Landing Gear 2

Landing Gear Operations

• Aircraft landing gear varies based on aircraft size, design, and operational area.
• Landing gear supports the aircraft, dampens vibrations during taxiing, and absorbs landing forces.
• Landing gear transmits braking forces to the aircraft structure.
• Landing gear is unnecessary in flight, only use is for ground or water maneuvering.
• Landing gear has two primary configurations: tricycle (nose wheel) and tail wheel (conventional).

Tricycle Landing Gear

• Tricycle landing gear features a nose wheel and two main gear assemblies.
• This setup keeps the aircraft fuselage level on the ground.
• Offers good pilot visibility.
• Cabin area is level for easier passenger movement, plus the configuration enhances stability during ground operations.
• Aircraft is easy to control due to its center of gravity being forward of the main wheels.

Wheelbase and Wheel Track

• Two key concepts related to landing gear are wheelbase and wheel track.
• Wheelbase is the measurement from the main landing gear wheel axle to the nose or tail gear center.
• Wheel track refers to the distance between the far left and far right main wheels.

Camber

• Camber angle is the angle of the aircraft wheels viewed from the front or rear.
• It describes the angle between the plane of the wheel's rotation.

Conventional Landing Gear (Tail Dragger)

• Conventional gear was the original design in early aviation.
• Consists of two main wheels and a tail wheel at the rear fuselage, this causes a loss in forward visibility.
• Aircraft has the center of gravity behind the main wheels.
• Provides reduced weight and drag.

Main Landing Gear

• Main landing gear provides primary support for the aircraft on the ground.
• It Includes: wheels, shock absorption, brakes, retraction mechanism, controls, warning devices, and cowling.

Nose Landing Gear

• Nose landing gear has similar construction to the main landing gear, is lighter.
• Limited or no braking function is found on the nose landing gear.
• Aircraft nose gear can have two, four, or six wheels.
• Four or six-wheel sets are connected in pairs to bogie beams.

Tail Wheels

• Tail gear can be either absorbing or non-absorbing type.
• It's mounted near the rudder on a spring, oleo, or similar assembly.
• The tail wheel can either be fixed with the fuselage or designed to swivel.
• Swiveling tail wheels can be steerable, free-swiveling, or lockable.
• Steerable tail wheels respond to rudder controls for ground maneuvering.
• Most incorporate a free-swivel mode for tight turns using main wheel brakes.
• Locking mechanisms aid directional control during takeoff and landing.
• When disengaged, the tail wheel returns to full swivel or steerable mode.

Tail Skids

• Two types of tail skids exist.
• One protects the stabilizer bulkhead and fuselage during over-rotation.
• On older aircraft, this skid replaces the tail wheel.

Non-Shock-Absorbing Landing Gear

• It does not dissipate energy during landing; instead, it stores energy for later.
• Commonly used on helicopters and sailplanes, rigidly mounted.
• It may use flexing to cushion ground contact.

Bungee or Shock Cord Landing Gear

• Landing gear struts attach to a tightly wound rubber cord to provide suspension.
• Cord stretches upon landing, storing impact energy that gradually returns during the landing roll.

Spring Steel Landing Gear

• Landing gear struts can be made of steel or composite material.
• The gear flexes upon landing to store impact energy like shock-cord gear.
• Stored energy returns to the aircraft during the landing roll.

Shock-Absorbing Landing Gear

• It converts landing impact energy into heat energy.
• Shock struts are self-contained hydraulic units that offer support and protect the aircraft.
• Mostly, shock is absorbed via the forcing of fluid through a restriction.
• Common versions include spring-oleo and oleo pneumatic.

Spring-Oleo Landing Gear

• Employs a piston-type structure with a heavy coiled spring.
• The piston-and-cylinder setup has an oil chamber and orifice for oil flow during landing.
• The strut extends when airborne, allowing oil to flow to the lower chamber.
• The oil is forced through the orifice into an upper chamber, cushioning the landing shock.
• The coil spring compresses to offer additional cushioning.
• The spring supports aircraft weight, while the oleo strut absorbs landing shock.

Oleo Pneumatic (Air-Oil) Shock Strut

• Employs a piston and cylinder with oil and gas (air or nitrogen) under pressure.
• The cylinder attaches to the aircraft structure.
• A piston attaches to the axle and can move freely inside the cylinder.
• Torsion links maintain alignment.
• Gas pressure extends the strut, acting as a spring.
• Uses dry nitrogen in transport aircraft.
• The nitrogen or compressed air transforms energy into pressure for shock absorption.
• Oil flow inside slows strut movement during extension.

