Principles of Flight
Principles of Flight tests lift, drag, stability, control, stall behaviour and high-speed aerodynamics, including Mach effects and swept wings.
Lift, drag and load factor
- Lift = ½ ρ V² S CL; increasing bank increases load factor and stall speed.
- Induced drag decreases with speed; parasite drag increases with speed.
- At 60° bank, load factor = 1/cos 60° = 2; stall speed increases by √2 ≈ 1.41.
Stability and Mach
- Static stability requires a restoring moment; aft CG reduces longitudinal static stability.
- The critical Mach number is the first point of supersonic airflow; shock waves cause buffet and Mach tuck.
- Swept wings delay the onset of shock waves but need higher takeoff/landing speeds.
Worked example
An aircraft stalls at 60 kt in level flight. In a 60° bank, load factor is 2, so the stall speed becomes 60 × √2 ≈ 85 kt. The same angle of attack now produces twice the lift but also twice the structural load.
Traps that cost marks
- Thinking stall speed is fixed; it rises with load factor and aft CG.
- Confusing induced drag with parasite drag.
- Assuming swept wings improve low-speed performance; they increase approach speeds.