8-STP Airframe Maintenance Procedures PDF

GENERAL This paragraph defines the recommended special measures to be taken when aircraft is operated in sand-laden atmosphere.  These measures are not restrictive, they should be complemented as experience is gained.  THE FOLLOWING STEPS ARE RECOMMENDED  Install the sand filters which...

GENERAL This paragraph defines the recommended special measures to be taken when aircraft is operated in sand-laden atmosphere.  These measures are not restrictive, they should be complemented as experience is gained.  THE FOLLOWING STEPS ARE RECOMMENDED  Install the sand filters which protect the power plant against erosion.  Protect blade leading edges whenever required  Blank air intakes and exhaust pipe after each flight.  Limit power check ground runs to a minimum on sandy(or dirty) areas.  Observe maintenance recommendations.  Check the main rotor blades for erosion every 10h these intervals prevail over those given in chapter 5.30 under normal conditions W.C. 57.10.601.  Check the tail rotor blades erosion every 10h in case of intensive operation in very sandy atmosphere, all precautions should be taken to ensure optimum operation of the aircraft; if required,W.C.56.10.601.  Clean the fuel filter of aircraft fuel system every 10h.  check the power plant compressor turbine blades for erosion every 10h.  Clean the power plant sand filters every 25h.  Clean the heating system filter every 50h.  Clean the hoist filter every 50h. Unpainted fixed parts apply a film of C-629.  unpainted moving parts apply G-359 grease. Metal surfaces(skins , structural components, casing)should be cleaned. Protection for electric plugs and connections Doors, fearing and panels inspection, clean the following parts with spirit and then grease with H-515oil, without removing every week during pre-flight. Flash power plant every 100h after extended hover or low altitude flying over sea water. As per W.C. NO-” TUBOMECA”.  wash MRB and coat with SI-4 compound every 25h after extended hover or low altitude flying over sea water, as per W.C.No-57.10.701. Wash structure with fresh water weekly and after extended hover or low altitude flying above sea water. Check condition of anticorrosion beads every 100h or 6 months. Visually check the non-rotating star control rods every 100h or 3 months as per Wc No- 40.11.601. GENERAL: This paragraph defines the precaution to be mandatorily taken when an aircraft is started after being parked in snow without a shelter. GENERAL MEASURES:  Removing the air intake and exhaust nozzle protection after cleaning the aircraft before starting the engine(s).  Remove carefully the snow or ice that has built up near the engine air intakes and on the air intake screens(when fitted). When the engine runs and heats up, these accretions may melt, come off or be ingested by the engine.  Remove carefully the snow or ice that has built up inside the engine air intakes screens and inside air intakes ducts. This operation may entail removal of the air intake screen or cowlings.  Check for no snow or frost on the vents, static vents, drains and scuppers if any; clean them.  Apply glycerin on the MRB before parking the aircraft.  TYPICAL INSPECTION GENERAL A. INCIDENTS AND ACCIDENTS LIABLE TO OCCUR:-  Following shock or damage to any item of the aircraft.  Analyses possible consequences and determine the checks.  Not only items involved but also on all parts, accessories and components the condition.  Subsequent to such incident. B. Cases of non-compliance with or exceeding of the various operating limitations laid down in the manufacturer’s approved flight and maintenance manuals also come under the heading of incidents. 1. In the event of main rotor over speed exceeding 420 rpm but less than 440 rpm: Remove the main rotor blades and check bonding of the skin. Carry out a detailed inspection of the tail rotor hub. 2. If rotor over speed reaches or exceeds 440 rpm: Carry out the above detailed inspection procedure. Remove main rotor hub and shaft and tail rotor head and return them to the factory for inspection. 1. MRH Checks:  The pitch change rods are true  There is no mutual interference between the upper and lower swash plates  The rods beneath the swash plates are true  The droop restrainers’ bolts are true.  Straightness of droop restrainer stop pins NOTE: If any defect is found, reject:  The defective parts  The main rotor hub  The pitch change levers  The swash plates  The rods beneath the swash plate  The droop restrainer stop pins. 2. Transmission systems checks:  Twisting and warping in the transmission system assembly  Condition of the shaft and universal joint assembly: warping, loose rivets. NOTE: If any defect is found, reject:  The gearing on the M.G.B. rear power output shaft  The lower flaired casing of the M.G.B. pinion gear  The transmission drive shafts  The T.G.B. casing 3. Additional checks: Carry out a detailed check of the:  landing gear: buckled oleo, damaged oleo attachments  body structure  tail boom Engine mounting “A” frame NOTE: If one of these components is damaged, reject: The M.G.B. “A” frames and their attachment bolts The pitch change rods on the main rotor.  IMPACT ON MAIN ROTOR  MAJOR IMPACT: it is a major impact if one defect is found on any of the following assemblies: a) Rotor blade: wrinkled skin, separation or warping of the trailing edge strip, camber outside tolerance and/or if the separation criteria detailed in the Maintenance Manual W.Cs. demand that the blades be returned to an authorized repair facility. b) Main rotor hub:  Blade spacing system assembly: failure of any component part, including the carbide bushes.  Drag dampers: abnormal time to complete their travel, warping of attachment arms (upper, lower and fixed).  LIGHT IMPACT: all defects other than those described above will be treated as light impacts.  IMPACT ON TAIL ROTOR 1 Resulting in serious damage or breaking up of the tail rotor blades, check for:  Twisting of the tail rotor drive shaft.  Condition of the shaft and universal joint assembly.  Flatness of the pitch change spider. discard if distorted.  TAIL ROTOR GUARD If the aircraft has suffered an impact causing twisting or cracks on the tail rotor guard, check very carefully: 1) The condition of the stabilizer and the longer on for twisting and cracks. 2) The condition of the tail boom at the attachment points to the body structure (lower longer on). 3) The body structure for tightness.  HARSH CLUTCH 1) Check the tail rotor drive shaft for twisting. If the degree of twisting is outside tolerances: 2) Discard:  The clutch power take off  The intermediate bearing shaft  The M.G.B. power input bevel gears 3) Then apply the directives of impact on tail rotor.  IMPACT OF A MRB ON TDS 1) For the MRH and the TGB ,apply the directives of impact on main rotor. 2) Reject: the parts located between the TGB power take off and the zone where the MRB impact upon the tail transmission:  The drive shaft  The shaft & universal joint assembly  The interlocking bevel gears oat the MGB power output & the flaired casing of the MGB pinion gear. 3) Return the TGB to an authorized repair facility to conduct checks on :  Interlocking bevel gears of the TGB & TDS  The 3 lugs of the TGB twisting & cracks by dye penetrant technique. 4) Replace the 3 TGB casing attachment bolts. FAILURE OF A COMPONENT AT THE TGB  TGB/NO- 8 frame attachment bolt cracked.  NO- 8 frame attachment lug cracked.  TGB attachment lug cracked.  Coupling of TGB. Actions to take: a) Drain & flush the oil system with service oil. b) Put the TGB back into service with new oil. Caution: if the oil deteriorates once again within 100 hours, preserve the MGB & send it to an authorized repair facility for reconditioning. On installation of the replacement MGB:  Flush the cooling system.  Fill the MGB with oil of a different grade.  SERVICE OIL DETERIORATION Characteristics of deteriorated oil: The deterioration of service oil is characterized by significant darkening or opacity and an abnormal odour, with or without emulsification.  SPECIAL OBSERVATION OF GEAR BOXES Introduction: the checking procedure described below relates to main gear boxes of which the oil has been contaminated by class A12, B22, C2 & D2 particles. It can also be applied to TGB, disregarding the instructions relating specifically to the MGB. Procedure: 1) Drain the oil from the gear box & oil cooler. Strain the oil (look for particles)(40.12.302). 2) Clean the oil cooler & pipes. NOTE: If a large number of particles is found (especially chips & flakes), replace the oil cooler. 3) Clean: (i) the oil intake filter, (ii) the suction strainer, (iii) the magnetic element. 4) Check the sump & visible parts of the MGB for particles, using a magnet secured to a steel wire holder, inserted through the filter neck. NOTE: The first conclusions may have to be reconsidered if fresh particles are found in the sump & strainer. 5) Install: (i) the suction strainer, (ii) the oil inlet filter. 6) Fill up the gear box & oil cooler with service oil. Carry out 10 mins hover at maximum permitted weight. After this, check the condition of the magnetic plug  ACTION TO BE TAKEN IN THE EVENT OF OIL LEAKS FROM TSP ASSEMBLIES The following are to be distinguished:  Seepage  A doubtful leak  A definite leak ACTIONS TO BE TAKEN: Seepage: No special measures (transmission system components are checked for leaks during pre-flight inspections). Affected areas should however be cleaned regularly to prevent an accumulation of oil which may look like a leak. Doubtful leak: The doubt must be removed:  Clean the suspect area thoroughly,  Ground run for about 15 mins,  Check the suspect area immediately after the ground run. If a definite leak is found, apply the measures listed below. If there is no running oil, continue flying but make a special check of the suspect area during pre –flight inspections.  