8/26/2010AVIM 103D Landing Gear – Notes Workbook

Course Outline• Landing gear– Types– Configurations– Alignment• Suspension systems– Fixed gear– RetractableCourse Outline• Retraction systems• Steering systems• Brakes– Dependent systems– Independent systems– Anti-skid control• Wheel assemblies• TiresSafety• Shock strut servicing• Gear retraction and extension• Shimmy damper service• Tire servicing and dismounting• Eye and skin protectionSafety• Caustic fluids– Burns skin– Damages surfaces• Flammable fluids• Fluid contamination– Leave containers closed– Read labels, use proper handling equip.Safety• Retraction can crush you if you are in the path of the gear• Retraction without proper support can destroy an aircraft as wellLanding Gear Purposes• Supports the aircraft on the ground• Absorbs landing shock (some)• Absorbs taxi shock (some)• Attachment point for:– Brakes– Steering–Wheels and tiresConventional GearDefn: Wheel Pants• The tapered tail end of the pant provides the major part of aerodynamic drag reductionDefn: Cowlings & Fairings• A shielded section that provides aerodynamic smoothness to some area or part of theaircraft

Defn: Wheel BaseJodel d140cC150 Tail Dragger ConversionConventional (Tail Wheel) ArrangementOlder design – C.G. aft of main gear• Steering:– Rudder pedal cable connection to tail wheel– Brake application and castering tail wheel– Differential braking to assist steering• Tail wheel as far aft as possible to extend wheelbase and increase stability.Conventional (Tail Wheel) ArrangementAdvantages• Prop clearance for low powered engines• Sturdy design for unimproved runways• Less drag in flight• Greater ground maneuverability• Tail wheel failure = minimal aircraft damageConventional (Tail Wheel) ArrangementDisadvantages• Ground loop and nose-over potential• Crosswind control problems• Restricted visibility during taxiTricycle GearTricycle (Nose Wheel) Arrangement• Nose gear as far forward as possible– Longer wheelbase – more stable– Lighter gear assembly due to longer lever arm• Castering types use differential braking to steerTricycle (Nose Wheel) ArrangementMain gear aft of C.G.Advantages• Difficult to nose over or ground loop• More familiar ground maneuverability• Better visibility during taxi• Less vulnerable to cross wind landing• Steering:– Direct linkage with nose wheel bungee– Hydraulic nose wheel steering– Differential brakingTricycle (Nose Wheel) ArrangementDisadvantages• Nose gear damage = major airframe damage• Generally not suited for unimproved runways• More expensive than conventional gear• Much heavier aircraftNose Wheel SkiSkis• Ski systems are usually pivot mounted to the aircraft wheel axle– incorporate travel limit straps or cables (front and rear)

– usually have a bungee or spring to keep the nose up, preventing pearling during landing• May be retractable (skis retract higher then bottom of wheel assemblies)Skis• Auxiliary gear, nose or tail, may or may not have a ski• Are subject to corrosion damage and hard landing damageFloatsFloatplane Configurations• Floats• Amphibious floats – wheels and floats• Hull floats – bottom of aircraft = boat• Outrigger pontoons– Hang from wing tips or struts– Fold down from wing tipsFloat/Hull/Pontoons• Most common are dual float assemblies• Usually are uniform shape• May have retractable, and or steerable rudder assembly• May require a vertical vane installed on lower side of fuselage below vertical stabilizerFloat/Hull/Pontoons• Almost all water aircraft use a float shape that includes a chined V hull• They usually have a stepped section that assists the aircraft in planing across the water(reduces water drag)• Flying CG and floating CG may not be the same– some hull planes have self flushing ballast sections / wheel well sectionsFloat/Hull/Pontoonsbasic shapeTandem Wheel ArrangementAircraft with narrow fuselage• Gear positioned directly beneath fuselageTandem Wheel Arrangement• Gliders• U-2• AV-8 Harrier• Usually has one main set of gears in center, one steerable nose gear, and outrigger gearson the wings• Can be fixed or retractableTandem Wheel ArrangementGear Types• Fixed Gear– Popular on older and low speed aircraft– Speed and fuel efficiency increase with pantsFixed Gear• Are not able to retract into some cavity or aerodynamic shielding within the aircraft

• May be fully rigid or able to absorb landing / taxi loadsFixed Gear• Are usually lighter and less complex than retractable gear aircraft• Have overall lower purchase and operating costs than retractable gear• The benefits from lighter weight can exceed the benefits of reduced drag from retractablegear• Are subject to corrosion damage and hard landing damageRetractable Gear• Streamlines aircraft reducing drag• More complex and heavier than fixed gear• Retraction methods:–Mechanical– Electrical– HydraulicAnatov AN 225Trailing Link landing GearB747-8 Landing Gear Ship SetSkid Landing Gear• Used on helicopters that do not ground taxi• High skids and pop-out floats available• May or may not have shock absorbing devices• May or may not have skid pads (stellite faced)• Left skid / nose low wear pattern• Loose skids may cause– Vibration– Ground resonance (fully articulated rotor)Skid Landing Gear• May have detachable wheel assemblies for ground handling• Are also found on early aircraft in place of the tail wheel assembly–Wooden skid with brass or steel plate for hard surface or leather plate for grassPop Out Floats• Spring Steel Gear - Cessna Type• Load transfer only• Minimal rebound protection• Generally not field repairable• Serialized Cessna component• Check Cessna maintenance manual table of limits for alignment data•• Tubular Steel Nose Gear – Grumman TR2• Load transfer only• Minimal rebound protection• Sometimes field repairable by welding• Some have bungee shock cordWheel Alignment• This is much more critical for tail draggers.• The aircraft should be level and the wheels should be on some form of grease plates to

eliminate gear binding.• The aircraft should be located inside where it is not subject to winds.• Adequate measuring equipment should be available.Toe in / out• Toe = the distance between the front of the tires and the back of the tires.• The best means to measure this is to project lines out to a distance and calculate to thespecifications.• Toe-in is front of tires in,• Toe-out is front of tires outCamber (- +)• Camber = the distance between the top of the tires and the bottom of the tires.• This can be seen using a large square.• Positive is top of tires out.• Negative is top of tires in.Castor• Castor = only really applies to a wheel assembly that turns or steers.• It is the measure of the angle that the pivoting axis tilts front or back.• This is similar to the concept of rake used on single strut assemblies such as nosegears or motorcycles.Inclination and Offset• Steering inclination = is similar to castor but it is the measure of the angle between thepivot axis and the vertical axis of the wheel with no camber.• Trail or offset = The amount of distance between the wheelaxis and the steering axis.Wheel Alignment Adjustment• Some may be adjustable by shimming the stub axle at the mounting flangeWheel Alignment Adjustment• Some may be adjustable by shimming the torque links at the center pivotWheel Alignment• The aircraft must be located on a flat smooth surface, resting on grease plates, leveled asper manufacturer's procedure• First determine the landing gear are properly mounted and not damaged or distorted– Damage and conformity inspection, symmetry checks, etcWheel Alignment• Several methods for checking toe:– Straight edge and a large square– Scribe and a measuring tape or bar– Line of sight projection to a referenceStraight edge and a large squareScribe and a measuring tape or bar

