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

Course Outline Jodel d140c • Landing gear C150 Tail Dragger Conversion – Types Conventional (Tail Wheel) Arrangement – Configurations Older design – C.G. aft of main gear – Alignment • Steering: • Suspension systems – Rudder pedal cable connection to tail wheel – Fixed gear – Brake application and castering tail wheel – Retractable – Differential braking to assist steering Course Outline • Tail wheel as far aft as possible to extend • Retraction systems wheelbase and increase stability. • Steering systems Conventional (Tail Wheel) Arrangement • Brakes Advantages – Dependent systems • Prop clearance for low powered engines – Independent systems • Sturdy design for unimproved runways – Anti-skid control • Less drag in flight • Wheel assemblies • Greater ground maneuverability • Tires • Tail wheel failure = minimal aircraft damage Safety Conventional (Tail Wheel) Arrangement • Shock strut servicing Disadvantages • Gear retraction and extension • Ground loop and nose-over potential • Shimmy damper service • Crosswind control problems • Tire servicing and dismounting • Restricted visibility during taxi • Eye and skin protection Tricycle Gear Safety Tricycle (Nose Wheel) Arrangement • Caustic fluids • Nose gear as far forward as possible – Burns skin – Longer wheelbase – more stable – Damages surfaces – Lighter gear assembly due to longer lever arm • Flammable fluids • Castering types use differential braking to steer • Fluid contamination Tricycle (Nose Wheel) Arrangement – Leave containers closed Main gear aft of C.G. – Read labels, use proper handling equip. Advantages Safety • Difficult to nose over or ground loop • Retraction can crush you if you are in the path • More familiar ground maneuverability of the gear • Better visibility during taxi • Retraction without proper support can destroy • Less vulnerable to cross wind landing an aircraft as well • Steering: Landing Gear Purposes – Direct linkage with nose wheel bungee • Supports the aircraft on the ground – Hydraulic nose wheel steering • Absorbs landing shock (some) – Differential braking • Absorbs taxi shock (some) Tricycle (Nose Wheel) Arrangement • Attachment point for: Disadvantages – Brakes • Nose gear damage = major airframe damage – Steering • Generally not suited for unimproved runways –Wheels and tires • More expensive than conventional gear Conventional Gear • Much heavier aircraft Defn: Wheel Pants Nose Wheel Ski • The tapered tail end of the pant provides the Skis major part of aerodynamic drag reduction • Ski systems are usually pivot mounted to the Defn: Cowlings & Fairings aircraft wheel axle • A shielded section that provides aerodynamic – incorporate travel limit straps or cables (front smoothness to some area or part of the and rear) aircraft – usually have a bungee or spring to keep the Defn: Wheel Base nose up, preventing pearling during landing • May be retractable (skis retract higher then • Are usually lighter and less complex than bottom of wheel assemblies) retractable gear aircraft Skis • Have overall lower purchase and operating • Auxiliary gear, nose or tail, may or may not costs than retractable gear have a ski • The benefits from lighter weight can exceed • Are subject to corrosion damage and hard the benefits of reduced drag from retractable landing damage gear Floats • Are subject to corrosion damage and hard Floatplane Configurations landing damage • Floats Retractable Gear • Amphibious floats – wheels and floats • Streamlines aircraft reducing drag • Hull floats – bottom of aircraft = boat • More complex and heavier than fixed gear • Outrigger pontoons • Retraction methods: – Hang from wing tips or struts –Mechanical – Fold down from wing tips – Electrical Float/Hull/Pontoons – Hydraulic • Most common are dual float assemblies Anatov AN 225 • Usually are uniform shape Trailing Link landing Gear • May have retractable, and or steerable rudder B747-8 Landing Gear Ship Set assembly Skid Landing Gear • May require a vertical vane installed on lower • Used on helicopters that do not ground taxi side of fuselage below vertical stabilizer • High skids and pop-out floats available Float/Hull/Pontoons • May or may not have shock absorbing devices • Almost all water aircraft use a float shape that • May or may not have skid pads (stellite faced) includes a chined V hull • Left skid / nose low wear pattern • They usually have a stepped section that • Loose skids may cause assists the aircraft in planing across the water – Vibration (reduces water drag) – Ground resonance (fully articulated rotor) • Flying CG and floating CG may not be the Skid Landing Gear same • May have detachable wheel assemblies for – some hull planes have self flushing ballast ground handling sections / wheel well sections • Are also found on early aircraft in place of the Float/Hull/Pontoons tail wheel assembly basic shape –Wooden skid with brass or steel plate for hard Tandem Wheel Arrangement surface or leather plate for grass Aircraft with narrow fuselage Pop Out Floats • Gear positioned directly beneath fuselage • Spring Steel Gear - Cessna Type Tandem Wheel Arrangement • Load transfer only • Gliders • Minimal rebound protection • U-2 • Generally not field repairable • AV-8 Harrier • Serialized Cessna component • Usually has one main set of gears in center, • Check Cessna maintenance manual table of one steerable nose gear, and outrigger gears limits for alignment data on the wings • • Can be fixed or retractable • Tubular Steel Nose Gear – Grumman TR2 Tandem Wheel Arrangement • Load transfer only Gear Types • Minimal rebound protection • Fixed Gear • Sometimes field repairable by welding – Popular on older and low speed aircraft • Some have bungee shock cord – Speed and fuel efficiency increase with pants Wheel Alignment Fixed Gear • This is much more critical for tail draggers. • Are not able to retract into some cavity or • The aircraft should be level and the wheels aerodynamic shielding within the aircraft should be on some form of grease plates to • May be fully rigid or able to absorb landing / eliminate gear binding. taxi loads • The aircraft should be located inside where it is Fixed Gear not subject to winds. • Adequate measuring equipment should be Scissor Link Disconnected available. END SECTION ONE 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 the specifications. • Toe-in is front of tires in, • Toe-out is front of tires out Camber (- +) • 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 nose gears or motorcycles. Inclination and Offset • Steering inclination = is similar to castor but it is the measure of the angle between the pivot axis and the vertical axis of the wheel with no camber. • Trail or offset = The amount of distance between the wheel axis and the steering axis. Wheel Alignment Adjustment • Some may be adjustable by shimming the stub axle at the mounting flange Wheel Alignment Adjustment • Some may be adjustable by shimming the torque links at the center pivot Wheel Alignment • The aircraft must be located on a flat smooth surface, resting on grease plates, leveled as per manufacturer's procedure • First determine the landing gear are properly mounted and not damaged or distorted – Damage and conformity inspection, symmetry checks, etc Wheel 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 reference Straight edge and a large square Scribe and a measuring tape or bar Line of sight projection to a reference Camber • Is checked using a ruler and a level Aircraft Suspension Systems • “Necked” diameter – worn, broken elastic Suspension Systems • Replacement considered preventive • Provide controlled flexibility to the landing gear maintenance – FAR 43 Appendix A systems while maintaining their structural Bungee Cord integrity Bungee Installation / Removal