Theory of Flight
Aeroplane aerodynamics and flight controls, high-speed flight, and rotary-wing (helicopter) aerodynamics.
Theory of flight, summary notes
- FIXED-WING: lift comes from a wing at an angle of attack (L = C_L·½ρV²·S); the primary controls act about three axes, ailerons roll, elevator pitches, rudder yaws, and the stall is an angle-of-attack event at any speed.
- HIGH-SPEED flight brings compressibility: the critical Mach number is where the local airflow first reaches Mach 1; beyond it shock waves form and drag rises sharply. Swept wings raise the critical Mach and delay the effect.
- ROTARY-WING: a helicopter rotor is a set of rotating wings. The COLLECTIVE changes the pitch of ALL blades together to vary total rotor thrust (climb/descend); the CYCLIC tilts the rotor disc to move the aircraft horizontally.
- The main rotor's torque reaction tends to spin the fuselage the opposite way; a TAIL ROTOR (or NOTAR/fenestron) provides anti-torque and yaw (directional) control.
- In forward flight the advancing blade sees more airflow than the retreating one, 'dissymmetry of lift', corrected by blade FLAPPING; retreating-blade stall ultimately limits a helicopter's forward speed.
- ⚠ Exam trap: on a helicopter the COLLECTIVE changes all blades' pitch together (total lift) while the CYCLIC tilts the disc for direction; the TAIL ROTOR counters main-rotor torque and gives yaw control.
- Lift
- L = C_L·½·ρ·V²·S
A helicopter pilot raises the collective lever. What happens to the rotor, and what secondary effect must be countered?
Raising the collective increases the pitch of all main-rotor blades simultaneously, increasing total rotor thrust so the helicopter climbs (with a matching power/RPM adjustment). The extra power increases the torque reaction trying to yaw the fuselage, so more anti-torque (tail-rotor) thrust, via the pedals, is needed to hold heading.
Lift, angle of attack & the stall
The four forces in flight
Theory of flight concept map
Theory of Flight
Theory of flight quiz
Theory of Flight, quiz
1. On a helicopter, the collective control changes:
The pitch of all rotor blades together (total lift)The pitch of one blade onlyThe tail-rotor speed only2. The cyclic control:
Tilts the rotor disc to move the helicopter horizontallyChanges engine RPMFeathers the tail rotor3. The tail rotor provides:
Anti-torque and yaw controlForward thrustMain lift4. 'Dissymmetry of lift' in forward flight is caused by:
The advancing blade seeing more airflow than the retreating bladeEngine vibration transmitted through the main transmission and into the rotor head in forward flightTail-rotor drag rising with forward speed and yawing the aircraft progressively out of balance5. A helicopter's maximum forward speed is ultimately limited by:
Retreating-blade stallTail-rotor failureFuel flow6. Fixed-wing ailerons control:
Roll (longitudinal axis)PitchYaw7. A stall occurs when the wing exceeds its:
Critical angle of attackMaximum altitudeNever-exceed speed8. The critical Mach number is where:
Airflow first reaches Mach 1 locally over the wingThe whole aircraft is supersonicThe engine surges