A shear web in a spar carries
Answer: C
The web takes the shear that the caps cannot, and in a thin web the load is carried after buckling as a field of diagonal tension rather than in pure shear. Designing deliberately for that post-buckled state saves a great deal of weight.
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In a diagonal tension field beam, the web is allowed to
Answer: D
Wagner showed that a thin web may buckle at a small fraction of its ultimate load and still carry far more as a series of inclined tension straps, provided the flanges and uprights can react the resulting inward pull. Accepting the buckling rather than preventing it is what makes such a beam light.
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Control surfaces such as ailerons and elevators are usually mounted so that they are
Answer: A
Placing part of the surface ahead of the hinge line reduces the hinge moment, and adding mass ahead of it moves the centre of gravity forward so that bending and rotation do not couple. Both measures raise the flutter speed, and mass balance in particular is a certification requirement.
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A fail-safe structure is one designed so that
Answer: B
Fail-safe design accepts that a member may crack and provides a second path to carry the load until the damage is found. Multiple load paths, crack stoppers and tear straps are the usual means, and the philosophy replaced the earlier safe-life approach for most transport structures.
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A safe-life structure differs from a fail-safe one in that it is
Answer: C
Safe-life design establishes a life by test and analysis and removes the part at that point, with no reliance on finding damage in service. It is used where redundancy is impractical, notably in landing gear and rotorcraft components, and it is inherently conservative.
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Tear straps bonded or riveted to a pressurised fuselage skin serve to
Answer: D
By providing a local increase in fracture toughness and load path, a tear strap turns a crack that would run for many frames into one that stops at a bay boundary. The result is a controlled decompression rather than a catastrophic failure, which is the central idea of damage tolerance.
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The main undercarriage loads on a transport are usually introduced into the structure at
Answer: A
The gear applies very large concentrated vertical, drag and side loads, so it is attached to the strongest available structure, typically the rear spar and a reinforced wing-to-body frame. Spreading those loads into the shell without a weight penalty is one of the harder layout problems.
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Aluminium alloys remain widely used in aircraft structures principally because of their
Answer: B
Aluminium offers a good balance of specific strength, formability, joining, inspectability and cost, which composites match on weight but not on cost or ease of repair. Its stiffness is well below steel's, and it corrodes readily without protection.
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Riveted joints remain common in metal airframes because they
Answer: C
A rivet line can be examined, individual fasteners replaced and its fatigue behaviour predicted from a large body of data. Bonded joints can be lighter and avoid the holes, but they are harder to inspect and to repair, which is why fasteners persist even alongside adhesives.
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The primary structure of an aircraft is defined as that whose failure would
Answer: D
Primary structure carries flight, ground or pressurisation loads whose loss would put the aircraft at risk, and it attracts the full weight of certification, inspection and repair control. Secondary structure, such as fairings, is treated far less stringently.
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