AVS1230_Lab4_electrical systems 2023

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Western Michigan University *

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Electrical Engineering

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Dec 6, 2023

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AVS 1230 Lab 4: Electrical Systems 2023 Name___________________________________________Date________________ Purpose: Research the operation of electrical components including batteries, switches, relays, circuit breakers and motors. Analyze aircraft electrical systems. Reference: Aircraft Publications- Cirrus SR20 and Piper PA-28R Arrow Pilot Operating Handbooks AMT textbook volume 1, chapter 9- and Internet research Activities: Select the best possible answer each question. Use your textbook, lab equipment and Pilot Operating Handbooks or Manuals in the Lab. Watch https://www.youtube.com/watch?v=gC0gxQV2c4M 1. Ohms Law provides the basic mathematical relationships of electricity. The primary formula is I =E/R . (E is V on the chart). R on the chart = ______________________________. a. current flow measured in amps b. resistance measured in ohms c. electromotive force measured in volts 2. Ohms Law provides the basic mathematical relationships of electricity. The primary formula is I =E/R . (E is V on the chart). E on the chart = _______________________________. a. current flow measured in amps b. resistance measured in ohms c. electromotive force measured in volts 1

3. Ohms Law provides the basic mathematical relationships of electricity. The primary formula is I =E/R . (E is V on the chart). I on the chart = ______________________________. a. current flow measured in amps b. resistance measured in ohms c. electromotive force measured in volts Tips: to find E (Volts) place thumb over V and multiple I x R To find I (amperes) place thumb over I and divide V/R To find R (ohms) place thumb over R and divide E/I 4 . Problem A. A 28Volt de-ice boot circuit has a current of 10 amps. Calculate the resistance of the deice boot. YOU must show your work! R =___________. 5. Problem B. Use the Ohms law primary formula above to calculate the total current in amps (I) of the landing light circuit. The landing light circuit is 28volts and has a lamp with 6 ohms of resistance. I=______(volts/ohms) YOU must show your work! Part 2: Cirrus Electrical System- Watch https://www.youtube.com/watch?v=D3mZlU4A4Uo And Research the Cirrus SR20 Pilot’s Operating Handbook to answer the following quesitons. 6. What controls the output of the alternators? 7. Power distribution for the SR20 comes from the _____________ distribution bus and the ____________________ distribution bus. 2

8. ALT 1 will feed the essential distribution bus only if _____________ fails. 9. What is the voltage and amperage rating of the electrical system? 10. Both alternators require voltage from the ________________ for operation. Part 3: Research your textbook to Define electrical component terms-describe the function of the following: 11. A. Busbar B. Voltage Regulator C. Magneto D. Alternator Part 4: Textbook research questions 12. How many circuits in a magneto? What are they? 13. An aircraft generator utilizes a __________________ magnet and an aircraft alternator utilizes an ________________ magnet. 14. What is the difference between a circuit breaker and a fuse? Part 5: Ignition sources -Magneto Notes (See below questions) 15.-20 Notes- Read magneto Notes then complete the questions below Magnetos use a rotating magnet with a wire passing through it the create electricity (inducted) The magneto is a self-contained voltage amplifier designed for constant rpm. It provides its own electrical energy. Magnets on the rotor shaft set up a magnetic field in the coil. through timing the right spark is distributed at the right time. Three internal circuits are involved. The primary is of heavy wire and few turns. This primary coil has 1-200 turns. Combined with a condenser and a powerful magnet this circuit produces a high current (amperage). At a precise moment in the cycle the 3

