Unit 6: High speed flow over airfoils and wings - Practice Quiz

1 What primarily causes shock stall on an airfoil?

2 Which aerodynamic change commonly occurs during shock stall?

3 What is a major advantage of selecting a supercritical airfoil for transonic flight?

4 Which shape is characteristic of a supercritical airfoil?

5 For a thin symmetric airfoil at zero angle of attack in ideal supersonic flow, what is the lift?

6 According to linearized supersonic theory, where is the aerodynamic center of a thin airfoil approximately located?

7 What does the transonic area rule seek to vary smoothly along an aircraft?

8 Why is an area-ruled fuselage often narrowed near the wings?

9 Which airfoil feature is generally preferred for reducing wave drag in supersonic flow?

10 Which profile is commonly associated with basic supersonic airfoil design?

11 What flow feature generally forms when supersonic flow turns around a convex corner?

12 What happens to static pressure as supersonic flow passes through an expansion fan?

13 Which wing planform is widely used for supersonic aircraft?

14 What is a principal aerodynamic benefit of wing sweep at supersonic speeds?

15 Why are sharp leading edges often used on supersonic aircraft?

16 Which design choice generally helps an aircraft achieve efficient supersonic cruise?

17 What is the main physical cause of aerodynamic heating at high speed?

18 Where is aerodynamic heating commonly greatest on a high-speed aircraft?

19 What type of drag is directly associated with shock waves on a supersonic profile?

20 What happens to static pressure when supersonic flow passes through a compression shock?

21 An airfoil operating in transonic flow experiences a sudden loss of lift, a rapid drag rise, and strong buffet as its angle of attack increases. What is the most likely cause?

22 As the angle of attack of a conventional airfoil is increased near its critical Mach number, which sequence most commonly leads to shock stall?

23 An aircraft is intended to cruise efficiently at a high-subsonic Mach number. Why would a supercritical airfoil be selected instead of a conventional airfoil?

24 Which geometric combination is most characteristic of a supercritical airfoil?

25 Using linearized supersonic theory, determine the lift coefficient of a thin flat plate at and . Use , with in radians.

26 For the flat plate in the previous linearized-flow case, estimate the lift-dependent wave-drag coefficient using .

27 Linearized supersonic theory predicts that the aerodynamic centre of a thin two-dimensional airfoil is located approximately at:

28 A thin symmetric supersonic profile has its resultant lift acting at mid-chord. Using the convention that positive pitching moment is nose-up, what is its pitching-moment coefficient about the quarter-chord point?

29 According to the transonic area rule, which aircraft property should vary as smoothly as possible along the longitudinal axis?

30 Why is the fuselage of an area-ruled aircraft often narrowed near the wing?

31 Which airfoil is generally most suitable for reducing wave drag in fully supersonic flow?

32 Two geometrically similar double-wedge airfoils operate at the same supersonic Mach number and angle of attack. If one has a smaller thickness-to-chord ratio, what is the expected effect?

33 In shock-expansion theory, how is supersonic flow around a convex corner treated?

34 Ideal supersonic flow passes through a Prandtl-Meyer expansion fan. Which combination correctly describes the changes across the fan?

35 For a swept wing, the Mach number normal to the leading edge is approximated by . At and , how is the leading edge classified?

36 Why are highly swept or delta wings commonly used on supersonic aircraft?

37 A designer increases the fineness ratio of a supersonic aircraft fuselage while keeping its volume approximately constant. What is the main aerodynamic objective?

38 An aircraft must cruise supersonically but also take off at an acceptable speed. Which design compromise most directly addresses both requirements?

39 A simplified stagnation-point heating relation is when other quantities remain fixed. If velocity increases by , by what factor does the heating rate increase?

40 For stagnation-point heating, suppose , where is nose radius. If the nose radius is increased by a factor of four, what happens to the heating rate?

41 An unswept wing section begins shock-induced separation when its local normal Mach number reaches approximately . Using the normal-flow approximation, estimate the free-stream Mach number at which the same section on a wing swept by would encounter this condition.

42 Pressure measurements show a strong upper-surface shock followed by a nearly constant-pressure region extending to the trailing edge. Which interpretation best explains an accompanying abrupt loss of lift and rise in drag?

43 Use the approximate Korn relation . For a supercritical airfoil with , , and cruise , what drag-divergence Mach number is predicted?

44 Four airfoils are evaluated at the design cruise condition. The minimum acceptable buffet-onset lift coefficient is , and must not exceed . Among qualifying sections, cruise drag must be minimized. Which airfoil should be selected?

45 A two-dimensional flat plate operates at and . Under linearized supersonic theory, what are approximately its lift coefficient and leading-edge pitching-moment coefficient?

46 A symmetric double-wedge airfoil has and operates at and . Using linearized theory, . What is ?

47 A supersonic profile has and a leading-edge pitching-moment coefficient . Neglecting any free aerodynamic couple, where is its centre of pressure?

48 Two wing-body configurations have the same maximum cross-sectional area. Configuration X has abrupt changes in total area near the wing roots, whereas configuration Y has a smooth, nearly Sears-Haack-like total-area distribution. Which conclusion follows from the transonic area rule?

49 At a wing station, the target total cross-sectional area is . The unmodified fuselage contributes and the wing contributes . What local fuselage modification best satisfies the area rule?

50 A symmetric double-wedge airfoil with flies at zero lift and . Using , estimate its wave-drag coefficient.

51 For a low-wave-drag supersonic cruise airfoil, which geometric choice is generally most appropriate when structural and low-speed constraints are temporarily ignored?

52 Flow expands isentropically from to through a Prandtl-Meyer fan. For , what is the static-pressure ratio ?

53 At , an attached oblique shock has wave angle and turns the flow through . For , use the normal-shock relation followed by . What is the downstream Mach number?

54 At , which leading-edge sweep angle, measured from the spanwise direction, makes the leading edge unambiguously subsonic according to ?

55 Linearized supersonic theory places a wing's aerodynamic centre at approximately of mean aerodynamic chord. If the centre of gravity is at chord and , what lift-induced pitching-moment coefficient acts about the centre of gravity?

56 A supersonic aircraft has the cruise drag polar . Ignoring propulsion variation, at what lift coefficient is maximized?

57 A designer can increase wing sweep enough to make the leading edge subsonic at cruise. Which system-level consequence must still be included before choosing still greater sweep?

58 Nacelles are added near the wing-body junction of an otherwise area-ruled aircraft. Which redesign most directly preserves low transonic wave drag?

59 For air at and , estimate the adiabatic-wall temperature using , with and .

60 Approximate stagnation-point heating by . If velocity increases by while nose radius doubles, what is the ratio of new to original heating rate?