Tools • Up to a point they will eliminate the unusual Spring Systems loads incurred during landing and takeoff • Flexible tapered bars and shafts operations Spring Systems • They can also reduce or eliminate ground • Flexible tapered bars and shafts operation vibrations from uneven or rough taxi Spring Systems surfaces • Less commonly there are numerous versions Suspension Systems of coiled spring, rubber disc, torsion bar, plastic • Suspension vs. Absorption flexible bar, etc. assemblies that all provide • Suspension systems are devices that allow some form of flexibility to the landing gear flexibility or bounce to occur between the ground Flexible Gear Servicing and a vehicle • Includes checking all fittings for security, • This can include low pressure tires, springs tightness, and appropriate free play (torsion, flex, coiled)(rubber, metal, plastic), • Inspect main gear for signs of corrosion, telescoping struts fatigue, hard landing damage or taxi damage Suspension Systems • Inspect auxiliary gear and steering connections • Suspension vs. Absorption for damage and corrosion • Absorption is a suppression or restriction to • Repair all worn or failed parts flexibility or bounce Flexible Gear Servicing • The most common form are air / oil filled • Some tubular structures may be repairable by telescoping struts welding • Less commonly are stiffeners such as plastic • All spring type structures are not repairable by or wood straps attached to flexing type gear welding Suspension Systems • Spring type may have serial numbers and may • Very early aircraft had rigidly mounted gear be matched pairs which means they are • As technology progressed two main forms of replaced in pairs suspension came into being Struts – Rubber bungee mechanical lever systems Suspension Systems – Flexible metal tapered bars or shafts • Oleo Telescoping Strut Suspension Systems • Over all aircraft it is the most commonly used • The main advantage of these two systems are: suspension system – they are light • Range from 1" in shaft diameter to 10", 12", – easy to maintain etc. – relatively inexpensive • Can be used as main gear, or as auxiliary gear – fairly aerodynamically clean • Can be steerable, fixed or free castoring • The main disadvantage is they provide no Suspension Systems permanent shock absorption • Oleo Strut - Basic principle of operation Suspension Systems • A telescoping strut that contains compressed • Air-Oleo struts were then designed to: gases and fluid, usually a light oil – suspend, or provide bounce • The compressed gas causes the strut to – and to truly absorb the shock energy, or extend thereby sustaining the changing weight prevent spring-back. of • Note: FAA test questions handle this badly the aircraft (suspension) • Springs and bungees only delay the shock Suspension Systems energy, but eventually spring back. • For the strut to change length the oil must pass Suspension Systems through a restricted orifice • Bungee System • Due to the nature of hydrostatic lock this Elastic Shock Ring restriction of oil flow "meters" the rate at which Shock Ring Notes: the strut can change length (shock absorption) • Remove boot for thorough inspection • The tapered metering pin determines the rate • Beware – safety hazard of compression • Oil stained cotton cover – damaged Suspension Systems • Torque or scissors links maintain wheel • Has no valve core alignment • Base nut and swivel are 3/4" • May have a flapper return valve that allows the • Has a roll pin to keep swivel valve in place strut to extend quicker then it compresses • Base nut torque is 110 in/lbs • Very slight seepage of seals is normal to • Swivel nut torque is 70 in/lbs lubricate the piston • Pressure rated to 5000psig • Oleo Strut MS 28889 Fill Valve • Oleo strut telescoping AN 6287 Fill Valve • Oleo strut telescoping • Has high pressure valve core (stamped H) and • Oleo strut telescoping a swivel nut valve • Oleo strut telescoping • Base nut is 3/4", Swivel nut is 5/8" Oleo Strut Parts • Base nut torque is 110 in/lbs • Main Strut, outer tube • Swivel nut torque is 70 in/lbs • Piston, piston rod, inner cylinder • Pressure rated to 3000 psig • Upper or inner strut seal rings • Do not interchange with MS 28889 • Upper inner bearing AN 6287 Fill Valve • Snubber or return valve (sometimes) AN 812 Fill Valve • Lower outer collar, bearing and gland nut • Has only a valve core Oleo Strut Parts • Base nut is 5/8" • Oil and gas fill plug / valves • Med. press. valve core short type stamped H • Neoprene V-ring seals • Base nut torque is 75 - 100 in/lbs • Orifice tube • Pressure rated to 1500psig • Orifice or snubber plate • Do not use in place of MS28889 or AN6287 • Tapered metering pin AN 812 Fill Valve • Oil Fill Valve Warning • Dry gas • All the fill valves are interchangeable Oleo Strut Notes • DO NOT DO INTERCHANGE THEM • Strut service is preventative maintenance • DO NOT ATTEMPT TO USE AUTOMOTIVE • Earlier struts used O-ring seals VALVE CORES WITH EITHER THE AN 6287 • Newer use stacked V-ring seals OR – Fluid pressure is applied to the inside of the V THE AN 812 – Or D-rings with round side facing movement • DO NOT INTERCHANGE VALVE CORES OR • Piston is hardened polished and or chromed CAPS BETWEEN ANY OF THEM steel Oleo Strut Servicing • Gland nuts are bronze (may or may not be • Servicing data may come from current adjustable) maintenance manual, or data plates Oleo Strut Notes • Depressurize, remove from plane • Deflating struts will protect piston from • Disassemble and clean, inspecting for any corrosion damage, corrosion or cracks • Piston may have a spline or cam that aligns the • Replace all rubber seal components, worn nose gear for retraction bushings, and failed parts • Strut extension distance at a given weight is Oleo Strut Servicing the common method for determining gas • Reassemble, add oil to level with filler opening, charge bleed air out, and seal • Seal compatibility determines type of oil • Reinstall and repressurize with nitrogen • Strut should have a data plate attached • 100hr / annual must include checking strut fluid Oleo Strut Notes and gas levels • Dried Nitrogen is the gas of choice • Typical pressures range from 150 - 1000 psi – Inert • You will not be able to service a strut with shop – Inexpensive air sources – No moisture Oleo Strut Servicing • Three type of filling Valves • Use a nitrogen charged bottle, or a strut pump –MS 28889 most common (12:1) – AN 6287 • Cycle pressurized strut several times to ensure – AN 812 older models seal seating and air bubble removal MS 28889 Fill Valve • Struts can have slow gas leaks, recheck fill • Ground lock or pin = prevents accidental after 24 hours retraction, should have red flag attached • Always rock the aircraft prior to measuring strut Retraction Parts extension • Weight on wheels switch, squat, ground safety Strut Servicing sw. etc = usually attached to gear torque Strut Service scissor links Strut Service • Limit switches = micro switches that electrically Strut Inflation sequence gear retraction Strut Inflation • Sequencing valve = hydraulic valves the Strut Inflation sequence gear retraction B737 Main Landing Gear Retraction Systems END SECTION TWO • Priority valve = same as sequencing valve but is actuated hydraulically AVIM 103D • Indicating system = red, amber, green lights, Aircraft Retraction Systems horns, barber poles that indicate gear position Retraction Systems • Red = unsafe, in transition • Aircraft gear retraction systems can be found • Green = down and locked, up and stowed on many aircraft • Lights may have push to test feature • From the small experimental Vari-eze to the Retraction Systems ultra-large AN 124 (winged building) • Retraction systems must be tested fully during • In most cases the retraction process is 100 hr and annual inspections accomplished