Flight Controls
Primary and secondary controls, hydraulic power control units and fly-by-wire with envelope protection.
Flight controls, summary notes
- 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.
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.
Flight controls & tab types
Flight controls concept map
Flight Controls
Flight controls quiz
Flight Controls, quiz
1. In the plan view shown, the surface marked P is at the outboard trailing edge of the wing. It is the:
AileronFlapElevator2. The primary flight controls are the:
Ailerons, elevator and rudderFlaps, slats and spoilersTrim tabs only3. Flaps and slats are:
High-lift (secondary) devicesPrimary controlsTrim devices only4. Fly-by-wire replaces the mechanical linkage with:
Electrical signalling to the actuatorsHeavier cablesPneumatic tubes5. A key advantage of fly-by-wire is:
Flight-envelope protectionHeavier controlsNo need for actuators6. Powered controls need artificial feel because:
The pilot no longer feels the air loads directlyThe controls are too light to seeFeel improves fuel burn7. A spoiler can act as a roll control, a speedbrake and a:
Lift dumper on landingFuel valveTrim tab8. A trimmable horizontal stabiliser is used to:
Trim pitch over a wide rangeProvide roll controlDeploy the gear