Sheet metal and non-metallic structures

Question 1

What is the grip length of a rivet?

Answer 1

The grip length is the combined thickness of the materials to be joined by the rivet.

Question 2

Where are special rivets, such as Huck or Cherry lock rivets used?

Answer 2

They are used in places where access to both sides of the riveted structure is impossible, or where
limited space will not permit the use of a bucking bar. These rivets require special tools,
Installation, and removal procedures. They are commonly called blind rivets.

Question 3

What is bonded honeycomb (sandwich) construction?

Answer 3

It is a laminar construction consisting of a combination of alternating dissimilar materials.

Question 4

What type of materials are used in honeycomb construction?

Answer 4

Honeycomb construction may employ stainless steel, titanium, magnesium, plywood, resin
impregnated paper, E-glass, nylon, or cotton cloth in various combinations.

Question 5

Where are sandwich construction assemblies used?

Answer 5

They are used for such areas as bulkheads, control surfaces, fuselage panels, wing panels,
Radomes , empennage skins, or shear webs.

Question 6

What procedures should be used to prevent damage to the hole when drilling though Plexiglas?

Answer 6

The Plexiglas should be backed with wood and the feed slowed as the drill point breaks through the
underside of the sheet. A drill bit that is to be used for this purpose should be modified to a 60 tip
angle, the cutting edge to a zero rake angle, and the back lip clearance angle increased to 12-15
degrees.

Question 7

What calculations must be made when bending sheet metal?

Answer 7

Bend allowance and setback must be determined

Question 8

What factors are used to determine setback?

Answer 8

The radius of the bend and the thickness of the material. Setback = Radius + Thickness.

Question 9

When bending sheet metal, how should the grain be in relation to the bend?

Answer 9

The grain should be perpendicular to the bend.

Question 10

What is a bend tangent line?

Answer 10

The line at which the metal starts to bend.

Question 11

What is a joggle?

Answer 11

A joggle is an offset formed on a part to allow clearance for a sheet or another mating part.

Question 12

What are several methods used in forming sheet metal?

Answer 12

Folding, bumping, crimping, shrinking, and stretching.

Question 13

What kind of metal forming is done by bumping?

Answer 13

Compound curves.

Question 14

What is crazing and how does it occur?

Answer 14

Hairline cracks in the surface of plastic. A form of heat damage caused by uneven heating, one side
expanding more than the other causing excessive stress. Subjecting plastic to large stresses and
exposure to harmful solvents will cause crazing.

Question 15

Briefly describe the anodizing process and what purpose it serves.

Answer 15

Aluminum alloys are placed in an electrolytic bath which causes a thin film of hydroxide to form on
the surface of the aluminum. This anodized coating not only provides excellent resistance to
corrosion, but it is also an excellent bond for paint.

Question 16

What are the proper dimensions for the shop head of a rivet?

Answer 16

1 and 1/2 times the diameter in width and 1/2 times the diameter in height after bucking.

Question 17

When inspecting Plexiglas. what should you look for?

Answer 17

Crazing and discoloration.

Question 18

What causes honeycomb structure to delaminate?

Answer 18

Moisture.

Question 19

What are the acceptable repair methods for bonded honeycomb structure that has been damaged?

Answer 19

There are two acceptable methods of repair currently being used on damaged skin and core
materials of bonded honeycomb structures. One is the potted repair method. The other is the
laminated glass fabric cloth overlay which is applied to honeycomb damage which exceeds the
repair limitations of the potted compound method.

Question 20

What size drill should be used for the common shank rivet diameters of 3/32 inch, 4/32 inch, and 5/32 inch?

Answer 20

For a 3/32 rivet, a number 40. For a 4/32 rivet, a number 30. For a 5/32 rivet, a number 21.

Question 21

What is used for hole filling in a bonded honeycomb repair?

Answer 21

Potting compound.

Question 22

What is a lightning hole?

Answer 22

Lightning holes are cut into rib sections, fuselage frames, and other structural parts to decrease weight. Flanges are pressed around the holes for strength.

Question 23

What special precautions should be observed when repairing a radome?

Answer 23

The repair must hold its strength and electrical transparency.

Question 24

What is a warp line?

Answer 24

A highlighted strand in the fabric used for ply orientation.

Question 25

What does “pot-life” mean?

Answer 25

The length of time a resin will remain workable after the catalyst has been added.

Question 26

What is a Barcol hardness tester?

Answer 26

A device that pushes a spike into material such as composites. The depth of penetration can be
measured to determine if resins in the composite have cured.

Question 27

Give an example of a self plugging mechanical lock rivet.

Answer 27

CherryLOCK, CherryMAX, CherrySST, Huck, Huck-Clinch, or HuckMAX.

Question 28

Name two core materials used in special applications of bonded honeycomb construction?

Answer 28

Kraft paper, thermoplastics, aluminum, steel, titanium, aramid paper, fiberglass, carbon, or ceramics.

Question 29

What is a potting compound repair used for in bonded honeycomb?

Answer 29

Hole filling.

Question 30

What will cause crazing in transparent plastic panels/windshields?

Answer 30

Stress, improper handling, and harmful cleaning solvents.

Question 31

what is done with the damaged area in bonded honeycomb?

Answer 31

The damaged area must be removed.

Question 32

Describe the criteria for replacement of a 2024 rivet with a 2117 rivet for general repairs.

Answer 32

For 5/32 or less diameter, use the next larger size rivet (2117) assuming that spacing and edge
distance meet minimum requirements.

Question 33

What should be done to twist drills that are to be used for drilling completely through Plexiglas?

Answer 33

Drill must be free from nicks and burrs that would affect the surface finish. Grind the drill with an
included angle of 150 degrees. The rake angle should be zero in order to scrape, and not cut.

Question 34

Describe rivet head markings for A, B, D, AD, and DD rivets.

Answer 34

Plain (1100), cross (5056), Raised dot (2017), dimple (2117), and double dash (2024).

Question 35

What is bonded honeycomb construction?

Answer 35

Two relatively thin, parallel face sheets bonded to and separated by a relatively thick, lightweight core.

Question 36

What is the purpose of lightning holes cut in rib sections?

Answer 36

To reduce weight.

Question 37

What is the single row spacing and edge distance for protruding head rivets?

Answer 37

Edge distance is two times the diameter; spacing is three times the diameter

Question 38

How do you determine the total length of a solid rivet for installation?

Answer 38

Grip length plus 1.5 times the shank diameter.

Question 39

What is done with the rivet head stem when a self plugging (friction lock) rivet is installed?

Answer 39

It is drawn up into the rivet shank forming a plug in the hollow center of the rivet and continues until
the excess portion of the stem breaks off at a groove.

Question 40

What must be done when two bends intersect?

Answer 40

Relief holes are drilled at the intersection

Question 41

Name two causes of delamination or deboned of a honeycomb construction?

Answer 41

(1)matrix cracks, (2)high or low-energy impacts