Aerospace Structures Questions and Answers

Answer: A

Semi-monocoque construction shares the load: the skin carries shear and part of the direct stress, while stringers and longerons running fore and aft take the bulk of the bending. Frames hold the section's shape and introduce concentrated loads but contribute little to beam bending.

Answer: B

In a pure monocoque the shell alone carries every load, which demands a thick skin to resist buckling and is heavy for anything large. Adding stringers lets a much thinner skin be used because the buckling length is shortened, and that is what semi-monocoque means.

Answer: C

Frames hold the shell round, stop the skin panels from buckling over long lengths, and distribute point loads such as those from the wing, undercarriage or floor into the shell. They are stability and load-introduction members rather than bending members.

Answer: D

Both run lengthwise, but a longeron is a heavy member used in small numbers, while stringers are light and numerous. The distinction matters for how the bending load is shared and how much skin each member has to stabilise, and modern transports favour many stringers.

Answer: A

Spar caps at the top and bottom of the box, acting with the skins, form the flanges of a deep beam and take the bending as direct tension and compression. The spar webs carry the vertical shear, and the ribs neither bend nor shear appreciably in the spanwise sense.

Answer: B

Ribs hold the section to its aerodynamic shape, divide the skin into shorter panels so it buckles at a higher load, and pass the air load into the spars. They also stop the spar webs and caps from failing by lateral instability.

Answer: C

Closing the section between front and rear spars produces a torsion box of very high stiffness, and the same members act as the flanges and webs of a bending beam. That one structure carries both actions is why it dominates wing design, and it usually contains the fuel as well.

Answer: D

The bulkhead seals the pressure vessel at each end and reacts the pressure acting on its own area as an axial load into the shell. The rear one is usually domed so that it works largely in membrane tension, which is far lighter than resisting the same load in bending.

Answer: A

An internally pressurised cylinder carries a hoop stress and a longitudinal stress, the hoop being twice the longitudinal for a thin shell. The cyclic nature of that loading over many flights is the reason fuselage fatigue and crack growth receive so much attention.

Answer: B

Formers are light shaping members placed between the heavier frames to keep the skin fair and shorten its unsupported length. Frames, by contrast, are stronger members that also introduce concentrated loads into the shell.