Definite leak: The actions to be taken depends on the extent of the leak. Three types of measure are possible:  TYPE A: Immediate repair (fitting new seal- carriers or seals,…) by the operator, or return of the transmission system to the factory if the operator cannot carry out the repair.  TYPE B: To meet essential operational requirements, the helicopter may continue flying but the leak must be checked BEFORE & AFTER EVERY FLIGHT. Repair must be carried out as soon as possible. While in flight, the leak may become worse (apply type A measures) or may improve (apply type C measures).  TYPE C: The decision to carry out repairs is left to the discretion of the operator. The helicopter can be flown normally. (special check on the progress of the leak during pre-flight inspections).  CORROSION  Destruction (or deterioration) of a metal through an unwanted direct chemical or electrochemical attack, by its environment, starting at the surface. OR  Disintegration of a metal that results from the interaction of metallic surfaces with one or more substances in the environment.  Chemical corrosion.  Direct Chemical Attack  High- Temperature Oxidation  Electrochemical corrosion.  Proceeds at a nearly even rate over the surface.  Common examples  Reaction of iron with moist atmosphere that produces rust.  Corrosive agent such as sulfuric acid pickling solution used to clean steel surfaces.  The surface is dissolved uniformly without the formation of protective layers and the attack continues at an almost constant rate.  DIRECT CHEMICAL ATTACK ALUMINUM ALLOY BASE ALUMINUM CLADDING MATERIAL  Above figure shows a photomicrograph of a clad aluminum alloy sheet. The thickness of the cladding should be noted.  DIRECT CHEMICAL ATTACK  A less severe example is that of aluminum exposed to air..  Aluminum oxide forms on the surface and, after it thickens, forms a barrier to the air and the corrosion process stops.  The aluminum oxide is unsightly and is often removed from clad aircraft skin by polishing.  As the pure aluminum cladding is very thin, continued polishing may remove the aluminum and expose the aluminum alloy base metal to the air.  The exposed aluminum alloy is subject to electrochemical corrosion as intergranular corrosion.  Above figure shows a photomicrograph of a clad aluminum alloy sheet. The thickness of the cladding should be noted.  High-temperature Oxidation  This type of corrosion involves the reaction of metals with oxygen at high temperatures, usually in the absence of moisture.  Engine and auxiliary power unit exhaust areas are affected by a discoloration or general dulling of the surface.  ELECTROCHEMICAL CORROSION  Metals vary in their resistance to corrosion.  There is a series called Galvanic Series. In this series the metals are listed in the order of their tendency to corrode.  The more anodic a metal is, the greater its galvanic corrosion will be when it is in contact with a less anodic(more cathodic) metal. FOUR CONDITIONS BEFORE ELECTROCHEMICAL CORROSION CAN OCCUR  There must be something to corrode(the anodic metal);  There must be a cause for corrosion(the cathodic metal);  There must be a continuous liquid path(the electrolyte, salt water or other contaminants);and  There must be a conductor to carry the flow of electrons from the anode to the cathode. This conductor is created when metal touches metal as around rivets, bolts, and welds.. 3 CONDUCTOR CONTINUOUS LIQUID PATH(ELECTROLYTE) ANODIC CATHODIC (METAL) AREA 2 (CAUSE) 1 AREA 4 ELECTRON FLOW ELECTRON CONDUCTOR METAL The four conditions that are necessary before electrochemical corrosion can proceed are shown in figure. The elimination of any of the four conditions will automatically stop corrosion.. NO CONTACT BETWEEN ELECTROLYTE AND ANODE AND UNBROKEN PAINT CATHODE FILM 3 CONTINUOUS LIQUID PATH (ELECTROLYTE) ANODIC CATHODIC 1 (METAL) 2 (CAUSE) AREA AREA 4 ELECTRON CONDUCTOR METAL A method of preventing corrosion by preventing the electrolyte from connecting the cathode and anode is by applying an organic film to the surface. This is shown in the above figure. Anodizing or cladding the surface will have a similar effect. 1. Suitable design and fabrication procedure 2. Use of inhibitors. 3. Modification of the corrosive environment 4. Use of protective coating 5. Use of cathodic protection 6. Alloying of metals 7. Heat treatment of metals Unpainted fixed parts apply a film of C-629.  unpainted moving parts apply G-359 grease. Metal surfaces(skins , structural components, casing)should be cleaned. Protection for electric plugs and connections Doors, fearing and panels inspection, clean the following parts with spirit and then grease with H-515oil, without removing every week during pre-flight. Flash power plant every 100h after extended hover or low altitude flying over sea water. As per W.C. NO-” TUBOMECA”.  wash MRB and coat with SI-4 compound every 25h after extended hover or low altitude flying over sea water, as per W.C.No-57.10.701. Wash structure with fresh water weekly and after extended hover or low altitude flying above sea water. Check condition of anticorrosion beads every 100h or 6 months. Visually check the non-rotating star control rods every 100h or 3 months as per Wc No- 40.11.601.  DIMENSIONS PRINCIPAL DIMENSIONS:  Main rotor diameter- 11.020  Tail rotor diameter-1.912  Overall length (blades folded)- 10.167  all width (blades folded)-2.602  Overall height-2.970  CLEARANCES Clearances : Ground clearance, main rotor (cyclic stick in neutral position)- 2.520 Ground clearance, tail rotor-0.660to 0.740 for chetak. Ground clearance, tail rotor guard- 0.420 to 0.500.  INSPECTION OF BEARINGS  Inspection applies either to sealed or non sealed type bearings.  which can be removed or not from the component.  Sealed type bearings do not normally require to be lubricated.  whatever their operating time, but although they are perfectly sealed.  they may admit some foreign matters which damage them or adversely affect their operation.  When a bearing develop binding or hard spots.  Replace the bearing. (1)Sealed type bearing with removable shields type bearings (a)non staked bearing: Any of the following servicing operation can be performed on the bearing after removal. (b)staked bearing: If the bearing cannot be removed from the supporting components, it must be processed together with the components or replaced with it if the component cannot withstand the processing or its nature preclude the application of the intended processing. (2)special cases, sealed type bearing with staked shield. Servicing is prohibited on bearing with staked shield. In case of malfunctioning the bearing must be mandatorily replaced. Cleaning: Rubber seals removed from bearing. The same processing as described here. Immerse bearing for 1h.30min at 70°c in a mixture consisting of water=94 & teepol=6 Then use tool no. 3130-95-00-553connected to the installation. Force a minimum of two liters of the above specified mixture through every bearing. submitted to cleaning , There after eliminate the Teepol by dipping he bearing in a hot water. GENERAL : Storage is the operation which consist In protecting the aircraft or its components against physiochemical alterations due to the corrosive action of the atmosphere which is usually characterized by Humidity Air laden with acid vapours Sea atmosphere Sun’s rays Variation in temperatures External preservation of gear boxes and oil cooler: Coat unpainted sections of the gear boxes and oil cooler with protective compound(c-620) Cover the oil filter cap with adhesive tape. Brush or spray protective compound (c-620) on the drive connections of the gear boxes and cover with grease proof paper.  Preserving the MRH/Shaft assembly: 1. Main rotor blade: Remove main rotor blades process them for storage. NOTE: Re-install bolts washers and nuts on the main rotor blades sleeve fitting 2. Main rotor shaft:  Clean the rotor shaft using a clean rag soaked in white spirit.  Coat the following with c-627 grease(orAIR-8135 for tropical climate). The lower pins and the pitch change rod fork-ends. The scissors hinge pins. GENERAL: The short-term storage configuration implies protection against alterations and therefore effects the availability of the aircraft. Before it can be returned to service a number of depreservation, repair checking and inspection operation will be necessary. IMPORTANT:  Storage affectivity= 6 months  Inspection Intervals= Every 2 months  STORAGE OF TRANSMISSION SYTEM C0MPONENTS A.PRESERVING TRANSMISSION COMPONRNTS:  Drain the MGB,TGB,MGB oil cooler,  Fill the MGB and TGB with internal inbiting oil (c.623)  Perform a 5 minute ground.  After ground run, drain the internal inhibiting oil from the MGB and TGB. NOTE: Do not drain the MGB & TGB.  Check, clean & reinstall the TGB magnetic plug, if fitted.  Check & clean the oil intake strainer.  Grease (with operating oil):  Trunnion yoke housings on rotating star (3 lubricators)  The ball-ring (1 lubricator). 1. STRUCTURE:  Remove all protective and blanking covers.  Air the aircraft by opening, access door, inspection door hatches.  Check condition of the corrosion inhibiting products.  