Wing and Airfoil Selection Questions and Answers

Answer: C

Correct answer: It extends aft, adding area and camber

A Fowler flap runs aft on tracks as it deflects, so the wing gains planform area as well as camber - and since lift is proportional to area, the gain is large, giving increments in maximum lift coefficient well beyond what camber alone achieves. A plain flap merely hinges down, adding camber at constant area. The Fowler pays for its performance in track and carriage complexity, and it certainly increases drag.

Answer: D

Both are leading-edge devices, but a slat opens a slot that ducts high-energy air over the upper surface, while a Krueger hinges forward from below to extend the lower surface. Slats are more effective and more complex.

Answer: A

Only the velocity component normal to the leading edge governs the section, so sweep makes the wing behave as though flying more slowly. The penalties are all at low speed: reduced maximum lift and a tendency to tip stall.

Answer: B

The winglet displaces and diffuses the tip vortex so the wing behaves as though longer, and it does so within the span limit an airport imposes. The added wetted area costs friction drag, so the device pays only where induced drag is a large share.

Answer: C

Volume scales roughly with thickness ratio and with chord squared, so thinning or tapering a wing sharply can leave the design short of tank space. Discovering this late forces either a centre tank or a compromise on the aerofoil.

Answer: D

The trapezoidal reference area extends the leading and trailing edges to the centreline, so it includes area buried in the fuselage. Since every coefficient is referred to it, quoting a coefficient without stating the reference is meaningless.

Answer: A

Correct answer: Between about 2.5 and 3.2

A clean transport wing reaches about 1.4. Slats add roughly 0.4, and a double or triple slotted Fowler system adds a great deal more, so the landing configuration typically reaches 2.5 to 3.2. Since stalling speed varies as the inverse square root of the maximum lift coefficient, more than doubling it cuts the stalling speed by about 30 per cent, which is what makes an aircraft of high cruise wing loading able to use ordinary runways.

Answer: B

Correct answer: Shorter field, but worse cruise and ride

Stalling speed depends on wing loading through

so a lower wing loading gives a lower stalling and approach speed and a shorter field. The same large wing carries more skin friction and more weight in the cruise, and it responds more sharply to gusts, giving a poorer ride. Wing loading is therefore a direct trade between field performance on one side and cruise efficiency and ride quality on the other.

Answer: C

A thicker, higher-lift section at the root suits the structural depth available and the loading, while a thinner tip section delays local shock formation and helps stall behaviour. The transition is lofted smoothly between them.

Answer: D

The spar runs along the sweep rather than straight out, so the structural span exceeds the aerodynamic one and the bending moment is carried over a greater length. Sweep therefore costs weight as well as low-speed lift.