Aerodynamics and Performance Fundamentals
This domain tests whether you can connect first principles to flight-manual numbers: lift and drag, thrust and power, and how mass, density altitude and configuration shift every performance speed.
Core relationships
- Lift is L = ½ρV²SC_L and drag is D = ½ρV²SC_D; density ρ falls with pressure altitude and temperature.
- Induced drag varies as 1/V², parasite drag as V²; total drag is minimum at L/D_max.
- Thrust required equals drag. Excess thrust sets climb angle; excess power sets rate of climb.
- V_X (best angle) is lower than V_Y (best rate); both increase with altitude and converge at the absolute ceiling.
- Stall speed V_S = √(2W/(ρSC_Lmax)), so V_S rises with √mass and with density altitude.
- Load factor n = L/W; V_A scales with √n.
Worked example
Stall speed is 52 kt at 1,000 kg. At 1,210 kg, V_S = 52 × √(1,210/1,000) = 52 × 1.10 = 57.2 kt. At 2 g the same aircraft stalls at 52 × √2 = 73.5 kt, which is why V_A is quoted well above clean stall speed.
Traps
- Quoting stall speed in TAS; certification and AFM speeds are IAS.
- Believing best-glide speed is fixed. It rises with √mass while the glide angle stays the same.
- Mixing thrust and power: a jet's climb gradient depends on excess thrust, a propeller aircraft's on excess power.
- Forgetting that a tailwind raises the ground speed for best range and lowers it for best endurance into wind.