Airframe Mechanic Certification Aircraft Structures & Materials 5 — Questions and Answers
Question 1: What is the primary difference between a truss-type fuselage and a monocoque fuselage?
- Truss-type uses skin to carry all loads; monocoque uses internal framework only
- Truss-type relies on an internal framework of tubes or beams; monocoque relies on stressed skin (Correct answer)
- Truss-type is only used in composite aircraft; monocoque in metal aircraft
- Truss-type is heavier but used exclusively in transport category aircraft
Correct answer: Truss-type relies on an internal framework of tubes or beams; monocoque relies on stressed skin
A truss-type fuselage uses welded or bolted tubes/beams for the primary structure with a non-structural skin covering, while monocoque relies on the skin itself to carry loads.
Question 2: What is the significance of 'limit load' in aircraft structural certification?
- The load at which the structure will collapse
- The maximum load expected in service, which the structure must carry without permanent deformation (Correct answer)
- The load used to determine fatigue life only
- The minimum design load for light sport aircraft
Correct answer: The maximum load expected in service, which the structure must carry without permanent deformation
Limit load is the maximum load anticipated in normal service operations; the structure must sustain limit load without permanent deformation.
Question 3: What condition is indicated when an aluminum surface shows white, powdery deposits?
- Cadmium plating degradation
- Active aluminum oxide (surface corrosion) (Correct answer)
- Hydraulic fluid contamination
- Zinc chromate primer breakdown
Correct answer: Active aluminum oxide (surface corrosion)
White, powdery deposits on aluminum indicate aluminum oxide forming from active surface corrosion, which must be removed and treated.
Question 4: Which fastener is most appropriate for joining composite panels where galvanic corrosion with aluminum must be avoided?
- Steel AN bolts with aluminum washers
- Titanium fasteners (Correct answer)
- Cadmium-plated steel rivets
- Monel rivets
Correct answer: Titanium fasteners
Titanium fasteners are used with carbon fiber composites because titanium is galvanically compatible with carbon fiber, preventing the galvanic corrosion that would occur with aluminum or steel fasteners.
Question 5: What is the purpose of 'drain holes' in aircraft lower skin panels and fairings?
- To reduce structural weight
- To allow moisture to drain out and prevent corrosion-causing water accumulation (Correct answer)
- To improve aerodynamic performance by reducing pressure buildup
- To provide inspection access to internal components
Correct answer: To allow moisture to drain out and prevent corrosion-causing water accumulation
Drain holes allow trapped moisture to escape from low points in the structure, preventing corrosive water accumulation in pockets and cavities.
Question 6: What is 'fatigue failure' in aircraft metals?
- Sudden fracture from a single overload event
- Progressive cracking caused by repeated cyclic stress below the ultimate strength (Correct answer)
- Deformation from sustained high temperature
- Cracking due to hydrogen embrittlement during plating
Correct answer: Progressive cracking caused by repeated cyclic stress below the ultimate strength
Fatigue failure is the progressive initiation and growth of cracks in a material subjected to repeated cyclic stresses, eventually leading to fracture at loads well below ultimate strength.
Question 7: What material is typically used for aircraft firewall construction to contain engine compartment fires?
- 2024-T3 aluminum sheet
- Stainless steel or titanium sheet (Correct answer)
- Carbon fiber composite laminate
- 4130 steel tubing only
Correct answer: Stainless steel or titanium sheet
Firewalls are constructed from stainless steel or titanium because these materials maintain structural integrity at the high temperatures generated by engine compartment fires.
Airframe Mechanic Certification Aircraft Structures & Materials 5
What is the primary difference between a truss-type fuselage and a monocoque fuselage?