Flight Controls Flashcards
Why do large jet transport aircraft have powered flight controls?
Do deal with the large loads and changes in CoG.
What level of redundancy is required for powered flight controls?
Triple redundancy is required if manual reversion is NOT available.
Would fly-by-wire require triple redundancy or could it use manual reversion?
triple redundancy would be required, because there are not direct cables (manual control), it is all electrically driven.
What is Q feel and why does it exist?
Because hydraulic forces are used to move the control surfaces, Q feel is used to provide some sort of feedback to the pilot to stop them from overstressing the airframe.
How does the Q feel system dictate what ‘feel’ is given to the pilots?
Based on airspeed.
What is the purpose of ‘control balancing’?
To reduce control loads
What is the purpose of the ‘flexible seal’?
To reduce the control pressure / hydraulic force
What is jack stalling?
When air loads are so strong that they actually prevent the hydraulic system from moving the controls.
What is the main benefit of a variable incidence tailplane?
Allows pitch to be trimmed over a large CoG range whilst still allowing full elevator control to be available. Compared to elevator trim tabs, it also produces less drag
Do trailing edge devices increase or reduce the body angle on approach?
reduce (remember flaps typically give you better forward vision on final)
What is the purpose of the fowler flaps?
Move back and down to increase surface area
What is the purpose of slotted flaps?
Re-energise the boundary layer (gaps in between the flaps will accelerate air, like lots of little wings)
What is a flap limiter?
A device which will automatically retract flaps (or prevent flap extension) if the speed is too high. NOTE that the flap position handle does NOT move.
What is a hydraulic blow back valve?
Allows the flaps to get retracted when the air loads are excessive (a form of flap overspeed protection)
Compared to a clean wing, what will trailing edge flaps do to the critical AoA?
Decrease (you will stall at a slower speed but lower nose attitude)
Compared to a clean wing, what will leading edge devices do to the critical AoA?
Increase
How do spoilers assist roll?
They are extended on the down-going wing to dump lift and increase drag.
Why is height lost during a turn with spoilers?
Because they significantly reduce lift on the downgoing wing, resulting in height loss.
What is aileron lockout?
A system which prevents OUTBOARD ailerons being used at high speeds. Inboard ailerons are active at all times.
How are the spoilers stopped from being deployed at high speed?
Blow down: The air loads will simply prevent deployment of the spoilers.
All powered flight controls have how many hydraulic units?
At least two (through 3 is required for certification)
Why are there two switches for electric aileron trim?
To prevent inadvertent activation of trim.
What is one of the risks associated with spoiler walk down?
Tendency for height to be lost when spoilers are used, therefore large roll inputs should be avoided at low aircraft speeds on approach.
What is the benefit of speed brakes?
In addition to aerodynamic drag, it also places the weight on the wheels which assists with braking.
To assist in yaw control redundancy, what systems are available?
Either have two components to the rudder (if one fails the other is still available), or have multiple actuators for the same rudder surface.
When rudder trim is applied, to the pedals move?
Yes, they are displaced proportionally
What is the purpose of a rudder ratio changer?
As speed increases, the hydraulic force available can overstress the rudder, so it will automatically reduce the amount of deflection available.
What is a rudder comparator?
For systems which have an upper and lower rudder surface, it will detect if the rudder ratio changer has jammed, causing an uneven displacement of the rudder.
What are the two types of yaw dampers?
Parallel type: rudder pedals are moved as the yaw damper moves (must be off for takeoff and landing)
Series type: rudder pedals are independent (therefore can be on at all times except gusty/crosswind conditions).
What are the two main purposes of the moveable stabiliser?
Reduce drag compared to trim tab, and to deal with large changes in CoG.
What is the natural tendency of the trim when trailing edge flaps are deployed?
Nose pitch down
What is the natural tendency of the trim when leading edge flaps are deployed?
Nose pitch up
When one of the two hydraulic systems controlling stab trim is inoperative, what happens to trim rate?
Halved
What protection is in place to prevent stab trim runaway?
Hydraulic cutoff valves
How are slats deployed?
they are deployed with the flaps (don’t have a seperate lever). Typically stage 1 of flaps will extend slats as well
What happens if there is a failure of the hydraulic system which moves the flaps?
Electrical system as a backup
What happens to the CoL if only the inboard flaps are extended on a swept wing aircraft?
Moves inwards and forward (pitch up)
What happens to the CoL if only the outboard flaps are extended on a swept wing aircraft?
Moves outwards and rearwards (pitch down)
How are flaps protected from operating asymmetrically?
There is a system which will identify if a specified value of flap asymmetry exists and will prevent further deployment of the flaps.
What is the purpose of slats?
Re-energise the boundary layer by providing larger surface. Useful for low speeds as wings are designed for high speed.
What systems can extend the leaing edge slats?
Hydraulics or pneumatics primarily, or electrically as a backup.
Why do large transport category aircraft have flight control position monitoring?
Because the flight deck inhibits view of the control movement (in the same way you want 3 greens for gear down)
What is a limitation of the flight control position monitoring system?
the system is used to indicate full control movement on the ground, however airborne full deflection is rarely used, and therefore doesn’t provide much information.
What information does the Digital stall Warning Computer require to activate the stick pusher/shaker?
Angle of airflow vane, flap position indicator, N1 speed, N2 speed, air/ground relay, ADC, leading edge module. If these weren’t available, the system would engage the pusher at innapropriate times (e.g. on the ground)
