Fuselage Design and Layout Questions and Answers

Answer: C

Correct answer: A small width change can double effective capacity

The step from 2.90 m to 3.15 m is only a quarter of a metre, but it takes the hold from one container abreast to two - the volume used goes from poor to good.

Capacity therefore changes discontinuously at the width where a second container fits, and everything between 1.60 and 2.90 m is wasted space. That is why container dimensions drive the cross-section of a freighter: the design must land on the right side of a step, not merely be generous.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is the reason. A circular shell under internal pressure carries the load entirely as membrane tension - hoop and longitudinal stress in the skin - with no bending anywhere.

Any other shape must resist part of the load in bending, which needs far more material for the same strength. The circle is therefore the lightest pressure vessel, and the cabin's shape is settled by structure before any aerodynamic consideration enters.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second explains the first. A plug aft of the wing lengthens the arm from the main gear to the tail, so the same rotation brings the tail lower.

The available angle falls, and with it the lift coefficient achievable at unstick. A longer undercarriage restores the clearance at the cost of weight and bay volume; a tail skid instead accepts an occasional strike and makes it survivable. Stretched variants commonly carry one or the other.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second gives the reason with the necessary force. Capacity changes in steps, not smoothly: a hold either takes two containers abreast or one.

A few centimetres short of the width for two therefore wastes nearly half the cross-section, and no amount of clever loading recovers it. The cross-section is consequently designed around the standard container dimensions from the outset, which is why freighter fuselages are sized differently from passenger ones.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is the reason. An ellipse has varying curvature, so the pressure load cannot be carried by membrane tension alone - the flatter regions must resist it in bending, which requires far more material.

Where a non-circular section is genuinely wanted, the double-bubble is used instead: two circular arcs tied at the floor, each still in pure tension, with the floor beams carrying the outward pull at the junction.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second is the structural reason. The wing bending moment at the root is enormous, and carrying the centre section continuously lets the upper and lower skins run through as continuous members.

Interrupting it would force that entire moment through joints, which would need to be very heavy and would become fatigue-critical. The cost of continuity is the volume the box occupies in the fuselage - below the floor on a transport, above the deck on a high-wing freighter.

Answer: A

Both statements are true and the second gives both reasons. Manufacturing economy and family growth potential point the same way, which is why the parallel section is extended as far fore and aft as the shaping allows.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second gives the reasons that outweigh the penalty. A high wing lets the fuselage sit close to the ground, so the cargo floor is low and flat and vehicles drive aboard up a shallow rear ramp.

It also keeps engines and propellers clear of debris on unprepared strips. The carry-through box above the deck is heavier and the fuselage must be reinforced to carry the wing loads down to the gear, but the operational gain settles the choice.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the second names the opposing effect. Lengthening the fuselage does ease the afterbody closure and reduce pressure drag - but it adds wetted area, and therefore skin friction, over the whole surface.

It also lengthens the beam carrying the tail loads, so the structure grows heavier, and it reduces the rotation angle. The optimum is where the falling pressure drag and the rising friction cross, which is why transports cluster between about 8 and 12.

Answer: D

Correct answer: 1 and 2 only

The first two are correct: a circular section carries pressure entirely in membrane tension, and a double-bubble uses the floor beams as a tie between two arcs so that each lobe stays in tension.

The third is the opposite of the truth. An ellipse has varying curvature and must carry part of the load in bending, which needs far more material - so it is heavier, and that is precisely why elliptical pressure cabins are avoided.