Principles of Flight
Principles of Flight tests lift, drag, stability, control, stall, load factor, high-speed aerodynamics and configuration effects. ATPL questions often ask why a change occurs, not just what happens.
Core rules
- Lift increases with angle of attack up to the stall; beyond critical angle of attack, lift drops and drag rises.
- Induced drag decreases with speed; parasite drag increases with speed squared.
- Load factor equals lift divided by weight; stall speed increases by the square root of load factor.
- Positive static stability means a disturbance produces a restoring moment.
- Swept wings delay Mach effects but need higher angle of attack; Mach tuck and shock stall are high-speed concerns.
- Flaps increase lift and drag; slats delay stall and improve low-speed handling.
Worked example
In a level 60 degree banked turn, load factor = 1 divided by cos 60 = 1 divided by 0.5 = 2.0. Stall speed in the turn = straight-and-level stall speed times square root of 2, about 1.41 times VS. If VS is 60 kt, the accelerated stall speed is about 85 kt.
Traps
- Thinking load factor depends only on bank angle in a climb or descent.
- Confusing induced and parasite drag trends.
- Assuming a swept wing stalls at the root first.
- Ignoring Mach effects when increasing speed in high-altitude cruise.