Aircraft Electrical System 4

Md. Nur Alam Course/Batch: FENDA09Page 11
Student ID: 33


Task 01
Serviceability check of Cessna 150 a/c landing and taxi light
At first have to put the battery switch on and check the light.
If the light comes on operation then it is ok.
If the light does not come then check the bulb filament. If the bulb is unserviceable then replace it.
After that if the light doesn't come on go for checking the switch of the light.
After checking the switch if the light comes on then has to sure the light is ok.
If not check the circuit and check the continuity of electrical power from the switch to light by a multi meter. If the light doesn't come on then replace the wire.
Then if the light remains unserviceable then check the main supply source. If the connections are loosen there then tighten the connections.
Defect
Acton
Landing light and taxi light was faulty.
Need to be replaced.

Sign: Md. Nur Alam
Authority no: FENDA12-09-33.
Place: WORKSHOP
Date: 17.03.2014
Replaced wire by a new one.
Check the operation, job satisfactory.

Sign: Md. Nur Alam
Authority No: FENDA12-09-33.
Place: WORKSHOP
Date: 17.03.2014

Task 02
Insulation Resistance Test: The insulation resistance test is also known as a Megger test. Its objective is to measure the total resistance between any two points separated by insulation. The test, therefore, determines how effective the insulation is in resisting the flow of electrical current. The voltage is typically around 500–1000 V dc; hence, the current is very low. Because the current is so low, this test is useful for checking the quality of the insulation not only when a product is first manufactured, but also over time as the product is used. [1]

Figure: Measurement principle of Insulation Resistance Test
Insulation resistance tester:
Direct test voltage depends on the circuit under test, but will be:-
250 V for extra-low voltage circuits
500 V for other circuits supplied at up to 500 V
1000 V for circuits rated between 500 V and 1000 V.
Must be capable of delivering a current of 1 mA at the minimum allowable resistance level, which is:-
250 kOhms for the 250 V tester
500 kOhms for the 500 V tester
1 MOhms for the 1,000 V tester
Basic instrument accuracy required is +/-5%
Must have a facility to discharge capacitance up to 5 microF which has become charged during the test.
May be combined with the low resistance ohmmeter [2]
Test Procedure: The EUT is connected to the measuring instrument, and the voltage is ramped up from zero to the final value, which in most cases is 500 V dc. Once the voltage reaches the selected value, it is kept at that value for a brief period (typically up to 5 seconds) before the resistance test is measured. The measured value should be very high (typically in the megohm region). The insulation resistance test is mandatory in some product safety standards, including IEC 60065 and UL 6500.

Figure: Insulation tests between poles
Ground Bond Test: Also known as the ground bond continuity test, the ground bond test must be conducted on all Class I products. The purpose of the test is to ensure that all accessible conductive parts of the product that could become live in the event of a single insulation fault are connected securely to the final earth point of the supply input. In other words, a ground bond test verifies integrity of the ground path by applying a high-current, low-voltage source to the ground-path circuit.
Compliance is checked by measuring the resistance of the connection between the protective earthling terminal or earthling contact and the parts to be earthed to ensure that resistance does not exceed certain values when subjected to a high current as specified in various product safety standards. It is important to bear in mind that from the constructional and design points of view, the protective earthling conductors should not contain switches or fuses.


