Stress Analysis of Wings and Fuselage Questions and Answers

Answer: A

Accumulating the distributed load from the tip towards the root gives the shear at each station, and integrating the shear in turn gives the bending moment. The net load already includes the relief from the wing's own mass and its fuel.

Answer: B

Each spanwise strip contributes a torque equal to its lift times the distance from the section's shear centre. Accumulating those contributions inward gives the torque the box must carry at each station, and control surface loads add to it.

Answer: C

Correct answer: Idealise, then properties, stresses, shear flows

Each step depends on the one before it. The section is first idealised into booms carrying direct stress and skins carrying shear; the section properties follow from that idealisation; the direct stresses follow from the properties and the applied bending; and the shear flows follow from the direct stress distribution. Deflections and margins come last, since both require the stresses to be known.

Answer: D

Bending supplies the direct stress along the span and torsion supplies the shear flow around the section, and both act at the same point. Resolving them into principal stresses or an equivalent stress is what allows a strength check to be made.

Answer: A

Rotating the element until the shear vanishes leaves only direct stresses, and those are the principal values. The planes of maximum shear lie at forty-five degrees to them, which is why ductile metals shear along such planes.

Answer: B

Distortion energy rather than total strain energy governs, which is why a purely hydrostatic state does not cause yielding however large. It agrees well with test data for ductile metals and is slightly less conservative than Tresca.

Answer: C

Tresca works on the maximum shear stress and inscribes a hexagon within the von Mises ellipse, so it predicts yielding a little earlier in most combined states. The two coincide in uniaxial tension and in pure shear differ by about fifteen per cent.

Answer: D

Correct answer: The allowable divided by the applied, less one

The definition is

Subtracting one places the break-even point at zero, so a positive margin means adequate and a negative margin means overloaded - which is far easier to scan down a page of a stress report than a column of ratios that must each be compared with unity.

Answer: A

Correct answer: Adequate, with no reserve

Zero margin means the allowable exactly equals the applied stress: the member carries its design load and not a newton more. That is acceptable and, on a weight-critical structure, desirable - a large positive margin is dead weight. What is not acceptable is a negative margin, which means the member is overloaded at its design condition.

Answer: B

The fuselage acts as a beam supported at the wing, carrying the tail loads at one end and the nose structure at the other, with payload distributed between. The resulting bending combines with the pressurisation stresses at every point.