Powered Flying Controls Flashcards
Powered flight controls are operated by
Hydraulic actuators or powered flying controlled units
Each actuator is operated by a servo controlled valve
Have 2 or 3 actuators per fling control
Disconnect levers
Protects against jamming of controls
Reduces roll rate
Each pilot in control of their side
Shear rivets
Protect against control jamming - shear at a designated load - allows the remaining aileron to be used
Rudder centring may be lost when this is used
Power assisted control operation
Stick is connected to the valve and the hydraulic jack
When moved - hydraulic lock is unlocked in the power control unit/ hydraulic servo unit - moves the
High loads will get feedback - reversible - not artificial feel req
Fully powered control operation
Stick only operates the servo valve actuator or if fly by wire - cables and levers
Irreversible- needs artificial feel
Control is lost if hydraulic pressure is locked
Artificial feel systems are fitted
In parallel and duplicated
Senses dynamic pressure and control deflection - reduces the chances of over stressing the a/c
Artificial feel Q feel operation
Q pot - senses dynamic pressure by having a feed from pitot and static pressure
Diaphragm moves up and down depending on airspeed - as it moves upwards (more IAS) - allows more hydraulic pressure to go into the piston = harder to move the control column
The a/c may need to be trimmed in flight as a result of
Changes of speed and power
Varying CG posn
Trimming reduced the control loads to zero - either a control wheel or a selection of switches
Methods of trimming
The trim tab - moves in the opposite direction of the control surface
Variable incidence tailplane
CG adjustment - moving fuel around
Adjustment of the artificial feel unit - feel trim unit - combination of artificial and trim unit
Disadv of a trim tab
Reduces control authority in the direction of the trimming
Also increases drag
Fixed tabs
Not adjustable in flight
A/c has a permanent out of trim posn
Adjusted on the ground
Horizontal stabiliser trim is operated by
Older a/c - hydraulically
New a/c = electric
Both move a screw jack
If the variable incidence tailplane is not in the t/o posn for t/o
Intermittent horn will sound in the f/d
Variable incidence tailplane can be operated by
Trim wheel
Or
Switches that operate in pairs - one controls the power and another does the direction - prevents trim r/y - must be moved together
Adv of variable incidence tailplane
Drag is less
Trimming does not reduce the control authority
Mach trim purpose and operation
C or p moves rearwards at high airspeed - large nose down pitch moment - this prevents it
System will kick in at a datum speed - will move trim/fuel to prevent tuck under
2 systems and diff in operation to prevent excessive rudder deflection at high airspeeds
Rudder ratio changer - Boeing - rudder pedals move through their full range - rudder deflection reduces with increasing IAS - not proportional
Variable stop systems - airbus - movement of the rudder is proportional to rudder travel - range of movement is reduced for both of them - starts to reduce at around 165kts
Fly by wire
Mechanical input converted into an electrical output
Adv of fly by wire
Relax the natural stability of the a/c - reduce the size of the tailplane - do not need to de ice as much - increases fuel efficiency - reduces weight
Reduces flight crew workloads
Flight envelope protection takes into account
Pitch attitude protection
Load factor protection
Bank angle protection
AoA protection
Control locks
A/c with reversible commands - when parked wind can damage the control surfaces - control locks manage this
