Stress Analysis of Wings and Fuselage Questions and Answers

Answer: C

Correct answer: The sum of the two longitudinal stresses

Pressurisation puts the whole shell into longitudinal tension of \( pr/2t \), and nose-up bending puts the upper skin into tension as well, so the two act along the same axis and add. This is why the two cases cannot be assessed separately: the combined stress may exceed the allowable although neither alone does. The hoop stress acts perpendicular to both and enters through the failure criterion rather than by addition.

Answer: D

The frame is a closed ring, so the bending moment distribution round it cannot be found from equilibrium alone and a redundancy must be released. Standard solutions exist for the common load cases, and they show the moment varying strongly with position round the ring.

Answer: A

The frame does not act alone: the skin feeds shear into it all the way round, and that distributed reaction is what balances the concentrated load applied to it. Ignoring it and treating the frame as a free ring badly overstates the bending moments.

Answer: B

The wing delivers its full root bending moment and shear through a handful of fittings, and that concentrated load has to spread into skins a millimetre or two thick. Heavy frames, machined fittings and generous doublers are the usual answer.

Answer: C

Correct answer: Net tension, tear-out and bearing

A loaded lug can fail three ways, and all three must be checked. Tension across the net section, where the hole has removed material; shear tear-out, where the pin pushes a plug of material out to the free edge; and bearing, where the pin crushes the hole. Each gives its own allowable, and the smallest governs. Buckling and torsion do not arise in a lug in tension.

Answer: D

The projected area of the hole is used rather than the true contact area, which makes bearing stress a nominal quantity compared against empirically derived allowables. It frequently governs a thin-sheet joint rather than fastener shear.

Answer: A

Eccentricities, uneven load sharing among fasteners and manufacturing variation all make a fitting's real stress distribution uncertain. An additional factor, typically about 1.15, is applied on top of the ultimate factor to cover it.

Answer: B

The outer rows pick up more load because of the differential stretching of the two sheets along the joint. The effect grows with the number of rows and with the stiffness mismatch, and it is why the end fasteners are the usual fatigue origins.

Answer: C

Load fed into one stiffener spreads into its neighbours through shear in the skin, and the distance required depends on the stiffness ratio. Shear lag analysis quantifies it, and it is the reason a fitting's influence extends well beyond its immediate attachment.

Answer: D

Both shear and bending accumulate towards the root, so the root section carries the largest loads and usually sets the sizing. The relief from inertia and the increase in structural depth moderate it but do not reverse the trend.