13.7 Flight Controls Flashcards
In a manually operated control system how are the requirements of CS 25 met following a control jam or severance?
- Duplicating aileron and elevator control runs
- Providing a disconnect unit so that the pilot’s and co–pilot’s controls can be disconnected from each other
- Pilot controls left aileron and left elevator, co–pilot controls right aileron and right elevator
- Control runs are separated by running along opposite sides of the fuselage
What is the maximum deflection of a cable through a fairlead?
3°
What must be ensured about the fitment of a cable guard?
Does not interfere with the rotation of the pulley
To achieve differential aileron movement a quadrant may be used. What other method may be employed?
Bellcrank levers
How are the primary flying controls in a manually operated system protected from damage due to wind gusts?
Gust locks or gust dampers
Where would you find the primary control stops and the secondary control stops?
In cable systems
Primary (first to make contact) – adjacent to the control surface
Secondary (will have a specified clearance when the primary stops are in contact) – control cabin end of the control run
Opposite is true of push pull systems
What are the advantages of flying control systems using a push pull tube operation?
- Only a single control run is required since push pull tubes transmit motion in both directions
- The control system does not apply loads to the structure, as with cable systems
- Tubes and aircraft structure are usually made of the same material and thus expand and contract by the same amount
- Less prone to damage and wear
- Overcomes stretching and reduces friction
What is the purpose of a bellcrank lever?
Transmit force and permit a change in direction of the force
What does the torque tube do?
Linear motion of a push pull tube is changed to rotary motion
What does a stall protection system continuously monitor?
Aircraft angle of attack and the position of the slats and flaps
At what speed is the stall warning system designed to operate at?
5% above the stalling speed for the particular flap/slat configuration
What would happen if the pilot took no action following a stall warning?
A stick pusher or nudger automatically recovers the aircraft from the stall
If an aircraft has duplicated stall warning and recovery systems, how many would have to operate in order for warning and recovery?
If either system detects a stall condition, it will vibrate the column
What does the electrically operated stick pusher do when the aircraft reaches a specified angle of attack and speed combination?
Actuator moves the control columns forward
What are the differences between power assisted and power operated controls?
Power assisted – Force exerted by the pilot is supplemented by hydraulic power, pilots gets feedback from control surfaces, controls are reversible and conventional trim tabs are used
Power operated (or fully powered) – Moved entirely by hydraulic power, pilot provides only the small force necessary to operate a servo valve, controls are irreversible and artificial feel is required for the pilot
What are the five requirements of a powered flying control system?
- Sensitivity
- Stability
- Irreversibility
- Feel
- Back–up
What is minimum valve overlap?
Minimum valve overlap gives sensitivity
This means that the ‘lands’ of the moving valve only just close off the pressure and return ports
Any movement of the valve, no matter how small, will allow fluid to flow to the actuator and cause it to move
What three factors ensure stability in a powered flight control system?
- Elimination of backlash or lost motion in the control system
- Keeping the hydraulic system free from air
- Fitting spring or hydraulic dampers in the control system
What would be the effect of the pilot having no feel or proportional feedback from the control surface?
The pilot wouldn’t be able to gauge the degree of deflection of the control surfaces
What are the two methods of achieving redundancy within a powered flying control system?
- Manual reversion
- Duplication of the power units or the power supply
How does a ram mounted power assisted control achieve negative feedback and ‘nulling’ of the actuator?
The pilot makes a selection with the control column, which remains in this position
The actuator body moves and the selector valve body moves with it until the drillings are covered
This stops the supply of fluid to the actuator, stopping the movement of the control surface and ‘nulling’ the input signal
What is the purpose of the interconnecting valve?
When there is no hydraulic pressure, the interconnecting valve opens under spring pressure
Allows hydraulic fluid to move from one side of the ram to the other
Allows control movement with powered controls selected OFF, or with a hydraulic failure
How does a body mounted power assisted control achieve negative feedback and ‘nulling’ of the actuator?
Pilot moves the control, the servo valve moves, which allows fluid to pass to an end of the actuator
The ram moves, which moves the control surface, and the summing lever returns the servo valve to the neutral or nulled position
What are the three functions of the servo valve?
- Direction of movement
- Rate of movement
- Magnitude of movement
What are the two types of PCU stuck valve detection system?
- Stuck valve detector struts
- Jam indicator
What effect would operation of the flying control unit transfer valve by the autopilot have on the cockpit controls?
Moves the associated cockpit control
What is a tandem actuator?
Double ended actuator with each actuator having its own servo or selector valve, ram and hydraulic supply
One supply has sufficient power available to operate the control surface
What three factors affect the force exerted by the control surface?
- Aircraft speed
- Air density (altitude)
- Deflection of control surface
What is the main disadvantage of a spring feel unit?
Only gives a ‘feel’ of the controls in proportion to the control surface deflection, taking no account of density and speed
What does the force required by the pilot to displace the diaphragm in the ‘Q’ pot depend upon?
Force required by the pilot to displace the diaphragm varies with aircraft speed and air density
What would happen to feel if the diaphragm of a ‘Q’ feel pot was to rupture?
The pilot would lose ‘feel’
What is the effect of trimming a fully powered system on a spring feel unit or ‘Q’ pot?
The spring feel unit or ‘Q’ pot should be returned to the neutral position or ‘no load’ condition
Give 3 examples of failsafe and multiple system provision.
- Tandem power control actuator
- Split control surface
- One piece control surface with two power control actuators
Why is it advantageous to move the entire stabiliser rather than to operate the elevators?
Moving the elevator out of continuation with the stabiliser causes drag
On jet transports, elevator drag has a significant effect on airspeed and fuel consumption
What are the three methods of repositioning the horizontal stabiliser?
- Energising an electric actuator motor using two switches on the control columns. Using two switches prevents actuator runaway. Both switches must be operated before the motor will run
- By a trim servomotor which is operated by signals from the AFCS, or where AFCS is not in control, by signals from a Mach trim system
- Manually operated trim wheels and control cables (used for emergency operation following failure of the other two methods)
The stabiliser screw Jack is operated by a two speed electrical motor. What determines motor speed?
Trailing edge flap position
Operates at low speed when the flaps are retracted
There are two stabiliser trim switches, one energising an arming solenoid one energising a command solenoid. How many switches need to be operated for the electrical motor to run in either direction?
Both switches are required to be made
When would the stabiliser need to be in the green range and what would happen if it wasn’t?
For take-off
Take-off warning horn will sound
When the stabiliser is trimmed, what automatically moves the elevators into their new faired neutral position?
Neutral shift rod mechanism
As speed increases beyond .7 Mach, The Mach trim actuator will retract causing the elevator PFCU servo to move. What now causes the stabiliser to move and fair the elevators?
The Mach trim actuator retracts to rotate the trim centring and feel unit