questions Flashcards
CS25 mandates aircraft must be able to fly and land safely after what 2 events in relations to the flying controls?
- a jam
- a severance
how are control systems arranged to allow for jamming and severance?
- duplicated
- interconnected
- routed separately
if a control system becomes jammed what two methods enable disconnection of the two parts of the system?
- manual disconnection by the pilot or first officer
- disconnection by the disconnect unit separating if a predetermined force is exceeded
how is differential aileron movement achieved?
the bell crank on the down side is positioned below the horizontal so an equal angular movement creates a smaller linear movement
how many switches need to be pressed to operate a typical electrical aileron trim system, what are they called and what do they do?
- two switches
- arm and command
- arm powers up the system, command supplies and moves the actuator
how does the roll disconnect unit work and and when can it be reset?
- a predetermined force overcomes a spring
- disconnects left and right ailerons in event of jam
- provides indication on flight deck but can only be reset on ground
what type of motor is used to operate the autopilot servo?
- a reversible motor
- or a split field motor
briefly describe how a gust damper works
- damper attached at rear spar and at flying control
- movement of fluid from one side of actuator piston to the other restricted so slows movement of flying control
where are the primary and secondary stops in a control rod system?
primary stops on the control column, secondary stops on the control surface
briefly describe the operation of a solenoid brake
- electrical power releases brake held on by spring
- this enables motor to rotate and move flying control system
- when electrical power is removed, spring applies brake and system is locked in required position, providing irreversibility
list 2 advantages and 2 disadvantages of a control rod system over a cable operated system
- control rods more robust and do not suffer differential expansion issues
- control rods heavier and more difficult to route
what speed does the stall warming operate at?
5% above stall speed for that configuration and phase of flight
if the stall protection operates what happens when the aircraft reaches a safe speed?
the stick pusher/nudger is disengaged and the control return to neutral at a safe speed
in a power assisted system, what happens to the pilots input?
it is amplified by a hydraulic actuator
in a power assisted system, what ‘nulls’ the servo valve?
the movement of the actuator body provides negative feedback and nulls the servo valve input by covering the hydraulic transfer ports
long answer: the pilot’s input moves a servo valve, which directs hydraulic pressure to one side or another of a piston which is anchored to the aircraft structure. this moves the actuator body providing negative feedback and nulling the pilots input
in addition to being safe, positive and instinctive, powered flying control systems must also provide… (5)
- sensitivity
- stability
- irreversibility
- feedback
- redundancy
what is meant by a control surface being irreversible?
once positioned, the aerodynamic forces acting on it cannot move it, it stays where it is until it receives an input to move
what does the interconnecting valve do and when?
connects both sides of the cylinder to prevent a hydraulic lock when system pressure fails
what five things does the servo valve control?
- size
- magnitude
- speed
- direction
- rate of movement
of the actuator
how does a stuck valve detector strut operate and what does it operate?
- in event of stuck servo valve, the strut ‘breaks’
- this allows other control inputs to keep operating in compression or tension
- this operates a microswitch which informs the pilot and operates the hydraulic clutch to isolate the hydraulics to the stuck servo valve
what should the maximum freeplay on a trim tab not exceed?
2.5% of the average chord length of the tab
in addition to the speed, attitude and altitude of the aircraft, list two other factors the stall warning system considers?
- position of high lift devices
- undercarriage position
- possibly altitude
what does the transfer valve do?
- turns electrical inputs from autopilot into proportional hydraulic flow via flexible pipe
- to direct pressure to operate the input linkage to the servo valve to operate the PCU
describe a tandem hydraulic actuator
- two separate hydraulic inputs
- two pistons
- two servos
- one cylinder
what is the simplest form of artificial feel device?
a spring
briefly describe a Q feel system that does NOT use hydraulics
- pitot and static pressures are on either side of a diaphragm and the diaphragm is connected to the control run
- as the pilot moves the stick he does so against the resistance of the diaphragm to move which is proportional to static and pitot pressure
what should a Q feel system do when the pilot releases the control column?
return the control column to neutral
name four ways to operate a hydraulic pump to pressurise an aircraft system in normal and emergency conditions
- engine driven
- electrical
- ram air turbine
- reversible motor
on a variable incidence stabiliser, list five inputs to the elevators
- neutral shift rod
- pilots input
- autopilot
- mach trim
- trim
what is neutral shift?
ensuring the elevator remains streamlined to the stabiliser when it moves
what are the conditions to extend the speedbrakes on a rejected take off (RTO)?
- throttles at idle
- thrust reverse selected
- wheel rotation
in a typical fly by wire system, if there are two PCU’s on a elevator and one is active and the other idling, what will make the other active?
if the active actuator fails or stalls under load
list four advantages of a FBW control system over a mechanical control system
- lighter
- less maintenance
- more economical
- better manoeuvre protection
- gust load alleviation
what three types of loads on the wings does active load control deal with?
- aero elastic loads (when gusts are encountered)
- manoeuvring loads (reduce wing bending)
- high lift loads (reduce wing bending under conditions of high lift, ailerons are raised a few degrees when the flaps are not fully up and the speed less than a specific value)
what would you use to carry out a static friction check on an aileron control system and what part of the system might have to be disconnected to get a true reading?
a spring balance and disconnect any feel springs
in ah hydraulically operated flap system, what does the bypass valve do if there is an asymmetry?
operates to remove the hydraulic lock so the alternate system can operate
what value will a torque limiter operate at?
system torque+ 20%
describe briefly the operation of the auto slat system
- slats deploy as part of the stall protection system depending on speed, AOA, config etc
- retract when the forward speed is at a safe level