Line of sight projection to a referenceCamber• Is checked using a ruler and a levelScissor Link DisconnectedEND SECTION ONE

Aircraft Suspension SystemsSuspension Systems• Provide controlled flexibility to the landing gear systems while maintaining their structuralintegrity• Up to a point they will eliminate the unusual loads incurred during landing and takeoffoperations• They can also reduce or eliminate ground operation vibrations from uneven or rough taxisurfacesSuspension Systems• Suspension vs. Absorption• Suspension systems are devices that allow flexibility or bounce to occur between the groundand a vehicle• This can include low pressure tires, springs (torsion, flex, coiled)(rubber, metal, plastic),telescoping strutsSuspension Systems• Suspension vs. Absorption• Absorption is a suppression or restriction to flexibility or bounce• The most common form are air / oil filled telescoping struts• Less commonly are stiffeners such as plastic or wood straps attached to flexing type gearSuspension Systems• Very early aircraft had rigidly mounted gear• As technology progressed two main forms of suspension came into being– Rubber bungee mechanical lever systems– Flexible metal tapered bars or shaftsSuspension Systems• The main advantage of these two systems are:– they are light– easy to maintain– relatively inexpensive– fairly aerodynamically clean• The main disadvantage is they provide no permanent shock absorptionSuspension Systems• Air-Oleo struts were then designed to:– suspend, or provide bounce– and to truly absorb the shock energy, or prevent spring-back.• Note: FAA test questions handle this badly• Springs and bungees only delay the shock energy, but eventually spring back.Suspension Systems• Bungee SystemElastic Shock RingShock Ring Notes:• Remove boot for thorough inspection• Beware – safety hazard• Oil stained cotton cover – damaged

• “Necked” diameter – worn, broken elastic• Replacement considered preventive maintenance – FAR 43 Appendix ABungee CordBungee Installation / Removal ToolsSpring Systems• Flexible tapered bars and shaftsSpring Systems• Flexible tapered bars and shaftsSpring Systems• Less commonly there are numerous versions of coiled spring, rubber disc, torsion bar, plasticflexible bar, etc. assemblies that all provide some form of flexibility to the landing gearFlexible Gear Servicing• Includes checking all fittings for security, tightness, and appropriate free play• Inspect main gear for signs of corrosion, fatigue, hard landing damage or taxi damage• Inspect auxiliary gear and steering connections for damage and corrosion• Repair all worn or failed partsFlexible Gear Servicing• Some tubular structures may be repairable by welding• All spring type structures are not repairable by welding• Spring type may have serial numbers and may be matched pairs which means they arereplaced in pairsStrutsSuspension Systems• Oleo Telescoping Strut• Over all aircraft it is the most commonly used suspension system• Range from 1" in shaft diameter to 10", 12", etc.• Can be used as main gear, or as auxiliary gear• Can be steerable, fixed or free castoringSuspension Systems• Oleo Strut - Basic principle of operation• A telescoping strut that contains compressed gases and fluid, usually a light oil• The compressed gas causes the strut to extend thereby sustaining the changing weight ofthe aircraft (suspension)Suspension Systems• For the strut to change length the oil must pass through a restricted orifice• Due to the nature of hydrostatic lock this restriction of oil flow "meters" the rate at whichthe strut can change length (shock absorption)• The tapered metering pin determines the rate of compressionSuspension Systems

• Torque or scissors links maintain wheel alignment• May have a flapper return valve that allows the strut to extend quicker then it compresses• Very slight seepage of seals is normal to lubricate the piston• Oleo Strut• Oleo strut telescoping• Oleo strut telescoping• Oleo strut telescoping• Oleo strut telescopingOleo Strut Parts• Main Strut, outer tube• Piston, piston rod, inner cylinder• Upper or inner strut seal rings• Upper inner bearing• Snubber or return valve (sometimes)• Lower outer collar, bearing and gland nutOleo Strut Parts• Oil and gas fill plug / valves• Neoprene V-ring seals• Orifice tube• Orifice or snubber plate• Tapered metering pin• Oil• Dry gasOleo Strut Notes• Strut service is preventative maintenance• Earlier struts used O-ring seals• Newer use stacked V-ring seals– Fluid pressure is applied to the inside of the V– Or D-rings with round side facing movement• Piston is hardened polished and or chromed steel• Gland nuts are bronze (may or may not be adjustable)Oleo Strut Notes• Deflating struts will protect piston from corrosion• Piston may have a spline or cam that aligns the nose gear for retraction• Strut extension distance at a given weight is the common method for determining gascharge• Seal compatibility determines type of oil• Strut should have a data plate attachedOleo Strut Notes• Dried Nitrogen is the gas of choice– Inert– Inexpensive– No moisture• Three type of filling Valves–MS 28889 most common– AN 6287– AN 812 older modelsMS 28889 Fill Valve

• Has no valve core• Base nut and swivel are 3/4"• Has a roll pin to keep swivel valve in place• Base nut torque is 110 in/lbs• Swivel nut torque is 70 in/lbs• Pressure rated to 5000psigMS 28889 Fill ValveAN 6287 Fill Valve• Has high pressure valve core (stamped H) and a swivel nut valve• Base nut is 3/4", Swivel nut is 5/8"• Base nut torque is 110 in/lbs• Swivel nut torque is 70 in/lbs• Pressure rated to 3000 psig• Do not interchange with MS 28889AN 6287 Fill ValveAN 812 Fill Valve• Has only a valve core• Base nut is 5/8"• Med. press. valve core short type stamped H• Base nut torque is 75 - 100 in/lbs• Pressure rated to 1500psig• Do not use in place of MS28889 or AN6287AN 812 Fill ValveFill Valve Warning• All the fill valves are interchangeable• DO NOT DO INTERCHANGE THEM• DO NOT ATTEMPT TO USE AUTOMOTIVE VALVE CORES WITH EITHER THE AN 6287 ORTHE AN 812• DO NOT INTERCHANGE VALVE CORES OR CAPS BETWEEN ANY OF THEMOleo Strut Servicing• Servicing data may come from current maintenance manual, or data plates• Depressurize, remove from plane• Disassemble and clean, inspecting for any damage, corrosion or cracks• Replace all rubber seal components, worn bushings, and failed partsOleo Strut Servicing• Reassemble, add oil to level with filler opening, bleed air out, and seal• Reinstall and repressurize with nitrogen• 100hr / annual must include checking strut fluid and gas levels• Typical pressures range from 150 - 1000 psi• You will not be able to service a strut with shop air sourcesOleo Strut Servicing• Use a nitrogen charged bottle, or a strut pump (12:1)• Cycle pressurized strut several times to ensure seal seating and air bubble removal

• Struts can have slow gas leaks, recheck fill after 24 hours• Always rock the aircraft prior to measuring strut extensionStrut ServicingStrut ServiceStrut ServiceStrut InflationStrut InflationStrut InflationB737 Main Landing GearEND SECTION TWO

