1/2 Chapters 7-9 & 11: Aircraft Materials, Hardware, and Processes (Includes Hand tools and Measuring Devices)

What is the alloy number of the most commonly used aluminum alloy for aircraft structural use?

2024-T

What is the alloy number of the high strength aluminum alloy that has zinc as an alloying component?

7075

What type of composite material is used when stiffness is the primary requirement?

Graphite (carbon)

What type of composite material is used when toughness is the primary requirement?

Kevlar

Why is a piece of steel tempered after it has been hardened?

When steel is hardened, it becomes brittle. Tempering removes some of this brittleness

How is steel annealed?

It is heated to just above its upper critical temperature until it reaches a uniform temperature throughout, then it is allowed to cool very slowly in the oven

How is steel hardened?

It is heated to its critical temperature and quenched in water, brine, or oil

What is meant by tempering steel?

The steel is first hardened; then some of the hardness is removed to relieve some of the internal stresses and brittleness

What is meant by case hardening?

The surface of the metal is hardened by the infusion of carbon or aluminum nitride. The interior of the metal remains strong and tough

What are two methods of case hardening?

Carburizing and nitriding

How is steel nitrided?

The steel part is heated in a retort in which there is an atmosphere of ammonia (a compound of nitrogen and hydrogen). Aluminum, an alloying element in the steel, combines with the nitrogen to form an extremely hard aluminum nitride on the surface of the steel

What is the method of solution heat treatment of an aluminum alloy?

The metal is hardened by heating it in a furnace to a specified temperature and immediately quenching it in water. It is soft when it is removed from the quench, but as it ages it regains its hardness

What is the method of precipitation heat treating of an aluminum alloy?

The metal is heated and quenched, then it is returned to the oven and heated to a lower temperature. It is held at this temperature for a specified time, then removed from the oven and allowed to cool in still air. This increases the strength and hardness of the metal. Precipitation heat treating is also called artificial aging

What is another name for precipitation heat treatment?

Artificial aging

Identify and explain the differences between heat-treated and non-heat-treated aluminum alloys

Heat-treated aluminum alloy designations are normally followed with a -T, followed by a number (1-10) that designates the type of heat-treat. A common aircraft aluminum alloy is 2024-T3. Heat-treated aluminum is stronger than non-heat-treated aluminum

Why is it important that a piece of aluminum alloy be quenched immediately after it is removed from the heat treating oven?

Any delay in quenching aluminum alloy after it is removed from the oven will allow the grain structure to grow enough that intergranular corrosion is likely to form in the metal

Describe and explain the forces placed on aircraft materials

Tension - A force tending to stretch or elongate the material

Compression - A force tending to compress or shrink

Torsion - A twisting force on an object

Bending - A perpendicular force on the longitudinal axis of an object, causing it to flex or bend

Strain - The stress on an object which can cause the object to change shape or to become distorted

Shear - A force that tries to cut or slice through an object. The force is parallel to the material cross section

What type of loading should be avoided when using a self-locking nut on an aircraft bolt?

A self-locking nut should not be used for any application where there are any rotational forces applied to the nut or to the bolt

What determines the correct grip length of a bolt used in an aircraft structure?

The grip length of the bolt should be the same as the combined thicknesses of the materials being held by the bolt

How tight should the nut be installed on a clevis bolt that is used to attach a cable fitting to a control surface horn?

The nut on a clevis bolt should not be tight enough to prevent the clevis bolt from turning in the cable fitting and the horn

What bolt is described by this number: AN6-14A?

AN6 = Hex head bolt, 6/16 (3/8) inch diameter

14 = Length = 1 and 4/8 (1 and 1/2) inches long

A = The shank is not drilled for a cotter pin

What is indicated by a triangle on the head of a steel bolt?

This is a close tolerance bolt

What is a correct application for self-tapping sheet metal screws on an aircraft?

They may be used to hold nonstructural components onto the aircraft

How can you tell when a self-locking nut must be discarded?

When you can screw the nut onto a bolt without having to use a wrench

What is a channel nut?

A series of nuts mounted loosely in a channel that is riveted to the aircraft structure. You can install screws in a channel nut without having to hold the nut with a wrench

Of what two materials are cotter pins made?

Low-carbon steel and corrosion-resistant steel

What is the smallest size cable that is allowed to be used in the primary control system of an aircraft?

1/8" diameter

What type of control cable must be used when pulleys are used to change the direction of cable travel?

Extra-flexible cable (7x19)

What is the purpose of safety wire?

To prevent a nut, bolt, or other component from loosening

After torquing a castellated nut, can the nut be loosened to align with the hole in a bolt for installing the cotter pin?

