Loads on Aircraft Structures Questions and Answers

Answer: A

No detrimental permanent deformation is permitted at limit load, since the aircraft must continue in service afterwards. It is at ultimate load that permanent set is accepted, provided the structure does not actually fail.

Answer: B

Correct answer: Burning the outboard fuel first

Burning the outboard fuel first removes the very weight that was relieving the root bending, so it increases the moment rather than reducing it. Wing-mounted engines, retained outboard fuel and a swept wing that washes out under load all work the other way, either by adding downward mass outboard or by shedding lift from the tip.

Answer: C

Below VA a single full deflection stalls the wing before the limit is reached, which is real protection. It does not extend to abrupt control reversals, combined manoeuvres in more than one axis, or gusts on top of a manoeuvre, all of which can still over-stress the aircraft.

Answer: D

The gust increment is inversely proportional to wing loading, so the same gust produces a larger load factor on a light aircraft. It follows that the gust envelope must be checked at light weight as well as heavy, since the critical case is not always the heaviest.

Answer: A

Correct answer: Its right-hand boundary is the stalling speed

The right-hand boundary is the design dive speed VD, the fastest the aircraft may be flown. The stall forms the curved left-hand boundary, where the wing cannot generate the load factor asked of it. The diagram is plotted against equivalent airspeed, and above the corner speed the top edge is the flat structural limit.

Answer: B

Correct answer: Rolling out of a turn to wings level

Rolling out reduces the bank angle, so \( n = 1/\cos\phi \) falls back towards 1 - the load factor decreases. A gust, a steeper bank and an abrupt elevator pull all raise it, the last being the case that VA exists to protect against.

Answer: C

A swept wing twists nose-down as it bends, shedding lift outboard and reducing the root moment. Ignoring that gives a higher predicted moment and therefore a heavier structure, which is safe but wasteful, and is why flexible distributions are computed routinely.

Answer: D

Correct answer: Ground loads are always smaller and so need less attention

Ground loads are not always smaller - a heavy landing can impose more on the undercarriage and its backup structure than anything met in flight, which is precisely why they are analysed separately. The other three statements are the actual reasons: different sources, different structure sized, and a magnitude that can exceed the flight cases.

Answer: A

Civil engineering commonly uses factors of three or more, but aircraft loads are known unusually well and every kilogram of structure costs payload for the aircraft's whole life. The 1.5 factor sits between limit and ultimate and applies across the categories.

Answer: B

A margin of safety of zero means the applied load exactly equals the allowable, so the member is adequate but has no reserve. Negative margins indicate failure, and designers usually aim for small positive values to avoid carrying unnecessary weight.