Principles of Flight
Principles of Flight
This domain covers lift, drag, angle of attack, stalls, spins, stability, load factor and ground effect. The exam tests why an aircraft flies and why it stops flying, not just definitions.
Core rules
- Lift: increases with airspeed squared, air density and angle of attack - up to the critical angle. Beyond the critical angle, the wing stalls regardless of speed or attitude.
- Drag: induced drag dominates at low speed and high angle of attack; parasite drag rises with airspeed. Total drag is lowest near best-glide speed.
- Load factor: increases in turns and pull-ups. At 60° bank, load factor is 2 g; stall speed increases by the square root of load factor.
- Stability: aft CG reduces static stability; forward CG increases it but can limit elevator authority.
- Ground effect: reduces induced drag near the surface, so the aircraft may float or climb better than expected just after take-off.
Worked example
An aircraft stalls at 50 kt in level flight. In a 60° bank, load factor is 2 g. The accelerated stall speed is 50 × √2 ≈ 71 kt. If you slow to 65 kt in that turn, you are below the accelerated stall speed and risk a stall, even though 65 kt is above the normal 1 g stall speed.
Traps that cost marks
Believing a stall is only a low-speed event, ignoring load factor in steep turns, and assuming ground effect increases with altitude are common. A spin requires both a stall and yaw; recovery begins with reducing angle of attack and stopping yaw.