Metering Pin Type

• Employs three chambers (A, B, C) interconnected by flow openings.
• Initial flow occurs between the metering pin and opening, linking Chambers A and B.
• Channels in the piston connect Chambers A and C.
• Aims to create comfortable strut characteristics for smooth landings.
• Struts start soft and become harder progressively.
• Tapered metering pin assists in achieving progressive action.
• The strut is partly fluid-filled with remaining area filled with nitrogen.
• The inner strut forces into the outer strut upon runway contact.
• Chamber B's volume decreases, increasing fluid pressure.
• Fluid flows faster to Chamber A due to the opening becoming smaller during compression.

Strut Operation During Landing

• With landing gear extended, the inner strut extends fully.
• The inner strut is forced into the outer strut upon runway contact.
• Chamber B decreases in volume, raising pressure.
• Fluid flows quicker to Chamber A via the opening between Chambers A and B.
• Fluid flows into Chamber C, increasing volume, but is smaller than Chamber B.
• Nitrogen pressure rises, converting landing energy into pressure.
• Strut compression stops when nitrogen pressure equals the aircraft's mass force.

Strut Operation During Take-Off

• The inner strut extends completely during takeoff, needing restriction of outwards movement.
• This prevents fast extension caused by high nitrogen pressure or damage.
• Fluid leaving Chamber C is controlled via smaller holes in the rebound check valve.
• The valve is pressed against the piston bottom, decreasing flow opening size.
• This delays fluid escape from Chamber C and slows the inner strut.

Oleo Strut Inspection

• Checks include external/internal fluid and nitrogen leaks.
• excessive torque link play and excessive play between the sliding member and cylinder.
• Landing gear oleo strut defects include fluid leakage.
• Seals are for keeping an air-oil seal between cylinders.
• Some aircraft have spare seals to isolate defects without cylinder removal.

Oleo Strut Servicing

• Services to correct fluid level and nitrogen pressure.
• Required pre-charge is on a graph that is often found on the strut.
• Must disengage nitrogen bottle an check leakage.
• Strut should be ready for operation for the maximum allowable weight.

Nose Landing Gear

• Nose gear works on the same principle as the main landing gear shock absorber.
• Some do not have a long metering pin for calibrated opening closure.
• Many nose gears are steerable when compressed, on the ground.

Nose Wheel Steering Centring Cam

• When fully extended, a centring cam aligns wheels with the aircraft's longitudinal axis.
• This maintains alignment to ensure proper landing.
• It ensures the wheels will contact the aircraft structure during gear retraction.

Landing Gear Assembly Components

• Assemblies consist of support and stabilization components.
• The components listed relate to retractable systems.
• Different firms may use varied language to refer to basic components.

Trunnion

• The trunnion attaches the landing gear assembly to the airframe.
• Bearing assemblies support the trunnion.
• The bearing assemblies allow gear pivot during retraction and extension.

Strut (Upper Member)

• This is the component that contains a shock-absorbing mechanism.
• A trunnion supports this component.
• The strut acts as a cylinder for the air-oleo shock absorber.

Strut Piston (Sliding Member)

• It's the moving part of the air-oleo shock absorber.
• This unit sits inside the strut.
• It also attaches to the part where the axle is mounted.

Landing Gear Torque Links

• They connect the strut cylinder to the wheel and axle.
• This limits extension during gear retraction.
• The landing gear torque link holds the wheels.

Landing Gear Wheel Alignment

• Aircraft main wheels require inspection and adjustment to be properly aligned.
• Tow-in or tow-out is the path a wheel takes relative to the aircraft's longitudinal axis.
• The top torque link goes into a clevis fitting on the shock strut cylinder.
• The upper and lower links connect at the apex with a bolt and washers.
• Alignment is adjusted by fitting or removing washers.

Landing Gear Assembly - Truck

• Bogie is located at the sliding member's bottom.
• A truck is used for tandem (one behind another) wheel configurations.
• The bogie beam must be in position for landing gear retraction.
• Hydraulic tilt actuator is used for positioning.

Landing Gear Assembly – Side Strut

• Side strut holds the main landing gear in extended position.
• Two parts exist, with a hinge at the center.
• Used to offer stability.

Landing Gear Assembly - Drag Strut

• Drag strut stabilizes the landing gear assembly.
• If the gear retracts forward or aft, the drag link is hinged for allowance.

Landing Gear Assembly – Shimmy Dampers

• Shimmy dampers reduce the shimmy between inner and outer shock strut cylinders during high speed taxing.
• It's constructed on one of two designs: piston type and vane type.
• Both types can provide power steering and shimmy damper action.

Piston Type Shimmy Dampers

• A piston type shimmy damper: -Is a piston rod and piston contained. -Is filled with hydraulic fluid. -An orifice restricts the movement.
• The damper piston rod is stationery.
• Movement causes the piston to move inside the cylinder.
• Slow movements result little resistance while fast have strong.

