A&P - Aircraft and Powerplant Sheet Metal Structural Repair Questions and Answers — Questions and Answers
Question 1: When performing a sheet metal repair on an aircraft, what is the generally accepted minimum edge distance for a single row of protruding head rivets?
- One and a half times the rivet shank diameter
- Two times the rivet shank diameter (Correct answer)
- Three times the rivet shank diameter
- The thickness of the sheet being riveted
Correct answer: Two times the rivet shank diameter
According to FAA Advisory Circular (AC) 43.13-1B, the minimum edge distance, measured from the center of the rivet hole to the edge of the sheet, should be no less than two times the diameter of the rivet shank for a single row. This ensures sufficient material is present to prevent the rivet from tearing out under load.
Question 2: A technician discovers a 1.5-inch long crack in a non-structural aluminum alloy skin panel. Which of the following is the correct initial step to repair the crack?
- Weld the crack from end to end.
- Immediately install a doubler patch over the crack.
- Stop-drill the ends of the crack. (Correct answer)
- Apply a bead of structural adhesive along the crack.
Correct answer: Stop-drill the ends of the crack.
The proper procedure to prevent a crack from propagating further is to stop-drill each end of the crack. This involves drilling a small hole at the very tip of the crack, which distributes the stress concentration over a larger area, effectively halting its growth until a permanent repair can be made.
Question 3: In a sheet metal lap joint repair, the rivet pitch (the distance between the centers of adjacent rivets in the same row) should generally be no less than:
- Two times the rivet diameter.
- The thickness of the thickest sheet.
- Four times the rivet diameter.
- Three times the rivet diameter. (Correct answer)
Correct answer: Three times the rivet diameter.
To ensure the strength of the joint and prevent the sheet metal from buckling or failing between fasteners, the standard minimum rivet pitch is three times the diameter of the rivet shank. Spacing them closer could weaken the material between the rivets.
Question 4: When fabricating a replacement part that requires a 90-degree bend, the term 'bend allowance' refers to:
- The extra material added to the flange for trimming.
- The length of the curved portion of the metal within the bend. (Correct answer)
- The total length of the part before bending.
- The amount the material will spring back after being bent.
Correct answer: The length of the curved portion of the metal within the bend.
Bend allowance is the specific length of the material in the curved area of a bend. It's calculated to ensure the final dimensions of the formed part are correct, as the material on the outside of the bend stretches and the inside compresses.
Question 5: A repair is being made to a section of 0.040-inch 2024-T3 aluminum skin using a doubler patch of the same material and thickness. According to common practice, what is the most appropriate solid shank rivet diameter to use for this repair?
- 3/32 inch (0.09375")
- 5/32 inch (0.15625")
- 1/8 inch (0.125") (Correct answer)
- 3/16 inch (0.1875")
Correct answer: 1/8 inch (0.125")
A general rule of thumb for selecting rivet diameter is to use a rivet with a diameter that is at least three times the thickness of the thickest sheet being joined. In this case, 3 x 0.040" = 0.120". The closest standard rivet size that is equal to or greater than this value is 1/8 inch (0.125").
Question 6: Which of the following is a primary objective when designing a sheet metal structural repair for an aircraft?
- To make the repair section significantly stronger than the original structure.
- To restore the original strength and stiffness of the structure while minimizing weight. (Correct answer)
- To use the thickest gauge material available for maximum durability.
- To complete the repair using only blind rivets for speed and convenience.
Correct answer: To restore the original strength and stiffness of the structure while minimizing weight.
The goal of a structural repair is to restore the aircraft to its original condition of strength, stiffness, and aerodynamic shape without adding unnecessary weight. A repair that is too strong can create stress concentrations in the surrounding original structure, potentially leading to new failures.
A&P - Aircraft and Powerplant Sheet Metal Structural Repair Questions and Answers
When performing a sheet metal repair on an aircraft, what is the generally accepted minimum edge distance for a single row of protruding head rivets?