Wing and Airfoil Selection Questions and Answers

Answer: C

Correct answer: Only three

Aspect ratio trades induced drag against structural weight, wing loading trades field length against cruise efficiency, and taper ratio trades the spanwise loading distribution against manufacturing simplicity - three correct pairs. Sweep is misdescribed: it trades the drag-divergence Mach number against low-speed maximum lift and structural weight, and while a swept wing does complicate the fuel tanks, that is not the trade it is chosen for.

Answer: D

Correct answer: Slat

The slat is a leading-edge device: it moves forward to open a slot through which high-energy air passes onto the upper surface, delaying separation and raising the stalling angle. Plain, split and Fowler flaps are all trailing-edge devices, acting by adding camber and, in the Fowler case, area. Leading and trailing-edge devices are complementary - the slat raises the angle at which the wing stalls, the flap raises the lift at any given angle.

Answer: A

Thickness ratio governs the critical Mach number, maximum lift and internal volume, but it has no bearing on induced drag, which depends on how the lift is distributed across the span. The other three all attack it directly.

Answer: B

Thickness-to-chord ratio describes the aerofoil section, whereas aspect ratio, taper and sweep all describe the shape of the wing in plan. The distinction matters because the two sets are chosen at different stages and for different reasons.

Answer: C

Taper affects the spanwise loading and the stall pattern but contributes nothing to the rolling moment due to sideslip. Dihedral, sweep and a high wing position all supply effective dihedral and are traded against one another.

Answer: D

Correct answer: A higher maximum lift coefficient

Sweep reduces the maximum lift coefficient, since only the normal component of velocity is effective over the section and the spanwise flow thickens the outboard boundary layer. The other three do follow: the drag-divergence Mach number rises, the tip tends to stall first because of that spanwise drift, and the structural span along the swept axis is longer than the aerodynamic span, which adds weight.

Answer: A

Thin air and a short runway both demand lift at low speed, which points to a large wing for the weight. The cruise penalty is tolerable because the sectors are short and the aircraft spends proportionally less time at cruise than a long-range type.

Answer: B

Correct answer: Tip stall from the taper, cured by adding washout

A taper ratio of 0.25 with no twist raises the local lift coefficient towards the tip, so the outboard sections reach their stalling angle first. The ailerons then sit in separated flow and lose authority just when they are most needed. Adding a few degrees of washout lowers the tip incidence and moves the initial separation inboard, restoring aileron effectiveness through the stall. Sweep and dihedral are unrelated to this symptom.

Answer: C

At constant area, raising aspect ratio from 9 to 11 stretches the span by about ten per cent, which can push an aircraft out of its airport category. Induced drag would fall, which is the point; it is the gate box and the structural weight that resist.

Answer: D

Correct answer: Fuel volume and structural depth

A thicker wing encloses more volume for fuel and gives the spar a greater depth, so it carries the bending moment with less material and weighs less for the same strength. Those are the reasons to accept the thicker section when tank volume is already marginal. The three rejected options all favour the thinner section, which has the higher critical Mach number and lower profile drag - a thicker wing is aerodynamically worse, not better.