Vane Type Shimmy Damper

• The housing of the vane type damper is usually mounted on a stationary part of the nose landing gear.
• Shaft lever is connected to the turning part.
• Movement of the wheel alignment causes movement of the vanes in the shimmy damper.

Landing Gear Extension and Retraction

• Gears retract during flight to reduce drag.
• It makes it possible to fly faster.
• Hydraulic systems have devices for fluid pressure control, like: -A selector valve -Downlock actuator -Retract actuator -Door un-latch actuator -Door actuators -An up-lock actuator -Sequence valves -Restrictors and check valves

Landing Gear Retraction

• The gear is usually retracted side-ward, with hydraulically operated cylinders.
• Extending cylinder causes rotation on the trunnion pin into a horizontal position.
• Upon reaching full up, the uplock engages with the gear.

Landing Gear Extension

• Movement of the cylinder releases the uplock.
• The cylinder reduces fall rate.
• Orifice check valve restricts fluid flow.

Hydraulic Landing Gear System – Typical Components

Selector Valve

• It's connected to the selector valve.
• The pilot sets it in the up or down position.

Up Position

• Pressure from the source is released into the valve.
• This process is used to: -Unlock and open wheel well doors. -Unlock the downlock actuator -Retract landing gear -Closing the wheel well doors

Down Position

• Pressure from the source is released into the valve.
• This process is used to: -Unlock and open wheel well doors. -Unlock the downlock actuator -Extend landing gear -Closing the wheel well doors

Off (Neutral) Position

• Hydraulic components are connected to the return line of the hydraulic power system.
• Gears locked by mechanical means.

Hydraulic Sequence Valves

• Required when a system has hydraulically operated landing gear with a uplock and downlock mechanism.
• Sequence valves is the operation of hydraulic components according at a fixed sequence.

Landing Gear System Actuators

Hydraulic Actuators

• Retraction needs greater force over extension.
• The actuating cylinder extends through fluid pressure.
• Classifying single-action and double-action is primary.

Single-Acting Linear Actuator

• Single-acting linear style of actuator often operates landing gear uplocks and downlocks.

Double-Acting Unbalanced Actuator

• Used when greater force is required to retract landing gear.
• This force has to overcome plus high air loads.
• Extension is assisted by gravity, and air loads.

Double-Acting Balanced Actuators

• They require the same piston movement in both directions.
• Actuators might be for nose wheel steering.

Restrictor and Check Valves

• Actuator has an internal restrictor to control gear movement.
• Extension is controlled.
• The check valve permits full flow into the actuator.

Rack-and-Pinion Actuators

• Rack-and-pinion linear actuators turn linear motion in rotary, and reverse.
• Used in Cessna retractable aeroplanes and can be found within the Fokker and airbus.

Walking Beam

• Some larger aircraft are fitted with walking beams.
• The force rotates the gear around its trunnion or pivot axis, forces of which go to the structure.

Over-Centre Link

• This link prevents the struts from pivoting.
• The over-centre link is hydraulically retracted to allow gear retraction.
• Ground locking pins are installed in the over-centre link.

Landing Gear Uplocks

• Hydraulic pressure can be released by holding the landing gear.
• The roller can moves the uplock mechanism into the locked position.
• Locked doors instead of separate uplock units hold gear.
• A micro switches send a signal to show its gear lights.
• The uplock can be free fall exended.

Landing Gear Downlocks

• This locks it in its extended position.
• The downlock actuator extends under spring pressure to lock the over-centre link.
• Spring pressure is engaged for releasing a downlock.

Nose Gear Up and Downlock – Example

• Nose gear drag strut assembly hold it in the UP and LOCKED or DOWN and LOCKED position.
• The mechanism keeps the drag strut from folding.
• The uplock and downlock actuator releases locks.
• The spring bungees hold the lock mechanism.

Wheel Well Doors

• They will only open during retraction and extension.

Landing Gear Door Uplock

• Is closed mechanically, unlocking doors.
• Can be done in free fall extension and ground door opening.

Hydraulic Landing Gear Operating Sequence

• Controlled sequence helps retract and extend.
• The system is shown and operates.

Electronically Controlled Landing Gear Operation

• Sequence is controlled and monitored.

Gear Extension

• It begins when lowering the gear to down
• Computer controls the extension sequence.

Door Opens

• It signals the doors to open.

Gear Gown

• Computer commands gear to extend while holding doors.

Door Closes

• Computer closes but maintains the gear extended.

Gear Retraction

• Retraction is initiated when setting the gear to UP.

Door Opens

• All shock absorbers are detected extended from lever to up.

Gear Up

• With that said they raise gear.

Door Closes

• System is in-place to press gear.

Emergency Extension System

• Systems must manually lower in system failures.
• Alternative source, air, electric etc.

Emergency Landing Gear Manual Extension System

• Manual override extends.
• Use if hydraulic pressure is unviable.

