Airframe Mechanic Certification Sheet Metal Structures 2 — Questions and Answers
Question 1: What is the minimum edge distance for a rivet hole measured from the center of the hole to the edge of the sheet?
- 1.5 times the rivet diameter (Correct answer)
- 2 times the rivet diameter
- 1 times the rivet diameter
- 2.5 times the rivet diameter
Correct answer: 1.5 times the rivet diameter
The minimum edge distance is 1.5 times the rivet diameter to prevent sheet tearing and ensure structural integrity.
Question 2: When forming a bend in sheet metal, the bend allowance refers to:
- The extra material added for overlap at the bend
- The arc length of material consumed in the curved portion of the bend (Correct answer)
- The setback subtracted from the flat pattern
- The springback angle after bending
Correct answer: The arc length of material consumed in the curved portion of the bend
Bend allowance is the arc length of material that forms the curved section of the bend, used to calculate flat pattern dimensions.
Question 3: Which type of corrosion appears as white or gray powdery deposits on aluminum sheet metal?
- Intergranular corrosion
- Galvanic corrosion
- Surface (uniform) corrosion (Correct answer)
- Stress corrosion cracking
Correct answer: Surface (uniform) corrosion
Surface or uniform corrosion on aluminum produces a white or gray powdery aluminum oxide deposit on the surface.
Question 4: A 'joggle' in aircraft sheet metal is used to:
- Strengthen a panel by adding curvature
- Allow one sheet to overlap another while maintaining a flush surface (Correct answer)
- Create a drainage channel in the skin
- Mark rivet hole locations accurately
Correct answer: Allow one sheet to overlap another while maintaining a flush surface
A joggle is an offset bend that allows overlapping sheets to remain flush with each other and the surrounding structure.
Question 5: What is the purpose of using a dimpling operation instead of countersinking on thin sheet metal?
- Dimpling is faster than countersinking for production work
- Thin sheet does not have enough material depth for a full countersink without knife-edge (Correct answer)
- Dimpling creates a stronger joint than countersinking
- Dimpling is required for all flush rivet installations
Correct answer: Thin sheet does not have enough material depth for a full countersink without knife-edge
On thin sheets, countersinking can leave a knife-edge around the hole, so dimpling displaces material rather than removing it.
Question 6: The term 'setback' in sheet metal layout refers to:
- The distance a bend line is moved inward from the intended bend location
- The distance from the outside mold line to the bend tangent line (Correct answer)
- The minimum clearance between adjacent rivets
- The amount springback is compensated for in the bend angle
Correct answer: The distance from the outside mold line to the bend tangent line
Setback is the distance from the outside mold line (OML) to the bend tangent line, used to locate bend lines on the flat blank.
Question 7: What does 'grain direction' mean when working with aircraft sheet metal?
- The direction of surface scratches from milling
- The preferred direction of paint application
- The direction the metal crystals were aligned during rolling (Correct answer)
- The orientation of corrosion protection coating application
Correct answer: The direction the metal crystals were aligned during rolling
Grain direction refers to the alignment of metal crystals caused by the rolling process, affecting strength and bend characteristics.
