Fundamentals of Aerodynamics Questions and Answers

Answer: B

Both pressure and density fall with height, which is why the same true airspeed produces less dynamic pressure and less lift as an aircraft climbs. The equation of state ties density to pressure and temperature together.

Answer: C

It is a reference model, not a forecast: fixing sea-level conditions and a lapse rate lets aircraft performance and instrument calibration be quoted on a common basis. Real conditions differ from it constantly, which is why corrections are applied.

Answer: D

By definition no fluid crosses a streamline, so in steady flow a streamline is also the path a fluid element follows. In unsteady flow streamlines, pathlines and streaklines differ, and the three coincide only when the flow is steady.

Answer: A

Steady means the time derivative vanishes at each fixed point, though properties still vary from place to place as the fluid accelerates around a body. A fluid element therefore still experiences acceleration while moving along a streamline.

Answer: B

Setting viscosity to zero removes the boundary layer and skin friction, which makes the equations far easier and is a good approximation outside the thin viscous region. Taken literally it also predicts no drag at all, which is d'Alembert's paradox.

Answer: C

Ideal-flow theory predicts that pressure recovered at the rear exactly cancels that at the front, giving zero net drag, which plainly contradicts experiment. The resolution is viscosity, whose boundary layer and separation destroy the symmetry.

Answer: D

Circulation measures the net swirl of the flow around a contour, and by the Kutta-Joukowski theorem the lift per unit span equals density times free-stream velocity times circulation. It is central to all classical airfoil theory.

Answer: A

Correct answer: Density, free-stream velocity and circulation

\[ L' = \rho_\infty V_\infty \Gamma. \] The theorem is remarkable for what it leaves out: the shape of the body appears only through the circulation it generates. Any two bodies with the same circulation in the same stream produce the same lift, whatever they look like.

Answer: B

The assumption is about density alone, and it is a property of the FLOW rather than of the fluid: air is compressible, but air moving slowly enough behaves as though it were not. Pressure and velocity vary freely under the assumption.

Answer: C

Correct answer: Velocity varies from point to point along its path

Steady means the velocity at a fixed point does not change with time, not that a particle moving through the field keeps its velocity. Following the particle, the convective term \( (\mathbf{V}\cdot\nabla)\mathbf{V} \) accelerates it - which is exactly what happens to fluid speeding up through a venturi in a perfectly steady flow.