Figure: Insulation test to earth.
Test Requirements: Most safety standards require the following parameters for conducting the ground bond test:
The EUT must be subjected to a high ac or dc current with a low test voltage for a certain period.
The voltage drop between the protective earthling terminal or earthling contact and the part to be earthed must be measured.
The resistance must be calculated from the current and the resulting voltage drop using Ohm's law.
Electronic equipment which could be damaged by the application of the high test voltage should be disconnected. Included in this category are electronic fluorescent starter switches, touch switches, dimmer switches, power controllers, delay timers, switches associated with passive infrared detectors (PIRs), RCDs with electronic operation etc. An alternative to disconnection is to ensure that phase and neutral are connected together before an insulation test is made between them and earth. [2]
Capacitors and indicator or pilot lamps must be disconnected or an inaccurate test reading will result.
The resistance should not exceed certain values as stated in various safety standards. For example, IEC 60950 requires that the test voltage not exceed 12 V. The current can be either ac or dc at 1.5 times the current consumption of the product or 25 A, whichever is greatest. The test duration must be 1 minute, and the resistance of the connection between the protective earthing terminal orearthing contact and parts required to be earthed must not exceed 0.1 . This value does not include the resistance of the power cable. Some standards, such as CAN/CSA-C22.2 No. 60950-00 or UL 60950 with Canadian deviation, require the test to be conducted at 30 A and for 2 minutes if the current rating of the circuit under test is 16 A or lower. [2]
Required test voltages and minimum resistance
Nominal circuit voltage


Test voltage
(V)
Minimum insulation resistance
(M Ohms)
Extra-low voltage circuits supplied from a safety transformer
250
0.25
Up to 500 V except for above
500
0.5
Above 500 V up to 1000 V
1000
1.0
The insulation resistance tester must be capable of maintaining the required voltage when providing a steady state of current of 1mA.
Understanding Resistance Values: With the exception of the Canadian standard, most standards require 25 A for 1 minute. The value of 25 A for 1 minute represents the worst current and the longest operation time of a mains overcurrent device. The maximum 25 A is approximately 1.5 times the mains circuit breaker value installed for most pluggable type A cord-connected equipment rated up to 16 A. The Canadian National Wiring Code requirements are very similar to these in the sense that they assume that fuses are expected to operate no more than 1 minute at twice their rated current. Because most mains circuits are protected with a 15–16 A fuse, the fault current would be 30 A for no more than 2 minutes.
Safety Precautions: Because any electrical safety test involves some risk of electrical shock, it is crucial that certain precautions be taken to avoid shock and injury to operators. Listed below is a sampling of precautions that can minimize the danger of electrical shocks and ensure all-around safety:
Train operators in the basic theory of electrical circuits and explain the object of each test.
Review and update all safety test procedures regularly.
Locate the testing area away from walkways and crowded areas on the shop floor.
Guard the testing area with nonconductive barrier.
Mark the testing area with a clear and visible sign such as "Danger" or "High Voltage Present."
Mark the testing area with a clear sign indicating "Qualified Personnel Access Only."
Ensure that all test equipment is properly connected to a reliable earth.
Reconfigure all testers (where possible) with push-button switches so that operators must use both hands to activate the test equipment or, alternatively, provide the equipment with a safety interlock that automatically shuts down the high voltage when a safety switch on the EUT is opened.
Connect the complete test setup to a palm-type switch that can shut off the power to the test bench in case of an emergency.
Defect
Acton
Some damages are found in the battery and the acid level of the battery is decreased. Wire was found defected.
Need to be replaced.

Sign: Md. Nur Alam
Authority no: FENDA12-09-33.
Place: WORKSHOP
Date: 17.03.2014
Replaced wire by a new one.
Check the operation, job satisfactory.



Sign: Md. Nur Alam
Authority no: FENDA12-09-33.
Place: WORKSHOP
Date: 17.03.2014

Task 03
Voltage regulator
A voltage regulator is an electricalregulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedbackcontrol loops. It may use an electromechanical mechanism, or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages. [3]
Electronic voltage regulators are found in devices such as computer power supplies where they stabilize the DC voltages used by the processor and other elements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant. In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line.
Voltage regulator test:
First time Connect multi meter negative lead to alternator ground terminal and positive lead to positiveoutput terminal.
Then Start and idle engine with no electrical loads at 1400rpm until multi meter voltage reading stabilizes at theregulator high end setting
Check voltage reading. If voltage reading exceeds30 volts, the voltage regulator is shorted. Replacevoltage regulator.