AVIM 103DAircraft Retraction SystemsRetraction Systems• Aircraft gear retraction systems can be found on many aircraft• From the small experimental Vari-eze to the ultra-large AN 124 (winged building)• In most cases the retraction process is accomplished with hydro-electrical force connectedto mechanical linkageRetraction Systems• In most cases the retraction process includes the opening, and closing of doors or coversthat complete the aircraft's aerodynamic shape• In most cases all the gear retract• With retractable conventional gear the tail wheel often doesn't retractRetraction Systems• In most cases steering gear needs to be repositioned correctly for retraction• Gear can retract in any direction, forward, backward, inboard, outboard, or rotating to fitinto a special compartment.• They can retract into the wing or the fuselage• They can change the aircraft CG when retracting or extendingRetraction Systems• They will contain many adjustable devices that limit travel or notify the pilot of landing gearconfigurations and conditions• They must have some emergency, auxiliary means of extension• Any hydraulic, or electrical failure cannot cause the gear to automatically retract• Most contain safety systems that limit when the gear retr./ext. may be operatedRetraction Parts• Trunion = the main pivot point, and attach point• Drag or Side braces = provide rigidity when locked down• Overcenter lock = similar to a knee joint

• Ground lock or pin = prevents accidental retraction, should have red flag attachedRetraction Parts• Weight on wheels switch, squat, ground safety sw. etc = usually attached to gear torquescissor links• Limit switches = micro switches that electrically sequence gear retraction• Sequencing valve = hydraulic valves the sequence gear retractionRetraction Systems• Priority valve = same as sequencing valve but is actuated hydraulically• Indicating system = red, amber, green lights, horns, barber poles that indicate gear position• Red = unsafe, in transition• Green = down and locked, up and stowed• Lights may have push to test featureRetraction Systems• Retraction systems must be tested fully during 100 hr and annual inspections• This includes inspection, lubrication, and an operational test with the gear off the ground• Any additional safety and alarm systems must also be tested, such as throttle horns,indicator lights• Avoid testing the squat switch the hard wayRetraction Operation• Down and lockedRetraction Operation• Inboard gear door open, gear in transitionRetraction Operation• Gear up, inboard gear door in transitionRetraction Operation• Gear cycle complete• gear upRetraction Systems• DC-10 uses Oleo strut gear• Mains retract inboard, nose retracts forward• Mains use a four wheel truck or bogee 2X2• Incorporates the use of axle beams and beam trim cylinders• Every wheel contains a brake assembly• Retraction and braking is hydro-mechanicalRetraction Systems• Retraction sequencing is accomplished with a follow-up hydraulic-mechanical control valve• System uses various cables, levers and bell cranks to control the landing gear control valveassembly• Main gear doors can be locked closed to use as a work platformEmergency Extension• All retractable gear system must have an alternate means to extend the landing gear

• In smaller systems a mechanical, or hydraulic release allows the gear to free fall into place• There may be an emergency hand pump, accumulator or auxiliary pump• There may be a pneumatic extension systemEmergency Extension• There may be a pneumatic extension system– Air flash blow down bottle• There may be a mechanical hand cranking system• Hydraulic/pneumatic may use a detented shuttle valve to separate the normal system• Once extended via emergency system the normal system should be defeatedEmergency Extension• Some use a freefall system• Release control for the main gears may be separate from the release control for the nosegear• Main gear may need to be extended first• Politically correct terminology for emergency extension is “Alternate Extension System”• Mechanical gear retraction system will prevent gear retraction with weight on wheel beamsRetraction Nomenclature• Ground Lock• Landing Gear Safety Switch• Limit Switches (Up and Down)• Down Lock• Up Lock•Indication and Warning• Green indicator light(s) or wheels symbol• In-transit indicator• Red warning light• Warning horn•Cessna 310Gear Indication and WarningBeechcraft King AirPIPER POWERPACKPIPER POWERPACKBeechcraft Retraction• MIL-H-5606 fluid, system capacity 10 quarts• No mechanical up locks• Powerpack – 28 vdc electric motor turns a variable displacement hydraulic pump• Regulated bleed air (18 PSI) for reservoir pressurization• Two solenoid selector valves direct pump discharge for gear extend and gear retractBeechcraft Retraction• 4-second time delay reservoir fluid level sensor• System accumulator nitrogen pre-charged to 800 PSI – serviced with aircraft on jacks• Fill tank for replenishment of reservoir

• Service valve permits gear retraction with aircraft on jacks; service valve micro switchdisables landing gear relayBeechcraft Retraction• Main gear actuators- external down locks• Nose gear actuator – internal down lock– 200 to 300 PSI required to unlock down locks• Three port actuators• Pressure check valve opens at 750 PSI to provide fluid return path during extension• Hand pump dump valve opens under hand pump pressure to provide fluid return path during•emergency extensionBeechcraft Retraction• Controls, Switches, Lights and Circuit Breakers– Handing gear handle• Illuminates red for gear unsafe• Manual down lock release– Two squat switches (one on each strut)• prevents retract relay operation• down hook spring loaded over landing gear control handleBeechcraft Retraction• Controls, Switches, Lights and Circuit Breakers– Three green down and locked indicator lights– Two ampere circuit breaker protects l.g. relay– Normal retraction 6-8 seconds; 14-second time delay relay opens landing gear relaycircuitBeechcraft Retraction• Pressure switch terminates retraction at 2775 PSI• Accumulator holds gear retracted• Powerpack may cycle every 30 minutes in flight• Down lock limit switches terminate power pack operation during extension• Powerpack duty cycle– One minute cooling cycle; five minutes after five cyclesTroubleshooting• Powerpack runs more than 10 seconds– On retraction or extension – check reservoir fluid level– On retraction - check stowage of alternate hand pump– On extension – faulty down lock limit switches––Troubleshooting• Powerpack motor cycles frequently in flight– Accumulator gas precharge low• Gear will not extend– Defective service valve micro switch– Defective power pack solenoid valve

– Defective down lock switch• Gear will not retract– Defective squat switch– Hand pump handle not stowedSHUTTLE VALVESSEQUENCE VALVESIMPLIFIED LANDING GEAR SCHEMATICRETRACTION SCHEMATICPRIORITY VALVERETRACTION ILLUSTRATION:RETRACTABLE NOSE GEAR:DOWN LOCK MECHANISM:UP LOCK MECHANISM:F4S Gear IndicationGear SwingB727 Gear SelectorCessna Citation L.G. Safety SwitchKing Air L.G. Safety SwitchGrob G120Military Aircraft Up LockCessna CitationCessna Gear RetractionCessna 182R PanelAirbusPiperTwin Comanche Bungee RollerComanche Over-Center Down lockEND SECTION THREE

Aircraft Steering SystemsKey Steering Needs• Pedals actuate steering gear and rudder– Large A/C may also have separate steering wheel• Extended steering gear needs to be straight ahead for touch down and gear stowage.• Needs to steer when weight on wheels (WOT)• Needs to allow rudder action when locked straight ahead or stowedSteering Systems• Two basic types• Open - found on conventional geared aircraft• Closed - most common, pedals, third gear and rudder are looped in the systemSteering Systems• Open loop systemSteering Systems• Closed Loop SystemSteering Systems• In open loop cable systems there are pedal return springs to maintain cable tension• Tail wheels are usually attached to rudder post assembly via bell cranks and springsSteering Systems• Tail wheels can be fully castoring, or steerable and castering

