Principles of Flight: Lift, Drag and Stability
What you must know
Principles of flight questions cover the four forces, the generation of lift, angle of attack, the lift coefficient curve, drag types, stability and control. Understand that lift depends on angle of attack, airspeed, air density and wing area, and that the critical angle of attack is the stalling angle regardless of airspeed, attitude or weight. Know induced drag versus parasite drag and the speed for minimum total drag. Understand static and dynamic stability, dihedral effect, and the purpose of trimming. Learn the effect of flaps on lift and drag, and the meaning of load factor in turns.
Traps in questions
- Believing an aircraft stalls at a fixed airspeed - it stalls at a fixed angle of attack.
- Forgetting that in a turn the stall speed increases with load factor.
- Confusing induced drag (from lift) with parasite drag (from form and skin friction).
- Assuming flaps always shorten take-off distance - they may not.
Worked rule of thumb
Stall speed in a turn scales with the square root of load factor. Example: at 60° bank, load factor is 2, so the stall speed rises by √2 ≈ 1.41, meaning a 50 kt stall becomes about 71 kt.
Study approach
Sketch the lift and drag curves and mark the critical angle of attack and the minimum-drag speed.