Principles of Flight
Core concepts
Principles of flight covers the four forces, lift generation, angle of attack, the lift coefficient curve, stalls, load factor, stability, control, and the effects of configuration and speed. You must understand the relationship between angle of attack and lift, the critical angle of attack, and why an aircraft stalls at any speed if the critical angle is exceeded. Know the four types of stability (static, dynamic, longitudinal, lateral/directional) and the factors affecting each.
Traps to watch
A frequent trap is the belief that an aircraft cannot stall at high speed: it can, if the critical angle of attack is exceeded (e.g., abrupt pull-up). Another is the effect of load factor: stall speed increases with the square root of load factor, so at 2 g the stall speed rises by about 41%. Questions on induced and parasite drag test whether you know induced drag decreases with speed while parasite drag increases. Also watch for the effect of flaps on the lift curve and on the stall speed.
Worked example
Stall speed at 1 g is 60 kt. At a load factor of 4, stall speed = 60 × √4 = 120 kt. This shows why steep turns and turbulence demand higher approach speeds.
Rule of thumb
Stall speed scales with the square root of load factor. Angle of attack, not speed, determines the stall.