• Castering pivot must be verticalor gear can get stuckSteering Systems• Smaller nose wheel systems use a Whiffle tree and mechanical linkage to close the "loop"• Larger aircraft use hydraulic power steering systems• In most nose wheel aircraft there is a shimmy damper that eliminates nose wheel shimmySteering Systems• Nose wheel shimmy is similar to control surface flutter, it can tear a nose gear off in lessthan a second• Two basic types of steering dampers are– Piston– VaneSteering Systems• Both types operate by creating chambers on either side of a moveable plate• Due to hydraulic lock the plate cannot move unless a small metering hole is introducedCessna 152 Nose GearNose wheelDe Havilland DH.82 Tiger Moth Tail WheelSTC SA2359NM XP Modification• XP Modifications Inc• XPM Tail Wheel, features a 500x5 tire mounted on a specially designed assembly that keepsbearings and key wheel parts up and out of soft sand and mud.• Advantages provided by the large tail wheel:Smooth operations• Less drag on soft ground• Better taxi visibility• Shorter take-off rolls• Improved ground handling• Improved maneuverabilityTurn LimitsSteering Systems• Larger aircraft must use some form of power assist, or full power steering system• Hydraulic power is used almost universally• There can be either– a separate nose wheel steering wheel– a rudder pedal nose wheel steering system– a mix of bothSteering Systems• Any time a hydraulic power/boost/assist system is used there must be some form of afollow-up differential control system• This functions by disengaging the hydraulic actuator after the nose wheel has pivoted thedesired amountSteering Systems• Dual Piston Steering Damper

• Oleo actuated shut off valve prevents steering when strut extended• Self centering device insures that nose gear is centered for retraction• Control cable moves bevel gears in differential control (Follow-up)Steering Systems• Orifice check valves are installed for shimmy damper action• Compensator valve maintains small positive pressure for two reasons:– Prevents cavitation if wheel is moved suddenly– Controls thermal expansion• Solenoid shut off valve allows inter-connection for towing, and failureDifferential Follow-up Steering ControlSteering Systems• The steering input is opposite the steering action therefore a gear set must be used toreverse the direction of the input or the output• The steering input unbalances the compensating device and the steering action rebalancesit.Differential Follow-up Steering ControlSteering Systems• The steering input is the same as the steering action• Again the steering input unbalances the compensating device and the steering actionrebalances it.Steering Systems• In most cases the large aircraft dual system steering will allow for limited steering from therudder pedals while allowing for more range from the cockpit steering assembly• There may be a steering wheel lock out above certain speeds• They may combine the differential steering control with the steering damperShimmy DamperPiper Steering (PA28R)• Roller alignment guide is disconnected from track while a/c is on the ground• Steering rods cause bell crank to pivot at center• Bushings on steering arm serve as a bearing surface for turning the steering arm• Torque is fed down through the center of strut to turning collarCessna Bungee Steering• Rudder pedal extensions attached to steering bell crank complete rudder "circuit" since it isimpossible to put cables under compression• Always inspect rubber boots for CO leakage

• Rudder pedals interconnect with rudder, nose wheel steering and rudder trim• Rigging order: Rudder, nose wheel steering, rudder trimCessna Bungee Steering• Functioning: On Ground:• Initial Movement of Pedal• Turning force is applied to steering bell crank (whiffletree)• Rudder moves by cable actuation• Spring bungee is compressed at this time and nose gear does not turn much until rollingCessna Bungee Steering• Torque is fed down through the center of strut to turning collarCessna Bungee Steering• In Flight:• Initial movement of Pedal• Rudder moves because action of cables through spring bungee• Nose wheel is locked out of system by centering camCessna Bungee Steering• Continued Movement of Pedal: Nose wheel remains locked out of system and bungeemoves• Rudder Trim Interconnect: Rudder trim prepositions rudder by means of threaded shaftwhich compresses spring within bungee and displaces rudder and pedal only. Since spring iscompressed within the bungee, the nose wheel does not turn.END SECTION FOUR

Aircraft Brakes–The basic principle behind any braking operation is to create a controlled friction processthat increases the rate of deceleration–Acceleration converts heat energy into motion–Deceleration converts motion into heat energyAircraft Brakes–Two main methods of increasing aircraft friction or drag in a controlled manner– Increase aircraft to surrounding air drag• Airbrakes, spoilers, flaps, reverse thrusters, drag chutes, etc..– Increase aircraft to ground drag• Anchors, skids, mechanical brakes, hydraulic brakes, pneumatic brakesAircraft Brakes–One main method of increasing aircraft friction or drag in an uncontrolled mannerAircraft Vs Automotive–Some of you may be familiar with the power assist systems used in automotive

–This type of system power assists the mechanical application of a hydraulic brake system.–The hydraulic brake system is independent from the power assist system (Pneu. or Hyd.)–This system is rarely used on aircraftAircraft Vs Automotive–Aircraft and automotive braking needs are very different–Aircraft braking speeds far exceed automotive–Aircraft braking weights far exceed auto–Auto braking duration far exceeds aircraft–Automotive ratio of braking/nonbraking much closer to 20/80, aircraft 0.0001/99.9999 (est.)Aircraft Brakes–In any case the braking system for any vehicle must be able to meet or exceed thecoefficient of friction between the tire and the braking surface–Anti-skid systems (covered later) are an attempt at splitting the line between meeting andexceeding the tire's skidding abilityBrake Maintenance–You must be at least Airframe rated to perform and return to service any brake work–Brake systems may be rebuilt, resealed, rehosed, new brake material installed, new fluidinstalled, new or serviceable parts installed, etc.–Remember to always be extremely clean and thorough with any brake work.Aircraft Brakes–Braking systems fall into three basic categories–Mechanical brakes - independent– Hydraulic brakes - both– Pneumatic brakes - dependent• (depends on external pressure source)Independent Brakes–Do not use an external power source other than the operator's mechanical application–Usually consist of one complete system for the left main gear, and one for the right maingear (nose gear use brakes on some large aircraft)–In some cases they will use the same reservoir for both sides (Piper)–Commonly the reservoir is a part of each M/CIndependent Brakes–Common manufacturers:–Bodell/Firestone–Cleveland–Goodrich–Goodyear–Matco–WarnerBrake Assemblies

–They all function by forcing a moving surface to rub or drag against a stationary surface–The two surfaces usually differ greatly in composition and hardnessBrake Assemblies–In most cases this rubbing motion is a rotating motion and is associated with wheel rotation–If the rotation rate of the wheel is slowed down then the linear speed of the aircraft will beslowed down providing the wheel does not slideBrake Assemblies–Extreme amounts of heat will be generated at any point where sliding friction occurs–Some Vehicle Gross Weights are established by the ability to brake, not the ability to carry aloadBrake Assemblies–The three sections of any brake system include:– The brake assembly: friction device– The control or actuating system– The linkage, plumbing, power boost systemBrake Assemblies–Mechanical Brakes–Tend to be very weak–Heavy–Need constant adjustment–Often subject to binding and failure–Used only on small early or experimental aircraftBrake AssembliesMechanical BrakesBrake Assemblies–Hydraulic Drum Brakes–Much stronger–Lighter systems overall–Are usually self adjusting–Rarely subject to binding and failure–Used only on small early or experimental aircraftBrake AssembliesHydraulic Drum BrakesLanding GearBrake Assemblies–Floating Hydraulic Drum Brakes–Even stronger–The piston actuates the primary shoe–The primary shoe begins to drag actuating the secondary shoe–The secondary shoe does most of the braking actionBrake AssembliesFloating Hydraulic Drum BrakesBrake Assemblies–Drum Brakes

