Airframe Mechanic Certification Aircraft Structures & Materials 4 — Questions and Answers
Question 1: What is the purpose of a fuselage bulkhead?
- To provide an aerodynamic fairing at the nose
- To carry concentrated loads and maintain fuselage cross-sectional shape (Correct answer)
- To house the aircraft's avionics
- To connect the tail rotor to the main fuselage
Correct answer: To carry concentrated loads and maintain fuselage cross-sectional shape
Bulkheads are strong transverse structural members that carry concentrated loads (such as wing attachment forces) and maintain the fuselage cross-sectional shape.
Question 2: Which composite fiber offers the highest stiffness per unit weight among commonly used aerospace reinforcements?
- Fiberglass (E-glass)
- Kevlar (aramid) fiber
- Carbon/graphite fiber (Correct answer)
- Boron fiber
Correct answer: Carbon/graphite fiber
Carbon/graphite fiber has the highest stiffness-to-weight ratio of common aerospace reinforcements, making it ideal for primary structural applications.
Question 3: What is 'delamination' in composite structures?
- Cracking within individual plies perpendicular to the fiber direction
- Separation of layers within the laminate (Correct answer)
- Fiber breakage at a stress concentration
- Moisture absorption causing swelling
Correct answer: Separation of layers within the laminate
Delamination is the separation of individual plies or layers within a composite laminate, often caused by impact, moisture, or manufacturing defects.
Question 4: What heat treatment process is used to increase the hardness and strength of 2024 aluminum after solution heat treatment?
- Annealing
- Normalizing
- Age hardening (precipitation hardening) (Correct answer)
- Stress relieving
Correct answer: Age hardening (precipitation hardening)
Age hardening (precipitation hardening) allows alloying elements to precipitate within the aluminum matrix over time, increasing strength and hardness.
Question 5: What does the term 'fail-safe' mean in aircraft structural design?
- The structure will never fail under any load condition
- If one structural member fails, alternate load paths prevent catastrophic failure (Correct answer)
- The structure is designed with a 10:1 safety factor
- All repairs must be approved before flight
Correct answer: If one structural member fails, alternate load paths prevent catastrophic failure
Fail-safe design ensures that if any single structural element fails, alternative load paths exist to prevent complete structural failure.
Question 6: Which type of load causes a structural member to twist about its longitudinal axis?
- Bending load
- Shear load
- Torsional load (Correct answer)
- Compressive load
Correct answer: Torsional load
Torsional loads cause twisting of a structural member about its longitudinal axis, such as the twisting experienced by a wing during aileron deflection.
Question 7: What is 'stress corrosion cracking' (SCC)?
- Cracking caused solely by mechanical fatigue
- Cracking resulting from the combined effects of tensile stress and corrosive environment (Correct answer)
- Surface pitting from chemical exposure alone
- Cracking caused by thermal cycling
Correct answer: Cracking resulting from the combined effects of tensile stress and corrosive environment
Stress corrosion cracking (SCC) occurs when tensile stress and a corrosive environment act simultaneously on a susceptible metal, causing cracks to initiate and propagate.
Airframe Mechanic Certification Aircraft Structures & Materials 4
What is the purpose of a fuselage bulkhead?