Basic Aerodynamics
What you must understand
Know the atmosphere: composition, the International Standard Atmosphere, pressure and temperature lapse, and how density altitude affects performance. Understand airflow: streamline, laminar and turbulent flow, boundary layer, and the meaning of stagnation point. Study lift generation via Bernoulli and Newton, the pressure distribution over an aerofoil, angle of attack, and the critical angle where the stall occurs. Know the four forces in steady flight and their balance, drag types (parasite, induced, profile), and the lift/drag ratio. Understand wing planform effects, aspect ratio, wingtip vortices, washout and dihedral, plus stability in pitch, roll and yaw and the function of the tail surfaces.
Traps in questions
- Stall angle: the stall occurs at a critical angle of attack, independent of airspeed, weight or attitude.
- Induced drag: greatest at low speed and high angle of attack; it decreases as speed rises.
- Density altitude: high temperature, high altitude and high humidity all reduce density and degrade performance.
- Bernoulli misreading: faster flow gives lower static pressure, not higher.
- Static versus dynamic pressure: total pressure = static + dynamic; pitot measures total, static port measures static.
Worked example
An aircraft stalls at 60 kt at maximum weight. If weight is halved, stall speed falls by the square root of the weight ratio: 60 × √0.5 ≈ 42 kt. This illustrates why stall speed is not a single fixed number.
Rule of thumb
Remember the stall is an angle problem, not a speed problem - any attitude at the critical angle can stall.