Landing Gear Flashcards
Tricycle Landing Gear
Two sets of main wheels near CG
Smaller Nose wheel assembly
Tail Wheel System
Provides propeller clearance
TO/LD can be difficult
Retractable Vs Fixed Gear System
Fixed requires less moving parts less maintenance costs
Drag penalty’s
Gear systems use hydraulics and have an emergency lowering ability
What is a Bogie
At least four wheels mounted to bogie beam
Internal space needed for stowage
Small turning radius give greatest load on torsion link
Think 787/747s
Shock Absorbers Role
Absorb 90% of shock
Via Oleo Strut
The Oleo Strut
Uses Gas (Nitrogen) pressure to absorb AC weight/spring to absorb load
Hydraulic oil to control compression/extension in leg assembly
Inner cylinder connected to wheel
Outer Cylinder connected to airframe
Sliding Restrictor prevents bouncing
Signs of Oleo Strut (shock absorber) being too small and damaged
Low gas pressure
Bottom out on landing
Focalised portion being too small
Hydraulic fluid leaking
Nose Wheel Assembly
Only direct compression loads
Max load is after main wheel have touched down
Features:
- Free castoring for steering
- Auto self venturing
- Shimmy Protection
- Steering
Components:
Retraction Actutator
Side brace
Torque Link
Oleo Strut
Steering Acutator
Taxi Lights
Retraction/Extension of gear controlled by…
Selector valves
Sequence valves to sequence open/closing
Landing Gear Speeds
VLE = max speed with gear down
VLO = max op speed for landing gear no faster
What is Down Lock
Prevents accidental retraction
Over centre locks
No hydraulic power/mechanical to break lock
What is uplock?
Hook lock controlled by hydraulic pressure
What is a Ground Lock?
Prevent collapse of undercarriage on ground
Pins which prevent ops
Very obvious warning flags
Indication of gear status
Green - Locked own
RED - Unlocked (travelling)
No Lights - gear up and locked
Amber - Door failure?
Gear Selector Lever
Prevent inadvertent retraction on ground
Spring loaded plunger via solenoid retains down position
Flick off in cockpit when ready to TO
3 x emergency gear extensions:
Manual systems via hand pump
Compressed Nitrogen to blow gear down
Gravity/free fall system
X 2 Types of steering on light AC
Differential Braking - Applied to main wheels causing wheels to castor
NO DIRECT CONNECTION BETWEEN RUDDER PEDALS AND NOSE WHEEL
Rude Pedal Steering - direct mechanical link between pedals and nose gear
What is castoring
Ability of nose wheel to turn to either side in response to differential braking of force from rudder
Large AC Steering
Electric/hydraulic motor on nose wheel strut driving it left or right
Can steer 75 degree left or right
Small lever located in flight deck to control
Nose wheel shimmy
Rapid sinusoidal oscillation of nose wheel and divergent in nature
Low/uneven tyre pressure
Wear in wheel bearing
Worn torque links
Prevention:
- hydraulic damper
- Heavy self centring springs
- Double nose wheels
- Twin contact tyres
Role of torque links
Prevent inner cycle rotating within outer cylinder
Limits max extension when in flight
Bearings required to enable smooth movement
Advantage of having steering capability on main landing gear
To relieve the sideway stress on main wheel assemblies