with hydro-electrical force • This includes inspection, lubrication, and an connected operational test with the gear off the ground to mechanical linkage • Any additional safety and alarm systems must Retraction Systems also be tested, such as throttle horns, • In most cases the retraction process includes indicator lights the opening, and closing of doors or covers • Avoid testing the squat switch the hard way that complete the aircraft's aerodynamic shape Retraction Operation • In most cases all the gear retract • Down and locked • With retractable conventional gear the tail Retraction Operation wheel often doesn't retract • Inboard gear door open, gear in transition Retraction Systems Retraction Operation • In most cases steering gear needs to be • Gear up, inboard gear door in transition repositioned correctly for retraction Retraction Operation • Gear can retract in any direction, forward, • Gear cycle complete backward, inboard, outboard, or rotating to fit • gear up into a special compartment. Retraction Systems • They can retract into the wing or the fuselage • DC-10 uses Oleo strut gear • They can change the aircraft CG when • Mains retract inboard, nose retracts forward retracting or extending • Mains use a four wheel truck or bogee 2X2 Retraction Systems • Incorporates the use of axle beams and beam • They will contain many adjustable devices that trim cylinders limit travel or notify the pilot of landing gear • Every wheel contains a brake assembly configurations and conditions • Retraction and braking is hydro-mechanical • They must have some emergency, auxiliary Retraction Systems means of extension • Retraction sequencing is accomplished with a • Any hydraulic, or electrical failure cannot cause follow-up hydraulic-mechanical control valve the gear to automatically retract • System uses various cables, levers and bell • Most contain safety systems that limit when the cranks to control the landing gear control valve gear retr./ext. may be operated assembly Retraction Parts • Main gear doors can be locked closed to use • Trunion = the main pivot point, and attach point as a work platform • Drag or Side braces = provide rigidity when Emergency Extension locked down • All retractable gear system must have an • Overcenter lock = similar to a knee joint alternate means to extend the landing gear • In smaller systems a mechanical, or hydraulic • Service valve permits gear retraction with release allows the gear to free fall into place aircraft on jacks; service valve micro switch • There may be an emergency hand pump, disables landing gear relay accumulator or auxiliary pump Beechcraft Retraction • There may be a pneumatic extension system • Main gear actuators- external down locks Emergency Extension • Nose gear actuator – internal down lock • There may be a pneumatic extension system – 200 to 300 PSI required to unlock down locks – Air flash blow down bottle • Three port actuators • There may be a mechanical hand cranking • Pressure check valve opens at 750 PSI to system provide fluid return path during extension • Hydraulic/pneumatic may use a detented • Hand pump dump valve opens under hand shuttle valve to separate the normal system pump pressure to provide fluid return path • Once extended via emergency system the during normal system should be defeated •emergency extension Emergency Extension Beechcraft Retraction • Some use a freefall system • Controls, Switches, Lights and Circuit Breakers • Release control for the main gears may be – Handing gear handle separate from the release control for the nose • Illuminates red for gear unsafe gear • Manual down lock release • Main gear may need to be extended first – Two squat switches (one on each strut) • Politically correct terminology for emergency • prevents retract relay operation extension is “Alternate Extension System” • down hook spring loaded over landing gear • Mechanical gear retraction system will prevent control handle gear retraction with weight on wheel beams Beechcraft Retraction Retraction Nomenclature • Controls, Switches, Lights and Circuit Breakers • Ground Lock – Three green down and locked indicator lights • Landing Gear Safety Switch – Two ampere circuit breaker protects l.g. relay • Limit Switches (Up and Down) – Normal retraction 6-8 seconds; 14-second • Down Lock time delay relay opens landing gear relay • Up Lock circuit •Indication and Warning Beechcraft Retraction • Green indicator light(s) or wheels symbol • Pressure switch terminates retraction at 2775 • In-transit indicator PSI • Red warning light • Accumulator holds gear retracted • Warning horn • Powerpack may cycle every 30 minutes in • flight Cessna 310 • Down lock limit switches terminate power pack Gear Indication and Warning operation during extension Beechcraft King Air • Powerpack duty cycle PIPER POWERPACK – One minute cooling cycle; five minutes after PIPER POWERPACK five cycles Beechcraft Retraction Troubleshooting • MIL-H-5606 fluid, system capacity 10 quarts • Powerpack runs more than 10 seconds • No mechanical up locks – On retraction or extension – check reservoir • Powerpack – 28 vdc electric motor turns a fluid level variable displacement hydraulic pump – On retraction - check stowage of alternate • Regulated bleed air (18 PSI) for reservoir hand pump pressurization – On extension – faulty down lock limit switches • Two solenoid selector valves direct pump – discharge for gear extend and gear retract – Beechcraft Retraction Troubleshooting • 4-second time delay reservoir fluid level sensor • Powerpack motor cycles frequently in flight • System accumulator nitrogen pre-charged to – Accumulator gas precharge low 800 PSI – serviced with aircraft on jacks • Gear will not extend • Fill tank for replenishment of reservoir – Defective service valve micro switch – Defective power pack solenoid valve – Defective down lock switch • Castering pivot must be vertical • Gear will not retract or gear can get stuck – Defective squat switch Steering Systems – Hand pump handle not stowed • Smaller nose wheel systems use a Whiffle tree SHUTTLE VALVES and mechanical linkage to close the "loop" SEQUENCE VALVE • Larger aircraft use hydraulic power steering SIMPLIFIED LANDING GEAR SCHEMATIC systems RETRACTION SCHEMATIC • In most nose wheel aircraft there is a shimmy PRIORITY VALVE damper that eliminates nose wheel shimmy RETRACTION ILLUSTRATION: Steering Systems RETRACTABLE NOSE GEAR: • Nose wheel shimmy is similar to control DOWN LOCK MECHANISM: surface flutter, it can tear a nose gear off in less UP LOCK MECHANISM: than a second F4S Gear Indication • Two basic types of steering dampers are Gear Swing – Piston B727 Gear Selector – Vane Cessna Citation L.G. Safety Switch Steering Systems King Air L.G. Safety Switch • Both types operate by creating chambers on Grob G120 either side of a moveable plate Military Aircraft Up Lock • Due to hydraulic lock the plate cannot move Cessna Citation unless a small metering hole is introduced Cessna Gear Retraction Cessna 152 Nose Gear Cessna 182R Panel Nose wheel Airbus De Havilland DH.82 Tiger Moth Tail Wheel Piper STC SA2359NM XP Modification Twin Comanche Bungee Roller • XP Modifications Inc Comanche Over-Center Down lock • XPM Tail Wheel, features a 500x5 tire END SECTION THREE mounted on a specially designed assembly that keeps Aircraft Steering Systems bearings and key wheel parts up and out of soft Key Steering Needs sand and mud. • Pedals actuate steering gear and rudder • Advantages provided by the large tail wheel: – Large A/C may also have separate steering Smooth operations wheel • Less drag on soft ground • Extended steering gear needs to be straight • Better taxi visibility ahead for touch down and gear stowage. • Shorter take-off rolls • Needs to steer when weight on wheels (WOT) • Improved ground handling • Needs to