Flight Controls

Primary and secondary controls, hydraulic power control units and fly-by-wire with envelope protection.

Notes

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Main ideas

PRIMARY controls (ailerons, elevator, rudder) manoeuvre the aircraft about its three axes; SECONDARY controls — flaps and slats (high lift), spoilers (roll/speedbrake/lift-dump), and trim (tabs or a trimmable horizontal stabiliser) — augment or offload them.
Actuation ranges from MANUAL (cables, pushrods, torque tubes) on light aircraft, through HYDRAULICALLY POWERED units (power control units/actuators, essential once air loads are too high to move by hand), to FLY-BY-WIRE.
FLY-BY-WIRE replaces the mechanical run with electrical signalling: the pilot's inputs go to flight-control computers that command the actuators and provide FLIGHT-ENVELOPE PROTECTION (limiting AoA, g, bank and speed).
Powered systems need ARTIFICIAL FEEL (the pilot no longer feels the air loads directly), plus autopilot integration, and are duplicated/triplicated for redundancy.
Rigging, cable tension, control-surface travel and gust locks are core maintenance items.
⚠ Exam trap: SPOILERS do double duty — deployed differentially they assist roll, deployed together in flight they are speedbrakes and on landing they act as lift dumpers; fly-by-wire adds flight-envelope protection that a mechanical system cannot.

Solved examples

Give three distinct functions a wing spoiler panel can perform.
1) Roll control — raising the spoilers on one wing reduces that wing's lift to help roll (roll spoilers, assisting the ailerons). 2) Speedbrake — raising spoilers symmetrically in flight increases drag to slow down or descend. 3) Lift dumper/ground spoiler — deploying fully on touchdown kills the wing's lift, putting weight on the wheels for effective braking.

Mind map

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