11.9 Flight Controls Flashcards
What is the function of roll spoilers?
To extend on the wing with upward aileron deflection (down going wing) to give a more accurate turn on larger aircraft
How do ruddervator surfaces on V-tail aircraft provide pitch and yaw control?
- Both deflect up or down to control pitch
- One deflect up and one down to control yaw
What is the advantage and disadvantages of V-tail controls?
+Less weight as no vertical stab is required
- More surface area is required
- Cannot have full rudder and elevator extension at the same time
- Aircraft less stable
- Control surface adjustment more complicated due to combined inputs
How do elevons on delta wing aircraft control pitch and roll?
- Both surfaces move up or down simultaneously to control pitch
- One moves up and one down to control roll (aileron function)
What do secondary flight controls consist of?
- Lift Devices
- Drag Devices
- Trim systems
What 3 things can all flight control systems be divided into?
- Control Inputs
- Control transmissions
- Control surface outputs
What component is required to combine inputs from the rudder pedals and control column in a ruddervator (V-tail) system?
A mixer unit containing a gimbal
What does the flap lever control?
Flaps and slats
What are 2 the main components in a mechanical control run?
- Cables
- Rods
What 2 types of components do Hydraulic control systems use?
- Mechanical components
- Hydraulic components
What 3 types of components do electrical control transmissions use?
- Mechanical components
- Hydraulic components
- Electrical components
Through what 3 properties is a control cable identified?
- Diameter
- Number of strands
- Number of wires in each strand
Where are extra flexible control cables used?
In sections that require several changes of direction
What is the advantage and disadvantage of cables compared to rods?
+Less weight
-Cannot transmit push forces
What is the disadvantage of a mechanical control system with many connections?
There will be greater total play in the system from all the connectors so the transmission will be less accurate
What is an advantage of cables over rods when under excessive stress?
Cables will show evidence of failing before it fails completely (broken wires/strands etc) whereas a rod will fail suddenly
What can be used to remove old lubrication, grease and dirt from the surface of control cables?
A lint free cloth
What 3 things must cables be inspected for?
- Broken wires
- Worn areas
- Corrosion
What are the 3 main type of quadrants used to transmit push-pull rod forces to cables?
- Normal quadrants
- Single quadrants
- Tension regulators
What are single quadrants used for?
To transmit movement from a cable to several outputs simultaneously
What 3 things make up a tension regulator?
- 2 quadrant halves mounted on a common axle
- A spring loaded cross head mounted on a guide
- Pull rods
How does a cable tension regulator compensate for increased tension in a warm aircraft?
The quadrant halves rotate the pull rods, moves the cross head and compresses the springs
How does the cable tension regulator compensate for reduced cable tension in cold aircraft?
The springs press against the cross head and this force is transferred via the pull rods and the quadrant halves to the cables. The cable tension is restored to normal.
What are the six cable wear patterns that can be found on pulleys?
- Cable tension too high
- Cable misaligned
- Pulley misaligned
- Cable too small for pulley
- Blocked pulley
- Normal wear
What is used to maintain an airtight seal around cables that pass through a pressure bulkhead?
Pressure seals
What is the purpose of fairleads?
To guide and support the cable along its routing, allowing a maximum direction change of 3 degrees
What are the 3 key components of an adjustable rod?
- Inner and outer lock washers
- A lock nut
- An inspection hole to check for minimum screw penetration
What are the 3 main components of a chain installation?
- The chain
- The wheel
- The protection guards
What is the purpose of torque shafts?
To transmit torque for linear movements
What is the purpose of torque tubes?
To transmit torque for rotary movements
What must the couplings between torque tubes in a torque tube system be capable of and what do they allow?
- Compensating for axial movement and change of alignment
- Allow torque tube rotation during wing bending
What are the 4 types of gearbox that can be found in a torque tube system?
- Angle gearbox
- Offset gearbox
- Rotary actuators
- Differential gearing
What does an Angle gearbox (aka bevel gearbox) do?
Facilitates change in direction when power is transmitted from one torque tube to another
What does an Offset gearbox do?
Moves the drive path forward and back
What is a rotary actuator used for?
To transmit torque tube rotation to an output lever (changes a low torque, high speed input into a high torque, low speed output)
What does a differential gear box do?
Connects 1 output shaft with 2 independently operating motors
What are the 3 main components of a screw jack transmission?
- A transmission gearbox
- The screwjack
- The ball nut
What are ball screwjack transmissions used for?
High torque transmissions with minimal friction such as in flap or stabiliser operation
What 2 safety measures are incorporated into a ball screwjack transmission?
