The chief service difficulty with honeycomb sandwich in aircraft is
Answer: A
Moisture that finds its way past a damaged facesheet collects in the cells, adds weight, and freezes and expands at altitude, driving the skin off the core. Detecting a disbond is not straightforward, which is why tap testing and ultrasonic inspection are routine.
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A multi-spar wing differs from a two-spar wing in that it
Answer: B
Distributing the material among several spars shortens the skin panels and provides alternative load paths, which suits thin, highly loaded wings such as those on fast military aircraft. A transport wing generally uses two or three spars and relies on stringers instead.
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A wing-to-fuselage joint on a large transport is usually made through
Answer: C
The wing root delivers very large bending and shear loads, so machined fittings take them from the spars into a group of strengthened frames and the centre section. The centre wing box carries the bending straight across the fuselage, which is why it is not interrupted.
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A sandwich panel has facesheets \( 1 \) mm thick separated by a \( 20 \) mm core. Compared with the two sheets laminated together, its bending stiffness is roughly
Answer: D
For the sandwich, \( I \approx 2At^2/4 \) with the sheets \( 21 \) mm apart, giving about \( 2 \times 1 \times 10.5^2 = 220 \) mm\( ^4 \) per mm width; laminated together the 2 mm section gives \( 2^3/12 = 0.67 \). The ratio is of order two hundred, which is why sandwich construction is used wherever stiffness governs.
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A centre wing box \( 6 \) m wide carries a bending moment of \( 2400 \) kN m across the fuselage. If the box is \( 0.5 \) m deep, the cap load is about
Answer: A
Idealising as two flanges, \( M/h = 2400/0.5 = 4800 \) kN. A load of this size is why the centre section is continuous through the fuselage rather than joined at the side of the body, and why the fittings there are among the heaviest on the aircraft.
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Assertion (A): The centre wing box is carried continuously through the fuselage.
Reason (R): Interrupting it would require the full wing bending moment to be transferred through joints.
Select the correct answer from the options below.
Answer: B
Both are true and the second explains the first. Cap loads of several thousand kilonewtons would demand enormous fittings if the box were broken at the side of the body. Running it straight through lets the bending balance from one wing against the other.
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Assertion (A): Honeycomb sandwich is used for floors and control surfaces but not for wing spar caps.
Reason (R): Sandwich construction is efficient where bending stiffness governs rather than direct load.
Select the correct answer from the options below.
Answer: C
Both statements are true and the second explains the first. A spar cap carries a large concentrated axial load, for which a solid section is right, whereas a floor panel or an elevator skin needs stiffness over an area at minimum weight, which is exactly what sandwich provides.
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Consider the following statements about integrally machined panels:
1. They remove the fastener holes that riveted panels rely on.
2. They give a smoother external aerodynamic surface.
3. They are easier to repair than riveted panels.
Which of the statements given above is or are correct?
Answer: D
The first two are the reasons integral machining is used. The third reverses the truth: a damaged integral stringer cannot be unbolted and replaced, so repair means a bonded or bolted patch and is considerably more awkward than on a built-up panel.
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Consider the following statements about honeycomb sandwich panels:
1. The facesheets act as the flanges and the core carries the shear.
2. Water ingress into the core is a recognised service problem.
3. The core carries most of the bending stress.
Which of the statements given above is or are correct?
Answer: A
The first two are correct. The third misplaces the load: the core is far too weak to carry direct stress and exists only to hold the facesheets apart and transfer shear between them. That is precisely why it can be so light.
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Which of the following is NOT an advantage of integrally machined skin-stringer panels?
Answer: B
Correct answer: Damaged stringers can be unbolted and replaced individually
That is exactly what an integrally machined panel gives up: skin and stringers are one piece of metal, so a damaged stringer cannot be removed and the repair is far more difficult than on a built-up panel. The advantages accepted in exchange are fewer parts, no fastener holes to start fatigue cracks, and a smoother external surface.
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