Principles of Flight
Lift and drag
Know the four forces: lift, weight, thrust, and drag. Understand that lift depends on air density, velocity squared, wing area, and the lift coefficient, which depends on angle of attack. Know the drag curve: induced drag decreases with speed, parasite drag increases with speed squared, and total drag is minimum at the speed for best glide (L/D max).
Stability and control
Know the three axes: pitch (lateral axis), roll (longitudinal axis), and yaw (normal axis). Understand static and dynamic stability, and the effect of the CG on longitudinal stability. Know the purpose of the horizontal stabiliser, vertical stabiliser, ailerons, elevators, and rudder.
Stalls and high-speed flight
Know that a stall occurs at the critical angle of attack, regardless of speed, and that load factor raises the stall speed (stall speed increases with the square root of load factor). Understand the meaning of Mach number, critical Mach, and the swept wing's role in delaying shock stall.
Traps
- Believing a stall depends on speed; it depends on angle of attack.
- Confusing the axes: pitch is about the lateral axis, roll about the longitudinal axis.
- Forgetting that induced drag dominates at low speed and parasite drag at high speed.
- Assuming a swept wing improves low-speed performance; it is for high-speed flight.
Worked example
At a load factor of 4, the stall speed increases by the square root of 4, i.e. it doubles. If the 1 g stall speed is 60 kt, the stall speed at 4 g is 120 kt.