Electrical Systems Flashcards

Question

What are relays and solenoids, and why are they important?

Answer 1

Relays and solenoids are remotely or automatically controlled switching devices built around electromagnets. In each device, a small amount of current is sent through a coil to move a switch or shaft. Relays, solenoids, and associated devices are very important in modern aircraft because of the trend toward computerized systems. They allow remote electronic control of all types of aircraft systems, whether hydraulically, pneumatically, or electrically powered.

Answer 2

A relay is an electrically powered remote control device that controls circuits carrying large amounts of current. However, newer technology solid-state devices are replacing relays for many applications.

Answer 3

A solenoid is an electrically powered remote control device that is designed to move a shaft over a short distance when powered. Solenoids are used to remotely operate hydraulic and pneumatic valves and small mechanical devices, as well as other switches. Remember this by thinking two S's. Solenoids move shafts.

Answer 4

An open, short, and logic failure.

Answer 5

An open is an uncommanded interruption of electrical supply to or in some electrical component or system. When an open occurs, the affected device or system stops operating and has little or no effect on other components outside the affected one.

Answer 6

A short is when electricity takes a “shortcut” through or around a component or system. You'll have a failed component or system and a drain of electricity out of the system. Power is traveling like spilled water to the aircraft’s metal structure and then back to the generator and battery. The gizmo is unpowered, and if unchecked, a short is likely to damage or ruin virtually every component on its circuit. It may also draw more electricity than the system power source (or sources) can produce, which would disable the power source. If the power source is not isolated immediately from the short, it will quickly fail due to its inability to produce an infinite amount of electricity.

Answer 7

This occurs when some component - often computer controlled - gets the wrong idea about what it’s supposed to do.

Answer 8

Bus ties are switches or relays used to connect or disconnect buses from one another. They serve to isolate failed buses from working ones and may be manually or automatically actuated, depending on the aircraft. They are also used to reroute electrical power to buses that have lost their normal power sources.

Answer 9

By running a magnet past a coil of wire. That creates a current in the coil. When you have a magnet inside a coil of wire, you have an electromagnet. An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a highly magnetic - known as ferromagnetic - material such as iron. The magnetic core concentrates the strength of the magnetic field, known as magnetic flux, and makes a more powerful magnet.

Answer 10

The electric field is on the outside, and the coil of wire on the inside rotates. That rotating coil of wire is called an armature, and the electromagnet is called the field. If you increase the volts in the field / the strength of the electricity, the field gets stronger, and the generator will put out more current.

Answer 11

The devices that collect the voltage in generators and alternators. They are in the center of the generator. Slip Ring - Used with alternators. Has different channels that essentially makes it a switch that goes from positive to negative and back and forth. That's alternating current. On a turbine aircraft, though, It's still called a generator even though it provides alternating current. It's known as an AC generator instead of a DC generator. Commutator - Used for DC power. It still has a slip ring, but little notches in the slip ring make it a commutator. A commutator gives you little blips of positive all the time instead of going from positive to negative. To switch current from AC to DC, you would use a commutator.

Answer 12

It goes up. The voltage, however, will stay the same.

Answer 13

Turns the magnetic field on and off.

Answer 14

It regulates the intensity of the electromagnetic field.

Answer 15

Polarity is when an entity contains two distinct and opposite poles that can either attract or repel each other. It describes the flow of electrons. When there is a constant voltage between two objects or poles, one of the objects or poles may have more electrons than the other. The pole with relatively more electrons is said to have negative polarity; the other has positive polarity. If the two poles are connected by a conductive path, such as a wire, electrons flow from the negative pole to the positive pole. This flow of charge constitutes an electric current. The direction of current flow is from a positive charge to a negative charge opposite the flow of electrons. The movement of particles that carry electric charge produces a magnetic field. In the case of an electromagnet, the charge carriers are electrons. When a direct current (DC) voltage is run through an electromagnet, it flows from the positive end to the negative end of the DC circuit. Electrons flow in the opposite direction of the current. This creates a magnetic field and magnetic polarity that has north and south poles.

Answer 16

From the negative pole of the battery through the electric motor to the positive pole. Thus, an ammeter will read negative when a battery is being discharged. However, if you are charging a battery instead, the electrons flow in the negative pole of the battery and out the positive pole. Thus, an ammeter will read positive.

