Aerodynamics
Overview
Aerodynamics tests how an aircraft generates lift and drag from airflow, and how the four forces balance in steady flight. Expect questions on airfoil geometry, angle of attack, pressure distribution and the lift formula.
Core rules
- The four forces are lift, weight, thrust and drag. In unaccelerated level flight L = W and T = D; in a climb or turn the balance changes.
- The chord line joins leading and trailing edges; camber is the curvature of the mean camber line. Angle of attack (AoA) is the angle between the chord line and the relative airflow - not pitch attitude.
- Lift arises mainly from lower static pressure over the upper surface and higher pressure below, plus downward momentum (downwash). Bernoulli alone does not explain lift; circulation and the Kutta condition complete the picture.
- L = ½ρV²SC_L. For a given configuration C_L rises almost linearly with AoA until the critical angle, then stalls.
- Induced drag is inseparable from lift; parasite drag rises with V².
Worked example
Mass 1,200 kg, wing area 16 m², C_L 1.2, ISA sea level ρ = 1.225 kg/m³. W = 1,200 × 9.81 = 11,772 N. V = √(2W/(ρSC_L)) = √(23,544/(1.225×16×1.2)) = √1001 ≈ 31.6 m/s ≈ 61 kt.
Traps
- Confusing AoA with pitch attitude: a nose-high aircraft can have a low AoA.
- Assuming more speed always needs more AoA; at fixed weight, faster flight needs less.
- Treating Bernoulli as the sole cause of lift.