Finite Wing Theory Questions and Answers

Answer: C

The assertion is false while the reason is true. Restricting the trailing vortices reduces the downwash at the wing, so the lift vector is tilted less and the induced drag falls rather than rises. The reduction is what pilots experience as the aircraft floating along the runway during the flare.

Answer: D

Both statements are true and the second explains the first. Lowering the tip incidence keeps those sections further from their stalling angle, so separation begins inboard and spreads outward. The ailerons remain in attached flow and roll control is preserved through the onset of the stall.

Answer: A

Both are true and the second is the reason for the first. Taper concentrates the loading outboard relative to the local chord, so the tip sections approach their stalling angle first. Washout offsets that tendency by geometry, restoring a root-first stall and with it aileron effectiveness.

Answer: B

Both statements are true and the reason explains the assertion. The trailing vortex pair induces upwash outside the tips, and a wing meeting a relative wind tilted upward has its lift vector tilted forward. Measured savings of the order of ten per cent have been recorded in formation flight trials.

Answer: C

Both statements are true, but the second is not the reason for the first. The drag rises because each coefficient enters the induced drag sum as a positive squared term weighted by its index. That the same harmonics drop out of the lift integral by orthogonality is a separate result, though together the two facts identify the elliptical case as optimal.

Answer: D

The first two are correct. Helmholtz's theorems force vorticity to be shed wherever the bound strength changes, and the counter-rotating pair induces downward flow between the tips. The third is wrong: outboard of the tips the induced flow is an upwash, which is exactly what formation flying and V-formation birds exploit.

Answer: A

All three are correct. With no lift on an untwisted wing there is no circulation, no shed vorticity and hence no induced drag. The expression for the induced drag coefficient shows the lift coefficient squared in the numerator and the aspect ratio in the denominator, which gives the other two statements directly.

Answer: B

The first two are correct and define the elliptical case as the minimum-drag reference. The third is false: an elliptical planform gives the distribution directly, but a combination of taper and twist can approach it closely, and production wings are designed that way because an elliptical planform is expensive to build.

Answer: C

The second and third are correct. Low aspect ratio means a large induced angle, which flattens the lift curve and pushes the stall to a higher geometric angle, as any slender delta demonstrates on approach. The first statement reverses the truth: low aspect ratio raises the induced drag coefficient rather than lowering it.

Answer: D

The first two are Helmholtz's theorems and are correct. The third is wrong: Kelvin's theorem requires the total circulation to stay zero, so the starting vortex must be equal in strength to the bound vortex but opposite in sense. Together the bound, trailing and starting vortices form one closed loop.