Check for, and remove, any traces of corrosion from the entire structure. A. MGB,TGB,MRS AND TAIL ROTER: TRASMISSION:  Check that the corrosion inhibitor on protected surface is intact.  Check for, and remove, any traces of corrosion.  Rotate the transmission system components by hand(4 or 5 times). B. MAIN ROTER BLADE AND TAIL ROTER BLADE:  Check that the corrosion inhibitor is intact.  Check the general condition of the engines. C. ENGINE:  Refer to the “TURBOMECA” maintenance manual.. D. SYSTEM:  Visually check the engine lubrication system and fuel system for leaks.  Bleed the fuel tank and the filter.  Hydro test the fuel system(fuel tank full).  LANDING GEAR: A. FOR ALUETTE III:  Visual check the shock strut and tyre pressures.  Check that there is no trace of corrosion.  Check the sliding cylinder of the shock struts and wipe them with a clean rag moistened white spirit (coat them with H.515 fluid).  Check the corrosion inhibitor beads.  Move the aircraft sufficiently to change the point of contact of the tyres with the ground.. B. FOR SA-315:  Ensure that the corrosion inhibiting protective coating on the shock absorber end- fittings and attachment bolts are intact. 4. CONTROLS:  Check all controls linkages visually for corrosion.  Examine the servo-unit piston rods, then wipe them with a rag moistened with white spirit and finally coat them with H.515 fluid..  Operate the flight controls.  Check the tightness of the servo-units. 5. FINAL STEPS:  Close access doors , inspection doors and hatches.  On the label specifying the type of storage, indicate the date of the inspection which has just been completed.  Fit the aircraft blanking and protective covers. 1.GENERAL:  This operation performed when the A/C is to be grounded more than six months.  The “long-term” storage standard differs from the “short-term” storage standard in that all the transmission systems are removed from the A/C and stored in containers.  A/C placed in “long-term” storage are not likely to be used immediately because of the components which have been removed and the protection which has been applied. INSPECTION INTERVALS: Every two months for a/c stored “in the open air” Every four months for a/c stored “under cover”  Drain: MGB-oil cooler W.C.40.12.302 TGB W.C.40.23.302  Fill the following with internal preserving oil (c.623).  Perform a 5 minute storage ground run.  Clean engine (remove salt.)  Protect the engine against salty atmosphere.  Preserve the engine fuel system.  After the ground run, drain: The MGB and oil cooler The TGB  Operate the foll0wing system: servo-units & wheel brake. While operating, check for leaks. Release pressure in the systems. Clean (white spirit) all unpainted metal surfaces of the hydraulic controls and equipment , then smear them with grease (c.620). Top up the hydraulic reservoir. Seal the air vent of the hydraulic reservoir with adhesive tape NOTE: No preservation of the parking accumulator is necessary. 1. Remove and store the following assemblies: TRB, TRH, TGB, Inclined drive shaft, MDS &free wheel, coupling shaft , engine, MRB, MRH,MRS,MGB, oil cooler. NOTE: Both oil connection of MGB blank with blanking plug. 5. PRESERVING THE SYSTEM: 1. Fuel system Preserving the pitot-static system 6. PRESERVING THE EQUIPMENT: 7. (a) instrument. 8. (b) Electrical equipment. 9. (c) Radio and navigation equipments. (a) Flying controls. (b) Engine control. 8. Preserving the landing gear. (a) For allouette iii. (b) For SA 315. 9. PRESERVING THE STRACTURE. (a) Clean a/c. (b) Open the doors to air a/c. (c) Remove the trace corrosion. (d) Touch up paint if required. (e) Paint unpainted metal area with C.620. 10.STORING THE REMOVAL EQUIPMENT. 11. FINAL STEPS. (a) Park the air craft out of the sun and away from damp. (b) Close cabin doors, inspection doors and hatches. (c) Fit the aircraft protective and blanking covers. (d) Affix a label to the aircraft indicating:  The type of storage (“long-term” storage)  The date of storage  The date at which the first checks must be performed. INTRODUCTION: tail rotor blade pitch variation is controlled through rudder pedals, witch are connected through control tubes to a grooved control quadrant installed on the body structure. the control quadrant operates the cables carried along the fuselage and tail boom by a run of pulleys leading to tail gear box. MAIN PARTS OF TAIL ROTER SYSTEM: Rudder pedals. Quadrants. Tail rotor control cables.  Cable drum. Pitch change spider. Pitch change links. TRB. Houdaille damper. OPERATION: Actuation of rudder pedals results in a rotational motion of the drum at the tail rotor. The cable is connected to a pitch change rod whose linear motion is transmitted to a pitch arm is connected to each blade lever by means of a link which changes the pitch change angle of the blades. ADJUSTEMENT: the adjustment we can say tail rotor rigging. PROCEEDURE: Remove all bottom fairing under the cabin and open tail boom fairing to the left of the a/c. Disconnect the control tube from control quadrant. Lock the rudder pedal to structure using a locking pin. Lock the quadrant in neutral positions with locking pin. Adjust the length of control tube directed to houdaillie damper it should be 205mm. Adjust the length of tube and connect it to quadrant. Disconnect the cables from turn buckle and remove the cable drum.  Move the drum shaft out until it buts its out board stop. Measure the dimension “D” between the drum shaft end and the tail gear box flange this dimension should be about 102mm. Move the shaft in by 15.7mm by rotating it anti-clock wise to set the drum shaft in neutral position i.e. D – 15.7 ±.3mm = 86.3mm ±.3mm Wind the cable on both side of locating bead housing, yellow cable, 2 ¾turns to the left and green cable 2¾ turn to the right, looking towards the tail boom. Fit the drum on the shaft with the locating bead forward & without rotating drum shaft. Tighten the drum attachment bolt to correct torque & connect the turn buckle..  Apply a cable tension of 6 ± 1kg (13 ± 2lbs) & lock the turn buckles.  Remove the rudder pedal & quadrant locking pins.  Apply 15kg load on RH rudder pedal. The drum shaft dimension to be = D – 3.2 ±.3mm.  Apply 15kg load on LH rudder pedal the drum shaft dimension should be = D – 28.3 ±.3mm.  Adjust the rudder pedal stops to obtain the above dimension.  Check the control system for completeness, correctness, security & freedom of operation.  Fit the bottom fairing & tail boom fairings. NOTE: the tension meter used for checking is to be calibrated, the calibration card is to be checked before using. ( a) CHECKING FOR TIMING AND LEAKAGE:- Remove the damper from the aircraft. Unscrew the filler plug and drain out the oil. Rinse the damper, place the damper with filler plug upwards and service with hydraulic oil OM-15,fit filler plug. with damper placed vertically and lever shaft downwards, check that the rate of leakage dose not exceed at an ambient temperature 20°c. Record the timing with a stopwatch and repeat this operation four times. Calculate the arithmetical average of the timings recorded. The average time should be 8 to 12 seconds.  Remove the shaft blanking screw to gain access to adjustment screw. To increase decent time- screw the adjustment screw in. To reduce decent time-unscrew the adjustment screw. When correct adjustment is obtained, mark the position of the adjustment screw head with RED paint. Re-install the shaft blanking screw and install a new washer. In stall the damper on the aircraft. ITRODUCTION:- The servo units are provided to eliminate control forces at both the cyclic stick and collective stick lever. they are irreversible, which means that there is no feed back to the pilot’s control. The hydraulic system provides the energy required for the operation of the servo unit installation. It consists of reservoir, filter and valve unit, pump, external power connector. Servo units shut off cock, lateral servo unit, longitudinal servo unit collective servo unit. CHARACTERISTICS:- Rotational speed- 2500rpm Delivery rate- 6ltr/min Operating pressure- 28bars(400psi) Torque under working pressure- o.27M daN Power- 0.25H.P  OPERATION:-  Minimum pressure of servo unit is 6 bar(85 psi).  Maximum pressure of servo unit is 28 bar (400psi)  Operating may be initiated as soon as the rotor starts to rotate.  Hydraulic fluid is delivered to the system by a pump through a 50 micron pressure filter.  Pressure increase causes opening of the safety valve set at 28 bars(400psi).  The fluid discharged by this valve return to the reservoir through a 20 micron filter.  In the event of clogging of this return filter, causing a pressure drop of 2 bars(29psi) the fluid returns to the reservoir through a by- pass valve.  In the event of servo unit failure, the aircraft remains flyable and control forces may be alleviated by moving the servo unit control cock to the off position. GENERAL: The two main units each comprise a steel leg secured to the rear cross tube. A shock strut of the oleo-pneumatic type extends from each leg to a special fitting on the body structure. The wheel are mounted on steel axles through bronze bearings fitted in the wheels. As the nose wheel, each main wheel consists of two pieces assembled by four bolts. The two main wheels are equipped with a rotating disc type brake(parking brake) controlled from the pilot’s station. NOTE: Certain a/c are equipped with double rotating disc- type brakes controlled from the pilot’s stations. this brake can act as a differential brake (through the pedals) or, as a parking brake(through the hyd control unit). MAIN COMPONENTS OF LANDING GEARS: Wheels Swivel arms Cross tube Main shock struts(olio legs) Nose oleo legs Tail rotor guard etc FILLIG WITH HYD OIL: Remove the shock strut as per procedure. Position the shock strut vertically with its lower end fittings resting on the support. Open the filler valve at top of the shock strut. Connect the hyd charging rig with monitoring gauge. Compress the shock strut. Charging the shock strut hand charging rig up to extend 50mm ,hold the strut and build up pressure to 20 bar (290psi). Open the relief valve of hand pump and compress the shock strut to expel excess fluid ,then close the relief valve. (repeat the steps 6&7 two or three time). Open the pump relief valve, fully compress the strut to expel excess fluid. Tighten the relief valve and disconnect rig.  