engineering beginner 10 sample questions

Aircraft Design MCQ Practice Test

Aerodynamics, wing design, and flight mechanics

Q1. For a high-speed civil transport (HSCT) aircraft, which of the following wing designs would minimize the sonic boom intensity while maintaining aerodynamic efficiency?

A. A swept wing with a high aspect ratio and a low taper ratio ✓
B. A delta wing with a low aspect ratio and a high taper ratio
C. A double-delta wing with a high aspect ratio and a high taper ratio
D. A cranked arrow wing with a low aspect ratio and a low taper ratio

Explanation: A swept wing design with a high aspect ratio and a low taper ratio would minimize the sonic boom intensity while maintaining aerodynamic efficiency. This is because the swept wing design would reduce the pressure gradient along the wing, resulting in a lower sonic boom intensity. Additionally, the high aspect ratio would provide a higher lift-to-drag ratio, while the low taper ratio would reduce the wing's thickness and thereby minimize the sonic boom intensity.

Q2. A high-speed civil transport (HSCT) aircraft is designed to cruise at Mach 2.4, while maintaining a constant angle of attack. The aircraft's wing is optimized for this condition. Which of the following statements regarding the wing's aerodynamic characteristics is correct?

A. The wing's lift curve slope is reduced due to the high angle of attack. ✓
B. The wing's drag is minimized due to the optimal angle of attack.
C. The wing's lift coefficient is maximized due to the constant angle of attack.
D. The wing's pitching moment is zero due to the symmetrical airfoil shape.

Explanation: At high angles of attack, the wing's lift curve slope is reduced due to the increased effect of wing stall. This is because the wing's upper surface is more horizontal, reducing the angle of attack at which stall occurs.

Q3. For a high-speed civil transport (SST) aircraft designed to cruise at Mach 2.4, what is the primary advantage of using a "double-wedge" shock-free airfoil on its wing?

A. It reduces the risk of shockwave-induced drag at high angles of attack.
B. It increases the wing's maximum lift coefficient by 15%.
C. It minimizes the formation of shockwaves on the wing surface, reducing wave drag. ✓
D. It enhances the wing's stability by increasing the moment of inertia about the longitudinal axis.

Explanation: The double-wedge shock-free airfoil is designed to eliminate shockwaves on the wing surface at high speeds, resulting in a significant reduction in wave drag. This design allows the SST aircraft to maintain efficiency and stability at high Mach numbers.

Q4. An aircraft designer is tasked with creating a high-speed business jet with a cruise altitude of 45,000 ft. The designer wants to minimize the aircraft\u2019s drag while maintaining a high lift-to-drag ratio. Which of the following wing shapes would be most effective in achieving this goal?

A. A symmetrical airfoil with a high cambered upper surface and a flat lower surface
B. A wing with a NACA 64-210 airfoil section and a 35\u00b0 sweep angle
C. A wing with a RAE 2211 airfoil section and a 45\u00b0 sweep angle
D. A wing with a supercritical airfoil and a 25\u00b0 sweep angle ✓

Explanation: A supercritical airfoil is designed to delay the onset of flow separation, resulting in a higher lift-to-drag ratio. The 25\u00b0 sweep angle also helps to reduce drag by reducing the wing\u2019s exposure to the oncoming airflow.

Q5. For a supersonic aircraft with a Mach 2 cruise speed, what is the minimum angle of attack required to prevent shock-induced separation on the upper surface of the wing, assuming a NACA 64-210 airfoil section and a Reynolds number of 10^7?

A. 2.5° to prevent shock-induced separation ✓
B. 4.2° to minimize drag
C. 5.1° to achieve maximum lift
D. 6.8° to prevent wing stall

Explanation: To prevent shock-induced separation, the angle of attack should be kept below the critical angle, which is approximately 2.5° for a NACA 64-210 airfoil section at a Mach number of 2 and a Reynolds number of 10^7. This angle of attack ensures that the shock wave formed on the upper surface of the wing does not separate, thereby preventing a significant loss of lift and an increase in drag.

Q6. For a supersonic aircraft designed to cruise at Mach 2.5, what is the minimum radius of curvature for the leading edge of the wing to prevent shock-induced separation at an angle of attack of 15°?

A. R = 2.5 × (Mach 2.5)^2 × (1 + 0.2 × sin(15°)) ✓
B. R = 2.5 × (Mach 2.5)^2 × (1 + 0.2 × sin(30°))
C. R = 2.5 × (Mach 2.5)^2 × (1 + 0.2 × sin(60°))
D. R = 2.5 × (Mach 2.5)^2

Explanation: The minimum radius of curvature for the leading edge of the wing is determined by the shock-induced separation criteria. The radius is a function of the Mach number, the angle of attack, and the wing geometry. The correct equation accounts for the increase in radius due to the angle of attack, which affects the shock strength and the separation point.

Q7. For a given supersonic aircraft, the drag coefficient (Cd) is influenced by the shock wave formation on its surface. Which of the following statements accurately describes the effect of shock wave strength on the drag coefficient?

A. The drag coefficient increases as the shock wave strength increases. ✓
B. The drag coefficient decreases as the shock wave strength increases.
C. The drag coefficient is unaffected by the shock wave strength.
D. The drag coefficient remains constant as shock wave strength varies within the transonic regime.

Explanation: As the shock wave strength increases, the pressure drag also increases due to the stronger pressure jump across the shock wave. This leads to a higher drag coefficient.

Q8. A high-speed commercial airliner is designed to cruise at Mach 0.85. The aircraft has a length of 70 meters and a wingspan of 25 meters. What is the minimum radius of curvature for the wingtip to avoid wingtip vortices and maintain a safe distance from the ground during takeoff and landing?

A. 10 meters
B. 15 meters ✓
C. 20 meters
D. 25 meters

Explanation: The minimum radius of curvature for the wingtip to avoid wingtip vortices and maintain a safe distance from the ground during takeoff and landing can be estimated using the wingtip vortex theory. A commonly used rule of thumb is to maintain a distance of at least 1.5 times the wingspan from the ground to avoid wingtip vortices, which translates to a minimum radius of curvature of 1.5 × 25 = 37.5 meters. However, this is a conservative estimate and can be reduced to 15 meters for high-speed commercial airliners, considering the aircraft's high lift-to-drag ratio and the absence of a horizontal stabilizer.

Q9. For a given supersonic aircraft, the shock wave angle is measured to be 40°. If the Mach number is increased to 1.5, which of the following statements regarding the shock wave angle is correct?

A. The shock wave angle will increase to 45° ✓
B. The shock wave angle will decrease to 38°
C. The shock wave angle will remain the same at 40°
D. The shock wave angle will increase to 42°

Explanation: As the Mach number increases, the shock wave angle also increases due to the increased temperature and pressure behind the shock wave. Using the Rayleigh–Pitot tube relation, we can calculate the new shock wave angle for a Mach number of 1.5, which is approximately 45°.

Q10. For a high-speed civil transport (SST) aircraft, the design team is considering a double-bubble fuselage to reduce drag and increase passenger space. Assuming a constant pressure distribution along the fuselage, which of the following statements accurately describes the effect of adding a second, smaller bubble to the fuselage?

A. The second bubble will increase the overall drag coefficient by 10% due to the additional wetted surface area.
B. The second bubble will decrease the overall drag coefficient by 5% due to the reduced pressure gradient along the fuselage. ✓
C. The second bubble will have a negligible effect on the overall drag coefficient, as the pressure distribution along the fuselage remains unchanged.
D. The second bubble will increase the overall drag coefficient by 20% due to the increased curvature of the fuselage.

Explanation: The addition of a second, smaller bubble to the fuselage reduces the pressure gradient along the fuselage, resulting in a decrease in drag coefficient. This is because the pressure distribution along the fuselage remains relatively constant, and the second bubble helps to smooth out the pressure gradient, reducing the drag-inducing effects of the fuselage.

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