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 stabiliser), augment or offload them.
- Actuation ranges from MANUAL (cables, pushrods) on light aircraft, through HYDRAULICALLY POWERED units once air loads are too high to move by hand, to FLY-BY-WIRE.
- FLY-BY-WIRE replaces the mechanical run with electrical signalling: pilot 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 and are duplicated/triplicated for redundancy; the autopilot interfaces through the same actuators.
- For the B2 technician the signalling, computers, sensors (position/force) and actuator control are the focus.
- ⚠ Exam trap: SPOILERS do triple duty, differential for roll, symmetric in flight as speedbrakes, and fully deployed on landing as lift dumpers; fly-by-wire adds flight-envelope protection a mechanical system cannot.
What does 'flight-envelope protection' mean in a fly-by-wire aircraft?
The flight-control computers monitor parameters such as angle of attack, load factor, bank angle and speed, and limit the commands sent to the actuators so the aircraft cannot be flown beyond safe boundaries, for example it will not let the wing exceed the stalling angle of attack or the structure exceed its g limit, regardless of how hard the pilot pulls. This protection is only possible because the electrical signalling sits between the pilot and the controls.
Flight controls concept map
Flight Controls
Flight controls quiz
Flight Controls, quiz
1. The primary flight controls are:
Ailerons, elevator and rudderFlaps, slats and spoilersTrim tabs only2. Flaps and slats are:
High-lift (secondary) devicesPrimary controlsTrim only3. Fly-by-wire replaces the mechanical linkage with:
Electrical signalling to actuatorsHeavier cablesPneumatic tubes4. A key advantage of fly-by-wire is:
Flight-envelope protectionHeavier controlsNo actuators5. Powered controls need artificial feel because:
The pilot no longer feels air loads directlyFeel saves fuelFeel is decorative6. A spoiler can act as a roll control, a speedbrake and a:
Lift dumper on landingFuel valveTrim tab7. A trimmable horizontal stabiliser:
Trims pitch over a wide rangeProvides roll controlDeploys the gear8. Hydraulic power control units are needed when:
Air loads are too high to move surfaces by handThe aircraft is very lightThere is no autopilot