allow rudder action when locked • Improved maneuverability straight ahead or stowed Turn Limits Steering Systems Steering Systems • Two basic types • Larger aircraft must use some form of power • Open - found on conventional geared aircraft assist, or full power steering system • Closed - most common, pedals, third gear and • Hydraulic power is used almost universally rudder are looped in the system • There can be either Steering Systems – a separate nose wheel steering wheel • Open loop system – a rudder pedal nose wheel steering system Steering Systems – a mix of both • Closed Loop System Steering Systems Steering Systems • Any time a hydraulic power/boost/assist • In open loop cable systems there are pedal system is used there must be some form of a return springs to maintain cable tension follow-up differential control system • Tail wheels are usually attached to rudder post • This functions by disengaging the hydraulic assembly via bell cranks and springs actuator after the nose wheel has pivoted the Steering Systems desired amount • Tail wheels can be fully castoring, or steerable Steering Systems and castering • Dual Piston Steering Damper • Oleo actuated shut off valve prevents steering • Rudder pedals interconnect with rudder, nose when strut extended wheel steering and rudder trim • Self centering device insures that nose gear is • Rigging order: Rudder, nose wheel steering, centered for retraction rudder trim • Control cable moves bevel gears in differential Cessna Bungee Steering control (Follow-up) • Functioning: On Ground: Steering Systems • Initial Movement of Pedal • Orifice check valves are installed for shimmy • Turning force is applied to steering bell crank damper action (whiffletree) • Compensator valve maintains small positive • Rudder moves by cable actuation pressure for two reasons: • Spring bungee is compressed at this time and – Prevents cavitation if wheel is moved suddenly nose gear does not turn much until rolling – Controls thermal expansion Cessna Bungee Steering • Solenoid shut off valve allows inter-connection • Torque is fed down through the center of strut for towing, and failure to turning collar Differential Follow-up Steering Control Cessna Bungee Steering Steering Systems • In Flight: • The steering input is opposite the steering • Initial movement of Pedal action therefore a gear set must be used to • Rudder moves because action of cables reverse the direction of the input or the output through spring bungee • The steering input unbalances the • Nose wheel is locked out of system by compensating device and the steering action centering cam rebalances Cessna Bungee Steering it. • Continued Movement of Pedal: Nose wheel Differential Follow-up Steering Control remains locked out of system and bungee Steering Systems moves • The steering input is the same as the steering • Rudder Trim Interconnect: Rudder trim action prepositions rudder by means of threaded shaft • Again the steering input unbalances the which compresses spring within bungee and compensating device and the steering action displaces rudder and pedal only. Since spring is rebalances it. compressed within the bungee, the nose wheel Steering Systems does not turn. • In most cases the large aircraft dual system END SECTION FOUR steering will allow for limited steering from the rudder pedals while allowing for more range Aircraft Brakes from the cockpit steering assembly –The basic principle behind any braking • There may be a steering wheel lock out above operation is to create a controlled friction certain speeds process • They may combine the differential steering that increases the rate of deceleration control with the steering damper –Acceleration converts heat energy into motion Shimmy Damper –Deceleration converts motion into heat energy Piper Steering (PA28R) Aircraft Brakes • Roller alignment guide is disconnected from –Two main methods of increasing aircraft friction track while a/c is on the ground or drag in a controlled manner • Steering rods cause bell crank to pivot at – Increase aircraft to surrounding air drag center • Airbrakes, spoilers, flaps, reverse thrusters, • Bushings on steering arm serve as a bearing drag chutes, etc.. surface for turning the steering arm – Increase aircraft to ground drag • Torque is fed down through the center of strut • Anchors, skids, mechanical brakes, hydraulic to turning collar brakes, pneumatic brakes Cessna Bungee Steering Aircraft Brakes • Rudder pedal extensions attached to steering –One main method of increasing aircraft friction bell crank complete rudder "circuit" since it is or drag in an uncontrolled manner impossible to put cables under compression Aircraft Vs Automotive • Always inspect rubber boots for CO leakage –Some of you may be familiar with the power assist systems used in automotive –This type of system power assists the –They all function by forcing a moving surface to mechanical application of a hydraulic brake rub or drag against a stationary surface system. –The two surfaces usually differ greatly in –The hydraulic brake system is independent composition and hardness from the power assist system (Pneu. or Hyd.) Brake Assemblies –This system is rarely used on aircraft –In most cases this rubbing motion is a rotating Aircraft Vs Automotive motion and is associated with wheel rotation –Aircraft and automotive braking needs are very –If the rotation rate of the wheel is slowed down different then the linear speed of the aircraft will be –Aircraft braking speeds far exceed automotive slowed down providing the wheel does not slide –Aircraft braking weights far exceed auto Brake Assemblies –Auto braking duration far exceeds aircraft –Extreme amounts of heat will be generated at –Automotive ratio of braking/nonbraking much any point where sliding friction occurs closer to 20/80, aircraft 0.0001/99.9999 (est.) –Some Vehicle Gross Weights are established Aircraft Brakes by the ability to brake, not the ability to carry a –In any case the braking system for any vehicle load must be able to meet or exceed the Brake Assemblies coefficient of friction between the tire and the –The three sections of any brake system braking surface include: –Anti-skid systems (covered later) are an – The brake assembly: friction device attempt at splitting the line between meeting and – The control or actuating system exceeding the tire's skidding ability – The linkage, plumbing, power boost system Brake Maintenance Brake Assemblies –You must be at least Airframe rated to perform –Mechanical Brakes and return to service any brake work –Tend to be very weak –Brake systems may be rebuilt, resealed, –Heavy rehosed, new brake material installed, new fluid –Need constant adjustment installed, new or serviceable parts installed, etc. –Often subject to binding and failure –Remember to always be extremely clean and –Used only on small early or experimental thorough with any brake work. aircraft Aircraft Brakes Brake Assemblies –Braking systems fall into three basic categories Mechanical Brakes –Mechanical brakes - independent Brake Assemblies – Hydraulic brakes - both –Hydraulic Drum Brakes – Pneumatic brakes - dependent –Much stronger • (depends on external pressure source) –Lighter systems overall Independent Brakes –Are usually self adjusting –Do not use an external power source other –Rarely subject to binding and failure than the operator's mechanical application –Used only on small early or experimental –Usually consist of one complete system for the aircraft left main gear, and one for the right main Brake Assemblies gear (nose gear use brakes on some large Hydraulic Drum Brakes aircraft) Landing Gear –In some cases they will use the same reservoir Brake Assemblies for both sides (Piper) –Floating Hydraulic Drum Brakes –Commonly the reservoir is a part of each M/C –Even stronger Independent Brakes –The piston actuates the primary shoe –Common manufacturers: –The primary shoe begins to drag actuating the –Bodell/Firestone secondary shoe –Cleveland –The secondary shoe does most of the braking –Goodrich action –Goodyear Brake Assemblies –Matco Floating Hydraulic Drum Brakes –Warner Brake Assemblies Brake Assemblies –Drum Brakes –43.13 indicates drums can sustain 1 inch – Backing plate cracks as long as they don't reach an edge – Landing gear axle assembly –Overall these brakes are limited in the amount –Wheel and tire assembly of friction surface area that can be Brake Assemblies compacted into a small space –Pneumatic brakes are not very common on Single Servo Shoe Brakes aircraft Single Servo Brake Assembly –They can be found used as a back up system Duo Servo Brake Assembly –Large non aircraft vehicles use pneumatic Bendix Duo-Servo systems (Trains, trucking, etc..) Brake Assemblies –They can be pressure applied, or pressure –One version of the drum type brake is the deapplied - spring applied expander tube brake used from the 30s - 50s Brake Assemblies –This uses a flat hydraulic inner tube that –Single piston brake assembly expands when pressurized causing the –Used on small general aviation aircraft surrounding braking pucks to rub against the –One piston with a floating caliper outer drum –Fixed disc (to the wheel assembly) –These tended to swell and leak causing –As the pressure increases the piston forces the dragging and occasional brake fires pressure plate lining into the disc, and the Brake Assemblies floating caliper forces the backplate lining into –Expander tube brakes the other side of the disc –Can have more than one row of pucks Brake Assemblies –Tend to take a set when extremely cold Brake Assemblies P47 Expander Tube –These assemblies can have more then one Expander Tube Brake piston Expander Tube Brake –They can have more then one caliper assembly Expander Tube Brake –The caliper assembly can be fixed and the disc Brake Assemblies is floating –Hydraulic Disc Brakes Brake Assemblies –Strongest type of brake system available –3 Piston Floating Disc Caliper Assembly –Lightest system overall Brake Assemblies –Are always self adjusting –Wear Indicator Caliper –Rarely subject to binding and failure –Has a pin sticking out the visible side that –Used on most aircraft indicates pad or puck wear Brake Assemblies –Pin also functions as a part of the piston –Hydraulic Disc Brakes retraction mechanism Brake Assemblies –Refer to manufacturer's specifications for –The discs are steel, and rotate with the wheel proper pin depths –The shoes, or pads/pucks are mixtures of Brake Assemblies asbestos, organic compounds such as nut –Auto adjusting piston shells, Goodyear Brakes and soft metal chips such as brass, lead, Goodyear Brake Linings aluminum, or carbon Linings, Rivets and Pins –These are installed in a hydraulic clamping Lining Limits device that is attached to the landing gear Linings Brake Assemblies Cleveland Brake Linings –As the aircraft gets bigger multiple disks and Brake Assemblies pads can be stacked into each assembly –Pad thickness –In some cases the metal discs rotate and the –Always refer to manufacturer's specifications braking discs are stationary –Pad material may come with back plate or is –In other cases the braking discs rotate and the riveted to old back plate metal discs are stationary Brake Assemblies Brake Assemblies –Pad or puck replacement –Parts include: –Usually done with aircraft wheel removed – Pads, pucks, or shoes –Reservoir vent opened, fluid level lowered as – Calipers, or wheel cylinders needed – Discs, or drums –Disassemble brake assembly as needed to –New brake pucks must be cured with heat from remove pad initial applications –If non-riveted type then replace pad and –Too much heat will burn the bonding resins reassemble –Too little heat will wear the cured pad portion Brake Assemblies away without curing the new surface material –If riveted type then remove rivets and old puck, Brake Maintenance by drilling and punching out old rivet –To properly condition brake pucks apply brakes –Clean & inspect backing plate medium amounts five to six times at 25 to –Install new pucks with new rivets installed in 30 MPH the same direction as old materials –Allow partial cooling between applications –Rivets are commonly copper, can be squeezed –Unusual brake puck wear, brake shimmy, with small hammer and drift, or an arbor brake pull can be due to improperly tempered press brake linings Brake Assemblies Actuating Systems –Pad/puck thickness measuring –It is very common for the brake pedals to be Matco Wheel and Brake the upper part of the rudder pedals T6 STC Brake Conversion –These are called toe brakes Brake Assemblies –In some installations the whole pedal pushes –Disc coneing and warpage for rudder / steering action, and rocks or –They can cone in either direction pivots for braking action –They can warp like a potato chip Actuating Systems –They can wear to uneven thickness radially –The most common type of brake actuating –They can wear to uneven thickness in system used on aircraft is the hydraulic system circumference –Two basic types –They can crack in many different ways (heat) – Independent: Not dependent on engine driven Brake Assemblies hydraulic system –Disc coneing – Dependent: Dependent on engine driven Shoe Brake hydraulic system Brake Cooling Independent Brakes –Main brake cooling system –A typical master cylinder will consist of a: –Ducted manifold system from air inlet scoop –Piston –Feeds ram air into wheel well –Cylinder –Directs cold air onto brake assemblies when –Piston connecting rod gear is retracted –Reservoir or inlet port –Probably doesn’t do much since brakes get –Pressure or outlet port hottest on landings, more than takeoffs –Pressure return or compensating valve Brake Maintenance Independent Brakes –Some brake pucks come with a back plate –In the relaxed position the compensating valve bonded to the lining is open, the piston is retracted –Some must have the lining riveted to a –The first section of travel the return valve mounting plate closes, no brake actuation occurs –Some linings are just inserted into a retainer –The next section of travel the piston moves and held in place by the assembly down creating pressure, which in turn actuates –Always use the manufacturer's brake pucks the brake assembly and retainer parts –When the brake returns to relaxed, the comp- Brake Maintenance ensating valve is opened, releasing all –To install puck linings on the puck backing pressure plate, use the appropriate manufacturer's rivets, Independent Brakes and the proper rivet set –Fluid return, and brake release is caused by –Can be set by hammer, or by an arbor press – Return springs in the brake assembly –Setting too tight will shatter the puck – Slight flexing of the caliper piston seals –Setting too loose will cause the puck to move – The disc rotor just pushes the piston back and wallow out the rivet hole Independent Brakes –The rivet shop end is usually on the puck side –Typical Master Cylinder Brake Maintenance Independent Brakes –New brake pucks must be seated into the discs –Typical Master Cylinder Independent Brakes –The various discs can be solid, segmented, –Typical Master Cylinder slotted, internal or external tangs or notches Independent Brake System Brake Assemblies Independent Brakes –In every case they will index alternately to the Independent Brake Troubleshooting inside or the outside, with one side being • Dragging brake attached to the gear and the other a part of the – Broken master cylinder return spring wheel – Dirty, corroded piston/caliper –These will have an even distribution of pistons – Restricted master cylinder compensating port in the complete circumference of the brake (contaminated