Mechanical/Electric Landing Gear (Typical)

• Aircraft use electrical operations for the extension and retraction.
• Operates on a 28-V.

Indication and Warnings

Landing Gear Position Indication

• Provides indicators.
• Indicator may also verify landing.
• Green indicates down and locked.
• Red signifies it is moving.
• Yellow indicates doors not closed.
• Light off indicates gear up and doors locked.
• It’s a warning that should be checked.

Landing Gear Micro Switches and Proximity Sensors

• Mechanical switches and sensors.
• Switches are easy but sensors are more reliable.
• Conventional switches open or close.

Proximity Sensors

• Inductance style.
• Limited cycles.
• Safe system.

Uplock and Downlock Proximity Sensors

• Confirmed the landings.
• Provides nesscary details.
• Supply data.
• The target has gear up.

Downlock Sensors

• It supplies its data.
• Provides ground is down and locked.

Landing Gear Lever Safety Switch

• Solenoid prevents lever movements by aircraft.

Landing Gear Lever Manual Override

• Manual allows it if things do not work.

Air-Ground Sensing Mechanism

• They must provide plane can be in the sky or on land.
• It has "squat" type set ups.

Landing Gear Tilt Proximity Sensors

• Detect that it has wheel.
• System prevents to move of of down.
• Targets show they know truck is close.

Visual and Mechanical Downlock Indications

• A visual also can help you.
• Mirrors show window.

Landing Gear Safety Ground Locks

• It's in-place for safe use of ground force.
• Pin is removed.

Landing Gear Warning Systems

• Warining lights is a way of system.
• Horn aids is use.

Inspection of Retractable Landing Gear

• It provides in working condition.
• There is tests on its use.

Aeroplane Wheels

• High loads and wheel issues need to be shown.
• Shocks and damage show wheel brakes.
• Special handling is in place.

Wheel Rims

• Rim is split for easier handling.
• Nuts connected it.
• Ring stops it from its damage.
• Keys assist transmission.
• Fuse helps contain it.

Wheel Bearings

• There are cones.
• Cages must be provided and cleaned.

Wheel Bearing Installation

• Two bearings for the same parts.
• Have two directions for safety.

Tyres

Construction of Tyres

• They function for all the needed parts.
• They have to provide stable loads.
• It needs to take the air and shock.
• Multiple rubber, steel, etc is there.

Carcass Ply

• Today nylon cord.
• Cord is its form.
• By wrapping it.

Bias Tyres

• Plies has to be angular.
• Runs diagonally.

Sidewall

• It has cover protection.
• It stops attacking.

Aircraft Tyre Ratings

Ply Rating

Load Rating

Aircraft Tyre Types

Type III

• Mainly low press.

Type VII

• High pressure units.

Aircraft Dimensions and Markings

• They shows data about tire.
• Inch form.
• Metrical code is also shown.

Other Markings

• Spot helps line up tire.
• With out vibration.
• Also extended its function.

Chine Tyres

• Also nose used one.
• Deters water away.

Aircraft Tyre Inflation

Wheel Inflation

• There in cage.
• It's fully used and loaded.

Inflation Pressure Checking

• Pressures affect prefromances.
• Checked every 24 hours.

Pressure/Temperature Relationship

• Increases from how much it has to take.

Tyre Inspection and Damage

• Damage and wear should checked.

Chevron Cutting

• Groove runaways can cause it.

Tread Chunk

• It fastes operation.
• This causes damage
• It could runing on unsafe lane.

Cut Damage

• All cause cord damage.
• Damagaed in wheel.
• Asements occur at shop.

Dry Braking Flats

• Has to not go any ware.
• And to find if there damages or need to taken away.

Wet Braking Flats (Aquaplane Damage)

• Happens to the tyre.
• Same a flats.
• Has to be removed.

Bulges

• It show you damaged.
• Call or mark and need return.

Shoulder Wear

• This is under condition for use.

Tyre Burst

• Should take a lot damage.
• With its time.

Heavy-Crosswind Landings

• It can result in major issues.
• It shows its unsafe.

Excessive Brake Heat

• Damage is easy found too.
• Check is show before use. -Blister is shown. -Or Brittness is there.

Sidewall Cracking

• That's comes from damage.
• Can happen during storage..
• Show it is okay before leaving.

Tread Groove Cracking and Rib Undercuts

• Operation is unsafe.
• Fuel can make a unsafe situation.
• It damage at bottom
• It's bad damage.

Procedures Following a Rejected Take-Off

• Not everything cause removel.
• See all needed parts are replaced.
• Get a new tyre from shop or repair station.

Flat Spot Due to Nylon Set

• It sits on air.
• If damage is too great.

Contamination of Tyres

• They can hurt rubber.
• It shows that its not safety for flight.

Tyres With Uneven Wear

• You can flip damaged air tire.
• So both sides wear.