Theory of Flight
Aeroplane aerodynamics and flight controls, stability, and high-speed (compressibility/Mach) flight.
Theory of flight, summary notes
- Lift comes from a wing at an angle of attack (L = C_L·½ρV²·S); C_L rises with AoA to the critical stalling angle, then the flow separates and the wing stalls, a stall is an angle-of-attack event at any speed.
- The three primary flight controls act about three axes: AILERONS roll (longitudinal axis), ELEVATOR pitches (lateral axis), RUDDER yaws (normal axis). Secondary controls, flaps, slats, spoilers and trim, change lift, drag or trim.
- Stability: static stability is the initial tendency to return to trim, dynamic is the behaviour over time; longitudinal stability depends on the tailplane and CG position (forward CG = more stable, heavier stick forces).
- HIGH-SPEED flight introduces compressibility: the critical Mach number (M_crit) is the flight Mach number at which the airflow FIRST reaches Mach 1 locally over the wing; beyond it shock waves form, drag rises sharply (drag divergence) and 'Mach tuck' can occur.
- Swept wings, thin aerofoils and area-ruling raise M_crit and delay compressibility effects; M_mo is the maximum operating Mach number.
- ⚠ Exam trap: the critical Mach number is where the LOCAL airflow first hits M1 (the aircraft is still subsonic overall); swept wings RAISE the critical Mach number and delay the transonic drag rise.
- Lift
- L = C_L·½·ρ·V²·S
- Mach number
- M = TAS / local speed of sound
Why do high-subsonic jet transports use swept wings?
Sweeping the wing reduces the component of airflow speed acting across the aerofoil, so the wing can be flown at a higher aircraft Mach number before the local flow reaches Mach 1. This raises the critical Mach number, delays the sharp transonic drag rise and shock formation, and lets the aircraft cruise efficiently at high subsonic speed.
Lift, angle of attack & the stall
The four forces in flight
Drag & the minimum-drag speed
Theory of flight concept map
Theory of Flight
Theory of flight quiz
Theory of Flight, quiz
1. The ailerons control the aircraft about the:
Longitudinal axis (roll)Lateral axis (pitch)Normal axis (yaw)2. The elevator controls:
Pitch (about the lateral axis)RollYaw3. The rudder controls:
Yaw (about the normal axis)PitchRoll4. A stall occurs when the aircraft exceeds its:
Critical angle of attackMaximum altitudeNever-exceed speed5. The critical Mach number is the flight Mach at which:
Airflow first reaches Mach 1 locally over the wingThe whole aircraft reaches Mach 1The engine surges6. Swept wings are used on jet transports to:
Raise the critical Mach number and delay the drag riseIncrease induced dragLower the critical Mach number7. Beyond the critical Mach number, drag:
Rises sharply (drag divergence) as shock waves formFalls to zero, because the shock wave carries the disturbance away from the aerofoilIs unchanged, since the drag coefficient depends only on the angle of attack and area8. 'Mach tuck' is a tendency to:
Pitch nose-down at high MachRoll uncontrollablyYaw left