11.9 Flight Controls Flashcards
How would you know how flexible a cable is
The more wires in a strand the more flexible a wire is
A cable is identified by what 3 characteristics
- The diameter
- The number of strands
- The number of wires in each strand
What types of cables are used when several changes of direction occur
Extra flexible cables
What is an obvious advantage of a cable flight control system over rods and levers
Cables weigh much less
What is an obvious disadvantage of using cable flight control systems over rods and levers
Cables cannot transmit push forces
What provides a more reliable control transmission cables or rods
Cables
As long as cables are inspected regularly they provide a safer transmission method
Rods will break suddenly with out warning
What must be done to cables on a regular basis
They must be cleaned, inspected and lubricated on a regular basis
What can be used to remove old grease, dirt or lubrication from control cables
A lint free cloth
Why can’t solvents be used to clean control cables
They remove grease and lubrication from inside the cable
How would you detect a broken wire on the outside of a cable
Running a lint free cloth along the outside of the cable
How would internal wires in a cable be detected
By bending the cable
What is used to protect cables from corrosion
They are lightly lubricated
As a cable is only capable of pulling forces, what would be used in the transmission run to close a component after being opened
A spring
What do duel cable transmissions use to transmit push and pull rod movements to cables
Quadrents
What are the 3 main types of quadrant used
- Normal quadrents
- Single quadrents
- Tension quadrents
What ensures that tension in a cable system is kept at a constant even at different temperatures
A cable tension regulator
What does a cable tension regulator consist of
- Two quadrent halves mounted on a common axle
- A spring loaded cross head mounted on a guide
- Pull rods
What are cable pulleys used for
To change direction in the control run
What is used to prevent cables from jumping off pulleys
Safety pins and guides
What are used around a cable when it’s being passed through a pressure bulkhead to create an air tight seal
Pressure seals
What are fairleads used for
To guide and support a cable along its routing
Fairleads allow a maximum cable direction change of how many degrees
3 degrees
What is a turnbuckle used for
To connect two externally threaded barrel ends
What do adjustable rods consist of
- Inner and outer lock washer
- A lock nut
- An inspection hole to check for minimum screw penetration
What are chains used for in a control run
To transmit forces to and from a cable system
What are the main components of a chain installation
- The chain
- The wheel
- The protection guards
What are torque shafts used for
To transmit torque for linear movements
What are torque tubes used for
To transmit torque for rotary movements
What are the 4 types or gearbox and gearing that torque tubes use
- Angle gearboxes
- Offset gearboxes
- Rotary actuators
- Differential gearing
What is a rotary actuator used for
To transmit torque tube rotation to an output lever
What is a differential gear
A differential gear connects one output shaft with two independently operating motors
What are screwjack transmissions used for
To convert rotary inputs to linear movements
What are the main components of a screw jack transmission
- The transmission gearbox
- The screwjack
- The ball nut
What is used to achieve high torque transmission with less friction
A ball screw jack
What is the no- back break used for
The no- back break is incorporated in the gearbox to hold the ball screw jack in its last position
What are the main components of a no back break
- A ratchet wheel
- Pawl
- A break disk
How is excessive torque prevented
A torque limiter
What are the main components of a torque limiter
- A friction break
- A ball ramp device with input and output members
- Springs which are preloaded to approx 120% of maximum operating torque
What are override devices sometimes known as
Load limiters
What are override devices used for
Used to prevent a complete jamming of a flight control system when one component is jammed
What are the 3 main override devices
- Force detents
- Shear rivets
- Force limiting struts
What are the main components of a force detent
- A cam
- A lever
- A spring loaded roller
What is the simplest form of load limiter
Shear rivets
How would you inspect a shear rivet
An inspection hole
What is a feel unit
In a hydraulic transmission the pilot cannot feel the force on the air directly so the feel unit is installed
Typically how many servo control units power each flight control
2 independently controlled units
What is used to restrict flight controls from flapping around in the wind whilst on the ground with no power
A dampening mode and restricted orifice
What is the advantage of a EHA (Electro Hydraulic Actuator)