Jack up the aircraft as per procedure. Remove valve cap. Connect inflator connecter with monitoring gauge. Connect the pressure regulator one in inflator connector other one is nitrogen cylinder. Open first the cylinder valve then the pressure regulating valve. Adjust the pressure regulator to obtain a pressure of 23.6 bars(342psi) check at monitoring pressure gauge. Open inflation valve. Allow a pressure to stabilize at 23.6 bars(342psi). Close valve. Close nitrogen cylinder and pressure regulating valves. Disconnect inflator connector. Install valve cap. Lower the jack completely and remove the shock strut extension clamp.  NOTE:- this operation is to be performing with the a/c resting on its wheels. on the cabin floor, remove the filler cap. Deflate and fully compress the shock strut. Remove cap and valve core. Connect the hyd charging rig with monitoring gauge. slowly fill the shock strut by actuating hand pump until the shock strut extend by about 50 mm. Evacuate the excess fluid by operating the pump relief valve when fully compressed, close the relief valve. Repeat step three times, refit valve core.  jack up the a/c as per procedure. Unscrew the dust cup. Install one of the approved inflator. Connect the pressure regulator with nitrogen cylinder. Open the cylinder with cylinder key , monitor the pressure (787psi). Open the valve by 1½ turn , allow the pressure up stabilized. Close valve and cylinder, disconnect inflator. Installed valve cap and lower the a/c.  Remove the valve cap fit the bleeding pipe one end other end immersed the fluid container. Connect hyd charging rig with wheel brake unit. Insure that brake handle in release position. Operate the rig loose the bleeding screw , remove the air bubbles than tighten the bleeding screw. Repeat step three time. Repeat same step an other side of wheel. Remove the charging rig and fit the cap. A. PRELIMINARY STEPS:- Remove the locking wire safe ting the screw , locking in position the play adjustment nut. Remove the screw. B PROCEDURE:- NOTE:- originally, the clearance between the disc and of two Ferrado linings is set at 0.2mm. The play taken up by turning the nut by one slot is 0.08mm. Measure the clearance between the disc and the lining By means of wrench 10mm A/F engaged on the hexagon, turn the nut anticlockwise, one notch at a time, until the clearance is 0.2mm. Apply and release the brake several times and check the clearance ( adjust as necessary). Install screw. Safety the screw with 0.8mm dia. stainless steel locking wire. MAIN ROTOR SHAFT AND SWASH PLATE ASSEMBLY:- PRELIMINARY STEPS:- shaft removed from a/c as per procedure. (a)cleaning (b)Protection (c)Greasing (d)Packing in container  Type of assy. Composition of compound.  anti-corrosion bead consisting of  100part, by weight, of putty minesota, EC-1239B.  12parts, by weight, of accelerator, EC-1031A Corrosion beads on MGB Corrosion bead between flared housing and main gear box. Corrosion beads on coupling shaft. Corrosion beads on TGB.  Jacking procedure. Control rigging. (a)collective control. (b) cyclic control. Main rotor rigging.  verniar caliper provides greater accuracy than ruler.  specially formed jaws for measure inside and outside dimensions.  Some slide caliper also contain a depth gauge for measuring the depth of blind hole.  Its provided main scale and sliding sub scale. FUNCTION OF A BEARING  The main function of a rotating shaft is to transmit power from one end of the line to the other.  It needs a good support to ensure stability and frictionless rotation. The support for the shaft is known as “bearing”.  The shaft has a “running fit” in a bearing. All bearing are provided some lubrication arrangement to reduced friction between shaft and bearing.  Bearings are classified under two main categories:  Plain or slider bearing : -  In which the rotating shaft has a sliding contact with the bearing which is held stationary. Due to large contact area friction between mating parts is high requiring greater lubrication.  Rolling or anti-friction bearing : -  Due to less contact area rolling friction is much lesser than the sliding friction , hence these bearings are also known as antifriction bearing. Rolling or anti-friction bearing  Ball and roller bearings. due to low rolling friction these bearings are aptly called “antifriction” bearing  Frictional resistance considerably less than in plain bearings  Rotating – non-rotating pairs separated by balls or rollers  Ball or rollers has rolling contact and sliding friction is eliminated and replaced by much lower rolling friction.  In plain bearing the starting resistance is much larger than the running resistance due to absence of oil film.  In ball and rolling bearings the initial resistance to motion is only slightly more than their resistance to continuous running.  Hence ball and rolling bearing are more suitable to drives subject to frequent starting and stopping as they save power.  Owing to the low starting torque, a low power motor can be used for a line shaft running in ball bearing. Types of rolling bearing  Single row deep-groove ball bearing:  Incorporating a deep hardened raceway which makes them suitable for radial and axial loads in either direction, provided the radial loads are greater than the axial loads.  Single row roller bearing:  Roller bearing have a greater load-carrying capacity than ball bearing of equivalent size as they make line contact rather than point contact with their rings.  Not suitable for axial loading, cheaper to manufacture, used for heavy and sudden loading, high speed and continuous service.  Ball and Roller bearing Races and balls are high carbon chrome steel (to provide resistance to wear) machined and ground to fine limits of 0.0025 mm, highly polished and hardened. The cages are made of low-carbon steel, bronzes or brasses, though for high temperature application case-hardened and stainless steels are used.  The ball and roller bearing consists of following parts:  Inner ring or race which fits on the shaft.  Outer ring or race which fits inside the housing.  Ball and roller arranged between the surfaces of two races. These provide rolling action between the races.  the radius of the track for balls is slightly greater 5 to 10 % than that of the ball themselves.  Note that the rotating surfaces rotate in opposite directions.  Cage which separates the balls or rollers from one another. The disadvantage of the ball and roller bearings are high cost, they cannot be used in half, and greater noise. Types of bearing Types of ball bearings Prelubricated sealed ball bearing Thrust ball bearings APPLICATIONS OF ROLLER BEARINGS  Tapered roller bearing (TRB):  TRB can take both radial and axial loads and used for gear boxes for heavy trucks, bevel-gear transmission, lathe spindles, etc.  Thrust ball bearing:  It can take only thrust loads.  Thrust ball bearing are used for heavy axial loads and low speeds.  Needle roller bearing:  It use small diameter of rollers. They are used for radial load at slow speed and oscillating motion.  They have the advantage of light weight and occupy small space.  They are used in aircraft industry, live tail stock centers, bench-drill spindles, etc. Needle ball bearing Selection of bearing through catalogue Bearing Arrangement  Shafts are generally supported by two bearings in the radial and axial directions.  The side that fixes relative movement of the shaft and housing in the axial direction is called the “fixed side bearing," and the side that allows movement is called the "floating side bearing."  The floating side bearing is needed to absorb mounting error and avoid stress caused by expansion and contraction of the shaft due to temperature change. In the case of bearings with detachable inner and outer rings such as cylindrical and needle roller bearings, relative movement is accomplished by the raceway surface. Bearings with non-detachable inner and outer rings, such as deep groove ball bearings and self-aligning roller bearings, are designed so that the fitting surface moves in the axial direction. If bearing clearance is short, the bearings can be used without differentiating between the fixed and floating sides. In this case, the method of having the bearings face each other, such as with angular contact ball bearings and tapered roller bearings, is frequently used. Positions of bearing Bearing fits:  Extreme fits, whether loose or tight, are not recommended. The effect of press fits on contact angle or radial play must be considered. As a rule of thumb, mounted radial play (and hence contact angle) will be reduced by approximately 75% of the press fit. This is important where precise control on deflection rates is required or where low-radial-play bearings are used.  