Principles of Flight - Kazakhstan PPL
Principles of Flight explains why the aircraft flies and how it behaves near the edges: lift, drag, stability, control, stall, spin, and load factor. PPL questions often ask for the correct cause, not just the definition.
Lift, drag, stability
- Lift depends on angle of attack, airspeed, air density and wing area. Angle of attack is the key control variable.
- Induced drag decreases with speed; parasite drag increases with speed. Total drag is lowest at best glide speed.
- Static stability tends to return the aircraft to its original attitude; dynamic stability describes the motion over time.
- Dihedral gives lateral stability; the fin gives directional stability; elevator trim adjusts pitch.
Stall and load factor
- Stall occurs at the critical angle of attack, at any speed, weight or attitude.
- Load factor increases in turns: at 60° bank, LF = 1/cos 60° = 2. Stall speed increases by √LF.
- A stall is preceded by buffet and reduced control effectiveness; recover by reducing angle of attack, then adding power.
Worked example
An aircraft stalls at 45 kt in level flight. In a 60° bank, LF = 2, so stall speed = 45 × √2 ≈ 64 kt. Reasoning: the wing must produce twice the lift, so it reaches the critical angle of attack at a higher speed. Do not add back pressure in the turn; reduce AoA.
Traps
Believing stall speed is fixed; confusing angle of attack with pitch attitude; ignoring load factor in steep turns; thinking downwind turns change stall behaviour.