The power for the EHA does not come from an external system but from an electric motor inside the unit, this saves weight as there is no need for heavy plumbing and fluid
What ATA chapter is flight controls
ATA 27
What does a hydraulic system require to provide the pilot with an artificial feel of the air load and to bring a deflected surface back to a neutral position
A feel unit
What are the two different feel unit designs
- A spring design
- A cam design
Why would a feel unit be required
With out a feel unit the pilot would be able to achieve full deflection of a control surface and could overstress the aircraft
What does the trim unit consist of
A electronic motor operated screw jack
When rigging an aircraft flight control, what is used to help determine the control surface is in the correct position
Rigging pins
As cable tension varies with temperature, how long must the aircraft temperature be stable for before the cable system is checked
(When rigging)
At least 1 hour
In transmission systems with out a tension regulator what must be used to measure the tension
A tensiometer
How are control cables adjusted
By adjusting the turnbuckles
Where would the correct tension for control cables be found
AMM
When adjusting turnbuckles how many threads is the limit from being exposed outside the terminal
3
When rigging a hydraulic operated surface what must be done first
The system must be pressurised
What is the minimum amount of control surfaces that is required to test flight control around all 3 aircraft axis
Minimum of 2 systems
How is hydraulic power supplied to the control surfaces
Through shut off valves
What is used to give priority to flight controls when there are many users
Priority valves
When would you see a stabiliser config warning
Usually before take off. Due to the stabiliser not being in the correct position for flight
When can you do a take off warning test and why would you do one
With the aircraft on the ground without the engines running.
The test simulates engines at full power
There are two aileron control wheels in the cockpit, of for f/o and one for captain, what are they connected by
Cables known as bus cables and a load limiter
What are the two aileron trim switches
One for arm and one for the controlling movement
What system is aileron position shown
EICAS (Engine Indication and Crew Alerting System)
What is the purpose of a load limiter
Allows control wheels to be disconnected if one gets jammed
What does CLCP stand for
Central Lateral Control Package
What is the purpose of CLCPs
The convert electrical inputs from the autopilot to hydraulically powered outputs to the aileron programmers
What is a lost motion device used for
To prevent undesired feedback from the right body cable to the control wheels
Up to 6 degrees either way is permitted
What do the aileron programmers do
Control the relationship between the control wheels and deflection of the ailerons
What problems does differential ailerons prevent
Avoids negative turning movement
What is the basic function of the rudder
To control the aircraft around the vertical axis and control yaw movement
On large aircraft what are the 3 main functions of the rudder
- Trim the aircraft
- For turning along with ailerons and spoilers
- For Dutch roll damping
How is the rudder operated
With the rudder pedals, pilots and co pilots are interconnected
What do the rudder pedals operate on the ground
Nose wheel steering and the brakes
What controls rudder trim
It is controlled electronically via the rudder trim computer
Where is the rudder position shown
One the EICAS (Engine Indication and Crew Alerting System)
What is different about the elevator feel system compared to other aircraft feel systems
The elevator system is a bit more complicated and required information on airspeed and aircraft loading from the FMC to prevent any dangerous manoeuvres
Where is the elevator feel unit found
In the tail section of the aircraft
The elevator feel unit needs to send signals to the control column depending on the speed and loading what is used to modulate this
It is supplied with a feel pressure by the elevator feel computer which depends on aircraft speed and loading
What does the electronic feel computer do when it detects a change in dynamic air pressure on the control surface
It controls hydraulic pressure inputs to the feel actuator
What are the main components of a Electrical Flight Control System (EFCS) also known as fly by wire
- Electrical Flight Control computes
- Sensors and wires for the input and output signals
What are the components in a conventional flight control system
- The cockpit controls
- The transmission system with cables and quadrents
- The hydraulic actuator and the flight control surface
What is the purpose of a fly by wire system
Saves weight and makes maintenance easier
