Chapter 2 - Aircraft Undercarriage System Flashcards
What are the basic undercarriage leg configurations?
Telescopic
Lever suspension
Forward lever
Sideways lever
Quadrilateral deformable
Semi-articulated
What is the purpose of the shock absorbers in the undercarriage?
Dampen shock of:
- Landing
- Taxying
- Movement over uneven surfaces
What two basic types of undercarriage shock absorber are used?
One utilised the incompressibility of oil
One utilises combinations and oil and nitrogen
What are the basic features of a retracting undercarriage?
Doors and Fairings
Sequencing
Jacks and Linkages
What role does Sequencing serve in retractable undercarriage systems?
It is a series of hydraulic valves or electrical switches that ensure everything happens in the correct order by not permitting one part of the sequence to commence until the preceding part has been completed.
What is responsible for holding the undercarriage in raised position?
Up locks
What is responsible for holding the undercarriage in its lowered position?
Down locks
What are the two common types of Down Lock in use?
Geometrically locked hinged lever
Integral with the extension jack
What does no light or flag on the undercarriage control represent?
Unit is locked UP
What do red lights or flags on the undercarriage control represent?
Gear is travelling
only between up and down?
What do green lights or flags on the undercarriage control represent?
Gear is locked DOWN
What are WOW switches and what is their purpose?
Weight On Wheels
Activated by the deflection of the undercarriage on the ground, used to prevent operation of the retraction mechanism and to unlock the ability for nosewheel steering.
Signals from these switches are used in other aircraft systems to either initiate their deployment upon take off or landing or to prevent their operation in the air/on the ground.
What are the design criteria for aircraft wheels?
Light weight
Minimum size
Good fatigue resistance
Accommodation for the brake unit and dissipation of the heat generated during braking
Easy tyre replacement
Why are aircraft wheels made in two halves?
The two halves unbolt which allows tyres to be fitted without stretching over the rims, and the wheels house the wheel bearings.
What type of tyres are aircraft usually fitted with?
Radial ply tubeless tyres
Note - Be able to label the parts in the diagram in the course manual
What are the advantages of radial ply tubeless tyres over the earlier cross ply tyres fitted with inner tubes?
Higher strength
Lower Weight
Cooler Running
Better overload capabilities
What is the purpose of ‘creep marks’ on aircraft tyres?
Allows creep to be monitored in tubed tyres because the valve could break if the inner tube is forced too far round the wheel and puts extra stress on it.
Could cause a blowout on landing.
What is the name of an emergency gear extension system that uses pneumatics (nitrogen)?
Blow-Down System
What is a Multi Disc braking assembly?
High performance disc brakes constructed as multiple stacks of discs made from carbon composites which are able to operate at the necessary temperatures.
Consists of rotors and stators.
Pressure of braking presses the rotors and stators together, resulting friction provides the retarding force.
When braking, what does the point of skidding depend upon?
Condition of the runway surface
Vertical load which the aircraft tyres exert on the ground
Retarding force applied by the brakes
Does changing the weight on the tyres affect the speed at which full aquaplaning occurs?
No, as the contact area also changes and the ratio of weight to area remains constant.
What causes aquaplaning?
Tyre displaces the stationary water, resulting in a change in momentum of the water, creating hydrodynamic pressure which reacts on the runway and tyre surfaces.
What is brake modulation?
Early anti-skid systems used the inertia of a flywheel to sense rapid changes in wheel rotational speed during a skid.
Reduced hydraulic pressure during a skid to stop it, reapplying it once the skidding reduced/stopped.
Created an on/off pulsing of the brakes, known as brake modulation.
How do modern anti-skid systems work?
Control technology varies the frequency (and amplitude (pressure)) to maintain the braking forces at a level immediately below that which would cause a skid for all speeds and surface conditions.
System also holds off the brakes until after touchdown, either for a given time or until the wheels have spun up to a set speed.
(Also applies the brakes after takeoff to spin down the wheels after undercarriage retraction has taken place)