REMOVAL:
Remove alternator belt
Disconnect wire at connector.
Remove 2 nuts and lock washers from terminals and remove 3 wire leads. Discard lock washers.
Remove nut and lock washer from terminal and remove 2 wire leads. Discard lock washer.
Remove locknut and washer from terminal and remove wire lead. Discard locknut
Remove bolt , lock washer , flat washer , and spacer from alternator and alternator bracket .Discard lock washer.
 Remove cap screw , flat washer , sleeve bushing , spacer , lock washer , and nut fromalternator . Discard lock washer.
Remove alternator.
Remove nut and lock washer. Discard lock washer.
Pry pulley from alternator.
 Remove screw, washer , and alternator bracket
INSTALLATION:
Position alternator bracket in place and install screw and washer.
Position pulley on alternator shaft and install new lock washer and nut.
Position alternator in place and install cap screw , flat washer , sleeve bushing , spacer , newlock washer , and nut
Install bolt , new lock washer , flat washer , and spacer in alternator bracket and alternator
Install washer and wire lead with new locknut .
Install 2 wire leads with new lock washer and nut .
Install 3 wire leads with 2 new lock washers and nuts .
Connect connector.
Install alternator belt and adjust
Cleaning and inspection
clean parts with dye cleaning solvent P.D 680 and dry thoroughly
inspect contact blades, clips and brackets for cracks, breaks r distorted condition and replace parts as necessary
inspect threaded parts for stripped or damaged threads and replace as necessary [4]
DC generator voltage: When connected to a load, the simple generator shown in produces a sinusoidal alternating current (AC) output. In many applications a steady direct current (DC) output may be preferred. This can be achieved by modifying the arrangement shown in replacing the brushes and slip ringswith a commentatorarrangement,The commentator arrangement functions as arotating reversing switch which ensures that thee.m.f. generated by the loop is reversed after rotating through 180 °. The generated e.m .f .for this arrangement It's worth comparing this waveform with that you should be able to spot the difference immediately!

Figure: cutaway view of generator
The generated e.m. f. while stun polar(i.e. having only one polarity, either all positive or all negative), is clearly far from ideal since a DC power source should provide a constant voltage output rather than a series of pulses. Onaway of overcoming this problem is with the use of a second loop (or coil) at right angles to the first,The commentator is then divided into four (rather than two) segmentsand the generated.m.f. produced by this arrangement is shown in Fig. 4.9 .In real generators, a coil comprising a large number of turns of copper wire replaces the single-turn rotating loop. This arrangement effectively increases the
total length of the conductor within the magnetic field and, as a result, also increases the generated outputVoltage. The output voltage also depends on the density of the magnetic flux through which thecurrentcarryingconductor passes. The denser the field the greater the output voltage will be.
Defect
Acton
Generator voltage fluctuation
Need to be replaced.

Sign: Md. Nur Alam
Authority no: FENDA12-09-33.
Place: WORKSHOP
Date: 17.03.2014
Replaced wire by a new one.
Check the operation, job satisfactory.

Sign: Md. Nur Alam
Authority no: FENDA12-09-33.
Place: WORKSHOP
Date: 17.03.2014

Task 04
Co-coordinating maintenance
The co-ordination and over sighting role is emphasized as it is not engineer's duty to undertake all aspects of equipment maintenance personally. During actuating device maintenance co-coordination is important because without co-coordination accident can happen at any time. Some basics requirements are given below for safety maintenance by co-coordination. [5]

