Principles of Flight
Principles of Flight tests lift, drag, thrust, weight, stability, control and the effects of speed, angle of attack and load factor on aircraft behaviour.
Core concepts
- Lift increases with angle of attack up to the critical angle; beyond it the wing stalls.
- Induced drag decreases with speed; parasite drag increases with speed squared.
- Stability is the tendency to return to equilibrium; aft CG reduces static margin.
- Load factor increases in turns; stall speed increases with the square root of load factor.
- Swept wings and high-speed flight introduce Mach effects, shock waves and buffet boundaries.
Worked example
In a level 45° bank turn, load factor n = 1/cos45° = 1.41. Stall speed increases by √1.41 = 1.19. If the straight-and-level stall speed is 60 kt, the accelerated stall speed is about 60 × 1.19 = 71 kt. The extra margin is required because the wing must produce more lift.
Traps
- Thinking stall speed is fixed; it changes with weight, load factor and configuration.
- Confusing angle of attack with pitch attitude.
- Forgetting that aft CG reduces stability but may reduce trim drag.
- Ignoring adverse yaw and the need for coordinated aileron/rudder input.
- Assuming a higher speed always improves turning performance; radius and rate depend on load factor and thrust.