Basic Aerodynamics
Atmosphere and the four forces
Standard atmosphere at sea level: 15 °C, 1013.25 hPa, with a lapse rate of about 1.98 °C per 1 000 ft up to 36 090 ft, then isothermal. In steady level flight lift equals weight and thrust equals drag; any imbalance produces acceleration.
Lift and drag
Bernoulli (faster flow gives lower pressure) and Newton (air deflected downward gives upward reaction) describe the same lift. Lift L = ½ρV²SC_L, so lift depends on density, speed squared, area and angle of attack - not on speed alone. Induced drag falls as speed rises while parasite drag rises with V², so total drag is minimum at V_MD. Angle of attack controls lift up to the critical angle, beyond which the wing stalls; stall speed rises with weight and with load factor, roughly V_s ∝ √n.
Speeds and stability
Distinguish IAS, CAS, EAS, TAS and Mach: for a given IAS, TAS rises with altitude. Understand static and dynamic stability, dihedral effect, and how a rearward CG reduces static margin.
The traps
Believing lift depends only on speed; confusing the induced and parasite drag curves; treating stall as a speed rather than an angle of attack; mixing IAS and TAS.
Worked example
Lift is proportional to V². If speed doubles and nothing else changes, lift becomes 2² = 4 times greater, so the aircraft must reduce angle of attack to stay level. Rule of thumb: a 10% speed increase gives about 21% more lift (1.1² = 1.21).