Principles of Flight
Lift, drag and the wing
Lift comes from the wing's circulation and pressure distribution; it increases with air density, speed squared, and angle of attack until the stall. Know the four forces in a glide: weight, lift, drag, and the resultant. In a steady glide, the glide angle depends on the lift-to-drag ratio, not on mass alone.
Stability and control
- Static and dynamic stability about each axis.
- Pitching moments: the tailplane and CG position determine trim and stick force.
- Adverse yaw from aileron deflection; counter with rudder.
- Stall: angle-of-attack driven, not speed driven. A glider can stall at any speed and in any attitude.
- Spins: incipient, fully developed, and recovery (power off, full opposite rudder, ease the stick forward, then recover).
Traps
Questions often state that a glider cannot stall at high speed or in a steep turn - both false. Another trap confuses the effect of mass on stall speed with its effect on stall angle. Also watch for questions on load factor in turns: load factor rises with bank angle, raising stall speed.
Worked example
Bank 60° in a level turn: load factor = 1/cos(60°) = 2. Stall speed rises by √2 ≈ 1.41, so a 40 kt stall becomes about 57 kt. Rule of thumb: at 60° bank, stall speed is 1.41 times the straight-and-level value.