What additional information along with the control I put would the electronic flight computers need to calculate the output order and ensure a smooth, economic and safe operation
- Aircraft roll and pitch attitude
- Airspeed
- Accelerations
- Angle of attack
- Flight/Ground status
What happens to the electronic flight control system when the aircraft is in autopilot rather than manual
The autopilot provides the inputs to the computers rather than the side stick
What turns electrical signals from electronically controlled flight computers to a mechanical motion
Hydraulically operated servo controlled actuators
Two independent servo controlled actuators are used for each rudder and aileron, what is the second used for
As a redundancy and provides a damping function
What is the white cross on the primary flight display for on Airbus
Allows the pilot to test the side sticks during pre flight check
The EFCS computers for fill safety requirements in what 3 ways
- A minimum of 2 different types of computers are used. Each have completely different software and hardware
- Calculations are done independently on 2 different channels
- There is only an output signal if both channels have the same result
What happens if there is a complete failure of the EFCS
There will be a mechanical backup to land the aircraft safely
How many of the EFCS computers are connected to a backup source of power
Minimum of 3
What changes in the EFCS when the aircraft is on the ground compared to being in the air
On the ground the computer uses direct law and in the air it uses normal law
How can the aircraft be operated with the flight computers in normal mode rather than in the ground in direct mode
Normal mode in the air the aircraft can be controlled on all 3 axis and and is in flight mode whereas on the ground only the ailerons, spoilers and elevators can be operated
What are the three groups of protection circuits are there which prevent wrong flight control orders being imputed and causing a dangerous situation
- Attitude limits
- Airspeed limits
- G load limits
How much g load is a typical aircraft structure designed to resist
+2.5g and -1g
Does the amount of g load that the aircraft airframe is able to resist change when the flaps are extended.
Yes to +2 and 0g
How would you be able to tell if a protection circuit is active
A double green line is shown on the primary flight display
What is alpha protection
At low speeds alpha protection prevents the angle of attack becoming too great for the speed of the aircraft and creating a stall even in the yolk is moved backwards
What special functions do the electronic flight control computers have apart from their normal operational functions and protections
- Auto ground spoiler control
- Yaw damping
- Rudder Tavel limitation
- Load alleviation
What does the load alleviation function do
Stops the wings from being bent beyond operational limits. Increases life of the aircraft
What large surface is used for pitch trim
The horizontal stabiliser
Why would the whole horizontal stabiliser need to move instead of just the elevators
As there is a greater imbalance on the longitudinal axis and it is more economical to use the horizontal stabiliser
How is the horizontal stabiliser controlled from the cockpit
There is one set on each control wheel, and the set comes as a arm and control switch. Once the arm switch has been activated then the control valve will open and allow the hydraulic pressure to move the control one the second switch is then pressed.
Both need to be pressed for a movement to occur
What are the main components of a trimmable horizontal stabiliser drive mechanism
- A screw jack with a ball nut
- A differential gear
- Two hydraulic motors
- A primary and a secondary brake
What prevents the stabiliser from moving up and down due to aerodynamic loads
An irreversible pawl controlled ratchet
What are the purpose of the stabiliser trim control modules
There are two completely identical independent modules.
They send hydraulic pressure to the drive mechanism.
What prevents the stabiliser from going out of range of safe flight
Limit switches and mechanical stops
What are the stabiliser pitch trims wheels connected to help carry out their command
They are connected to gears and chains which as then connected to cables below the pedestal.
The input from the wheels is transmitted via the cables to the aft chain and from the aft chain to the input shaft on the actuator
How does the ball nut of the screw jack transmit the motion of the drive mechanism to the attachment fittings which will deflect the surface
Via a gimble
How is the stabiliser position shown on the displays in the cockpit
- Electronic Centralised Aircraft Monitor (ECAM) system display
- On a scale with a pointer adjacent to the pitch trim wheels
- On a moving scale on the pedestal
- On the aircraft body adjacent the stabiliser leading edge
What is tuck under
The centre of lift moves forward as the MACH no increases.