or binding pedal disc assembly assembly) Brake Assemblies • Spongy brake –Multi disc assemblies – Air Brake Assemblies – Deteriorated brake hose Multi disc • Brake grabs assemblies – Fluid leak on brake lining Brake Assemblies • Brake fade or parking brake creeps “Off” Multi disc – Internal master cylinder leak assemblies Independent Brakes Brake Assemblies • Pedal Pulsing Multi disc assemblies – Uneven wear on rotor Mig 21 Tire, Wheel, Brake –Warped rotor Off-Aircraft Inspection/Servicing • Wheel shimmy with brakes applied • AN MS and Special bolts and other hardware – Uneven wear on rotor – Visual, dimensional and magnetic particle –Warped rotor inspection • Scraping noise with brakes applied • Inlet and bleeder adapter – Linings worn out • Torque tube and pressure plate • Puddles on ground – Visual, dimensional and magnetic particle – Failed o-rings or hoses inspection Independent Brakes • Piston Housing –Flushing – Visual, dimensional and fluorescent penetrant –Done to clear system free from contaminates inspection –Water, air, dirt, oil, debris – Pistons, seals, backup rings and insulators –System can be flushed from low to high using a Off-Aircraft Inspection/Servicing pressure pot • Stationary and rotating discs –System can be flushed from high to low using a – Thickness, wear, cracks at relief slots hose and a bottle of fluid – Tangs and slots –Most common fluid used is H-5606 – Loose rivets and pads that are curled Parking Brakes – Glazed pads –Is usually a racheting master cylinder that • Self-adjusters feeds both independent brakes – Visual and magnetic particle inspection –Not wise to leave aircraft locked with this brake • on Semi-Boosted Brakes – heat can rupture a system –Boost assisted brakes hydraulic systems are – Aircraft cannot be moved by ground support not independent of each other Brake Bleeding –The mechanical action of the operator does END OF SECTION FIVE some of the work –Engine driven hydraulics do the rest of the Brake Assemblies work –Multi disc assemblies Semi-Boosted Brakes –Commonly use carbon braking disc Power Boosted Brakes –Still use steel wearing discs –Similar to semi-boosted in theory, the –These systems are designed to withstand very operator's actuating force is not part of the brake extreme temperature, and weather actuating force operating conditions –They are similar to the independent brakes in that left pedal operates left brake, and right pedal operates right brake –Deboosters Emergency valve –They operate by diverting a controlled amount –Shuttle valves Pressure cylinder of hydraulic fluid from the engine driven Power Boosted Brakes pump to the brake assemblies –Debooster Assemblies Power Boosted Brakes –Much like an electronic transformer, trading –In some large aircraft systems the nose gear pressure for volume instead of voltage for will also have braking capabilities current –If both pedals are being applied equally the –As the debooster reaches the maximum range nose brake will assist braking of its travel a pin opens a through flow check –In theory of operation they are also similar to valve allowing full pressure to reach brakes: the differential follow-up steering devices used for emergency situations such as a leak –They are dependent on the aircraft hydraulic –Lockout Debooster Assemblies system for operating power –Much the same as a normal debooster except Power Boosted Brakes it can be locked to a closed through flow –The braking function calls for the operator to state when the debooster piston reaches full apply a fixed amount of pedal travel to get a extention fixed amount of braking –It must be manually set to open via pin handle –As long as the pedal remains in the same –This allows for a complete lock out of each position you should get the same amount of brake in the event of t major leak braking Power Boosted Brakes Power Boosted Brakes –Shuttle valve –Although hydraulic valves can regulate they still –Keeps the normal brake hydraulic system either let fluid flow or don't let it flow, separated from the emergency system during based upon a fixed amount of travel normal operation –By modifying the valves to be self adjusting –Will allow brake system to swap to an alternate using balancing springs, and pressure pressure source during emergency braking differential changes across the spool valve, we Power Boosted Brakes create a valve system that will allow a fixed –Air / oil transfer tube amount of fluid flow for a fixed amount of pedal –This is a tank full of oil that will be fed into the travel hydraulic system during emergency brake No Boost Brakes operations Power Boosted Brakes –The oil is forced into the system by gas –By modifying the valves to be self adjusting pressure from an emergency discharge bottle – using balancing springs –In principle it is very similar in operation to a – pressure differential changes across the spool pressure accumulator valve Power Boosted Brakes – we create a valve system that will allow a fixed –Air / oil transfer tube amount of fluid flow for a fixed amount of Power Boosted Brakes pedal travel –Air / oil transfer tube Power Boosted Brakes Power Boosted Brakes –Pressure Ball-Check Brake Control Valve –Air / oil transfer tube –Very similar to PBCV Anti Skid Brakes –Instead of a spool for valving it uses a piston –The main purpose of aircraft anti-skid is to and a check-ball maximize braking effectiveness during all –Instead of two coiled balanced coil springs it braking conditions uses one coil spring and a flexing lever –The basic operation is to monitor all wheel –The application of hydraulic pressure on the rotation speeds piston springs closes the check-ball –When a difference begins to occur the Power Boosted Brakes offending brake is automatically deactivated –Pressure Ball-Check Brake Control Valve slightly, Power Boosted Brakes until it comes back up to speed –Hydraulic fluid source, High pressure Anti Skid Brakes –Power brake control valves –Will prevent the aircraft from touching down –Pedal assemblies and linkage with the brakes on –Control valves Emergency Pneumatics –Will reduce the possibility of tire hydro planeing –Anti skid Air/oil transfer tube –Generally does not operate under 20 mph –Usually has several common components • Operates just below the skid point at an found on most vehicles that use anti skid impending skid Anti Skid Brakes • Warning lamp illuminates when the system off –Used exclusively on aircraft with power brake or during a system failure systems • Skid sensed – control valve relieves pressure –Some form of wheel speed sensor, usually one from brake for each braked wheel • Touchdown protection through squat switch – –Some form of brake servo valve, usually one no signal sent to control box for each braked wheel Ground System Test –Some form of electronic control unit, often • Simulates wheel lock-up, release and internally independent for each wheel restoration of brakes: Anti Skid Brakes – Cockpit anti-skid switch “ON” –To prevent an inadvertent locked wheel during • Depress pedals – left and right brake lights touchdown the systems leaves the brakes illuminate fully released until the WOW switch is moved to • With pedals still depressed, press test switch – ground lights remain on; switch released – –Two basic types of wheel speed sensors are brake lights extinguish and then illuminate an A/C sine wave signal generator, and a D/C Fight System Test voltage generator. Aircraft configured for landing –The A/C type control box has an internal signal – Cockpit anti-skid switch “ON” converter. Probably a rectifier circuit Simulates touch down protection feature: Anti Skid Brakes • Depress pedals – left and right brake lights –The wheel servos operate by releasing brake remain off fluid pressure back to return, until the wheel Simulates normal brake function: comes back