Basic Aerodynamics
What the module tests
Basic aerodynamics covers the atmosphere, airflow, Bernoulli and Newton, aerofoils, lift and drag, stability, and flight controls. The exam tests relationships and definitions more than complex calculation.
Core rules
- Lift L = 0.5 × ρ × V² × S × CL.
- Induced drag falls as speed increases; parasite drag rises with the square of speed.
- Density altitude rises when temperature or humidity rises or pressure falls, reducing performance.
- The centre of pressure moves with angle of attack; the centre of gravity is fixed for a given loading.
- Dihedral gives lateral stability; sweepback delays compressibility effects; a horizontal stabiliser provides longitudinal stability.
- A stall occurs at the critical angle of attack, not at a fixed speed.
Worked example
An aircraft with wing area 16 m² flies at 50 m/s in air of density 1.225 kg/m³ with CL = 0.5. Find lift. L = 0.5 × 1.225 × 50² × 16 × 0.5. First 50² = 2500. Then 0.5 × 1.225 = 0.6125; 0.6125 × 2500 = 1531.25; × 16 = 24,500; × 0.5 = 12,250 N. The aircraft would need about 12.25 kN of lift at that condition.
Traps
Using indicated airspeed instead of true airspeed in the lift equation; treating stall as a speed; forgetting that density falls with altitude; mixing induced and parasite drag trends; assuming the centre of pressure is fixed.
Exam approach
Write the lift equation, convert units, and check whether density or speed is the changed variable. For stability questions, link the feature to the axis it stabilises.