Size tolerance of the shaft and housing should be equal to those of the bearing bore and OD. Roundness and taper should be held to one-half of size tolerance. Surface finish should be held as close as possible.  Extreme fits will depend upon tolerances on the bearings, shaft, and housing. Upon request, the bearing manufacturer will code the bearing bores and OD into increments within the size tolerance. These increments are normally 0.0001 in., but can be supplied as low as 0.00005 in.  When operating at a temperature considerably different from room temperature, material expansion differences must be considered.  Adhesives offer several advantages in producing proper fits:  End play can be removed by applying a light external thrust load during curing time.  Extreme fits can be eliminated, since the adhesive will fill up any reasonable clearance.  Rotational accuracy can be improved by driving the shaft at slow speed during cure time.  Disadvantages to using adhesives include:  Certain adhesives are attacked by lubricants or solvents.  To ensure a good bond, bearing surface, shaft, and housing must be thoroughly clean of oil and dirt.  Adhesives may get into the bearing and cause damage.  To ensure a good bond without rotational inaccuracies, clearance should be held reasonably close. The tolerances on the shaft and housing should be of the same magnitude as standard-fits practice. Actual clearance depends upon the specific adhesive.  Under vibration, some adhesives may break loose. Assembly of ball bearing Bearing Mounting  For instrument bearings, certain special considerations should be emphasized:  Heavy press fits should be avoided.  Accuracy of mounting surfaces should be equal to accuracy of mating bearing surface.  Misalignment for low torque and running accuracy should not exceed 1/4°. Loading across the bearing during assembly should be avoided. Axial positioning:  Accurate axial positioning of the shaft relative to the housing requires shoulders, snap rings, or bearing flanges.  Shaft and housing shoulders: Diameter of a shaft or housing shoulder must be sufficient to ensure solid seating and support for applied thrust loads, yet small enough to avoid interference with other parts of the bearing. Most manufacturers provide recommended shoulder dimensions for each bearing size. Fit accuracy between shoulder and mounting diameter should be as good as bearing accuracy.  The corner between the shoulder and mounting diameter should be undercut because undercutting provides a more accurate machining of the shoulder surface. However, a radius is permissible if proper clearance is allowed.  Retaining rings: Certain cautions must be observed with this method:  Recommendations as to the groove dimensions should be followed.  Locating grooves machined into the shaft or housing must be controlled for squareness of groove face to bearing mounting diameter. Recommended value is 0.0002-in. TIR max.  Parallelism of the faces of the ring should be held to 0.0002-in. TIR max.  Lug dimensions should be checked to ensure there is no interference with the bearing. (Extended inner-ring bearings may offer an advantagehere.)  Avoid a snap ring that locates directly on the shaft or housing diameter (no groove) if heavy thrust loads are involved.  Flanges: Squareness of face-to-bore of the housing is critical and should be maintained to within 0.0003-in. TIR. Corners may be broken or left sharp because the flange is undercut and flush seating is ensured. Axial adjustment:  Removal of excess bearing end play, when required, may involve preloading of the bearings. However, the most common requirement is to establish an allowable range of end play under a given reversing thrust load.  Shims: Best material is stainless steel. Brass shims can also be used; however, they wear more easily and produce abrasive particles that could contaminate the bearing. Shims, particularly brass or other soft materials, should be used only against the nonrotating ring.  Spring washers: Belleville and wave washers are the two most common types used. The washer should exert a very light load on the bearings. If extreme rigidity under external load is required, preloaded bearings should be used.  The use of a spring washer usually involves a loose fit between the bearing ring and its mounting surface. Therefore, the washer should apply its force against the nonrotating ring.  Threads: Generally, threads are not recommended to remove end play. They are too easily overtightened and can cause brinelling in the bearings.  If threads must be used, the bearings should be locked against a solid shoulder or spacer. It is important to achieve a solid locking force without overloading the bearing rings. A Class 2 fit is normally recommended because it provides for slight misalignment of the nut, enabling the nut face to be flush with the bearing. The nut-face squareness to the thread pitch circle should be held to 0.0005-in. max wherever possible. SLIDING CONTACT BEARING Classification of the sliding contact bearing Journal bearing Footstep bearing Collar thrust bearing  Journal bearing – in this the bearing pressure is exerted at right angles to the axis of the axis of the shaft. The portion of the shaft lying within the bearing in known as journal. Shaft are generally made of mild steel.  Foot step or pivot bearing – in this bearing the bearing pressure is exerted parallel to the shaft whose axis is vertical. Note that in this case the end of the shaft rests within the bearing.  Thrust bearing – in this bearing supporting pressure is parallel to the axis of the shaft having end thrust. Thrust bearing are used in bevel mountings, propeller drives, turbines, etc. note here the shaft ,unlike foot-strep bearing passes through and beyond the bearing.  Thrust bearings also known as “collar bearing”. Journal bearing  Simple journal or solid bearing  It is simply a block of cast iron with a hole for the shaft providing running fit. An oil hole is drilled at the top for lubrication.  The main disadvantage of this type of bearing are  There is no provision for wear and adjustment on account of wear.  The shaft must be passed into the bearing axially, i.e. endwise.  Limited load on shaft and speed of shaft is low. Solid bearing  Bush bearing  In this the bush of soft material like brass or gun metal is provided and the body or main block is made of cast iron. Bush is hollow cylindrical piece which is fitted in a housing to accommodate the mating part. When the bush gets worn out it can be easily replaced. Bushed bearing Note that the insertion of the shaft in this bearing is endwise.  The outside of the bush is a driving fit (interference fit) in the hole of the casting where as the inside is a running fit for the shaft.  The bearing material used may be white metal (Babbit – Tin/Cu/Lead/antimony) , copper alloy (brass, gunmetal) or aluminum alloy.  Solid bushes are entirely made of bearing material and find the general application. In lined bush as the bearing material is applied as a lining to a backing material.  Applications: turbines, large diesel engines etc Bush and Direct-lined housing  Direct lined housings  In this type of the housing is lined directly by means of metallurgical bonding.  Low-melting point white metal is used as a lining on the cast iron housing Plummer block or Pedestal bearing  It is a split type of bearing. This type of bearing is used for higher speeds, heavy loads and large sizes.  The component of the bearing:  Cast iron pedestal or block with a sole  Brass or gun-metal or phosphorus-bronze “Brasses”, bushes or steps made in two halves.  Cast iron cap.  Two mild steel bolts and nuts. Care is taken that the brasses do not move axially nor are allowed to rotate. For preventing this rotation , usually a snug at the bottom fitting inside a recess at the bottom of the pedestal is provided. This bearing facilitates the placements and removal of the of the shaft from the bearing. Unlike the solid bearing which are to be inserted end-wise and hence are kept near the ends of the shaft, these can be placed anywhere. This bearing ensures a perfect adjustment for wear in the brasses by screwing the cap. Journal bearing Prevention of rotation of brasses  The steps are made octagonal on the outside and they are made to fit inside a corresponding hole.  A snug is cast on the lower brass top which fits a corresponding hole in the casting. The oil hole is drilled through the sung.  Snug are provided at the side, and the corresponding recesses left in the casting  The steps on the lower brass are made rectangular on the outside and they are made to fit inside a corresponding hole. Prevention of rotation of brasses Footstep or pivot bearing  suitable for supporting a vertical shaft with axial loads.  In a footstep bearing a gun metal bush having a collar on top is placed inside the C.I. sole. The end of the shaft rests on a gun metal disc placed at the bottom in the bush. The disc is prevented from rotation with the help of a pin or sung fitted in the sole. The disc act as a thrust bearing whereas the bush fitted in the casting supports the shaft in position. The bush can take radial loads, if any, on the shaft.  The disadvantage of footstep bearing is that it cannot be efficiently lubricated and there is unequal wear on the bottom disc. Advantages and disadvantages of the plain bearing  Plain bearing are cheap to produce and have noiseless operation. They can be easily machined, occupy small radial space and have vibration damping properties. Also they can cope with tapped foreign matter.  