Secondary flight controls Flashcards
Secondary Flight control
Controls that DO NOT HAVE DIRECT control over pitch, yawn and bank of aircraft
Difference beween Primary & Secondary flight controls
Primary:
* Has direct control of yawn, bank and pitch
* moves constantly in small or large deflections
* controlled by autopilot or pilot
Secondary
* Has no direct control of yawn, bank and pitch
* moves in one-off movements: in, out, up, down
* Needs lock mechanism
* improves the performance characteristics
* Not manadatory on all aircraft
Types of Secondary flight controls
Speed brake - reduce speed
* extends from wing to fuselage
* creats drag to slow aircraft or control speed in steep descent
spoiler - dumps lift
* On groundafter touchdown - Dumps lift
* In air- dumps a little lift on one wing only to assist aileron for roll control
Trailing edge flaps
* Used at low speeds
* Increases lifting ability of wing
* Reduce stalling speed and reduce landing
Leading edge flaps
* Same function
* Found on larger aircraft - sophisticated
Timming Devices
* Trim aircraft into a stable flight condition
* composed of Trim Tabs and Horizontal Stabilizers
Leading edge devices
* devices such as flaps and slats on the leading edge
* help aircraft operate at higher angle of attack before stalling
Flaps on light aircraft
Usually:
* Rudimentary speed brake system
* Trailing edge flaps.
* Flaps: mechanical lever or electric motor switch systems to move them
* Trims tab: manual knob or wheel / electric motor switch systems to move them
Slats: no contols or indicators. They work automatically by natural aerodynamics
No:
leading edge traps or slats
sometimes no speed braking system
Flaps on heavy aircraft
Trailing edge flaps
* have Fower and Flap Tracks that allow flap to extend outwards, then move downwards*
* Take off: flaps extended a little downwards
* Landing: flaps exteded down drastically
* provide high lift at low velocity (not extended much)
*
Operated by:
* Hydraulic system OR Electric Motors (backup)
* Operates the screw jack to rotate & extend
* Locks to hold the position
How it works:
* Pull a lever
* Sends a signal to the PDU (Power Drive Unit)
* Flaps change position
* When they reach their position, a signal is sent back to PDU to stop
Flap & slat display
On small aircraft:
Flat indicator guage
For each wing - shows 2 needles for each wing (flaps & slat) - one needle in front of the other.
if you see both needles, it means they are locked for further travel by assymetry detection system
In modern aircraft
S & F seperate light indicators on MFD or PFD
PFD shows the speed tape (speed of the flap movement and maximum speed limit)
Placarded speed
speed printed on placard stuck next to the instrument pannel next to the flap lever
In any position, except when slightly extended, strong aerodynamic forces create drag and can affect the wing and flaps. Therefore:
there is a flap maximum airspeed limit set by designers
Flap Protection
flap load relieve system
If flap speed exceeds the ‘maximum airspeed’, the position of the flap changes and may detract till the airspeed goes below the maximum airspeed. The flap goes back to the original setting.
flap lever doesn’t move.
Flap asymmetry
Flaps help with lift
but if…
flaps fail on one wing and work on the other, the aircraft will roll
Flap asymmetry system
1) Indicator/signal condition
2) Isloate flap selector handle so you can’t input anything
3)Interrupts the flap movement if the flap positions disagrees with the preset amount from the intended selection
4)Detect excessive asymmetry and swtiches off power to the flap operating system so the flaps freeze position
flap asymmetry lighting indications
LEADING EDGE - indication Amber
1) EICAS: LE SLAT DISAGREE
* when leading edge of slat position disagrees with commanded position
* Hydraullic power drive units shuts off
2) EICAS: LE SLAT ASYM
* when leading edge of slat position and not symmetrically extended
* Hydraullic power to all flap and slats drive units shuts off
TRAILING EDGE - indication Amber
1) EICAS: TE SLAT DISAGREE
* when trailing edge of slat position disagrees with commanded position
* Hydraullic power drive units shuts off
2) EICAS: TE SLAT ASYM
* when trailing edge of slat position and not symmetrically extended
* Hydraullic power to all flap and slats drive units shuts off
Leading edge devices
Leading flap
* Extends outwards
* increases overall wing camber
Leading slat/Auto slats
* Most extend automatically with natural aerodynamic
* Powered by haudralics or electric
* Extends outwards and downwards
* leaves a gap between flap and leading edge for air to flow
* increases overall wing camber ( so lift increases)
* imporves low characteristics of main part of the wing
* Increases stall angle so aircraft can fly at high angle of attack
Droop nose:
* slides downwards
* increases overall wing camber
Krueger flap
* Located in lower surface of leading edge
* In the inboard section of the wing
* Extends outwards and forwards
* increases wing camber but relatively small radius of leading edge
* Increases lift while ensuring that hte wng roots stall before the tips
Auto slat
Slats move automatically when
1) If the ‘stall warning position’ indicates there is excessive angle of attack:
slats automatically extend from mid position to extended landing position
Slats retract when signal ceases
2) If trailing edge flaps are selected
Alternate options
Electric driven back ups
ALTN FLAPS
- disables normal flaps control
- arms alternate mode
- Engages the electric motors
- Disables the link that operates slats in conjunction with flaps
Speed breaks an spoilers
Location:
* Flap-like, at the top of the wings
- spoiler and speed brake are usually same physical device
- extends upwards
when they act as spoilers
* when 1 or more are are extended
* reduce lift over that part of the wing
* They act asymetrically to roll control
when acting like speed brake
* all spoilers are raised further and together
* increase drag thus affecting speed
Lift dump
* if all devices are extended to max upward
* They spoil and remove lift over the upper surface
* used immedately after touch to ground the aircraft
