Fuselage Design and Layout Questions and Answers

Answer: A

Correct answer: 1, 2 and 3

All three are correct and together they describe the trade. Too low a fineness ratio forces the afterbody to close abruptly, the flow separates and pressure drag rises; too high a value adds wetted area and structural weight for no aerodynamic gain.

The optimum lies between, and transports fall in the range of about 8 to 12. The narrowness of that band is what the two opposing penalties produce.

Answer: B

Correct answer: 1 and 2 only

The first two describe the method correctly: plugs are inserted fore and aft of the wing so the centre of gravity moves as little as possible, and the cross-section is unchanged, which is what makes the plug approach cheap.

The third reverses a real consequence. A plug aft of the wing lengthens the arm from the main gear to the tail, so the rotation angle available falls - which is why stretched variants often gain a longer gear or a tail skid.

Answer: C

Correct answer: 1 and 2 only

The first two are correct and the second follows from the first: on a low-wing transport the box passes below the cabin floor, so it takes depth from the hold and divides it into forward and aft compartments.

The third contradicts both. The carry-through is one of the principal constraints on the internal layout - on a high-wing aircraft it crosses above the cabin instead, which is a different intrusion rather than none.

Answer: D

Correct answer: A-2, B-1, C-4, D-3

Each region is shaped by a different requirement. The nose is set by cockpit view angles and the radome's antenna size, neither of which has anything to do with the cabin.

The constant-section barrel is set by the cabin layout and by the wish to keep stretch possible. The rear fuselage is set by rotation clearance and afterbody closure. The centre section is set by the wing carry-through and the main gear loads - the two heaviest concentrated loads on the aircraft.

Answer: A

Correct answer: A-2, B-1, C-4, D-3

Each parameter fixes one dimension of the layout. Seats abreast, with seat and aisle widths, gives the cabin width and hence the fuselage diameter.

Seat pitch multiplied by rows gives the cabin length. Occupant count determines the emergency exit provision, in defined capacity bands. Container width determines the hold cross-section on a freighter, where capacity changes in steps rather than smoothly. Width, length, exits and hold - four parameters for four decisions.

Answer: B

Correct answer: A-2, B-1, C-3, D-4

The four differ in where the carry-through goes. A low wing puts the box below the floor: clear cabin, reduced hold depth. A high wing puts it above: low flat cargo floor, heavier structure.

A mid wing would carry it through the middle of the cabin, which is why it is confined to fighters and the occasional business jet. A wing on a pylon above the fuselage leaves the fuselage clear but pays in drag and in the structure carrying the loads across the gap.

Answer: C

Correct answer: A-2, B-1, C-4, D-3

Each load finds its own structure. Pressurisation is carried by the shell itself, in hoop and longitudinal tension, distributed over the whole surface.

The other three are concentrated and need local reinforcement: tail loads into reinforced rear frames with the shell working in torsion, the main gear reaction into heavy frames around the bay, and wing bending into the centre section carry-through box. Distributed loads use the skin; concentrated loads need frames.

Answer: D

Correct answer: Generating the majority of the aircraft's lift

The wing generates the lift. A fuselage produces a little at incidence, and a lifting-body design produces more, but on a conventional transport the contribution is small and largely incidental.

The other three are its real functions: containing the payload, acting as a pressure vessel, and carrying bending and torsion between the wing and the empennage. It is a beam and a container, and the lift it produces is a by-product of being in the airstream.

Answer: A

Correct answer: It gives the largest possible cabin floor width

A circle is in fact poor at that. The floor sits below the widest point, so a good deal of the cabin's width is at head height where it is least useful - which is exactly the shortcoming a double-bubble addresses.

The other three are the genuine reasons, and they are one reason stated three ways: uniform curvature means pressure is carried in membrane tension, so no bending arises and the material works through its full thickness.

Answer: B

Correct answer: The cross-section is widened too

A stretch inserts plugs of the existing cross-section, so the cabin is exactly as wide as before. That constancy is the whole point: every frame in the plug is identical to those already in production, which is what makes the method cheap.

The other three are true. Capacity and payload increase, plugs go fore and aft of the wing to limit the centre of gravity shift, and the rotation angle falls as the tail moves further behind the main gear.