Principles of Flight
Principles of Flight
This domain tests lift, drag, thrust, weight, stability, control, stalls, load factor and turning flight. The exam expects you to explain why an aircraft behaves as it does, not just quote definitions.
Core rules
- Lift depends on angle of attack, airspeed, air density and wing area. A stall occurs at the critical angle of attack, at any speed or attitude.
- Induced drag decreases with speed; parasite drag increases with speed. Total drag is lowest near best glide speed.
- Stability: static stability is the initial tendency to return; dynamic stability is how that tendency changes over time.
- Load factor increases in turns and pull-ups. At 60° bank, load factor is 2 g.
Worked example
An aircraft stalls at 50 kt in level flight. In a 60° bank, load factor = 1 ÷ cos 60° = 2. Stall speed increases by √2, so the new stall speed is about 50 × 1.41 = 71 kt. The reasoning is that the wing must produce twice the lift, increasing the angle of attack needed and raising the stall speed.
Traps
A stall is an angle-of-attack event, not simply a low-speed event. Increasing bank increases stall speed. Do not confuse induced and parasite drag. Do not assume a tailwind improves climb performance.