Breakdown maintenance:
Breakdown maintenance is the repair of something that has broken or malfunctioned, in order to restore it to an operating condition. Preventative maintenance, on the, other hand is the process of keeping an item in a good, safe operating condition. Regular checks, inspections and tests are examples of preventative maintenance; and are activities that most brigade members should be able to perform competently. Testing a pump may be an example of such an activity. Vehicle repair on the other hand, may require specialist training or licensing of the repairer to conform with government regulations. Motor vehicle repairs are a good example of where a licensed repairer may be required to restore a vehicle to a safe operating condition. Some brigade organizations may use a tradesperson to service nominated items. This would not override the need for checks, inspections and tests to be carried out on a regular basis by members. All that such a system does is to identify a particular individual or group of individuals whose task is to
Carry out servicing that requires specific expertise. Drawing the attention of these individuals to a need for servicing rests with your brigade's membership as a whole, and you, as EQO in particular.
Equipment checks - after use
Equipment used for firefighting and other emergencies should be checked after each use. A "check" is a simple, usually visual, confirmation that the equipment is ready for further use and stowed correctly. The most efficient way of ensuring that equipment is in good working order and ready for next use is to check it before it is put away. Because ours is largely a volunteer
Service, you can't usually leave this job to the next shift. Post-fire checks of any equipment used, immediately upon return to the station, should ensure that equipment is clean and ready for its next use. Relying on a maintenance session some time after a response can result in equipment not being ready should you get another fire call. Checking equipment upon returning to the station is a good habit. The presence of the crew should also mean that there are many hands to make the workload easier.
Recording of maintenance:
Records are essential to establish what has been done and what remains to be done. The amount of maintenance completed versus that needed reflects the effectiveness of your maintenance programs. An example of a record sheet is shown at the end of this Handbook.
Equipment Checklists:
Check Consists of a check (usually visual) by brigade personnel of items/components for readiness for service.
Inspection Consists of an inspection by brigade personnel of the items/components for wear or damage where major disassembly of the item/component is not required, and to also include any "check" items for that piece of equipment.
Test Consists of a specified test sequence designed to evaluate whether or not the piece of equipment still performs to specification.
Service Consists of any work prescribed by law or by the Fire Control Officer to be conducted by a qualified/licensed technician, or where major disassembly of items/ components is required, and is to be to the manufacturer's instructions/specifications. [6]
An example of functional checks on actuation device is given below:
Rudder removal and installation
Equipment
Hydraulic jack.
Ladder.
Required tools
Ring Spanner-7/16"-qty-2.
Spanner-3/8"- qty-2 and ¼"- qty-3.
Philips Screw driver 4".
Safety precaution
Vertical stabilizer and rudder gap should be checked for any obstruction.
The area underneath the rudder should be cleared to prevent any damage.
Aircraft should be chocked.
Tag should be hanged on the starter switch including name, date and work description.
Fire extinguisher should be available in the working spot.
At least three people are required to do the job.
Preparation
we issued the required tools and equipment.
We took the maintenance manual.
We cleaned the working area.
We took a ladder.
Need two man powers.
Rudder removal
At first disconnected tail navigation light quick disconnect.
Then remove the cockpit panel by using 4" Philips Screw driver.
Then relieve the turnbuckle cable tension by using ¼" spanner.
Then remove clevis bolt by using 3/8" spanner and disconnect clevises form rudder bell crank.
At last by using 7/16" ring spanner remove supported hinge bolts and lift rudder free of vertical fin.
Inspection
Rudder is inspected for deformation and damaged.
Installation
At first install the rudder with vertical fin by using 7/16" ring spanner.
Then connect the tail navigation light.
Install clevis bolt by using 3/8" spanner and connect clevises with rudder bell crank.
Adjust the turnbuckle cable tension by using ¼" spanner.
At last screw the cockpit panel by using 4" Philips Screw driver.
Inspection report
During inspection rudder is found OK.





Bibliography
http://www.proz.com/kudoz/italian_to_english/energy_power_generation/1653892-battiture_e_megeraggio_cavi.html
Cessna 150 maintenance manual page-370-375
http://en.wikipedia.org/wiki/Voltage_regulator
Cessna 150 maintenance manual page-390-392
http://www.huizenga.nova.edu/coursematerials/5463/Readings/C005%20Coordination%20in%20Disaster%20Management.Prizzia.pdf
Cessna 150 maintenance manual page-370-375



Unit title/no: Aircraft Electrical System [84]
Assignment title/no: carry out real or simulated aircraft electrical system maintenance activities [04]

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