Airframe Mechanic Certification Sheet Metal Structures 3 — Questions and Answers
Question 1: When selecting a replacement rivet after removing a damaged rivet, what size rivet should typically be used if the hole is not damaged?
- Same diameter and same length as the original (Correct answer)
- Next larger diameter and appropriate length
- Same diameter but 1/8 inch longer than original
- Next smaller diameter to avoid stressing the hole
Correct answer: Same diameter and same length as the original
If the hole is undamaged, the replacement rivet should be the same diameter and appropriate driven length as the original specification.
Question 2: Which alclad aluminum alloy sheet is most commonly used for aircraft skin applications due to its high strength-to-weight ratio?
- 2017-T4
- 6061-T6
- 2024-T3 (Correct answer)
- 7075-T6
Correct answer: 2024-T3
2024-T3 alclad is the most common aircraft skin material, offering high strength combined with the corrosion protection of the pure aluminum cladding.
Question 3: A scratch or gouge in aluminum skin that does not penetrate more than 10% of the sheet thickness is typically classified as:
- A repairable crack requiring a patch
- Negligible damage requiring no repair (Correct answer)
- Damage requiring immediate sheet replacement
- A corrosion pit requiring alodine treatment
Correct answer: Negligible damage requiring no repair
Scratches not exceeding 10% of sheet thickness are generally classified as negligible damage and require only cleaning and protective treatment.
Question 4: When riveting near a formed flange or edge, which direction should the bucking bar force be applied relative to the rivet shank?
- At a 45° angle to maximize driven head spread
- Parallel to the rivet shank (axially) (Correct answer)
- Perpendicular to the rivet shank
- At the angle matching the countersink angle
Correct answer: Parallel to the rivet shank (axially)
The bucking bar must be held perpendicular to the sheet surface and aligned axially with the rivet shank to form a properly shaped driven head.
Question 5: What is the primary advantage of using a flush (countersunk) rivet on external aircraft skin?
- It is stronger in shear than a protruding head rivet of the same diameter
- It reduces aerodynamic drag by maintaining a smooth surface (Correct answer)
- It is easier to install in thin sheet materials
- It does not require a bucking bar during installation
Correct answer: It reduces aerodynamic drag by maintaining a smooth surface
Flush rivets create a smooth aerodynamic surface by seating the head level with the skin, reducing drag compared to protruding head rivets.
Question 6: The K-factor in sheet metal bending is used to determine:
- The minimum bend radius for a given material and thickness
- The location of the neutral axis within the material thickness (Correct answer)
- The maximum allowable springback angle
- The required die width for a press brake operation
Correct answer: The location of the neutral axis within the material thickness
The K-factor defines the position of the neutral axis within the material thickness, which determines accurate bend allowance calculations.
Question 7: Which statement about deburring rivet holes in sheet metal is correct?
- Deburring is optional on interior structure not subject to fatigue loads
- All rivet holes must be deburred to remove sharp edges that could initiate cracks (Correct answer)
- Deburring is only required on holes larger than 3/16 inch diameter
- Deburring removes material and therefore weakens the sheet around the hole
Correct answer: All rivet holes must be deburred to remove sharp edges that could initiate cracks
All rivet holes must be deburred because sharp edges and burrs concentrate stress and can initiate fatigue cracks.
Airframe Mechanic Certification Sheet Metal Structures 3
When selecting a replacement rivet after removing a damaged rivet, what size rivet should typically be used if the hole is not damaged?