–43.13 indicates drums can sustain 1 inch cracks as long as they don't reach an edge–Overall these brakes are limited in the amount of friction surface area that can becompacted into a small spaceSingle Servo Shoe BrakesSingle Servo Brake AssemblyDuo Servo Brake AssemblyBendix Duo-ServoBrake Assemblies–One version of the drum type brake is the expander tube brake used from the 30s - 50s–This uses a flat hydraulic inner tube that expands when pressurized causing thesurrounding braking pucks to rub against the outer drum–These tended to swell and leak causing dragging and occasional brake firesBrake Assemblies–Expander tube brakes–Can have more than one row of pucks–Tend to take a set when extremely coldP47 Expander TubeExpander Tube BrakeExpander Tube BrakeExpander Tube BrakeBrake Assemblies–Hydraulic Disc Brakes–Strongest type of brake system available–Lightest system overall–Are always self adjusting–Rarely subject to binding and failure–Used on most aircraftBrake Assemblies–Hydraulic Disc BrakesBrake Assemblies–The discs are steel, and rotate with the wheel–The shoes, or pads/pucks are mixtures of asbestos, organic compounds such as nut shells,and soft metal chips such as brass, lead, aluminum, or carbon–These are installed in a hydraulic clamping device that is attached to the landing gearBrake Assemblies–As the aircraft gets bigger multiple disks and pads can be stacked into each assembly–In some cases the metal discs rotate and the braking discs are stationary–In other cases the braking discs rotate and the metal discs are stationaryBrake Assemblies–Parts include:– Pads, pucks, or shoes– Calipers, or wheel cylinders– Discs, or drums

– Backing plate– Landing gear axle assembly–Wheel and tire assemblyBrake Assemblies–Pneumatic brakes are not very common on aircraft–They can be found used as a back up system–Large non aircraft vehicles use pneumatic systems (Trains, trucking, etc..)–They can be pressure applied, or pressure deapplied - spring appliedBrake Assemblies–Single piston brake assembly–Used on small general aviation aircraft–One piston with a floating caliper–Fixed disc (to the wheel assembly)–As the pressure increases the piston forces the pressure plate lining into the disc, and thefloating caliper forces the backplate lining into the other side of the discBrake AssembliesBrake Assemblies–These assemblies can have more then one piston–They can have more then one caliper assembly–The caliper assembly can be fixed and the disc is floatingBrake Assemblies–3 Piston Floating Disc Caliper AssemblyBrake Assemblies–Wear Indicator Caliper–Has a pin sticking out the visible side that indicates pad or puck wear–Pin also functions as a part of the piston retraction mechanism–Refer to manufacturer's specifications for proper pin depthsBrake Assemblies–Auto adjusting pistonGoodyear BrakesGoodyear Brake LiningsLinings, Rivets and PinsLining LimitsLiningsCleveland Brake LiningsBrake Assemblies–Pad thickness–Always refer to manufacturer's specifications–Pad material may come with back plate or is riveted to old back plateBrake Assemblies–Pad or puck replacement–Usually done with aircraft wheel removed–Reservoir vent opened, fluid level lowered as needed

–Disassemble brake assembly as needed to remove pad–If non-riveted type then replace pad and reassembleBrake Assemblies–If riveted type then remove rivets and old puck, by drilling and punching out old rivet–Clean & inspect backing plate–Install new pucks with new rivets installed in the same direction as old materials–Rivets are commonly copper, can be squeezed with small hammer and drift, or an arborpressBrake Assemblies–Pad/puck thickness measuringMatco Wheel and BrakeT6 STC Brake ConversionBrake Assemblies–Disc coneing and warpage–They can cone in either direction–They can warp like a potato chip–They can wear to uneven thickness radially–They can wear to uneven thickness in circumference–They can crack in many different ways (heat)Brake Assemblies–Disc coneingShoe BrakeBrake Cooling–Main brake cooling system–Ducted manifold system from air inlet scoop–Feeds ram air into wheel well–Directs cold air onto brake assemblies when gear is retracted–Probably doesn’t do much since brakes get hottest on landings, more than takeoffsBrake Maintenance–Some brake pucks come with a back plate bonded to the lining–Some must have the lining riveted to a mounting plate–Some linings are just inserted into a retainer and held in place by the assembly–Always use the manufacturer's brake pucks and retainer partsBrake Maintenance–To install puck linings on the puck backing plate, use the appropriate manufacturer's rivets,and the proper rivet set–Can be set by hammer, or by an arbor press–Setting too tight will shatter the puck–Setting too loose will cause the puck to move and wallow out the rivet hole–The rivet shop end is usually on the puck sideBrake Maintenance–New brake pucks must be seated into the discs

–New brake pucks must be cured with heat from initial applications–Too much heat will burn the bonding resins–Too little heat will wear the cured pad portion away without curing the new surface materialBrake Maintenance–To properly condition brake pucks apply brakes medium amounts five to six times at 25 to30 MPH–Allow partial cooling between applications–Unusual brake puck wear, brake shimmy, brake pull can be due to improperly temperedbrake liningsActuating Systems–It is very common for the brake pedals to be the upper part of the rudder pedals–These are called toe brakes–In some installations the whole pedal pushes for rudder / steering action, and rocks orpivots for braking actionActuating Systems–The most common type of brake actuating system used on aircraft is the hydraulic system–Two basic types– Independent: Not dependent on engine driven hydraulic system– Dependent: Dependent on engine driven hydraulic systemIndependent Brakes–A typical master cylinder will consist of a:–Piston–Cylinder–Piston connecting rod–Reservoir or inlet port–Pressure or outlet port–Pressure return or compensating valveIndependent Brakes–In the relaxed position the compensating valve is open, the piston is retracted–The first section of travel the return valve closes, no brake actuation occurs–The next section of travel the piston moves down creating pressure, which in turn actuatesthe brake assembly–When the brake returns to relaxed, the comp- ensating valve is opened, releasing allpressureIndependent Brakes–Fluid return, and brake release is caused by– Return springs in the brake assembly– Slight flexing of the caliper piston seals– The disc rotor just pushes the piston backIndependent Brakes–Typical Master CylinderIndependent Brakes–Typical Master Cylinder

Independent Brakes–Typical Master CylinderIndependent Brake SystemIndependent BrakesIndependent Brake Troubleshooting• Dragging brake– Broken master cylinder return spring– Dirty, corroded piston/caliper– Restricted master cylinder compensating port (contaminated or binding pedalassembly)• Spongy brake– Air– Deteriorated brake hose• Brake grabs– Fluid leak on brake lining• Brake fade or parking brake creeps “Off”– Internal master cylinder leakIndependent Brakes• Pedal Pulsing– Uneven wear on rotor–Warped rotor• Wheel shimmy with brakes applied– Uneven wear on rotor–Warped rotor• Scraping noise with brakes applied– Linings worn out• Puddles on ground– Failed o-rings or hosesIndependent Brakes–Flushing–Done to clear system free from contaminates–Water, air, dirt, oil, debris–System can be flushed from low to high using a pressure pot–System can be flushed from high to low using a hose and a bottle of fluid–Most common fluid used is H-5606Parking Brakes–Is usually a racheting master cylinder that feeds both independent brakes–Not wise to leave aircraft locked with this brake on– heat can rupture a system– Aircraft cannot be moved by ground supportBrake BleedingEND OF SECTION FIVE