Disadvantages are they require large supply of lubricating oil, they are suitable only for relative low temperature and speed; and starting resistance is much greater than running resistance due to slow build up of lubricant film around the bearing surface.  INTRODUCTION What is a Vernier Caliper, How to Read a Vernier Caliper A vernier caliper consists of a sliding scale which is divided such that the distance between two marks on this scale is smaller than the distance between two marks on the main scale. To measure an object, the object is kept between the jaws and the vernier scale is moved. By looking at which mark on the vernier scale lines up with a mark on the main scale, the distance between the jaws could be read off to a higher precision than the least count of the main scale. Typically, vernier calipers can measure lengths to a precision of 0.1 or 0.05 mm. Most vernier calipers are equipped with a set of smaller jaws for measuring internal diameters and a depth probe to measure depths. Digital vernier calipers come with a small display that shows the value directly, and their accuracy could be as high as 0.01 mm. The diagram below shows a standard analogue set of vernier calipers. Specifically, note the numbered parts (1) outside jaws, (2) inside jaws, (3) depth probe, (4) main scale and (6) the vernier scale  read a vernier caliper The diagram below shows a standard analogue set of vernier calipers. Specifically, note the numbered parts (1) outside jaws, (2) inside jaws, (3) depth probe, (4) main scale and (6) the vernier scale.  A Vernier Caliper – How to read a vernier caliper In a micrometer, the object to be measured is placed between the jaws and the thimble is rotated until the jaws move together and clasp the object. A screw attached to the thimble rotates along with it and allows for precise values of distances to be read off from the scale. A typical micrometer has a precision of 0.01 mm. For measuring inner diameters and depths, different types of micrometer are used. The diagram below shows, from bottom to top an outside micrometer, an inside micrometer and a depth micrometer (note that these particular micrometers have been calibrated for the imperial system).  What is a Micrometer In a micrometer, the object to be measured is placed between the jaws and the thimble is rotated until the jaws move together and clasp the object. A screw attached to the thimble rotates along with it and allows for precise values of distances to be read off from the scale. The video posted below explains how to read a micrometer. A typical micrometer has a precision of 0.01 mm. For measuring inner diameters and depths, different types of micrometer are used. The diagram below shows, from bottom to top an outside micrometer, an inside micrometer and a depth micrometer (note that these particular micrometers have been calibrated for the imperial Micrometer  Difference between Vernier Caliper and Micrometer It is important to remember that both micrometers and vernier calipers can give zero errors. Before measuring an object, it is always good practice to put the two jaws together and see whether the instrument gives a reading of 0. If this is not the case, the reading should be noted and should be added/subtracted to the measurement of the object. WORKING PRINCIPLE OF VERNIER CALIPER AND MICROMETER Vernier calipers use a sliding vernier scale to measure small movements of its jaws. Micrometers use a screw to amplify small movements of its jaws to larger movements of the rotating scale. POSSIBLE MEASUREMENTS Vernier calipers typically allow a user to measure external diameters, internal diameters as well as depths. Micrometers usually only allow users to measure external diameters. Other, more specialized types of micrometers are available for measuring internal diameters and depths. PRECISION Vernier Calipers traditionally have a precision of 0.1 or 0.05 mm. Digital vernier calipers have a precision of 0.01 mm. Micrometers typically have a precision of 0.01 mm.  GOOD MEASUREMENT PRACTICE GOOD MEASUREMENT PRACTICE There are six guiding principles to good measurement practice that have been defined..They are: The Right Measurements: Measurements should only be made to satisfy agreed and well specified requirements. The Right Tools: Measurements should be made using equipment and methods that have been demonstrated to be fit for purpose. The Right People: Measurement staff should be competent, properly qualified and well informed. Regular Review: There should be both internal and independent assessment of the technical performance of all measurement facilities and procedures. Demonstrable Consistency: Measurements made in one location should be consistent with those made elsewhere. The Right Procedures: Well-defined procedures consistent with national or international standards should be in place for all measurements.  Types of vernier callipers Vernier, dial and digital callipers specifies two types of standard vernier callipers, the M-Type and the CM-Type. The M type has independent jaws for internal and external measurement. With the CM type the faces for internal and external measurement are on the same jaws. CM-Type vernier How to read  Handling and storage of calipers Handling and storage of calipers Calipers are often used in hostile environments and their maintenance tends to be overlooked perhaps because of their apparently simple construction and the low accuracy use to which they are often put. However, in order to obtain the best possible performance from calipers and to ensure economical use, it is essential to implement effective maintenance control. As with other types of measuring instruments, companies should have standardized rules that govern purchasing, training, handling, storage, maintenance and periodic inspection of calipers.  Storage of callipers Observe the following precautions when storing callipers. 1. Select a place where the callipers will not be subject to dust, high humidity or extreme temperature fluctuations. The storage area should not be damp and it is worth taking the extra precaution of placing a bag of silica gel in the tool draw. 2. Lay callipers in a manner such that the main scale beam will not bend and to give adequate protection from damage to the vernier. 3. Leave the measuring faces so that they are not in contact. A gap of about 2 mm is suggested 4. Do not clamp the slider 5. Store the calliper in a case or plastic bag. 6. When storing large size callipers, which are not frequently used, apply a rust preventative to the sliding and measuring faces and separate the two jaws. Avoid rust preventatives that leave a coating on the material being protected. This type of rust preventative material can affect the calibration of dial type callipers. 7. For callipers that kept in storage and are seldom used, at least once a month, check the storage condition and movement of callipers to ensure that no deterioration has occurred. 8. Prevent vapours from chemicals such as hydrochloric or sulphuric acid from permeating storage rooms. 9. Keep a record of callipers that are stored. Maintain detailed information on all callipers in use on the shopfloor.  Storage of callipers It is also good practice, during the daily use of a calliper, to wipe it clean of dirt and fingerprints with a clean lint-free cloth and store it with the outside jaws slightly open on completion of measurements. Never leave callipers unprotected on a swarf-covered bench or in an environment where the graduated face is regularly exposed to cutting chips and dust, since the graduations may become hard to read due to scratches or stains and slider movement may become uneven. Once measurements are complete, clean and properly store the callipers.  Periodic inspection and calibration It is good practice to carry out periodic inspections of callipers at least once a year, the exact interval depending on the frequency of use. In addition, implement inventory control methods to prevent inadvertent use of callipers known to be in need of repair or are beyond repair and are for disposal. There are two systems of making periodic inspections. One is to inspect the callipers at each work site and the other is to collect all the callipers at predetermined intervals and inspect them all at a central testing site. Inform all personnel who use callipers in the workplace of the inspection process adopted. Closing the jaws tightly and holding the calliper to a light source is a good daily check on jaw wear. If you do not see light breaking through at any point along the jaw boundary the callipers are suitable for continued use. If wear is spotted, make further checks on the jaw faces using optical flats. Frequency of calibration will depend on frequency of use and on the previous history of the calibration errors. Only perform calibration using traceable standards. Control of callipers An effective method of maintenance control for measuring tools, such as callipers, which are frequently used on the shop floor, is to limit the number of tools in the tool room and on the shop floor. Although callipers are relatively cheap, they are not consumables and you should not treat them as such.  