AGK - Landing Gear / Brakes

Torsion Links:

Landing gear torsion links
prevent piston rod rotating in cylinder
highest load is in tight turns
connects to inner and outer cylinder

Auto braking after take off

stop rotation of wheels after take off, to prevent gyroscopic forces and stop damage to wheel well.

Landing Gear Locks

2 Main Types:

Geometric Over Centre Lock - most common for down locks

Hook Lock, engage without hydraulic pressure but require hydraulic to release

Oleo Struts

shock absorbers for landing gear

Inner metal tube connected to wheel, which moves up and down in an outer cylinder
Gas = Spring Effect
Hydraulic fluid = damping

What hydraulic system does landing gear have?

Landing gear is an active hydraulic system, as it requires external power to operate. the power comes from engine driven pumps.

Emergency Gear Extension

• compressed nitrogen (in a bottle), 1 shot

• free fall - release handle mechanically releases hydraulic cut off valve

• mechanical

Gear Speeds

VLE - max speed with Landing gear Extended

VLO - max speed with landing gear operating (moving)

Free castoring Nose wheel

steer by differential braking / thrust
prone to shimmy, so damped.

Nose wheel shimmy

main causes:

• tyre imbalance

• mechanical movement

• lateral movement

• rapid sinusoidal oscillation
  
  

• Reduced by:

• shimmy damper (damping cylinder / accumulator)

• self centre springs

• hydraulic locks on nose streering jacks

• twin wheels
  
  

Main wheel steering

• only used at low speeds

• turn opposite to nose gear

• reduce sideways stress

• gives smaller turn radius

Auto Brake

• can be armed while taxying, manual braking does not deactivate it, has to be over 70kt to become engaged

• full manual braking with anti ski is the same as RTO

• required operation anti skid to work

• can be hydraulic or electrically actuated

• ABS operates until stand still

• is a set deceleration, so if reverse thrust is engaged, brake pressure will reduce

• if not set it will NOT generate a take off warning as not required

• does not apply straight away, there is a delay to allow nose to come down, max is straight away

Anti Skid

• required for auto brake to work

• prevents brakes being applied before touchdown, so wheels can spin when touching runway

• can release pressure on individual wheels, and apply on others

• reduces stop distance & allows less take off distance (due to shorter stop)

• inputs = wheel speed and ground speed

RTO

max braking but not constant decel, as slippery spots will give less braking

applied above 85kt when thrust levers close

press brakes to deactivate (once stopped)

Pneumatic Brake Backup

Will feel spongy / soft as gas is compressible

Steel vs Carbon Brakes

Steel brakes:

• cheaper

• better at low temp

• keep cool to reduce where (use softly, short bursts)

• can absorb less heat than carbon

• lower friction coefficient than carbon

Carbon:

• better when warm

• apply firmly less applications

• wear dependent on number of applications

• has higher friction coefficient

• 
  

Ply rating:

strength or rating of a tyre
not checked by pilot on preflight

Pre flight tyre inspections:

• tyre creep

• embedded objects

• brake pin with brakes on - shows brake wear

• safety pins

Thermal Plugs / Fusible plug on wheels

in the wheel hub, allows controlled deflation due to temperature increase

tread separation:

• hard to detect

• can lead to tyre burst