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primary circuit is broken and the electro-magnetic flux field collapses and cuts through the thousands of thin wire coils in the secondary system. The secondary coil induces voltage into the 15,000 turn secondary coil. This sends a 20,000-volt surge toward the spark plug. This produces a critically timed high voltage but low current surge, which arcs across the points of the spark plug. It uses a mechanical spark advance, is independent of the electrical system, and is driven by the engine. The faster you pass a magnet past a wire the higher the current. The magneto secondary coil is used to create a current that cuts across the primary coil of numerous fine wires. The secondary coil multiplies the voltage, and it is delivered to the spark plugs. The timing of the voltage to the plugs is done by a rotating magnet, which makes a brief contact that allows the high-voltage to leave the coil and reach the spark plug. Starting the engine with the starter causes the magneto to initially retard the spark and activate a spring loading device called an impulse coupling that supercharges the initial starting spark to the plugs. The magneto generates the electricity needed by the spark plugs and engine operation. Bendix and Slick are the major manufacturers. A mechanic can repair Bendix. The latest Slicks are sealed units not for local repair. Points and gap inspections required at 100 and 500, respectively. Bendix recommends dissembling and inspection every 500 hours. The magneto uses a permanent magnet coil, a condenser, and timed-gapped points to generate a high voltage (25-30,000 volts)/low amperage spark. This spark is sent through a rotor to the spark plugs. The arc of the spark across the tip of the spark plug ignites the fuel/air mixture. An impulse coupling is between the gear driven by the engine and the magneto shaft. It has 2 swinging weights and a large clock spring in it. At very low speed (when the engine is being cranked) the weights dangle and get caught on a pin, so stopping the rotation of the magneto shaft. Of course, the engine gear is still turning so what it does is to wind up that big spring. After a few degrees of rotation, the weight that is caught by the pin is mechanically released by another part of the coupling. The spring unwinds with great enthusiasm, momentarily spinning the magneto shaft very fast, so producing a nice fat spark. That is the first benefit. The second benefit is that because the magneto shaft has been held stationary for a moment, when the spark does occur it is retarded from the usual running position, thus helping the engine to start smoothly - i.e., the spark timing is retarded for starting by the impulse coupling. The second benefit is the reason for starting on only one magneto, if only one is fitted with the coupling. If you start on both magnetos in that case, the one without the coupling (and so not retarded) will spark first, frequently causing a backfire and in any case giving the starter motor a hard time. If impulse couplings are fitted, you can hear the "clack" as they release when pulling the prop through. P-Lead The P-lead is part of the primary coil of the magneto. If the magneto will not stop the engine, it means that the P-lead is not grounding out the magneto. If the P-lead is unable to ground through 4

the starter switch 'off' position the engine will continue to run if fuel is provided. Occasionally make a magneto check for a defective contact or broken P-lead. When the magneto switch is to OFF the system is supposed to be grounded so any turning of the propeller will not activate the magneto voltage and start the engine. Distributor The harness of the engine consists of multi-layered insulated wiring from the distributor to the spark plugs. The positioning of the harness protects it from engine heat and weather. The construction of the harness reduces electrical radio interference and other magnetic effects. Spark Plugs The spark plug is made up of a ceramic insulator, which protects the electrode and acts as a heat sink to cool the plug. the outer casing of the plug is made of machined steel threaded to fit into the cylinders. The spark plug gets the burst of high voltage produced by the magneto via the distributor and harness at a timed moment to produce an arc of flame that will ignite the fuel air mixture in the cylinder. By avoiding rich mixtures and sudden full movements of the throttle you give the spark plug temperature to increase with the increase in power. Lead fouling may not be removed by leaning when the plug temperature is above 1300 degrees. Removal may be the only solution. Carbon fouling is most likely to occur at low power settings with the plug temperatures below 800-degrees as when first starting or taxiing. Added power during runup or shutdown can be used to raise the plug temperature to burn off the carbon. The best preventative is to lean the mixture at every opportunity to keep the plug in the proper heat range that will keep carbon fouling away. 21. What is the function of the spark plug? 22. What is a P lead? 23. What is the function of the impulse Coupling? 24. What can a pilot do about Lead fouling on a spark plug? 25. True or False- If the P-Lead is broken and not grounded, and the magneto switch is to OFF any turning of the propeller will activate the magneto voltage and start the engine. 26-50. Watch https://www.youtube.com/watch?v=gC0gxQV2c4M Draw (or paste your drawing) the SR20 Electrical system and label all major components and state their function. 5