OPERATING PRINCIPLES MICROMETER Operating principles A micrometer is a device that uses a graduated screw mechanism to produce precise linear displacement of a spindle along its axis. Distance measurement is achieved referencing the linear displacement of the spindle to a fixed measuring face on the axis of the spindle (the anvil). Figure shows the main components of a micrometer. MICROMETER  MICROMETER The main components are described below. The inner sleeve, which has the guide threads of the feed mechanism, is fixed to one end of the frame. The anvil, which serves as a fixed measuring face, is attached to the opposite end of the frame. The spindle has a measuring face at one end and an external thread at the other. It is fitted to the inner sleeve, which ensures the linearity of the spindle motion in the axial direction. The spindle’s external thread engages with the internal thread of the inner sleeve. The measuring face of the spindle serves as a contact point for measuring the workpiece. Measurement is performed by feeding the spindle so that both the anvil measuring face and the spindle measuring face touch the workpiece. The outer sleeve has graduations that correspond to the spindle’s thread pitch and an index line to aid reading of the graduations on the thimble. The thimble is fixed to the spindle so that both components turn together and is knurled for ease of turning.  MICROMETER The ratchet stop applies constant pressure to the workpiece being measured and consists of a leaf spring and a ratchet mechanism. The clamp, fixed to the spindle guide section of the frame, locks the spindle against the inner sleeve. A standard micrometer has a screw thread of 0.5 mm pitch with a thimble graduated in fifty equal divisions around its circumference. Micrometers are manufactured in size ranges of 0 mm to 25 mm, 25 mm to 50 mm, …, 575 mm to 600 mm etc. As an example, you would measure a dimension of 19.45 mm with a 0 mm to 25 mm micrometer and a dimension of 580.25 mm with a 575 mm to 600 mm micrometer.  MICROMETER Standard external micrometer Figure shows an external micrometer of the type described in the section on operating principles and shown sectioned in above figure. It is probably the most common type of micrometer that the reader will encounter.  SPHERICAL ANVIL AND SPINDLE TYPE Spherical anvil and spindle type A spherical anvil type micrometer is shown in figure. The anvil and spindle measuring faces of this type of micrometer are either both spherical or spherical and flat.  Spline micrometer Spline micrometer The anvil and the spindle of this type of micrometer are of small diameter in order to measure splined shafts, slots and keyways for which standard outside micrometers are not suitable. POINT MICROMETER Point micrometer This instrument has a pointed spindle and anvil and is typically used for measuring the web thickness of drills, root circle diameters of external threads and small grooves where access is restricted. The point anvils are usually 0.3 mm radius with 15º or 30º anvils.  DISCRIMINATION Standard micrometer (0.01 mm discrimination) With 0.01 mm discrimination micrometers the gap between the measuring faces changes by 0.5 mm for one full turn of the thimble. Therefore, for a spindle movement of 1 mm, the thimble will have turned through two revolutions. Figure shows the sleeve of a standard metric micrometer with the 1mm divisions above the datum line and the 0.5 mm divisions below the datum line. Example readings are given in figure 47 and figure 48. The thimble has fifty divisions; therefore a rotation of one division of the thimble scale produces a change in gap between the measuring faces of a fiftieth of 0.5 mm; equal to 0.01 mm. Each thimble graduation therefore equals one hundredth of a millimeter  Discrimination To perform a measurement with a micrometer the general procedure is that the value of the nearest visible graduation on the sleeve to the thimble is determined and added to the value of the graduation on the thimble which lines up with the datum line on the sleeve. Figure shows how to read a metric micrometer. In the top half of the figure, the sleeve reading is 7 mm. The thimble reading is just over 37 divisions. The excess has been estimated to be 0.3 of a division hence the total reading is 7.373 mm. In the bottom half of the figure the sleeve reading is 7.5 mm. The thimble reading is just over 37 divisions. The excess has been estimated to be 0.3 of a division hence the total reading is 7.873 mm DISCRIMINATION  Take care not to misread the smallest graduation on the sleeve (potentially resulting in an error of 0.5 mm on a standard metric micrometer), figure 51 shows a method of reading a micrometer to discriminate 0.001 mm. This method relies on the fact that the width of a thimble graduation line equals one fifth of a thimble division.  HANDLING AND STORAGE OF MICROMETERS Handling and storage of micrometers This section covers the handling and storage of micrometers. Routine checks of micrometers On a regular basis, make the following routine checks. Check the condition of the plating and paint. There should be no discoloration,peeling or rust. Check that the measuring faces should be free from scratches and burrs. Check the fit of the threads. The screw should turn freely over the entire operation and be free from backlash. The threads of the spindle and inner sleeve should permit easy adjustment of the fit when they become worn.  HANDLING AND STORAGE OF MICROMETERS Any misalignment that may exist between the spindle and the anvil should be small enough so as not affect measurement (0.002 inch for a 0 inch to 1 inch micrometer). The spindle should be easy to clamp. The micrometer reading should not change by more than 2 μm when the spindle is clamped. The ratchet stop should rotate smoothly. The clearance between the thimble and the sleeve should be even around the circumferences. The runout of the thimble should be minimal (should not be seen by the naked eye). When the zero line on the thimble is aligned with the index line on the sleeve, the end of the thimble should be aligned with a graduation line on the sleeve but should not overlap the graduation line so as hide it.  MAINTENANCE OF MICROMETERS Maintenance of micrometers The following actions are required to maintain micrometer accuracy: daily inspection; cleaning and rust prevention; and storage of micrometers. Each action is described in more detail below Daily inspection The following points should be addressed on a daily basis Checking the zero point Even if the zero point of a micrometer has been adjusted accurately, it may need to be adjusted again after a few hours use since changes in temperature and other environmental conditions can cause the zero point to change.  MAINTENANCE OF MICROMETERS Checking the measuring force A variation in the measuring force significantly affects the accuracy. For micrometers with a ratchet stop, check that the ratchet barrel turns smoothly and otherwise functions correctly. Checking the fit Check the fit of the spindle and spindle guide, and the threads of the spindle and inner sleeve. Make sure that the spindle and other threaded parts move smoothly and evenly over their entire traverse. Eliminate excessive play or backlash with the adjusting device (taper nut). Checking the micrometer after it has been dropped or subjected to a blow If the micrometer has been dropped or subjected to a blow, check the zero point, measuring force, fit conditions, runout of the thimble, parallelism between the measuring faces and the instrumental error.  CLEANING AND RUST PREVENTION Cleaning and rust prevention After using the micrometer, wipe off oil, cutting or grinding fluid, fingerprints and contaminants (fingerprints may cause rust). Wipe carbide tipped measuring faces thoroughly with a dry cloth. If the measuring faces are not carbide tipped, wipe clean and apply rust-preventing oil. Separate the two measuring faces slightly before storing the instrument. Wipe cutting or grinding swarf from the spindle before using the micrometer as these particles may become trapped between the spindle and the spindle guide. If a micrometer is not going to be used for an extended period, wipe it thoroughly and apply high-grade rust-preventing oil. Protect the micrometer from dampness by tightly wrapping the instrument with an oil soaked paper or cloth before putting it in the case. Select a storage place where humidity is low and temperature changes are small. If the micrometer has been stored for a long period, inspect it thoroughly before use.  STORAGE OF MICROMETERS Storage of micrometers Note the following points when storing a micrometer. When storing the micrometer do not expose it to direct sunlight. Store the micrometer in a low humidity, well ventilated and dust free environment. Leave the measuring faces separated by 0.1 mm to 1 mm. Do not clamp the spindle Store the micrometer in a case.  DEPTH MICROMETER The depth micrometer Depth micrometers (figure 71) are used to measure the depths of holes, slots and steps. British standard BS6468:1984 Specification for depth micrometers covers depth micrometers. The classifications for depth micrometers are 1. single rod type; 2. interchangeable rod type; and 3. sectioned rod type. Of the above three types, the interchangeable rod type is the most widely used. DEPTH MICROMETER  SINGLE ROD TYPE DEPTH MICROMETER Single rod type depth micrometer The single rod type depth micrometer (figure 72) consists of a micrometer head, spindle and base. The construction of the sleeve and the thimble is the same as that of a standard outside micrometer, but the graduations are given in the reverse direction. The typical measuring range is 25 mm. The end face of the spindle serves as the measuring face. The base is of hardened steel. Since the bottom face of the base is used as a reference face, it is precision lapped to high degree of flatness.  