No. Never over-torque or loosen a torqued nut to align safety wire or cotter pin holes. The nut should be torqued to the minimum torque, and then tightened to align with the safety hole, without exceeding the maximum torque.

What kind of measuring instrument is used to measure the runout of an aircraft engine crankshaft?

A dial indicator

What measuring instruments are used to measure the fit between a rocker arm shaft and its bushing?

The outside diameter of the shaft is measured with a micrometer caliper. The inside of the bushing is measured with a telescoping gauge and the same micrometer caliper.

In what increments can a vernier micrometer caliper be read?

One ten thousandth (0.0001) of an inch

What is an advantage of a vernier caliper over a micrometer caliper?

The range of a vernier caliper is far greater than that of a micrometer caliper

What precision tool is used to measure piston ring side clearance?

Thickness gauge

What precision tools are used to measure the inside diameter of a cylinder?

A telescoping gauge and a micrometer caliper

What precision tools are used to measure the inside diameter of a small hole?

A small hole gauge and a micrometer caliper

What kind of solder is recommended for soldering electrical wires?

60/40 resin-core solder

What is the function of the flux used in soldering?

Flux covers the cleaned and heated metal to keep oxygen away from it so oxides cannot form. Oxides keep the solder from adhering to the surface of the metal

What are the three most common types of torque wrenches?

Deflecting beam, dial indicating, and micrometer setting types

Where would an aviation mechanic find the appropriate hardware specifications for use on a particular aircraft?

In the aircraft manufacturer's illustrated parts catalog (IPC)

Where would an aviation mechanic find the material specifications for structural repairs on an aircraft?

In the aircraft manufacturer's structural repair manual (SRM)

Why is it very important that the surface of a piece of clad aluminum alloy not be scratched?

The pure aluminum used for the cladding is noncorrosive, but the aluminum alloy below the cladding is susceptible to corrosion. If the cladding is scratched through, corrosion could form

What is the preload value when torquing a nut?

Preload is the force or torque required to overcome the friction between the threads on the nut and the threads of the bolt prior to the nut contacting the mating surface

How is the preload value used when torquing a nut?

The preload torque is added to the specified torque to obtain the required setting on the torque wrench

How can the material of a bolt be identified?

By manufacturer markings that are on the bolt head

How is the welding flux removed from a piece of aluminum that has been gas-welded?

It should be removed by scrubbing it with hot water and a bristle brush

What are the visual characteristics of a good weld?

A good weld is uniform in width; the ripples are even and well feathered into the base metal and show no burn due to overheating. The weld has good penetration and is free of gas pockets, porosity, or inclusions

What are the visual characteristics of a bad weld?

A bad weld has irregular edges and considerable variation in the depth of penetration. It often has the appearance of a cold weld

What must be done to a welded joint if it must be rewelded?

All traces of the old weld must be removed so the new weld will penetrate the base metal

What is meant by normalizing a piece of steel after it has been welded or machined?

Normalizing removes stresses that are locked into the material by welding or machining

How is a steel structure normalized after it has been welded?

Heat the steel structure to a temperature above its critical temperature and allow it to cool in still air

What determines the size of tip that is to be used when gas-welding steel?

The thickness of the material being welded. The size of the tip orifice determines the amount of flame produced and thus the amount of heat put into the metal

How do you work harden a piece of metal?

By cold working the metal

Describe the primary difference between a thermosetting and a thermoplastic resin

A thermosetting resin doesn't soften when heated and chars or burns rather than melting. A thermoplastic resin becomes soft and pliable when heated, and hardens when cooled

Explain how thermoplastic and thermosetting resins are commonly used in modern aircraft

Plexiglass is a thermoplastic resin commonly used for windshields and windows. Thermosetting resins are most often used as the matrix material in composite structures

Name one of the types of resin commonly used as a matrix material for aircraft composite laminates

Polyester resin or Epoxy resin

What are some of the materials that are commonly used as the reinforcing component in a composite structure?

Fiberglass, Aramid (Kevlar), Graphite (carbon) fiber, linen and paper

What are the reasons that alloy steel that is responsive to heat treatment is usually less suitable for welding?

It may become brittle and lose its ductility in the area of the weld

Give one advantage of pre-preg (pre-impregnated) materials, other than saving time in the construction or repair of composite components

1. Pre-preg fabrics contain the correct amount of matrix

2. The matrix material evenly and completely permeates the reinforcing fibers

3. The matrix has the resin and hardener in the correct proportions

What property is essential for metals used in making wire and tubing?

Property of ductility