Brake Assemblies–Multi disc assemblies–Commonly use carbon braking disc–Still use steel wearing discs–These systems are designed to withstand very extreme temperature, and weatheroperating conditions

–The various discs can be solid, segmented, slotted, internal or external tangs or notchesBrake Assemblies–In every case they will index alternately to the inside or the outside, with one side beingattached to the gear and the other a part of the wheel–These will have an even distribution of pistons in the complete circumference of the brakedisc assemblyBrake Assemblies–Multi disc assembliesBrake AssembliesMulti discassembliesBrake AssembliesMulti discassembliesBrake AssembliesMulti disc assembliesMig 21 Tire, Wheel, BrakeOff-Aircraft Inspection/Servicing• AN MS and Special bolts and other hardware– Visual, dimensional and magnetic particle inspection• Inlet and bleeder adapter• Torque tube and pressure plate– Visual, dimensional and magnetic particle inspection• Piston Housing– Visual, dimensional and fluorescent penetrant inspection– Pistons, seals, backup rings and insulatorsOff-Aircraft Inspection/Servicing• Stationary and rotating discs– Thickness, wear, cracks at relief slots– Tangs and slots– Loose rivets and pads that are curled– Glazed pads• Self-adjusters– Visual and magnetic particle inspection•Semi-Boosted Brakes–Boost assisted brakes hydraulic systems are not independent of each other–The mechanical action of the operator does some of the work–Engine driven hydraulics do the rest of the workSemi-Boosted BrakesPower Boosted Brakes–Similar to semi-boosted in theory, the operator's actuating force is not part of the brakeactuating force–They are similar to the independent brakes in that left pedal operates left brake, and right

pedal operates right brake–They operate by diverting a controlled amount of hydraulic fluid from the engine drivenpump to the brake assembliesPower Boosted Brakes–In some large aircraft systems the nose gear will also have braking capabilities–If both pedals are being applied equally the nose brake will assist braking–In theory of operation they are also similar to the differential follow-up steering devices–They are dependent on the aircraft hydraulic system for operating powerPower Boosted Brakes–The braking function calls for the operator to apply a fixed amount of pedal travel to get afixed amount of braking–As long as the pedal remains in the same position you should get the same amount ofbrakingPower Boosted Brakes–Although hydraulic valves can regulate they still either let fluid flow or don't let it flow,based upon a fixed amount of travel–By modifying the valves to be self adjusting using balancing springs, and pressuredifferential changes across the spool valve, we create a valve system that will allow a fixedamount of fluid flow for a fixed amount of pedal travelNo Boost BrakesPower Boosted Brakes–By modifying the valves to be self adjusting– using balancing springs– pressure differential changes across the spool valve– we create a valve system that will allow a fixed amount of fluid flow for a fixed amount ofpedal travelPower Boosted Brakes–Pressure Ball-Check Brake Control Valve–Very similar to PBCV–Instead of a spool for valving it uses a piston and a check-ball–Instead of two coiled balanced coil springs it uses one coil spring and a flexing lever–The application of hydraulic pressure on the piston springs closes the check-ballPower Boosted Brakes–Pressure Ball-Check Brake Control ValvePower Boosted Brakes–Hydraulic fluid source, High pressure–Power brake control valves–Pedal assemblies and linkage–Control valves Emergency Pneumatics–Anti skid Air/oil transfer tube

–Deboosters Emergency valve–Shuttle valves Pressure cylinderPower Boosted Brakes–Debooster Assemblies–Much like an electronic transformer, trading pressure for volume instead of voltage forcurrent–As the debooster reaches the maximum range of its travel a pin opens a through flow checkvalve allowing full pressure to reach brakes: used for emergency situations such as a leak–Lockout Debooster Assemblies–Much the same as a normal debooster except it can be locked to a closed through flowstate when the debooster piston reaches full extention–It must be manually set to open via pin handle–This allows for a complete lock out of each brake in the event of t major leakPower Boosted Brakes–Shuttle valve–Keeps the normal brake hydraulic system separated from the emergency system duringnormal operation–Will allow brake system to swap to an alternate pressure source during emergency brakingPower Boosted Brakes–Air / oil transfer tube–This is a tank full of oil that will be fed into the hydraulic system during emergency brakeoperations–The oil is forced into the system by gas pressure from an emergency discharge bottle–In principle it is very similar in operation to a pressure accumulatorPower Boosted Brakes–Air / oil transfer tubePower Boosted Brakes–Air / oil transfer tubePower Boosted Brakes–Air / oil transfer tubeAnti Skid Brakes–The main purpose of aircraft anti-skid is to maximize braking effectiveness during allbraking conditions–The basic operation is to monitor all wheel rotation speeds–When a difference begins to occur the offending brake is automatically deactivated slightly,until it comes back up to speedAnti Skid Brakes–Will prevent the aircraft from touching down with the brakes on–Will reduce the possibility of tire hydro planeing–Generally does not operate under 20 mph

–Usually has several common components found on most vehicles that use anti skidAnti Skid Brakes–Used exclusively on aircraft with power brake systems–Some form of wheel speed sensor, usually one for each braked wheel–Some form of brake servo valve, usually one for each braked wheel–Some form of electronic control unit, often internally independent for each wheelAnti Skid Brakes–To prevent an inadvertent locked wheel during touchdown the systems leaves the brakesfully released until the WOW switch is moved to ground–Two basic types of wheel speed sensors are an A/C sine wave signal generator, and a D/Cvoltage generator.–The A/C type control box has an internal signal converter. Probably a rectifier circuitAnti Skid Brakes–The wheel servos operate by releasing brake fluid pressure back to return, until the wheelcomes back up to speed–They then start reapplying the brake to a lessor degree, attempting to achieve maximumbraking action–Using a linear elector motor that deflects fluid flow, the valve spool is position by varyingdegrees of fluid pressureAnti Skid Brakes–The computer control unit is able to sense when a wheel is begging to change speed andpredicts impending skid–By using data from the other wheels, and remembering the what the wheel speed was priorto slippage it can determine when the wheel is back up to proper speedAnti Skid Brakes–Since the aircraft is decelerating it is actually looking for a change in the rate ofdeceleration of any given wheel–There are various different activation thresholds for different systems, but it is common forthese modern systems to be reacting within several hundredths of a second–All systems include operator indication and self test functionsAnti-Skid Highlights• Electro-hydraulic system• Armed by a cockpit switch• Electric AC or DC wheel speed sensors

