Primary Controls Flashcards
Advantages of fly by wire
Lighter than conventional control systems
Reduces pilot workload
Offers advanced envelope protection
Even out control inputs in turbulence
Fly By Wire
Controls inputs from pilots controls and translated to digital signals fed to series of computer that compare and make decision
Safety Measures in FBW
Multiple Computers
Difference hardware
Different software
Different sensors
Airbus FBW
X 3 Primary x2 secondary
Normal law - AOA protection etc
Alternate Law - x2 failures basic control law
Direct Law - Complete computer failure direct with controls
Mechanical Law - Control pitch/trim/rudder
Boeing FBW
X 3 primary computers
Normal - full function
Secondary - loss of flight envelope protection
Direct - direct from pilots controls
Rudder ratio changer
Protect fin from excessive rudder loads from pilot
Limited at higher speeds
Trim Runaway Protection
Double pole trim both need to be pressed together to operate trim jack motor
Q Feel System
Receives dynamic pressure info from pitot static system and used to control hydraulic load jack inside Q feel unit
Spring Feel System on fully powered flight controls
Connected to the control column
When deflected one way opposite spring stretches with opposing force
Electro-Hydraulic systems
Electro-Hydraulic Actuator (EHA) - Hydraulic pump driven by high power stepper motor. Pump electrically signalled to control operation. NO HYDRAULIC LINES
Electro-Mechanical Actuator (EMA) - entirely driven by electric motors - restricted to secondary flight controls
EBHA - Basically EHA with a back up EHA
Manual Control
Used on light ac
Stainless steel cables run from each control via pulley wheels
Turnbuckles for tension
Reversible system
Non reversible system
Movement of control surface cannot move control column
Primary Controls
Elevator
Ailerons
Rudder
Roll Spoilers
Partially Powered Controls
Hydraulic actuator attached in parallel to direct link between pilots control and control surface.
Actuator controlled by hydraulic servo linked to control system.
Reversible connection
Fully Powered Controls
Removes direct link between control and control surface - relies on hydraulic actuator
PFCU - Power flying control unit
Reasons for trim
Changes in CG, Changes in speed and Changes of power
Blow Back System
Blow back valve relieve excessive loads before load causes damage to controls
Rudder applied force changes with speed
Advantages of a variable incidence tailplane
Large horizontal stabiliser through very small angle to reduce drag
Elevator retains its full range of motion
Less drag in trimmed state
Trimming does not reduce range of pitch control
Fairing Role
Cover aileron actuator
Disadvantages of FBW
Sensor failure causing wrongly triggered interference of valid pilot inputs
Disadvantage of side stick controls
Make it difficult for one pilot to see and understand what other is doing. Inputs are averaged
Gust LOCK
Device that limits the movement of control surface when parked
Reasons for being trimmed in pitch
Varying CG position
Changes of speed
Changes of power
Primary stop controls
Set the range of movement of the control surface
Flutter is and preventions
Flutter of control surface is divergent oscillatory motion of control surfaces caused by natural frequency interaction of forces and stiffness of structure.
Flutter occurs when external forces is applied to the ac with periodic frequency that is equal to the natural structural frequency of that ac
Flutter can be avoided by remaining in flight envelope and speed limitation in turbulent conditions
Zero force position changes on
Ailerons trim
Rudder trim
Zero position force does not change on
PET:
Pitch controls
Elevator
Trim
3 ways to limit rudder deflection
Rudder ratio changer - limits deflection at high speeds
Variable stops - rudder peals and rudder physically reduced
Block back - applies constant movement force to rudder dictated by pedal deflection deflecting rudder depending on speed of the airflow
THS is usually controlled by
Hydraulically actuated jack
Fairings cover
Aileron actuators and flap tracks
How is redundancy achieved on fully powered primary flight controls
Duplex parallel control runs per control axis linked to control surfaces actuator which supply hydraulic systems
If failure of wiring on fly by wire ac what happens
Use a different actuator with a different computer
Rudder trim does what
Moves the rudder and the rudder pedals in the corresponding direction
Aileron trim system does what
Control wheel turns in the direction of trim
Elevator trim does what
Control column does not move - zero force position does not change
Direct Law
Pilot controls are not augmented by internal computers
Exact control sent direct to hydraulic servo valves
Autopilot lost
Aural and visual warning will remain for over speed/stall
Trimming of aileron and rudder in an irreversible control system
Achieved by adjusting the zero force point of the feel system
Route of operation of fly by wire
Pilot operates control —— primary flight computer convert to electrical output —— actuator control electronics covert electrical signal to analogue signals —- sent to power control unit —— hydraulic actuator moves flight control surface