up to speed • With pedals still depressed, press test switch – –They then start reapplying the brake to a lessor lights illuminate as long as switch degree, attempting to achieve maximum depressed braking action Tweak Test - Wheel Speed Sensor –Using a linear elector motor that deflects fluid Simulates skid followed by normal braking: flow, the valve spool is position by varying • Remove hub cap degrees of fluid pressure • With brake applied, spin sensor blade Anti Skid Brakes • Brake will momentarily release, then reapply –The computer control unit is able to sense DC Wheel Speed Sensor Tweak Test when a wheel is begging to change speed and • Remove wheel hub cap to expose sensor predicts impending skid blade. –By using data from the other wheels, and • With anti-skid switch “ON” and brake applied, remembering the what the wheel speed was give blade sharp spin with your finger. prior • In a properly operating system, brakes to slippage it can determine when the wheel is momentarily release then reapply. back up to proper speed • If the sensor fails the tweak test, check the Anti Skid Brakes resistance using a sensitive ohmmeter. –Since the aircraft is decelerating it is actually DC Wheel Speed Sensor Resistance Test looking for a change in the rate of • Remove cable connector and measure deceleration of any given wheel resistance of armature while slowly rotating –There are various different activation blade thresholds for different systems, but it is 3600. common for • Uniformity and amount of resistance through these modern systems to be reacting within blade travel should be within maintenance several hundredths of a second manual specifications. –All systems include operator indication and self DC Wheel Speed Sensor Polarity Test test functions • Place meter on lowest DC voltage scale; attach Anti-Skid Highlights positive lead to pin “B” and negative lead to • Electro-hydraulic system pin “A”. • Armed by a cockpit switch • Tweak blade in clockwise direction viewed • Electric AC or DC wheel speed sensors from drive end. • Meter should read upscale. Control Box –Must not have any air pressure in tire when • Check by substitution method loosening bolts, (remove valve core) – Swap cables –Can use an arbor press or drill press, turned • Problem changes sides – control box defective off, to press bead off of rim, on both sides • Problem remains on same side – wheel speed –Wheel inspection is critical for cracks, sensor or control valve defective corrosion, or damaged bead/bolt areas Control Valve Aircraft Wheels • Measure control valve coil resistance using –If any fusible plug shows sign of damage, sensitive ohmmeter replace all of them – Resistance within specification, control valve –Eddy current inspection is the best way to parts are defective check for subsurface damage B757 HYDRAULIC CONTROL PANEL –Fix a flat tire injection formulas can contain B757 CONTROL explosive gasses B757 NOSE LANDING GEAR –Cracks can also develop in the brake disc B757 NWS mounting areas B757 MAIN GEAR Aircraft Wheels B757 PROXIMITY SWITCH –Bolts may be unidirectional - interference B757 BRAKE SYSTEM –Tighten in a criss cross pattern, in stages B757 ANTI-SKID –Do not use soap on tube type tires, the sudden B757 AUTOBRAKES acceleration of landing will cause them to B757 AUTOBRAKES slip Anti-corrosion Sealant –Mount the tire with red dot to the valve stem B787 Electric Brake –When reassembling tube types be careful to B737-800 Brake Change not pinch the tube or leave any wrinkles Beechcraft Super King Air Aircraft Wheels END OF SECTION SIX –Tapered conical wheel bearings –Slightly loose is better than slightly too tight Aircraft Wheels –Notch in plate washer is used to move washer –Aircraft Wheels to test for correct tension –Usually two piece –Spin wheel when adjusting wheel bearings –Two opposing conical tapered bearings for –Always thoroughly clean and regrease each wheel bearings and wheels when halves are separated –Can be tube type or tubeless Aircraft Wheels –Tubeless will have seal rings or sealing –Always replace both the bearing assembly and compound between halves the bearing cup when replacing a bearing Aircraft Wheels –Some axle seals can be reused, but most lip –Wheels are either aluminum alloy or seals should be replaced when removed magnesium alloy –Always renew cotter pin –Are either cast or forged, and therefore can be –Make sure cotter pin isn't dragging on dust cap subject to intergranular corrosion or flange. Builds static charge that can wreck –The bead seat area and the bolt hole areas are havoc on many things the most critical inspection areas Aircraft Wheels –The inboard half also houses the brake –Wheels bearings usually fail due to assembly contamination or being set too tight Aircraft Wheels –Heat discoloration, brinelling, spalling, galling, –Commonly has fusible plugs that will release and welding are the stages of wheel bearing pressure if tire exceeds a critical temperature failure –Bearing cups are usually interference fit into –Bearing cup can wallow loose in wheel half each half, or into one half with a flange for the –Always replace bearings by part number only other half Aircraft Wheels –Inflation valve, or hole is usually on the –It is best to use boiling water and ice to change outboard half bearing cups Aircraft Wheels –Any damage to metal or plastic bearing cage is –Aircraft tires are generally removed by splitting cause for rejection of the bearing the wheel in half –DO NOT, FOR ANY REASON, AIR SPIN A BEARING RACE OF ANY TYPE –Replace any bearing with rust, or water marks • Heavy aircraft verify before each flight Aircraft Wheels – Tire cool, or at least 2 to 3 hours after flight –Bearing lubrication • Check wheel weight security –MIL-G-3545C or MIL-G-81322 • Brake tangs must align with wheel slots –Coloration of grease is due to dyes used by • Axle nut torque manufacturer – Too loose, bearing cup could spin –Some extra grease in the hub area will assist in – Too tight, damaged bearing heat dissipation Off Aircraft Inspection –Too much grease will push the wheel seals out • Deflate tire first Aircraft Wheels • Break the bead –Pressure packing bearings is the quickest way, • Remove and properly store bearings always keep grease systems very clean • Note wheel weight location –Hand packing is done by working grease into • Remove tie bolts bearing cage dragging cage lip across a hand • Clean wheel assembly full of grease • Clean and inspect bearings –Do not contaminate the brake components with Bearing Inspection wheel bearing grease Bearing Cup Replacement –Repacking wheel bearings is P.M. Removal Wheel Types • Heat wheel • Drop Center (Single Piece) – Boiling water for 1 hour – Tire bead forced over rim (automotive) – Oven for 30 minutes at 2250 F. • Demountable (Removable) Flange • Tap cup out with fiber drift – Easier tire mount and dismount for stiffer tires Replacement • Split Center (Split Rim) • Reheat wheel Wheel Materials and Manufacture • Chill cup with dry ice • Aluminum alloy or Magnesium alloy • Coat cup exterior with zinc chromate primer • Cast or Forged • Drift cup in with fiber drift • O-ring between wheel halves -Tubeless Inspect Wheel Halves • Knurled flanges (on some wheels) -Tube • Bead seat Wheel Classification for Tire Casing – Eddy current inspection • Type I - Smooth contour • Keys or Key slots • Type II - High pressure – Dye penetrant, Magnetic particle, Dimensional • Type III - Low pressure – Check key attachment screw stake • Type IV - Extra low pressure • Internal and external surfaces • Type VI - Low profile – Dye penetrant, Dimensional • Type VII - Extra high pressure • Bolts and other hardware • Type VIII - Extra high pressure – Low Profile –Magnetic particle Drop Center Wheel Inspect Wheel Halves Split Center (Split Rim) • Fusible plug(s) Inboard Wheel