsetting.

The repair material must duplicate the strength of the original structure.

Across the grain.

The alloy, the metal thickness, and its hardness.

A plane within the metal that neither stretches nor shrinks when the metal is being bent.

An extension of the flat sides beyond the radius.

A line in a flat pattern layout at which the bend starts.

The distance the jaws of a brake must be set back from the mold line to form a bend.

in a flat pattern layout. The actual amount of metal in a bend. It is the distance between the bend tangent lines.

A line drawn on a flat pattern layout within the bend allowance that is one bend radius from the bend tangent line. When the sight line is directly below the nose of the radius bar on the brake, the bend will start at the bend tangent line.

Throatless shears are used to cut mild carbon steel up to 10-gauge, and stainless steel up to 12-gauge. They can be used to cut irregular curves in the metal.

Simple curves with a large radius.

Compound curves in sheet metal.

The flanges must be stretched for a convex curve and shrunk for a concave curve.

Start at the edges and work toward the center.

A joggle is a small offset near the edge of a piece of sheet metal that allows the sheet to overlap another piece of metal.

A patented fastener that is inserted in the rivet holes and used to hold two pieces of sheet metal together until they can be riveted.

A universal head rivet.

The combined thickness of the metal sheets plus 1-1/2 times the rivet shank diameter.

The identifying mark on the head of an aluminum alloy rivet indicates the specific alloy used in the manufacture of the rivet.

7075-T6, 2024-T81 aluminum alloys, and magnesium alloys should be hot-dimpled.

Two times the diameter of the rivet shank.

Three-fourths of the distance between the rivets in the rows.

A stringer in the lower surface.

Excessive hammering will work-harden the rivets and make them difficult to drive.

The thickness of the sheet. Countersinking should be done only when the thickness of the sheet is greater than the thickness of the rivet head

Coat the faying surface with a corrosion-inhibiting primer, dip the rivets in the primer, and drive them while the primer is wet.

It holds the rivet set in the gun and allows the gun to vibrate the set.

The gasoline fumes must all be purged from the tank by running live steam through it for at least 30 minutes, by soaking it in hot water, or by filling it with nitrogen or carbon dioxide.

Do not allow the drill to enter into the space behind the structure, as the drill may cause damage to other structures or systems.

Oxygen and acetylene.

Oxygen and hydrogen.

Acetylene gas becomes unstable when it is kept under pressure of more than about 15 psi.

Balanced-pressure torches and injector torches.

The size of the orifice in the torch tip.

An oxidizing flame has a pointed inner cone, and the torch makes a hissing noise. A neutral flame has a rounded inner cone, and there is no feather around the inner cone. A reducing flame has a definite feather around the inner cone.

Skip welding minimizes distortion. Tack weld the materials together and then complete the welds between the tacks, starting at a tack and working back toward the finished weld.

Tack welding is the use of small welded spots to hold the material together until the final bead is run.

Preheating is a method of controlling the expansion and contraction of the metal being welded. Preheating minimizes the stresses that are caused when welding thick metal.

It must be normalized by heating it to a uniform red heat and allowed to cool slowly in still air.

Welding flux is corrosive and it must be removed to keep the metal from corroding.

In brazing, the base metal is not melted, but is covered with a low-melting-point alloy. In welding, the base metal is melted.

A soft, neutral oxy-hydrogen flame.

About 5 psi.

A slightly carburizing flame.

The joint should have 100% penetration.

A soft flame is one that is made when the pressures of the gases are low enough that the flame does not make a noise and does not blow the puddle.

Green or brown.

Blue.

TIG welding.

A small-diameter tungsten wire.

DC-straight polarity, DC-reverse polarity, and AC.

DC-straight polarity.

DC-reverse polarity.

Helium and argon.

The inert gas forms a shield to keep oxygen away from the weld puddle so oxides cannot form and weaken the weld.

The heat is concentrated in the weld and does not cause as much distortion as gas welding.

A patch may be welded over the damage.

A patch may be welded over the damaged area with fingers extending up along each member of the cluster.

An inner sleeve splice.

It is held in place with rosette welds.

This type of splice is not suitable where it would cause a bulge in the fabric.

Cut it with a 30° fishmouth.

It should fail in shear. The rivets should shear before the sheet tears at the rivet holes.

The repair material should be the same strength as the original material.
Material that is too weak will cause the repair to be weaker than the original.
Material that is stronger than the original will cause stresses to move to other structure, increasing the risk of failure to the surrounding structure. Choosing a dissimilar metal for the repair increases the chance of corrosion.

Use caution when working around equipment such as metal shears and breaks which can cause personal injury.
Freshly cut sheet metal has sharp edges that can cause personal damage or scratches and gouges on adjoining structure.
When drilling out rivets or rivet holes, metal shavings will be present. Use extra caution when drilling overhead.
Use caution with drills. Never place fingers or hands behind the area being drilled and be careful to not damage surrounding structure or systems when the drill bit passes through.

Use eye protection at all times. Use gloves when working with sharp edges or drills. Use ear protection when working in closed areas, especially when driving rivets.

When handling compressed gas cylinders:
-Be careful not to drop or bang cylinders, and prevent cylinders from striking each other or hard surfaces.
-Secure cylinders in a boot or by chain to a fixed support to prevent them from being dropped or from falling over.
-Do not use the valve cover (cap) to lift a cylinder.

When storing cylinders:
-Always keep valve protection caps on cylinders except when the cylinder is being used or serviced Store them in an upright position and secure them with a chain, strap, or cable to a stationary building support.
-Store in a location where they will not be subject to mechanical or physical damage, heat, or electrical circuits. Separate compressed gas cylinders from each other based on the hazard class of their contents.
-Oxygen cylinders should be kept a minimum of 20 feet away from flammable gases, liquids, solids, greases, and oils.
-Do not expose cylinders to an open flame, or any temperatures above 125 degrees Fahrenheit.

Electric welding requires the completion of a circuit. It is important that this circuit is kept complete, and the materials being welded must be well grounded as well as the surface area or bench where the welding is taking place. Poor electrical grounds can cause electric shock to the individual doing the welding.