Principles of Flight
The Principles of Flight paper tests how forces, angle of attack, speed and load factor combine to produce lift, drag, stability and control. Expect questions on stalls, turns, climb, ground effect and wake turbulence, with simple numerical reasoning.
Forces and stall
Lift depends on angle of attack, speed, air density and wing area. The critical angle of attack is fixed; the stall speed changes with mass, load factor, bank and configuration. Induced drag decreases with speed; parasite drag increases. Best glide occurs near the speed for maximum lift/drag ratio.
Turns and stability
In a level turn, load factor = 1/cos(bank). At 60° bank it is 2, so the stall speed rises by the square root of 2 (about 41%). Aft CG reduces static stability; forward CG increases it but raises stall speed and trim drag. Ground effect reduces induced drag near the surface. Wake turbulence is strongest behind heavy, slow, clean aircraft.
Worked example
An aircraft stalls at 50 kt in level flight. In a 60° banked level turn, load factor is 2 and the new stall speed is 50 × √2 = 70.7 kt. If the pilot tries to hold 50 kt in that turn, the wing is already stalled; lower the bank or increase speed.
Traps
Believing stall depends on speed alone; forgetting bank increases stall speed; assuming lift is only Bernoulli; and ignoring wake turbulence from a heavy aircraft.