Unit 3: Aerodynamics, Flight Mechanics and Aircraft Systems
Core concepts
Unit 3 builds a working model of how an aircraft generates and controls forces. Candidates must understand the four forces (lift, weight, thrust, drag), Bernoulli's principle and Newton's third law as complementary explanations of lift, angle of attack, the lift equation (L = ½ρv²SC_L), induced versus parasite drag, and the drag curve's minimum-drag point. Stability and control require the three axes (roll, pitch, yaw) and their surfaces (aileron, elevator, rudder), plus static versus dynamic stability. Systems content covers hydraulic, pneumatic, electrical and fuel systems, their redundancy, and the purpose of primary and secondary flight controls.
Traps
Questions often swap cause and effect: increasing angle of attack raises lift only up to the critical angle, beyond which the wing stalls. Another trap is confusing the axis with the motion: pitch is about the lateral axis, roll about the longitudinal axis, yaw about the normal axis. Candidates also misapply the drag curve, assuming more speed always means more total drag; induced drag falls with speed while parasite drag rises. Distinguish static stability (initial tendency to return) from dynamic stability (the manner of return over time).
Worked example
If speed doubles at constant density, area and lift coefficient, lift increases by a factor of four because lift is proportional to v². Use this rule of thumb: identify which variables are held constant before comparing.
Study tip
Link each system to the failure it protects against; examiners reward functional reasoning, not lists.