Principles of Flight: lift, drag, high speed and stability
Lift and the stall
Lift = ½ρV²SC_L, arising from the pressure distribution around the aerofoil. C_L rises linearly with angle of attack up to the critical angle, then falls - the stall. Stall speed varies with √mass and √load factor: Vs(n) = Vs × √n. The stall always occurs at the critical angle of attack, so mass changes the speed, not the angle.
Drag
Parasite drag ∝ V²; induced drag ∝ 1/V² and ∝ C_L², so it is driven by weight and lift distribution. Minimum total drag occurs where parasite equals induced drag - the speed for maximum glide ratio, roughly 1.32 Vs for a typical aerofoil. Aspect ratio and winglets reduce induced drag; gear, flaps, ice and rain raise parasite drag.
High speed and stability
As speed rises, local airflow accelerates and may become sonic before the aircraft does - the critical Mach number. The resulting shock wave causes Mach buffet (shock stall) and loss of high-speed stall margin. Sweepback raises the critical Mach number but worsens low-speed characteristics and encourages tip stall. Know longitudinal, lateral and directional stability, dihedral effect, Dutch roll, and how CG position modifies static and dynamic stability.
Worked example
In a 45° banked level turn, n = 1/cos 45° = 1.41. Stall speed rises by √1.41 = 1.19, about 19%. An aeroplane stalling at 100 kt level stalls near 119 kt in that turn; at 60° bank (n = 2) it stalls near 141 kt.
Traps
Confusing the angle of attack at the stall with the speed; assuming slipstream and gyroscopic effects are negligible; treating V_NE as a routine operating speed rather than a limit.