Principles of Flight
Principles of flight questions test the four forces, the generation of lift, and the factors that change performance. Understand the lift equation qualitatively: lift depends on air density, velocity squared, wing area and lift coefficient, and the coefficient depends on angle of attack and configuration. Know the critical angle of attack, the stall, and that a wing stalls at the same angle of attack regardless of weight, speed or attitude. Understand induced and parasite drag, the lift/drag ratio, and best glide speed as the speed for maximum L/D.
Traps: candidates think a heavier aircraft stalls at a higher angle of attack - it stalls at the same angle but at a higher speed. Others forget that load factor increases stall speed (stall speed rises with the square root of load factor), or confuse centre of gravity effects: a forward CG increases stability but raises stall speed and reduces performance; an aft CG reduces stability. Also know the effect of density altitude: high, hot and humid means less lift and thrust.
Worked example: at a load factor of 4 (a 60° banked level turn), stall speed increases by the square root of 4, i.e. doubled. If the clean stall speed is 50 kt, the accelerated stall speed in that turn is about 100 kt. Rule of thumb: in a 60° level turn, load factor is 2 and stall speed rises by about 41%; at 4 g it doubles. Always respect the critical angle of attack - it is the only thing that stalls the wing.