Subsonic and Supersonic Flow over Wings Questions and Answers

Answer: A

The first two are correct. The third is reversed: as the cone narrows, more sweep is needed to stay inside it, so a fixed sweep that was subsonic at Mach 2 may well be supersonic at Mach 3. This is the difficulty a fixed planform faces over a wide speed range.

Answer: B

Each device answers a different transonic difficulty. Sweep postpones the whole problem, the supercritical shape weakens the shock once it appears, area ruling smooths the volume distribution, and the fence deals with the spanwise drift that sweep itself introduces.

Answer: C

In each case the required sweep is ninety degrees less the Mach angle. The trend is what matters: the faster the aircraft, the more sweep is needed to hide the edge inside the cone, and beyond about Mach 3 the requirement becomes impractical.

Answer: D

Keeping the four apart is essential in supersonic design, because the levers differ. Thickness governs volume wave drag, loading governs both lift-dependent wave drag and induced drag though by different routes, and only friction responds to wetted area.

Answer: A

The progression tracks the compromise between induced drag, which rewards span, and wave drag, which rewards sweep and slenderness. A variable-sweep wing tries to have both, and pays for the attempt in the weight and complexity of its pivot.

Answer: B

These four terms cover the vocabulary of the topic. The first two are distinct Mach numbers and must not be conflated: sonic flow appears first, and only later does the shock grow strong enough to force the drag up sharply.

Answer: C

Correct answer: Increasing the thickness-to-chord ratio

A thicker section accelerates the flow over it more, so the local flow reaches sonic speed at a lower free-stream Mach number and the drag rise arrives *earlier*. The three genuine measures all work the other way: a thinner section reduces the local acceleration, sweep reduces the component of velocity the section sees, and a supercritical section is shaped to keep the supersonic region weak and terminate it in a mild shock.

Answer: D

Sweep barely changes the wetted area, so skin friction is essentially unaffected. The genuine penalties are all low-speed ones: reduced maximum lift, the spanwise drift and the tip stall it produces, and the extra high-lift machinery needed to compensate.

Answer: A

Correct answer: It may be rounded without penalty

That is the incorrect statement. Where the normal component of velocity is supersonic the leading edge must be sharp: a rounded edge produces a strong detached bow shock and a large wave drag penalty. A subsonic leading edge, lying behind the Mach cone, may and should be rounded, since it still develops leading-edge suction. The other three statements correctly describe the supersonic case.

Answer: B

The volume-dependent wave drag coefficient does not simply fall with Mach number; it is governed by thickness. The other three all decrease, the lift quantities because linearised theory divides by the square root of the Mach number squared minus one, and the cone angle because its sine is the reciprocal of the Mach number.