11.9 - Flight Controls Flashcards
What does the control wheel move in a boosted system?
A hydraulic actuator is in parallel with the mechanical operation of the controls, and in addition to moving the control surface, the normal control movement by the pilot also moves a control valve that directs hydraulic fluid to the actuator to help move the surface.
A typical boost ratio is about 14, meaning that a stick force of one kg will apply a force of 14kg to the control surface.
What happens in the event of a hydraulic failure on a boosted system?
The control forces are too great for the pilot to manually move the surface (hydraulic actuator fail)
So they are controlled with servo tabs
In the manual mode of operation, the flight control column moves the tab on the control surface, and the aerodynamic forces caused by the deflected tab move the main control surface
What controls an aileron or rudder tab?
The flight control column moves the tab on the control surface, and the aerodynamic forces caused by the deflected tab move the main control surface.
How is pitch controlled on a horizontal stabiliser? (3 ways)
Adjusting the position of the leading edge stabiliser
THS (Trimmable Horizontal Stabiliser) can be moved either manually or automatically
This can be done by:
- Pilot
- Autopilot
- Flight Management Computer
Explain a follow up control?
During transonic flight, shock waves form on the control surfaces and cause control surface buffeting
To prevent these forces fed back into control surface and reaching pilots, a Follow-up system is used to close the control valve of a servo control unit when it has reached the desired position
Also known as ‘a power-operated irreversible control system.’
What is feedback used for in a fly by wire system?
When a hydraulic actuator is used, an artificial feel system must be provided to prevent over control by the pilot
When a trim tab is used, explain how this affects the control column?
Puts ‘0’ load on the control column
It allows for ‘hands off’ straight and level flight
Adjusted independently of control surface from cockpit
What do the trailing edge flaps do?
Increase the camber (fixed hinge point with hydraulic cylinder)
or
Increase the area and camber (rollers with specially formed tracks)
What is the purpose of a flap synchronisation cable?
To prevent a difference in flap position which could cause a dangerous roll
A heavy steel cable is used (synchronisation cable)
Used mostly for aircraft with hydraulic cylinders that drive the flaps
How if flap position indicated?
The position of the flap handle in the cockpit
Also an indication system on the flight deck indicates the position of the flaps
What signals are needed for the ground spoiler system to work?
- Ground / flight signal
- Wheel spinning signal
- Throttle lever angle signal
- Aircraft speed signal
Explain stall protection?
Most transport aircraft are equipped with a stall prevention and warning system.
If aircraft nears stall:
- Auto-Slat - Slats are automatically moved to mid position and manual control is given to pilots
- Stick shaker
- Stick pusher actuator is activated, pushing the stick forward
How does a rudder travel limiter work?
A rudder travel limiter protects the empennage from overload in case of inadvertent application of excessive rudder control at high speeds.
Older aircraft - pitot tube on vertical stabiliser. The higher the airspeed, the more RAM air in which restricted the movement of the rudder.
Modern aircraft - electrical signal from Air data system
What is a yaw damper?
The full time system provides directional stability augmentation throughout the entire flight envelope.
The yaw damper operates the rudder in series mode with the pedals, but usually movement is not reflected on the pedals.
Manual operation of the rudder will not affect yaw damper operation.
- prevents dutch roll
- gives a new ‘0’ position of the rudder irrespective of what flight crew do
Name the different kinds of primary flight control operating method and the application of them:
Cable Operated System - Cockpit controls connected to surfaces via high-strength steel cable - low speed aircraft e.g gliders
Boosted Cable Operated System - Hydraulic actuator used in parallel with mechanical operation to aid pilot in deflecting surfaces - aircraft ligher than 60 ton
-Servo tab used as backup if hydraulics fail
Hydraulic Power Operated System - Even heavier aircraft, can’t use servo tab - full hydraulic and need a power-operated irreversible control system - artificial feel and redundant servo actuators (3 or 4 needed)
Fly-By-Wire System - Wire sends electrical signals to computers then hydraulic valves - A320
Explain the difference in operation methods between pitch trim systems and the other two primary control systems
Transport aircraft are trimmed longitudinal by adjusting the position of the leading edge of the horizontal stabiliser.
Raising the leading edge gives nose down trim, lowering the leading edge gives nose up trim. THS system
The other two primary control systems (aileron and rudder) use trim tabs
What are the two different flap hinging methods?
- Fixed hinge point moved by hydraulic cylinder (increase camber only)
- Flaps which have rollers and are installed in specially formed tracks (increase camber and surfacec area)
How do Torque tubes work?
Torsional load is turned into linear motion
