Airframe Mechanic Certification Sheet Metal Structural Repairs 5 — Questions and Answers
Question 1: When bending sheet metal, the 'bend allowance' is the amount of material:
- Added to the flat pattern length to account for the curved section (Correct answer)
- Subtracted from the sheet before cutting to prevent springback
- Used to calculate the setback at each bend
- Required for the overlap in a lap joint
Correct answer: Added to the flat pattern length to account for the curved section
Bend allowance is the additional flat material length that becomes the arc of the bend, added to the flat pattern to get the total blank length.
Question 2: Springback after bending aluminum sheet is compensated for by:
- Annealing the material before bending
- Overbending the material slightly beyond the desired angle (Correct answer)
- Using a larger bend radius than specified
- Heating the material during the bend
Correct answer: Overbending the material slightly beyond the desired angle
Overbending compensates for springback so the sheet returns to the correct angle after the bending force is released.
Question 3: Which rivet material is required when repairing magnesium alloy aircraft structure to prevent galvanic corrosion?
- 2117-T4 aluminum rivets
- Monel rivets
- Stainless steel rivets
- Magnesium or aluminum 5056 alloy rivets (Correct answer)
Correct answer: Magnesium or aluminum 5056 alloy rivets
5056 aluminum rivets must be used with magnesium structure because they are galvanically compatible; other aluminum or steel rivets cause severe galvanic corrosion.
Question 4: What condition exists when a rivet exhibits a 'smile' or crescent-shaped crack in the manufactured head after driving?
- The rivet was overdriven (too many hammer blows) (Correct answer)
- The rivet hole was undersize causing head fracture
- The rivet was driven with an improperly fitted rivet set
- The material is too hard for solid shank rivets
Correct answer: The rivet was overdriven (too many hammer blows)
A crescent crack in the rivet head is a sign of overdriving; the excessive deformation stress cracks the head, requiring the rivet to be removed and replaced.
Question 5: When a structural repair is made to a pressurized fuselage, special attention must be given to:
- Painting the repair the same color as the original skin
- Using only AN rivets regardless of original fastener type
- Restoring the original pressure-sealing capability using sealant (Correct answer)
- Increasing rivet spacing to reduce stress concentration
Correct answer: Restoring the original pressure-sealing capability using sealant
Pressurized fuselage repairs must restore the original airtight seal using approved sealant to maintain cabin pressurization and structural integrity.
Question 6: The 'grip length' of a rivet is defined as:
- The total length of the rivet shank
- The length of shank that protrudes above the sheet after driving
- The thickness of the material being fastened through which the shank passes (Correct answer)
- The minimum edge distance from the rivet centerline to the sheet edge
Correct answer: The thickness of the material being fastened through which the shank passes
Grip length is the total thickness of material being joined, which determines the required rivet length for proper bucktail formation.
Question 7: When inspecting a completed rivet installation, an acceptable shop head (bucktail) should have a diameter of approximately:
- 1.0 times the rivet diameter and 0.3 times the rivet diameter in height
- 1.5 times the rivet diameter and 0.5 times the rivet diameter in height (Correct answer)
- 2.0 times the rivet diameter and 0.5 times the rivet diameter in height
- 2.5 times the rivet diameter and 1.0 times the rivet diameter in height
Correct answer: 1.5 times the rivet diameter and 0.5 times the rivet diameter in height
An acceptable bucktail should be 1.5 times the rivet diameter wide and 0.5 times the rivet diameter tall, indicating a properly driven rivet with full bearing strength.
Airframe Mechanic Certification Sheet Metal Structural Repairs 5
When bending sheet metal, the 'bend allowance' is the amount of material: