Fundamentals of Aerodynamics Questions and Answers

Answer: C

Correct answer: Lower pressure on that surface

Bernoulli’s equation ties higher velocity to lower static pressure along a streamline, so the faster flow over the upper surface is accompanied by a suction there. It is worth being clear about the direction of the argument: the pressure field and the velocity field are two aspects of the same solution, neither one causing the other.

Answer: D

Viscosity belongs to the substance itself and depends on temperature, whereas the other three describe a particular flow or geometry. Keeping the distinction clear helps in deciding which quantities change when conditions do.

Answer: A

Correct answer: Pascal

One pascal is one newton per square metre. It is a small unit for aerodynamic purposes - standard sea level pressure is about 101,325 of them - so the kilopascal and the bar are common in practice, and the millibar or hectopascal in meteorology.

Answer: B

Correct answer: One hundred and one kilopascals

The International Standard Atmosphere fixes sea level conditions at 101,325 Pa, 288.15 K and 1.225 kg per cubic metre. These are the reference values against which altimeters and airspeed indicators are calibrated and against which performance is quoted.

Answer: C

The instrument responds to dynamic pressure, which falls with density, so the same true speed reads lower as height increases. Stall speed in indicated terms stays nearly constant for the same reason, which is convenient for the pilot.

Answer: D

Correct answer: Increasing the angle of attack below the stall

\[ L = \frac{1}{2}\rho V^2 S C_L, \] and at fixed speed the only term the pilot can change quickly is \( C_L \), which rises nearly linearly with angle of attack until the stall. Reducing area or density, or reducing the angle, all move the wrong way.

Answer: A

Correct answer: Four

Dynamic pressure is \( \frac{1}{2}\rho V^2 \), so doubling the speed quadruples it - and quadruples the lift and the parasite drag with it. The square law is why a small increase in cruise speed costs so much in thrust, and why structural loads rise so sharply with airspeed.

Answer: B

Correct answer: Both contribute, and their relative importance depends on the body

A streamlined body at low angle of attack is dominated by skin friction; a bluff body such as a cylinder or a deployed undercarriage is dominated by the pressure difference between its front and its separated wake. The same two mechanisms operate in every case, and only their proportion changes.

Answer: C

Free-stream conditions are the reference against which coefficients and Mach and Reynolds numbers are defined, and they are measured far enough upstream that the body has no influence. Conditions near the surface differ greatly from them.

Answer: D

Fluid that has passed through the boundary layer has lost momentum, so the wake is slower than the free stream and its total pressure is reduced. Measuring that deficit is one practical way to determine the drag of a body.