Principles of Flight
Principles of Flight explains why the aircraft flies: the four forces, lift generation, angle of attack, drag, stability, control, and the effects of load factor and configuration.
Lift and angle of attack
Lift = ½ρV²SC_L. It grows with airspeed squared and with angle of attack up to the critical angle. A stall is an exceedance of the critical angle of attack, at any speed and in any attitude.
Drag
Induced drag falls as speed rises; parasite drag rises with speed squared. Total drag is minimum at the speed for best glide (L/D max). Flap and interference drag add to the total.
Stability and control
Static stability is the initial tendency to return to equilibrium; dynamic stability is how it behaves over time. Pitch stability comes from the tailplane and CG position. Dihedral gives lateral stability; the fin gives directional stability.
Load factor and turns
In a level turn, load factor n = 1/cos(bank). At 60° it is 2g; stall speed rises by √n, so a 50 kt stall becomes 71 kt. The limit is structural, not aerodynamic.
Worked example
An aircraft stalls at 50 kt in level flight. In a 60° bank, n = 2, so stall speed becomes 50 × √2 ≈ 71 kt. Slowing to 70 kt in that turn leaves you on the edge of the stall, and pulling further raises the stall speed again.
Traps
Believing a stall requires low airspeed; confusing best glide with minimum sink; and forgetting that flaps increase both lift and drag.