- Stops to restrict total ball screw travel
- A safety rod to secure the transmission if the screwjack breaks
What is a disadvantage of a screwjack transmission and how can it be counteracted?
- Strong aerodynamic loads can drive the screwjack backwards
- A No-Back brake can be used to prevent flaps being pushed back by airflow
What are the 3 main components of a No-back brake?
- A ratchet wheel
- Pawl
- A brake disc
What happens to the No-back brake during flap retraction?
The retraction force overrides the brake disc friction, allow the surface to move in the airflow direction
Excessive torque can damage the torque tube system and aircraft structure, what is used to prevent this?
A torque limiter
What are the 3 main components of a torque limiter?
- A friction brake
- A ball and ramp device with input and output members
- Springs which are preloaded to approx 120% of the maximum operating torque
An over-torque indicator is included in the torque limiter, what is its function?
It extends when an over torque has occurred and must be manually reset to ensure an over torque does not go unnoticed
Override devices prevent the entire flight control system jamming when 1 component is jammed, what are the 3 main types?
- Force detents
- Shear rivets
- Force limiting struts
Force detents limit rotation forces, what are their 3 main components?
- A cam
- A lever
- A spring loaded roller
How is the condition of a shear rivet check and where can information be found regarding rivet replacement?
- An inspection hole is present
- A placard located near the shear rivets displays information on replacement rivets
Force limiting struts limit linear forces, what are they made up of?
An internal pre-loaded spring installed between 2 washers that are held in position by 4 stops on the inner rod and 4 stops on the outer rod
What forces compress the spring in the force limiting strut?
Push and Pull
What does a feel unit do and why is it used on hydraulic transmission aircraft?
- It simulates an airload on the flying controls that is less than the actual airload so the pilot can still easily control the aircraft
- Because the pilot cannot feel the airload directly with a hydraulic transmission
What does the feel unit do to a deflected surface?
Centres it, bringing it back to a neutral position
What does the servo Control unit do?
Moves the control surface in a direction and distance proportional to the input signal
How many independent servo Control units power each individual flight-control surface?
2
What 2 sections is a servo Control unit divided into?
- Power section
- Distribution section
Was does the power section of a servo Control unit do?
Converts hydraulic pressure into mechanical force
What are the 3 main components of the power section of a servo Control unit?
- Cylinder
- Piston
- Piston rod
What are the 2 main components of the distribution section of the servo Control unit?
- Control Valve
- Bypass Valve
What are the 2 main operating modes of the servo Control unit?
- Damping mode
- Control/Active mode
What Valve allows hydraulic fluid to flow between the cylinders in a servo Control unit in dampening mode?
Bypass Valve
What is meant by ‘damping speed’ in dampening mode and what does it depend on?
- The speed of piston movement
- Depends on the flow rate between the cylinder chambers
What does the dampening orifice do?
Limits the flow rate between the cylinder chambers, ensuring a low damping speed
Why must damping speed be low?
To prevent damage to components due to unexpected control surface movement (eg. gusts of wind)
What happens to the bypass valve as soon as the servo Control unit is pressurised?
It moves to the left position against the spring
When the mechanical input lever for the servo Control unit is set to neutral, how much pressure is being supplied to the cylinder chambers?
None
When the mechanical input lever for the servo Control unit is moved to the right, which way is the control valve displaced?
To the left
In the servo Control unit, which cylinder chamber is the pressure line connected to and which is the return line connected to?
- Pressure = right
- Return = left
What is the only way to stop the piston rod in an intermediate position in a servo Control unit?
Manually moving the mechanical lever to the neutral position
What does the servo valve do in a servo Control unit?
Transfers an electrical signal into a proportional hydraulic signal
Why does the use of an Electro Hydraulic Actuator (EHA) reduce weight on an aircraft?
It moves fly control systems using its own hydraulic power, generated internally by an electro motor so no external hydraulic pipes are required
What signal is required to stop the piston rod in a pre-selected Intermediate position in a servo loop?
An actual position signal
What lever provides the actual position signal in a servo loop?
The summing lever
What 3 things is the summing lever connected to in a servo loop?
- Control Input rod
- Valve input lever (via a connecting rod)
- Piston rod
What are two types of feel unit design?
- Spring design
- Cam design
What 2 springs are found in the spring design feel unit?
- Double acting feel spring
- Centring spring
When used to change the neutral position of a control surface, what does the trim system do the control column to aid the pilot?
Holds the control column in a position proportional to the control surface position without pilot input to remind them of current trim
How is the screwjack in a trim system operated?
By an electric motor
What are the 4 components of a Cam design feel unit?