Half – Visual, replace all if any distorted • Steel reinforced keyways or steel keys • Corrosion • Bearing cup (interference fit) – Check bead seat for trapped water • Tapered caged roller bearing – Remove corrosion per manufacturers’ • Grease seal, two retainers and snap ring instructions • Fusible plug(s) – Treat aluminum surfaces with Alodine • Over-inflation valve (on very large wheels) – Treat magnesium surfaces with Dow 19 –May also be mounted on outboard wheel half – Finish with two coats zinc chromate primer Outboard Wheel Half (except mating surfaces and bolt bosses – one • Bearing cup (interference fit) coat only) • Grease seal, two retainers and snap ring Fusible Plugs • Inflation valve (tubeless tires) or hole for inner- Reassemble Wheel (Tubeless Tire) tube valve stem • Clean bead seat area – isopropyl alcohol • Axle cap and retaining ring • Usually inboard wheel half first • Anti-skid bracket attached to cap – Inspect and lubricate wheel O-ring (tubeless) On Aircraft Wheel Inspection • Install tire on inboard wheel half • Light aircraft verify proper tire pressure daily • Index outboard wheel half so that red dot on – Section width usually wider than bead tire is adjacent to inflation valve diameter. • Lubtork bolts, washers and nuts if specified – Lower pressures possible, as bead seat traps • Torque per manufacturers’ recommendations tire • Inflate tire in cage to ½ static inflation pressure – Size: Section Width X Wheel Diameter • Final tire inflation or adjustment on aircraft – TSO C62 Reassemble Wheel (Tube Tire) –Type IV: Extra Low pressure • Clean bead seat area – isopropyl alcohol – Rough and Unimproved runways (donut type) • Prepare and position inner tube – Obsolete • Prepare and position tire – Size: OD X Section Width X Rim Diameter • Position brake disk (Cleveland brakes) Aircraft Tires • Lubtork bolts, washers and nuts if specified –Type V: Streamlined tires • Torque per manufacturers’ recommendations –Type VI: Low profile tire • Inflate tire in cage to ½ static inflation pressure –Main wheel space saver tire • Adjust axle nut torque – Limited height decreases the amount tire will • Final tire inflation or adjustment on aircraft drop when flat 2006 Mechanic Killed – Size: OD X Section Width X Rim Diameter B737 Nose wheel Tire –Type VII: Extra High Pressure 166 PSI required – exposed to 3000 PSI from – Standard for turbine aircraft unregulated nitrogen cylinder – High load carrying ability Cleveland 40-76A – Size: OD X Section Width P38 Main Gear Wheel Aircraft Tires T38 Nose Aircraft Tires END OF SECTION SEVEN –Tire Data: –Tubeless tires are marked tubeless Aircraft Tires –Tire deflection 32%-35% twice what is found in –Aircraft Vs automotive/truck automobile tires – Auto/truck need a medium speed tire –Nylon Stretch: New tires stretch in the initial 24 – Long duration hr period after mount – Low bounce protection –May result in a 5 to 10 percent drop in pressure – High traction needs Aircraft Tires – High water displacement needs –Suggested to let tire stand for 12 hours and –Weight / size not very critical inflate Aircraft Tires –Tubeless Air Diffusion: Maximum diffusion is –Aircraft tire needs 5% for any 24 hr. period. Allow tire to stand 12 – High speed hours before check – Short duration –Dual Tires: Difference of more than 5 PSI, note – Very high bounce protection it in the log book – Low traction Aircraft Tires – Low water displacement –Source of Pressure Data: Aircraft maintenance –Weight and size very critical manual Aircraft Tires –Air pressure in a tire will drop by 1 PSI for –The major difference is the aircraft tire sustains every 4 degree F change much higher side wall deflection –Inflation Pressure As specified in the –Tires: maintenance manual –Type I Smooth contour type, from smooth –Always use safety cages and safety gear when profile filling aircraft tires – Non retractable landing gear Size: = 0D –Tire size Obsolete –Tire type –Type II High Pressure Tire –Date of Man – Retractable landing Gear Made obsolete by –Slippage mark Type VII –Balance mark – Size: OD X Section Width –Ply rating Aircraft Tires –Band material –Type III: Most popular on GA aircraft –Retreading Co. –Number of Ret. –Name of Manuf. corrected. Aircraft Tires Aircraft Tires –Ply rating –Always look for damage or debris inside the –This is a means of rating tires based upon the tire, wrinkles in the tube, damaged fill valves original cotton plys found in early tires –Any ribbed section cut more than 1/2 way –Today's tires usually have less plys then the across should be retreaded or scrapped stamped rating value –Any plies showing is cause for replacement Aircraft Tires –Any sidewall damage is cause for scrapping –Bead: Anchors carcass and provides mounting the tire of tire to bead. Aircraft Tires –Bundles of wire –Small weather checking is not cause for –Apex strip: Streamlines bead concern –Flippers: Insulate carcass plys from bead –Move aircraft once in a while to prevent –Carcass: rubber coated nylon cord fabric cut on permanent tire set a bias for balance and strength –Always keep tire at proper inflation for the type Aircraft Tires of landing being conducted –New classification system –Harder for paved strips, softer for gravel or –(prefix) (nominal outside dia.) X (nominal grass strips section width) - (bead dia.) Aircraft Tires –Prefix determines width ratio and bead ledge –Corner wear is usually a camber problem angle –Rapid wear and shifting weight at higher lighter –Width ration = section width / rim width speeds is a toe in problem –Bead ledge = angle at the base of the bead Tire Maintenance Size Designations • Nylon flat spotting: roll aircraft Aircraft Tires • Leaks: check with water –Tire storage • Replace all valve caps –Store in a cool, dry, dark area • Tread injury: follow aircraft manufacturers’ –Do not stack, store vertically instructions –Avoid any petroleum product exposure • Cuts exposing or penetrating cord body: –Avoid any electrical equipment the generate remove, repair, recap or scrap. ozone in the storage area • Sidewall or tread bulges: remove, mark area Tire Care before deflation • Guard against heat build-up Schrader Valve – Short ground rolls, slow taxi, minimum braking, Tire Deflection Markers proper tire inflation Aircraft Jacking • Maintain tire pressure in accordance with • Jack per manufacturer’s directions aircraft maintenance manual • Use correct tools and jacks • Visual inspection • Leave nothing under the aircraft in case it – Tread condition and depth, sidewalls drops Tire Maintenance • Jack evenly • Avoid exposure to gasoline, oil, grease, electric • Locate aircraft out of high wind areas motors (ozone) • Use caution for CG shift when jacking • Store racked in a cool, dark, dry place –May need tail/nose weight • Check pressure weekly or sooner; • May need several persons recommended before each flight Tailweight • Check pressure tire pressure when cool (two Mounting and Demounting hours after flight; three hours on a hot day) • Dust inside of tire and outside of tube with talc Tire Maintenance • Index tube valve stem • New mountings: check pressure for several • Assemble wheel correctly; use tire cage for days inflation • Allow for nylon stretch: 5% to 10% drop in air • Inflate, deflate and re-inflate tube-type tires pressure in 24 hour period Tire Cage • Tubeless Diffusion: After 12 hour inflation, B747 Tire Rupture maximum 5% loss in any 24 hour period. Tube Inspection • Dual inflation pressure: More than 5 PSI • Size “should” match tire difference, log book entry noted and condition • Inflate no more than to “round-out” tube • Valve stem • Wrinkles: if excessive scrap • Chafing or thinning: scrap Aircraft 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 Stand Selecting Balance Weight Balancing Weights Screw Balance Weight END OF SECTION EIGHT