Principles of Flight
Lift, drag and stability
Principles of flight questions cover the four forces, aerodynamic force production, the lift equation, drag types, angle of attack, the stall, and stability and control about all three axes. Understand why lift depends on angle of attack and airspeed, the difference between induced and parasite drag, and the behaviour of the wing near the critical angle.
Traps
Common traps include confusing angle of attack with pitch attitude, assuming a stall depends on airspeed alone, and mixing up the axes and the controls that act about them. Another trap is treating the centre of pressure as fixed; it moves with angle of attack. Questions may also test how load factor raises stall speed.
Worked example
A wing stalls when the critical angle of attack is exceeded, regardless of airspeed, mass or attitude. In a steep turn, load factor increases, so stall speed rises by the square root of the load factor. At a load factor of four, stall speed doubles.
Rule of thumb
Stall speed scales with the square root of load factor. Angle of attack, not airspeed, is the direct cause of the stall.