Principles of Flight
Principles of Flight tests lift, drag, stability, control, stall and high-speed aerodynamics. The exam expects equation-level understanding and correct interpretation of graphs.
Lift and drag
L = 0.5 ρ V² S CL. Induced drag falls with speed squared while parasite drag rises; total drag is minimum where they cross. Load factor n = L/W; stall speed increases with √n.
Stability and control
Static stability resists displacement; dynamic stability returns over time. Dihedral gives lateral stability; sweep and fin give directional stability. Aft CG reduces pitch stability.
Worked example
If speed doubles at constant altitude, dynamic pressure quadruples. To keep lift constant, CL must fall to one quarter. Induced drag, proportional to CL², falls to one sixteenth, so total drag may drop until parasite drag dominates.
High speed
Critical Mach is the first local supersonic flow; Mach tuck and shock stall follow. Swept wings raise critical Mach.
Traps
Using IAS for Mach effects; assuming stall speed is constant with weight; confusing static and dynamic stability; ignoring load factor in turns.