INTERCHANGEABLE ROD TYPE DEPTH MICROMETERS Interchangeable rod type depth micrometers This type of micrometer (figure 73) uses a hollow spindle without a measuring face. An interchangeable rod passes through the spindle and the base. The rod has a precision lapped measuring face on one end. The other end of the rod is fixed to the spindle. The method of clamping the rod to the spindle depends on the manufacturer, for example, using a rod collar and setscrew or pressing the ratchet stop screw against the rod end. Interchangeable rods of various lengths are available in 25 mm increments and these can be easily fitted to achieve the desired measuring length. The standard measuring range is 0 mm to 150 mm although rods are available to measure to a depth of up to 300 mm  SECTIONED ROD TYPE DEPTH MICROMETER Sectioned rod type depth micrometer The sectioned rod type depth micrometer is designed to overcome the measuring range limitations of the single rod type micrometer and the disadvantage of the interchangeable rod type micrometer that various lengths of rods are required for different measuring situations. The sectioned rod type micrometer allows the user to select the effective rod length. It contains one long rod that has vee grooves around its circumference at 25 mm intervals along the axis. The spindle is hollow (similar to that of the interchangeable rod type) and it has a groove at one end for clamping the rod at one of the groove positions. The standard measuring range of this type of instrument is 0 mm to 300 mm. TORQUE WRENCHES TORQUE CALCULATION  TEN GOLDEN RULES TO OBSERVE: Ten golden rules to observe: don't mix nuts, bolts or fasteners up: after you remove them, replace on the engine (if possible) wire brush and clean ALL nuts, bolts or fasteners (do NOT use lubricant of any kind!) clean out drillings to ensure there is NO residual oil left check threads on ALL drillings into alloy housings and clean up with a tap & die set (remove all swarf!) clean everything thoroughly! Carbon, dirt, grit and grime are your enemies - don't let them undo your work. inspect all bolts and nuts carefully! Bin and replace any that look suspect -even if it screws up your schedule take care of your torque wrench: don't use it to slacken anything (use a breaker bar instead) don't use solvents or cleaners that might compromise the special grease inside a torque wrench after using your torque wrench, always reset it to its lowest setting ideally, have the torque wrench recalibrated every 12 months/5,000 uses (or after it has been dropped)  PROPER TORQUE WRENCH USE AND MAINTENANCE Proper Torque Wrench Use and Maintenance A torque wrench is a precision instrument designed to apply a specific amount of force to a fastener. Whether tightening head bolts on an automobile engine, lugs for tire and rim installation or inspecting fastener tolerances on high-performance equipment, it is extremely important that proper care is used. Guidelines are typically provided noting acceptable torque ranges, the order in which specific fasteners are tightened and the number of times a fastener must be tightened and loosened to ensure uniform torque application. Failure to properly torque fasteners can lead to e  PRECAUTIONS It is important to follow acceptable maintenance and use practices, such as: 1. Safety glasses or goggles should be worn at all times when using any hand tool. 2. Always follow the manufacturer’s directions regarding torque direction, proper force, torque pattern/sequence, use or non-use of lubrication on fasteners and torque “tighten/release” cycles. 3. Do not exceed the recommended working range of the torque wrench. Reliable measurements are based on a percentage of the working range. In general, most mechanical wrenches have a useable range from 20% to 100% of full scale. Most electronic wrenches have a useable range from 10% to 100% of full scale. 4. Do not use accessories or handle extensions unless specifically allowed by the torque wrench manufacturer. 5. Take time to inspect the tool and check for worn or cracked sockets. Properly lubricate and replace worn parts.  PRECAUTIONS 6. Avoid dropping or sliding a torque wrench. Dropping a torque wrench on a hard surface can cause the instrument to lose reliable calibration. If you suspect that a wrench has been dropped, have the tool inspected by the manufacturer or reputable calibration service. 7. Always store a torque wrench in a protective case and/or location when not in use. 8. Avoid exposure to temperature extremes, high humidity, fluid immersion and corrosive environments. 9. If using a click-type torque wrench, always store it at the lowest level on the scale. 10. Avoid marking, etching or placing labels on torque wrenches. 11. Use a torque wrench to apply a specific torque value during the final assembly process. Do not use a torque wrench as the primary means of tightening or loosening fasteners.  PRECAUTIONS 12. As most torque wrenches are length specific, always grasp the torque wrench in the center of the handle. If two hands need to be used, place one hand on top of the other. 13. Apply torque in a slow, methodical manner and avoid sudden, “jerking” movements. 14. When the wrench signals (by clicking, beeping or lights) that a specific torque has been reached, stop pulling immediately. 15. After 5000 cycles or up to one year of use, whichever comes first, have your torque wrench inspected and recalibrated by the manufacturer or reputable calibration service. With proper care, a high-quality torque wrench should provide accurate measurements for many years. SEALS Seals are of two types:-  One way seals  Two way seals  One way seals- Chevron or V ring packing, U ring packing and D ring packing all get their name from their shape and all are one way seals. This means that the seal will stop the flow of fluid in one direction only. to prevent a flow from both directions , two sets of seals must be installed, each having their open end facing the direction from which the pressure is applied. The apex , or pointer of the seal rests in the groove of a metal backup ring on the half shaft and spreader ring having a triangular cross section fits into the groove of the seal. When both seals are assembled on the shaft , the adjustment nut tightened to spread the seal and hold them tight against the wall of the actuating cylinder.  Chevron seals  O-ring seals  Chevron Seals :- There are many different type of seals used in ac applications, ranging from flat paper gaskets up through complex, multi-component packing. V ring packing or chevron seals have found extensive use in the past. O- ring seals:- Most modern hydraulic and pneumatic systems use o ring for both packing and gaskets. O rings fit into the grooves in one of the surfaces being sealed. The groove should be about 10% wider than the width of the seal, and deep enough that the distance between the bottom of the groove and the other surface will be little less than the width of the o ring  High pressure seals  Seals are used throughout hydraulic and pneumatic systems to minimize internal leakage and the loss of system pressure. There are two types of seals in use: gaskets, where there is no relative motion between the surfaces, and packings, where relative motion dose exist. O RING SEAL CHEVRON SEAL CHEVRON SEAL O RING SEAL V TYPE CHEVRON SEAL O RING SEAL SEAL  Two way seals:-the most commonly used two way seals is the O ring seals which may be used as either a gasket or packing. This type of seal fits into a groove in one of the surface being seals. The groove should be wider. This provides the squeeze, or pinch necessary to seal under the condition of zero pressure. O RING SEAL CABLE CONSTUCTION  Cable system:- A/C control cable is availablein both corrosion resistance steel and carbon steel. The corrosion resistance steelis somewhatmore expensive and has a slightly lower strength, but its longer life makes it the better of the two cables for use wherecorrosion may be problem, such as in agricultural A/c and seaplane.  CABLE CONSTUCTION  There are three types of steel cable used for A/C control system: nonflexible, flexible and extra flexible. Nonflexible cable may be of either the 1 ×7 or 1 ×19 type this designation means that the 1 ×7 cable is made up of seven strands, each having only one wire. The 1 × 19 cable made of 19 strands of one wire each. None flexible wires may be used only for straight runs where the cable does not pass over any pulleys. Flexible cable made up of seven strands, each of which has seven wires. Flexible wires may be used only straight runs or where the pulleys are large. When cable must change direction over relatively small diameter pulleys, extra flexible cable must be used. This type of cable is made up of seven strands, each having 19 separate wires. All A/c control cables is pre formed, which means that the wires were shaped in their spiral form before the cable was wound, and they will not spring out when the cable is cut. CROSS SECTIONAL ILLUSTRAES CROSS SECTIONAL ILLUSTRAES TURNBUCKLE SAFETYING  PURPOSE:- After the cable tension has been adjusted with the turn buckle, they must all be checked for the proper amount of thread showing and than safe tied.  No more than three threads exposed at each side.  Turnbuckle should never lubricated.  Long barrel should adjust for cable tension TURNBUCKLE SAFETYING  Type of safe ting :-  Single wrap straight  Double wrap straight  Single wrap spiral  Double wrap spiral.  we used two clips for lock or joint two cables.