Sheet Metal Repairs

The primary objective of aircraft repair is to

restore damaged parts to their original condition.

Is a sheet metal repair always possible?

No, a replacement is often done

Inspecting the damage is necessary because it

determines how large a repair will be, type of repair, thickness of material, # of rivets

True or False

Repairs are custom made to the aircraft and situation

True

The repair and the original should have the same _______

strength

Should the repair be the same weight as the original?

Yes, or slightly heavier

Stress follows the path of

least resistance

True or False

Damage can’t exist in parts far from impact

False

Depending on the scale of the damage a ______ inspection may be used

Non destructive

When inspecting ____ must be removed

dirt, grease, and paint

Make sure to inspect the skin for

wrinkles

Check the _____ of all moveable parts in the area when inspecting

operation

What is the goal of an aircraft sheet metal repair?

An aircraft that is the same strength as the original

In which of these repairs is strength the most important characteristic?

Repair to underlying structure

A well designed sheet metal repair must be custom designed to fit which of these?

The damage on the aircraft

To maintain strength, the cross sectional area of the repair must be ___ to or _________ than the cross section of the damage.

equal to or greater

Should you use rectangular patches on sheet metal repairs?

Avoid them but if necessary use at least 1/2” radius on the corners

If the member is subject to compression or bending loads, the patch should be placed on the _______ of the member

outside

If it isn’t possible to place the patch on the outside of the member, build the patch out of

one heavier gauge than the member

It is necessary to replace buckled or bent parts but it is also possible to

reinforce the part with an additional layer of material

True or False

You must use a stronger material than the original

False, the same material must be used

If a different material must be used you can use

a thicker piece of a weaker alloy

True or False

You can also use a thinner piece of a stronger alloy

False, only a thicker piece of a weaker alloy

If the rivets fail, leaving the structure intact, it is called a

shear failure

If the rivets fail, leaving the rivets intact, it is called a

bearing failure

The number of rivets used should make the part nearly

equal in strength to the rivets.

If repairing a rotating part you need to make a

balance patch on the opposite side as well.

Repairs to flight controls need to match original strength in

compression, tension, and torsion.

After repairing a flight control make sure to

check it is within manufacturer’s spec for balance.

If the repair doesn’t fit within manufacturer’s specs

rebalance the flight control

How can a mechanic avoid areas of sudden change in cross section?

Taper the patch layout

If a repair is loaded in compression, the repair patch should be placed on the outside of the structure. If this is not possible, what should you do?

Use a patch that is one gauge thicker than the material being patched.

A well designed rivet joint should have

The rivets and the structure equally strong.

Does negligible damage need to be repaired before operating an aircraft?

No

All sheet metal repairs should be kept as light as possible. What special thing should you do when repairing a nose spinner?

Duplicate your repair on the opposite side.

What is the difference between erosion and corrosion?

Erosion happens from mechanical means, corrosion from chemical.

Lap or scab patches are laid

over the top of the material

The edges of a scab patch

lap over the top of the original skin

Skin repairs are classified as

open or closed based on access to the rear of the skin

The outside doubler and scab is

4D larger than cutout in skin patches

The inside edge of the double is

4D smaller than cutout in skin patches

The rivet spacing in a skin patch is

as close to 6D as possible

A corrugated skin repair is

found on flight control surfaces of smaller airplanes.

When replacing a panel your seam must be

as strong as the strongest adjacent seam.

The replacement panel will usually be put in with

lap joints

Typically, rivets are not driven into

flanges

True or False

In a pressurized repair you must dip rivets into sealant before installation

True, the doubler should also have a thin layer

On stringers, repair by patching is acceptable when damage is

less than 2/3 width of one leg and less than 1/2 inches long

In a bulkhead or former repair

fabricate a doubler that is one size thicker.

Use only these type of repairs on leading edge surfaces

flush rivets and flush type patches

A fixture

supports the work and aids in alignment

A jig

holds the plane or parts in exact position, and ensures that all holes, etc, line up

The techniques outlined in AC 43.13-1B are only valid if

there is no manufacturers maintenance manual

When doing a major repair make sure to fill out

Form 337