AMT Airframe Structures Questions and Answers 1 — Questions and Answers
Question 1: In a semi-monocoque fuselage, what is the primary function of longitudinal members such as longerons and stringers?
- To provide the cross-sectional shape of the fuselage.
- To absorb and transmit bending, tensile, and compressive stresses. (Correct answer)
- To act as the main attachment points for the wings and empennage.
- To transfer shear stresses from the skin to the wing spars.
Correct answer: To absorb and transmit bending, tensile, and compressive stresses.
Longerons and stringers are the primary longitudinal members in a semi-monocoque fuselage. Their main role is to resist bending moments and carry axial loads (tension and compression) along the length of the fuselage. [3, 6] While formers and bulkheads provide shape, the longerons and stringers form the key load-bearing framework that prevents the fuselage from bending under flight loads. [15]
Question 2: A technician performing a detailed visual inspection on an aluminum aircraft skin notices a fine, dark, sooty line trailing back from a rivet head. What is this condition commonly called, and what does it indicate?
- Galvanic corrosion, indicating an incompatibility between the rivet and skin materials.
- Filiform corrosion, indicating a breakdown of the paint coating.
- Rivet rash, indicating an over-driven rivet during installation.
- Smoking rivet, indicating movement and fretting of a loose rivet. (Correct answer)
Correct answer: Smoking rivet, indicating movement and fretting of a loose rivet.
A 'smoking rivet' is a term used to describe the black, sooty trail of aluminum oxide that appears behind a loose rivet. [5] This trail is caused by the rivet moving slightly in its hole under load, which causes fretting (a type of wear) between the rivet and the surrounding skin. This movement grinds the material into a fine, dark powder that is then streaked by the airflow. [2, 16] It signifies that the rivet is no longer securely fastening the joint and must be investigated and likely replaced. [5]
Question 3: Which of the following structural components is primarily responsible for giving a wing its aerodynamic shape (airfoil) and transferring loads from the skin to the spars?
- Longerons
- Stringers
- Ribs (Correct answer)
- Bulkheads
Correct answer: Ribs
Ribs are the structural components within a wing that are shaped like the airfoil. [8] Their primary functions are to give the wing its required aerodynamic shape, support the skin against buckling, and transmit the aerodynamic loads from the skin and stringers to the main load-carrying members, the spars. [9, 11]
Question 4: An aircraft structural design philosophy that relies on redundancy, where the failure of a single structural element will not cause catastrophic failure of the entire structure, is known as:
- Safe-life
- Fail-safe (Correct answer)
- Damage tolerant
- Single-path structure
Correct answer: Fail-safe
The fail-safe design philosophy assumes that structural failures may occur but are contained. It uses redundant structures (multiple load paths) so that if one component fails, other adjacent components can carry the redistributed loads until the damage is discovered and repaired. [17, 19, 20] This is in contrast to the safe-life philosophy, which aims to retire a part before any cracks are expected to initiate. [17]
Question 5: During an inspection of a composite honeycomb panel, a technician uses the coin tap test method and hears a dull thud or dead sound in a specific area, compared to the clear, ringing sound elsewhere on the panel. This change in sound most likely indicates what type of defect?
- A crushed core
- Water ingress in the honeycomb cells
- A delamination or disbond between the skin and the core (Correct answer)
- A properly bonded and structurally sound area
Correct answer: A delamination or disbond between the skin and the core
The coin tap test is a common and simple method for inspecting composite structures. A clear, sharp, ringing sound typically indicates a well-bonded, solid structure. A dull thud or dead sound indicates a void or separation, such as a delamination (separation of composite layers) or a disbond between the face sheet and the honeycomb core, because the separated area absorbs the sound energy instead of transmitting it through a solid structure. [25]
Question 6: What is the primary purpose of formers and bulkheads in a fuselage structure?
- To carry the primary bending loads along the length of the fuselage.
- To provide attachment points for the engines only.
- To provide the cross-sectional shape and to which stringers and skin are attached. (Correct answer)
- To serve as the primary structure for absorbing landing gear impact.
Correct answer: To provide the cross-sectional shape and to which stringers and skin are attached.
Formers and bulkheads are transverse (circumferential) structural members that define the shape of the fuselage. [1] They provide the framework to which the longitudinal stringers and the outer skin are fastened. [14, 15] While certain heavy-duty bulkheads may serve as attachment points for wings or act as firewalls, their fundamental role across the entire fuselage is to maintain its cross-sectional shape. [13]
AMT Airframe Structures Questions and Answers 1
In a semi-monocoque fuselage, what is the primary function of longitudinal members such as longerons and stringers?