• Operates just below the skid point at an impending skid• Warning lamp illuminates when the system off or during a system failure• Skid sensed – control valve relieves pressure from brake• Touchdown protection through squat switch – no signal sent to control boxGround System Test• Simulates wheel lock-up, release and restoration of brakes:– Cockpit anti-skid switch “ON”• Depress pedals – left and right brake lights illuminate• With pedals still depressed, press test switch – lights remain on; switch released –brake lights extinguish and then illuminateFight System TestAircraft configured for landing– Cockpit anti-skid switch “ON”Simulates touch down protection feature:• Depress pedals – left and right brake lights remain offSimulates normal brake function:• With pedals still depressed, press test switch – lights illuminate as long as switchdepressedTweak Test - Wheel Speed SensorSimulates skid followed by normal braking:• Remove hub cap• With brake applied, spin sensor blade• Brake will momentarily release, then reapplyDC Wheel Speed Sensor Tweak Test• Remove wheel hub cap to expose sensor blade.• With anti-skid switch “ON” and brake applied, give blade sharp spin with your finger.• In a properly operating system, brakes momentarily release then reapply.• If the sensor fails the tweak test, check the resistance using a sensitive ohmmeter.DC Wheel Speed Sensor Resistance Test• Remove cable connector and measure resistance of armature while slowly rotating blade3600.• Uniformity and amount of resistance through blade travel should be within maintenancemanual specifications.DC Wheel Speed Sensor Polarity Test• Place meter on lowest DC voltage scale; attach positive lead to pin “B” and negative lead topin “A”.• Tweak blade in clockwise direction viewed from drive end.• Meter should read upscale.

Control Box• Check by substitution method– Swap cables• Problem changes sides – control box defective• Problem remains on same side – wheel speed sensor or control valve defectiveControl Valve• Measure control valve coil resistance using sensitive ohmmeter– Resistance within specification, control valve parts are defectiveB757 HYDRAULIC CONTROL PANELB757 CONTROLB757 NOSE LANDING GEARB757 NWSB757 MAIN GEARB757 PROXIMITY SWITCHB757 BRAKE SYSTEMB757 ANTI-SKIDB757 AUTOBRAKESB757 AUTOBRAKESAnti-corrosion SealantB787 Electric BrakeB737-800 Brake ChangeBeechcraft Super King AirEND OF SECTION SIX

Aircraft Wheels–Aircraft Wheels–Usually two piece–Two opposing conical tapered bearings for each wheel–Can be tube type or tubeless–Tubeless will have seal rings or sealing compound between halvesAircraft Wheels–Wheels are either aluminum alloy or magnesium alloy–Are either cast or forged, and therefore can be subject to intergranular corrosion–The bead seat area and the bolt hole areas are the most critical inspection areas–The inboard half also houses the brake assemblyAircraft Wheels–Commonly has fusible plugs that will release pressure if tire exceeds a critical temperature–Bearing cups are usually interference fit into each half, or into one half with a flange for theother half–Inflation valve, or hole is usually on the outboard halfAircraft Wheels–Aircraft tires are generally removed by splitting the wheel in half

–Must not have any air pressure in tire when loosening bolts, (remove valve core)–Can use an arbor press or drill press, turned off, to press bead off of rim, on both sides–Wheel inspection is critical for cracks, corrosion, or damaged bead/bolt areasAircraft Wheels–If any fusible plug shows sign of damage, replace all of them–Eddy current inspection is the best way to check for subsurface damage–Fix a flat tire injection formulas can contain explosive gasses–Cracks can also develop in the brake disc mounting areasAircraft Wheels–Bolts may be unidirectional - interference–Tighten in a criss cross pattern, in stages–Do not use soap on tube type tires, the sudden acceleration of landing will cause them toslip–Mount the tire with red dot to the valve stem–When reassembling tube types be careful to not pinch the tube or leave any wrinklesAircraft Wheels–Tapered conical wheel bearings–Slightly loose is better than slightly too tight–Notch in plate washer is used to move washer to test for correct tension–Spin wheel when adjusting wheel bearings–Always thoroughly clean and regrease bearings and wheels when halves are separatedAircraft Wheels–Always replace both the bearing assembly and the bearing cup when replacing a bearing–Some axle seals can be reused, but most lip seals should be replaced when removed–Always renew cotter pin–Make sure cotter pin isn't dragging on dust cap or flange. Builds static charge that can wreckhavoc on many thingsAircraft Wheels–Wheels bearings usually fail due to contamination or being set too tight–Heat discoloration, brinelling, spalling, galling, and welding are the stages of wheel bearingfailure–Bearing cup can wallow loose in wheel half–Always replace bearings by part number onlyAircraft Wheels–It is best to use boiling water and ice to change bearing cups–Any damage to metal or plastic bearing cage is cause for rejection of the bearing–DO NOT, FOR ANY REASON, AIR SPIN A BEARING RACE OF ANY TYPE

–Replace any bearing with rust, or water marksAircraft Wheels–Bearing lubrication–MIL-G-3545C or MIL-G-81322–Coloration of grease is due to dyes used by manufacturer–Some extra grease in the hub area will assist in heat dissipation–Too much grease will push the wheel seals outAircraft Wheels–Pressure packing bearings is the quickest way, always keep grease systems very clean–Hand packing is done by working grease into bearing cage dragging cage lip across a handfull of grease–Do not contaminate the brake components with wheel bearing grease–Repacking wheel bearings is P.M.Wheel Types• Drop Center (Single Piece)– Tire bead forced over rim (automotive)• Demountable (Removable) Flange– Easier tire mount and dismount for stiffer tires• Split Center (Split Rim)Wheel Materials and Manufacture• Aluminum alloy or Magnesium alloy• Cast or Forged• O-ring between wheel halves -Tubeless• Knurled flanges (on some wheels) -TubeWheel Classification for Tire Casing• Type I - Smooth contour• Type II - High pressure• Type III - Low pressure• Type IV - Extra low pressure• Type VI - Low profile• Type VII - Extra high pressure• Type VIII - Extra high pressure – Low ProfileDrop Center WheelSplit Center (Split Rim)Inboard Wheel Half• Steel reinforced keyways or steel keys• Bearing cup (interference fit)• Tapered caged roller bearing• Grease seal, two retainers and snap ring• Fusible plug(s)• Over-inflation valve (on very large wheels)–May also be mounted on outboard wheel halfOutboard Wheel Half• Bearing cup (interference fit)• Grease seal, two retainers and snap ring• Inflation valve (tubeless tires) or hole for inner-tube valve stem• Axle cap and retaining ring• Anti-skid bracket attached to capOn Aircraft Wheel Inspection• Light aircraft verify proper tire pressure daily

• Heavy aircraft verify before each flight– Tire cool, or at least 2 to 3 hours after flight• Check wheel weight security• Brake tangs must align with wheel slots• Axle nut torque– Too loose, bearing cup could spin– Too tight, damaged bearingOff Aircraft Inspection• Deflate tire first• Break the bead• Remove and properly store bearings• Note wheel weight location• Remove tie bolts• Clean wheel assembly• Clean and inspect bearingsBearing InspectionBearing Cup ReplacementRemoval• Heat wheel– Boiling water for 1 hour– Oven for 30 minutes at 2250 F.• Tap cup out with fiber driftReplacement• Reheat wheel• Chill cup with dry ice• Coat cup exterior with zinc chromate primer• Drift cup in with fiber driftInspect Wheel Halves• Bead seat– Eddy current inspection• Keys or Key slots– Dye penetrant, Magnetic particle, Dimensional– Check key attachment screw stake• Internal and external surfaces– Dye penetrant, Dimensional• Bolts and other hardware–Magnetic particleInspect Wheel Halves• Fusible plug(s)– Visual, replace all if any distorted• Corrosion– Check bead seat for trapped water– Remove corrosion per manufacturers’ instructions– Treat aluminum surfaces with Alodine– Treat magnesium surfaces with Dow 19– Finish with two coats zinc chromate primer (except mating surfaces and bolt bosses – onecoat only)Fusible PlugsReassemble Wheel (Tubeless Tire)• Clean bead seat area – isopropyl alcohol• Usually inboard wheel half first– Inspect and lubricate wheel O-ring (tubeless)• Install tire on inboard wheel half