The result is a pitch down effect which would increase the Mach number. As this is an unstable condition it must be avoided
What is the purpose of the Mach trim sub system
Counteracts or prevents the tuck under effect by moving the stabiliser leading edge down when the Mach number increases
What computer supplies the Mach number and what would then calculate the necessary trim command to prevent tuck under
The air data computer would supply the Mach number and then the trim computer calculates the required deflection depending on the aerodynamic characteristics of the aircraft
What are considered as high lift devices
Flaps and slats
How do flaps contribute to being high lift devices
They change the camber of the wing and some also increase the surface area
What high lift flaps are normally found on Airbus aircraft
Fowler flaps
What high lift flaps are mostly used on Boeing aircraft
Triple slotted flaps
What are the 4 different types of leading edge high lift devices
- Leading edge flaps (Kruger flaps)
- Variable camber flaps
- Slats
- Droop nose
What are Krueger flaps also known as
Leading edge flaps
They are the upper side of the wing when retracted
What does the variable camber flap consist of
- A fibre glass panel
- A folding nose
- Many rods and levers
Operated via a drive arm of a rotary actuator
When the slats are extended it creates a slot, what does this do to the air
It allows air from the high pressure area under the wing to come up and flow over the wing
How does a droop nose work
A rotary actuator moves the complete leading edge of the wing so increase the camber
Why does the flap lever have gates at detents 1 and 20
T prevent the handle being moved past these detents with out stopping
What happens to the slats and flaps in the landing position
They are both fully extended and full extension
What are the effects of slots in the flaps
High pressure air from underneath the wing is able to travel through the slot to the top of the wing re energising airflow and delaying flow separation
How does the drive system operate the flaps
Via torque tubes, rotary actuators and tracks
If one electronic flap slat computer fails can it also take on the work of another
Yes but only at 50% of the speed
If all 3 flap slat computers fail and there is no hydraulic supply how can they still be extended and retracted
Via an electric motor
What two variations of independent power systems do the flaps and leading edge devices have
- Two independent hydraulic systems
- One hydraulic and one electric
- One Pneumatic and one electric
What is a PCU
Power control unit
For flaps and slats
If there is a single failure in the flap slat system will it continue to operate
Yes but with only 50% of normal speed
What angle of attack gives maximum lift
14 degrees
What is alpha lock
A system to prevent the flaps being retracted to prevent stall
If the angle of attack is 10 degrees with flaps deployed, the angle would go higher if they are retracted hence why with alpha lock engaged they cannot retract and thus cannot stall
What is the load relief system/ overload protection
Flaps retract automatically from the full position to the take off position if the airspeed is too high. This prevents damage to the flaps
What is important regarding flaps and slats before turning hydraulic power on
The handle must be in the same position os the flaps the selfs
Why should flaps not be operated too much during maintenance
To prevent the electric motors overheating
What are the 3 main functions of the spoilers
- Used as speed brakes during flight
- As roll spoilers to assist ailerons
- As ground spoilers after touch down
Why do the spoilers never go to full deflection during flight
To prevent disturbing the airflow to the horizontal stabiliser
What are the spoilers powered by
Actuators which as electrically controlled by flight control computers
What are the speed brakes 3 positions
- Down
- In flight
- Up
How can the speed brakes be operated from the cockpit
Manually via the speed brake leaver or automatically via the auto spoiler actuator
What is necessary to have on the speed brake lever to prevent dangerous situations during flight
He lever is limited by a energised lock lever solenoid and the extended stop
What must be done to the speed brake lever on the ground during maintenance
A locking device must be installed to prevent unintended injury
What are the three operating modes of servo control actuators for the spoilers
- Active mode - Used to extend or retract the spoilers with hydraulic pressure
- Blow down mode - Used in the event of pressure loss
- The locked mode - Used to prevent spoiler extension with out pressure
