Principles of Flight
Principles of Flight tests lift and drag, stability and control, load factor and high-speed aerodynamics.
Lift and drag
- Lift = ½ρV²SCL. Induced drag decreases with speed; parasite drag increases with V². Total drag is minimum at L/D max.
- Angle of attack controls lift; the stall occurs at the critical AoA regardless of speed, weight or attitude.
Stability and control
- Static stability is the initial tendency; dynamic stability is the tendency over time. Positive longitudinal stability requires the CG forward of the neutral point.
- Dihedral gives lateral stability; sweepback contributes to directional stability and raises critical Mach.
- Load factor: n = 1/cos φ in a level turn. Stall speed increases by √n.
High-speed flight
- Critical Mach is reached when local airflow reaches Mach 1. Shock stall, Mach tuck and buffet follow.
- Swept wings raise critical Mach; vortex generators and area rule reduce drag rise.
Worked example
Level turn at 45° bank: n = 1/cos 45° = 1.41. If clean stall speed is 60 kt, accelerated stall speed = 60 × √1.41 ≈ 71 kt. At 60° bank, n = 2 and stall speed = 60 × √2 ≈ 85 kt.
Traps
- Thinking stall depends only on speed.
- Confusing induced and parasite drag.
- Ignoring load factor in turns.