- A cam (mounted on the same shaft as the input quadrant)
- A cam follower (includes a roller)
- A pivot point on the support assembly
- Feel and centring spring (between the cam follower and mechanism support assembly)
What do the ball bearings in surface hinges do?
Compensate for misalignment
What load is each failsafe bolt in a surface hinge capable of holding?
The full load of the surface if the other failsafe bolt is damaged or broken
What is used in a primary hinge to hold the right hand fork in position?
A spacer
What do the two sleeves in a normal hinge allow it to cope with?
Surface expansion and contraction due to temperature change
Are the two sleeves in a normal hinge different, or the same as eachother?
Different
What 2 things result in surface flutter?
- The down-going tendency of a surface with a centre of gravity aft of the hinge line
- The Up-going effects of the air loads
What is used to prevent surface flutter in mechanically operated control surfaces?
Static balancing
How is static balance achieved in mechanically operated control surfaces?
By fitting weights forward of the hinge line of a control surface to offset the mass of the surface behind the hinge line. The surface is considered balanced when the centre of gravity coincides with the hinge line.
How must the static balance be adjusted when a repair has been made to the control surface?
- Remove surface from aircraft and set in a horizontal position
- Support it on its bearing with a special frame
- Support it at the trailing edge with a weighing scale
- Add adjustable balance weights to the surface until the scale reads zero
What are rigging pins used for?
To check the positions of components in a flight control transmission by ensuring the rig pin holes line up
How long must the aircraft temperature be stable before the cable system is checked before rigging?
1 hour
What 3 things must be done before rigging a hydraulically operated control surface with an electrical input?
- The Hydraulic system must be pressurised
- The electric flight control computer must be switched on
- The Control input must be set in the zero position
What is the deflection angle of a control surface measured in relation to?
The zero position (Where the wing reference plane is aligned with the surface reference plane)
What type of plate do surfaces like elevators and the rudder require to establish the zero position?
Index plate
What is used to measure the deflection angle of an elevator once the zero position has been established?
An Inclinometer
What 5 supplies is flight control hydraulic distribution divided into?
- Tail supply
- Wing supply
- Flap supply
- Stabiliser supply
- Elevator feel supply
Where are the shut-off valves for the tail and wing hydraulic supplies operated from?
Flight control hydraulic power panel in flight deck
What type of switches are the flight control hydraulic shut-off switches?
Guarded toggle switches
How are the shut-off valves for the stabiliser hydraulic supply operated?
The stabiliser cut-out switches on the pedestal
How many of the 3 hydraulic systems on an aircraft is a rudder controlled by?
All 3
Leak measurement valves supply hydraulic power to which category of flight controls?
Primary
What 2 sets of flight controls do priority valves supply hydraulic power to?
- Flaps
- Leading edge devices
If a pressure decrease is detected, what does the priority valve do?
Closes, shutting off supply to the flaps and leading edge devices to ensure the primary flight controls have access to a suitable pressure
What is the purpose of leak measurement valves and what position are they in during flight?
- Performing the leak measurement check when the aircraft is on the ground
- Always open in flight
How are leak measurement valves controlled?
By push button switches on the maintenance panel on the overhead panel
If an aircraft is on the ground, with engines at full take off power, what 3 circumstances will cause a flight control take off warning to activate?
- Any one of the flaps/leading edges are outside the limits for take off
- The stabiliser trim are outside the take off range
- The speed brakes are outside the take off range.
What does a take off warning test switch allow maintenance crews to do?
Test the flight control take off warnings without turning on the engines by simulating full engine take off power
What are the two aileron trim switches?
- Arming switch
- Control switch
What does a load limiter do? (In relation to Control wheels)
Allows the control wheels to disconnect from each other if one gets jammed
What connects the left and right aileron programmers?
A load limiting bus rod
How many degrees of movement is permitted either way before input is transmitted to the control wheels?
6 degrees
What do the aileron programmers control?
The relationship between the movement of the control wheels and deflection of the ailerons
Where is the output of the aileron programmer transmitted to?
The inboard and outboard aileron quadrant (via wing cables)
What type of unit moves the inboard and outboard aileron?
Servo Control unit
What is the difference in use between inboard and outboard ailerons?
- Inboard are used to control the aircraft at all speeds
- Outboard are used to control the aircraft during low speed flight with the flaps extended
What is the purpose of the aileron lockout mechanism?
To lock the outboard aileron in the neutral position during high speed flight and connects it to the aileron control system during low speed flight
What are the 3 main functions of the rudder during cruise flight?
- Trim the aircraft
- Turn co-ordination with ailerons and roll spoilers
- Dutch roll dampening
