Principles of Flight
What the exam tests
Principles of flight covers lift and drag, stability, control, stalls, load factor, high-speed flight and wake turbulence.
Core rules
- Lift = CL × ½ρV²S; induced drag falls with speed, parasite drag rises with V².
- Stall occurs at the critical angle of attack, independent of weight, but stall speed rises with weight and load factor.
- Load factor in a level turn: n = 1/cos(bank). At 60° bank, n = 2.
- Stability: longitudinal (pitch), lateral (roll), directional (yaw); dihedral gives lateral stability.
- Critical Mach is where local airflow first reaches Mach 1; sweep and thin wings raise it.
- Wake turbulence sinks and drifts with the wind; avoid it by staying above and upwind.
Worked example
An aircraft stalls at 60 kt in 1 g. In a 60° bank, load factor is 2, so stall speed rises by √2: 60 × 1.41 ≈ 85 kt. The same reasoning explains why accelerated stalls occur in steep turns or pull-ups.
Traps
Confusing induced and parasite drag; thinking stall speed is fixed; and forgetting that aileron deflection increases load factor and can trigger an accelerated stall.