Cleaning and Corrosion Control

Question 1

What areas of an aircraft are most prone to corrosion?

Answer 1

Battery compartment, exhaust system and exhaust trails, wheel wells, lower area of the belly (bilge), piano hinges, areas of dissimilar metal contact, welded areas, inside of fuel tanks especially integral tanks, metal fittings under high stress, lavatories, and foodservice areas.

Question 2

Where is filiform corrosion most likely to occur on an aircraft?

Answer 2

Under a dense coating of topcoat enamel such as polyurethane. Filiform corrosion is caused by improperly cured primer.

Question 3

Where is fretting corrosion most likely to occur on an aircraft?

Answer 3

In a location where there is a slight amount of relative movement between two components, and no way for the corrosive residue to be removed as it forms.

Question 4

Where is intergranular corrosion most likely to occur on an aircraft?

Answer 4

Along the grain boundaries of aluminum alloys that have been improperly heat-treated. Extruded aluminum alloy is susceptible to intergranular corrosion.

Question 5

Where is dissimilar metal corrosion most likely to occur on an aircraft?

Answer 5

Anywhere different types of metal come in contact with each other, especially where moisture is present.

Question 6

Where is stress corrosion most likely to occur on an aircraft?

Answer 6

In any metal component that is continually under a tensile stress. The metal around holes in castings that are fitted with pressed-in bushings are susceptible to stress corrosion.

Question 7

What must be done to a piece of aluminum alloy to remove surface corrosion and to treat the metal to prevent further corrosion?

Answer 7

Remove the corrosion residue with a bristle brush or a nylon scrubber. Neutralize the surface with chromic acid or with some type of conversion coating. Protect the surface from further corrosion with a coat of paint.

Question 8

What is used to keep corrosion from forming on structural aluminum alloy?

Answer 8

An oxide coating or aluminum cladding.

Question 9

How may rust be removed from a highly stressed metal part?

Answer 9

By glass bead blasting, by careful polishing with mild abrasive paper or by using fine rubbing compound on a cloth rubbing wheel.

Question 10

How should corrosion be minimized at piano hinges?

Answer 10

They should be kept as clean and dry as practicable and lubricated with a low viscosity moisture dispersing agent.

Question 11

What tools are proper for removing corrosion from aluminum alloy?

Answer 11

Aluminum wool or aluminum wire brushes. Severe corrosion can be removed with a rotary file.

Question 12

What is used to clean transparent plastic windshields and windows of an aircraft?

Answer 12

Mild soap and plenty of clean water.

Question 13

What is used to neutralize the electrolyte from a lead-acid battery that has been spilled on an aircraft structure?

Answer 13

A solution of bicarbonate of soda and water.

Question 14

What is used to neutralize the electrolyte from a nickel-cadmium battery that has been spilled on an aircraft structure?

Answer 14

A solution of boric acid and water, or vinegar.

Question 15

What solvent is recommended for removing grease from aircraft fabric prior to doping it?

Answer 15

Methyl Ethyl Ketone (MEK) or lacquer thinner.

Question 16

What can be used to repair the anodized surface of an aluminum alloy part?

Answer 16

A chemical conversion coating such as Alodine® (also known as Bonderite®).

Question 17

What type of device is used to remove surface corrosion from a piece of magnesium alloy?

Answer 17

A stiff hog-bristle brush.

Question 18

How is the inside of structural steel tubing protected from corrosion?

Answer 18

The tubing is filled with hot linseed oil and then drained.

Question 19

Why are some portions of the structure of an aircraft dope proofed before they are covered with fabric?

Answer 19

Dope proofing keeps the fabric from sticking to the structure when the first coat of dope is applied. The fabric normally sags enough to touch the structure before it begins to pull taut.

Question 20

What is done to cotton and linen fabrics to protect them from mildew?

Answer 20

The first coat of dope that is used on cotton and linen fabric has a mildewcide mixed in it.

Question 21

How is polyester synthetic fabric shrunk on an aircraft structure?

Answer 21

It is shrunk with heat from an iron or from a heated blower.

Question 22

Why should wooden wing spars be finished with a transparent varnish?

Answer 22

The transparent finish allows any decay or rot that develops in the wood to be detected.

Question 23

What is used as a protective finish for the inside of steel tubing?

Answer 23

Hot linseed oil.

Question 24

What happens to an enamel finish when paint remover is applied to it?

Answer 24

The enamel softens and swells so that it pulls away from the surface of the metal.

Question 25

What should be done to an aircraft surface that is covered with paint remover to give the remover the maximum amount of time to soak into the old finish?

Answer 25

The surface should be covered with a piece of polyethylene sheeting, such as a paint drop cloth. This will keep the solvents from evaporating before they have time to penetrate the paint film.

Question 26

When mixing epoxy paint, should the converter be added to the resin or the resin to the converter?

Answer 26

The converter should always be added to the resin, never the resin to the converter.

Question 27

What is the general reason for runs and sags in a finish that is being sprayed onto a flat surface?

Answer 27

Too much paint is being applied. The film is too thick.

Question 28

What can be done to remedy blushing that has formed on a doped surface that has just been sprayed?

Answer 28

Spray a very light mist coat of a mixture of one part retarder to two parts of thinner over the blushed area. Allow it to dry and spray on another coat. If this does not remove the blush, the blushed dope will have to be sanded off and new dope applied.

Question 29

What safety precaution must be observed when sweeping a paint room that has dried dope or lacquer overspray on the floor?

Answer 29

The floor must be wet down with water before it is swept. Static electricity from dry sweeping can cause a fire.

Question 30

What will happen if dope is sprayed over an enameled surface?

Answer 30

The thinner in the dope will penetrate the enamel surface and cause it to swell.

Question 31

What are three types of primer that may be used when painting an aircraft?

Answer 31

Zinc chromate primer, wash primer, and epoxy primer.

Question 32

How is the finish removed from a fiberglass aircraft component that is being repaired?

Answer 32

The finish must be sanded off. Paint remover can soften the resin that forms the component.

Question 33

What are the two basic types of dope that are used on fabric-covered aircraft?

Answer 33

Nitrate dope and butyrate (CAB) dope.

Question 34

What kind of dope is used on polyester synthetic fabric that has been heat-shrunk on an aircraft structure?

Answer 34

Nontautening butyrate dope.