Principles of Flight
Scope
Principles of Flight tests lift, drag, stalls, stability, load factor, and control. The exam expects you to explain why an aircraft behaves as it does, not just name the four forces.
Core rules
- Lift depends on angle of attack, airspeed, air density, and wing area; it increases with angle of attack until the critical angle, then stalls.
- Induced drag decreases with speed; parasite drag increases with speed. Total drag is lowest at a specific speed.
- Stability: forward CG improves pitch stability but increases landing distance; aft CG reduces stability.
- Load factor increases in turns and pull-ups. Stall speed increases with the square root of load factor.
- Wake turbulence is generated by lift and is strongest behind heavy, slow, clean aircraft.
Worked example
An aircraft stalls at 50 kt in level flight. In a 60° bank, load factor = 1 ÷ cos 60° = 2. The stall speed becomes 50 × √2 ≈ 70.7 kt. Reasoning: the wing must produce twice the lift, so it reaches the critical angle of attack at a higher speed. The pilot must increase power and avoid steepening the bank near the stall.
Traps
Believing a stall is caused by low speed rather than excessive angle of attack. Forgetting that load factor raises stall speed. Thinking aft CG is always better because it reduces control force. Ignoring wake turbulence because the preceding aircraft is already gone.