Wing and Airfoil Selection Questions and Answers

Answer: A

Leading-edge devices extend first, then flaps in stages as the speed falls, with the full landing setting last and the aircraft stabilised at approach speed thereafter. Selecting a large flap setting before decelerating would exceed the placard speed.

Answer: B

Wing loading comes from the constraint diagram, area follows from it and the weight, and only then are the planform variables and the sections chosen. Working in another order means selecting an aerofoil before knowing the lift coefficient it must deliver.

Answer: C

The four-digit series of the 1930s was followed by the five-digit, then the six-series laminar-flow sections of the 1940s, and finally the supercritical sections of the late 1960s. Each answered a limitation of its predecessor.

Answer: D

Each step adds a mechanism and buys more lift: camber alone, then a separated lower surface, then a slot energising the upper surface, and finally area extension combined with slots. Complexity and weight rise in the same order.

Answer: A

Correct answer: 1, 2, 3, 4

A well-designed wing stalls from the root outward. The root reaches its stalling angle first, the separation spreads progressively outboard, and the tip is the last to go - which keeps the ailerons in attached flow for as long as possible and produces a nose-down pitching moment as the inboard lift is lost. Washout and section variation along the span are the means; without them, taper alone would give exactly the reverse and dangerous order.

Answer: B

Mach number rises steadily through the climb as the speed of sound falls with temperature, peaks in cruise and falls away in the descent. The wing must be efficient across that whole range, not only at the cruise point.

Answer: C

Correct answer: Only three

Washout delays tip stall, dihedral provides lateral stability in sideslip through the rolling moment it generates, and a winglet raises the effective span by weakening the tip vortex - three correct pairs. Taper has nothing to do with thickness ratio: it is the ratio of tip to root chord, and it exists to approach elliptical loading and to save structural weight.

Answer: D

The first three are correct. The five-digit series was developed to move the maximum camber forward and raise maximum lift, and it has nothing to do with supersonic flight; supersonic sections are thin and sharp-edged instead.

Answer: A

Correct answer: Only three

Krueger flaps and slats are both leading-edge devices, and Fowler flaps are at the trailing edge - three correct pairs. The split flap is wrong: it is a trailing-edge device in which the lower surface alone hinges down, leaving the upper surface undisturbed. It gives a useful lift increment with a great deal of drag, which suits it to landing rather than take-off.

Answer: B

Correct answer: Only three

Higher aspect ratio lowers induced drag, sweep raises the drag-divergence Mach number, and winglets increase effective span - three correct pairs. Thickening the section does the opposite of what the fourth claims: a thicker section accelerates the flow more over its upper surface and reaches sonic conditions at a lower free stream Mach number, so the critical Mach number falls.