• Index outboard wheel half so that red dot on tire is adjacent to inflation valve• Lubtork bolts, washers and nuts if specified• Torque per manufacturers’ recommendations• Inflate tire in cage to ½ static inflation pressure• Final tire inflation or adjustment on aircraftReassemble Wheel (Tube Tire)• Clean bead seat area – isopropyl alcohol• Prepare and position inner tube• Prepare and position tire• Position brake disk (Cleveland brakes)• Lubtork bolts, washers and nuts if specified• Torque per manufacturers’ recommendations• Inflate tire in cage to ½ static inflation pressure• Adjust axle nut torque• Final tire inflation or adjustment on aircraft2006 Mechanic KilledB737 Nose wheel Tire166 PSI required – exposed to 3000 PSI from unregulated nitrogen cylinderCleveland 40-76AP38 Main Gear WheelT38 NoseEND OF SECTION SEVEN

Aircraft Tires–Aircraft Vs automotive/truck– Auto/truck need a medium speed tire– Long duration– Low bounce protection– High traction needs– High water displacement needs–Weight / size not very criticalAircraft Tires–Aircraft tire needs– High speed– Short duration– Very high bounce protection– Low traction– Low water displacement–Weight and size very criticalAircraft Tires–The major difference is the aircraft tire sustains much higher side wall deflection–Tires:–Type I Smooth contour type, from smooth profile– Non retractable landing gear Size: = 0D Obsolete–Type II High Pressure Tire– Retractable landing Gear Made obsolete by Type VII– Size: OD X Section WidthAircraft Tires–Type III: Most popular on GA aircraft

– Section width usually wider than bead diameter.– Lower pressures possible, as bead seat traps tire– Size: Section Width X Wheel Diameter– TSO C62–Type IV: Extra Low pressure– Rough and Unimproved runways (donut type)– Obsolete– Size: OD X Section Width X Rim DiameterAircraft Tires–Type V: Streamlined tires–Type VI: Low profile tire–Main wheel space saver tire– Limited height decreases the amount tire will drop when flat– Size: OD X Section Width X Rim Diameter–Type VII: Extra High Pressure– Standard for turbine aircraft– High load carrying ability– Size: OD X Section WidthAircraft TiresAircraft Tires–Tire Data:–Tubeless tires are marked tubeless–Tire deflection 32%-35% twice what is found in automobile tires–Nylon Stretch: New tires stretch in the initial 24 hr period after mount–May result in a 5 to 10 percent drop in pressureAircraft Tires–Suggested to let tire stand for 12 hours and inflate–Tubeless Air Diffusion: Maximum diffusion is 5% for any 24 hr. period. Allow tire to stand 12hours before check–Dual Tires: Difference of more than 5 PSI, note it in the log bookAircraft Tires–Source of Pressure Data: Aircraft maintenance manual–Air pressure in a tire will drop by 1 PSI for every 4 degree F change–Inflation Pressure As specified in the maintenance manual–Always use safety cages and safety gear when filling aircraft tires–Tire size–Tire type–Date of Man–Slippage mark–Balance mark–Ply rating–Band material–Retreading Co.–Number of Ret.

–Name of Manuf.Aircraft Tires–Ply rating–This is a means of rating tires based upon the original cotton plys found in early tires–Today's tires usually have less plys then the stamped rating valueAircraft Tires–Bead: Anchors carcass and provides mounting of tire to bead.–Bundles of wire–Apex strip: Streamlines bead–Flippers: Insulate carcass plys from bead–Carcass: rubber coated nylon cord fabric cut on a bias for balance and strengthAircraft Tires–New classification system–(prefix) (nominal outside dia.) X (nominal section width) - (bead dia.)–Prefix determines width ratio and bead ledge angle–Width ration = section width / rim width–Bead ledge = angle at the base of the beadSize DesignationsAircraft Tires–Tire storage–Store in a cool, dry, dark area–Do not stack, store vertically–Avoid any petroleum product exposure–Avoid any electrical equipment the generate ozone in the storage areaTire Care• Guard against heat build-up– Short ground rolls, slow taxi, minimum braking, proper tire inflation• Maintain tire pressure in accordance with aircraft maintenance manual• Visual inspection– Tread condition and depth, sidewallsTire Maintenance• Avoid exposure to gasoline, oil, grease, electric motors (ozone)• Store racked in a cool, dark, dry place• Check pressure weekly or sooner; recommended before each flight• Check pressure tire pressure when cool (two hours after flight; three hours on a hot day)Tire Maintenance• New mountings: check pressure for several days• Allow for nylon stretch: 5% to 10% drop in air pressure in 24 hour period• Tubeless Diffusion: After 12 hour inflation, maximum 5% loss in any 24 hour period.• Dual inflation pressure: More than 5 PSI difference, log book entry noted and condition

corrected.Aircraft Tires–Always look for damage or debris inside the tire, wrinkles in the tube, damaged fill valves–Any ribbed section cut more than 1/2 way across should be retreaded or scrapped–Any plies showing is cause for replacement–Any sidewall damage is cause for scrapping the tireAircraft Tires–Small weather checking is not cause for concern–Move aircraft once in a while to prevent permanent tire set–Always keep tire at proper inflation for the type of landing being conducted–Harder for paved strips, softer for gravel or grass stripsAircraft Tires–Corner wear is usually a camber problem–Rapid wear and shifting weight at higher lighter speeds is a toe in problemTire Maintenance• Nylon flat spotting: roll aircraft• Leaks: check with water• Replace all valve caps• Tread injury: follow aircraft manufacturers’ instructions• Cuts exposing or penetrating cord body: remove, repair, recap or scrap.• Sidewall or tread bulges: remove, mark area before deflationSchrader ValveTire Deflection MarkersAircraft Jacking• Jack per manufacturer’s directions• Use correct tools and jacks• Leave nothing under the aircraft in case it drops• Jack evenly• Locate aircraft out of high wind areas• Use caution for CG shift when jacking–May need tail/nose weight• May need several personsTailweightMounting and Demounting• Dust inside of tire and outside of tube with talc• Index tube valve stem• Assemble wheel correctly; use tire cage for inflation• Inflate, deflate and re-inflate tube-type tiresTire CageB747 Tire RuptureTube Inspection• Size “should” match tire• Inflate no more than to “round-out” tube

• Valve stem• Wrinkles: if excessive scrap• Chafing or thinning: scrapAircraft Tires–Tire balancing–Most common to see it not done, or done statically on small G/A–Any tire should be balanced dynamically with a computerized spin balancer–Allow for tire to stretch initially prior to balancing (24 hours)Static Balance StandSelecting Balance WeightBalancing WeightsScrew Balance WeightEND OF SECTION EIGHT