Answer 17

You have a primary coil and a secondary coil. Both are wrapped around the same piece of metal. The primary coil changes its field from positive to negative, and that induces a current in the secondary. You have to have a changing field in the primary to get a current in the secondary. Alternating current does this automatically.

Answer 18

AC Generators / alternators use apparent power to measure volt amps. Watts = real power - volts x amps. AC current is like trying to get a stuck car unstuck by having a team of people rock it by pushing and pulling. If everyone rocks together, you have real power. However, sometimes in an AC circuit, everyone doesn't always rock together. It's like two people pushing when the other two are pulling. You use the same effort, but the car's not moving. So while there's a lot of potential energy, you're not producing anything. That is called apparent power. Apparent power is measured in volt amps. Real power is measured in watts.

Answer 19

The electrical field in the middle usually rotates and the coil of wire around it called the armature is stationary. That's because the field has less electricity than the armature. On a big plane, the armature pulls of a tremendous amount of current. Since the field doesn't carry as much current as the coil of wire around it, there will be less arching. Arching is when electricity jumps from one connection to another. At times you hear electric switches producing a sizzling/ cracking sound. Typically, this happens when you turn them either on or off and could be cause by two things. 1. A damaged cable / wire. If the cause is a damaged wire, the wiring cannot endure the current flowing, which is why the arcing takes place. In small alternators, usually the armature rotates and the field is stationary. If you ever hear about exciting a rotor, that relates to exciting a rotating field in a large jet.

Answer 20

Rotors rotate and stators stay in place. They are used in electrical systems in alternators and generators as well as in turbine engines. So the rotor is the field. In small alternators, the armature rotates and the field is stationary. With big alternators, the field rotates and the armature is stationary. The armature is the winding - or set of windings - of an electric machine which carries alternating current. The armature can be on either the rotor / rotating part or the stator / stationary part.

Answer 21

Transformers allow you to easily change the voltage of AC power either up or down - so to more or fewer volts. Transformers can only change AC voltages - not DC.

Answer 22

Hertz is the cycles per second of the sine wave - when AC power goes from positive to negative and back again. In the United States, all electricity is generated at 60 hertz. Large aircraft like Boeings and Airbuses usually use a frequency of 400 hertz.

Answer 23

The peak value of the current in the sine wave.

Answer 24

When large amounts of power need to be transmitted and where voltage changes by using transformers are required. The largest aircraft use AC with AC generators. High voltage power lines also transmit AC power.

Answer 25

Atoms. The central blob is the nucleus, and tiny electrons circle around it. The electrons have a negative charge. The nucleus is made up of two things that are about the same size. 1. Protons - they carry a positive charge of electricity. 2. Neutrons - don't have an electrical charge Both are quite a bit larger than electrons. Different items have different numbers of electrons going around the nucleus. However, each item has the same number of electrons orbiting around the protons. For example, aluminum has 13 electrons going around the 13 protons in the nucleus. This means the negative and positive charges are equal, and the whole atom is electrically neutral.

Answer 26

In some substances, the electrons in the outer orbit are not held tightly, and they can be dislodged fairly easily. When this happens, the atom is left with a surplus of protons in its nucleus, so the atom will have a positive charge. A charged atom is called an ion.

Answer 27

When the electrons are discharged from an atom because they are not held tightly, they are called free electrons. All electrical effects are caused by the movement of these free electrons.

Answer 28

A substance that allows the flow of current and has electrons that are dislodged easily is called a conductor. Silver, copper, and aluminum are good conductors.

Answer 29

It's energy caused by the movement of negatively charged electrons.

Answer 30

1. EMF / electromotive pressure measured in volts. 2. Current measured in amps. 3. Resistance measured in ohms. To save writing ohms every time, the Greek letter omega is used instead.

Answer 31

Ohm’s Law states that... Amps x ohms = volts To put it another way... a. Amps / current / electron flow b. Multiplied by the resistance in the wire / ohms c. = volts / pressure Example 1 - A 28-volt landing light circuit has a lamp with 4 ohms of resistance. The total current of the circuit is 7 amps. Example 2 - A 28-volt deice boot circuit has a current of 6.5 amps. The resistance of the deice boot is 4.3. Example 3 - A taxi light has a resistance of 4.9 Ω and a total current of 2.85 amps. The system voltage is 14 volts.

Answer 32

Watts are the amount of power an electrical device uses. Volts x amps = watts.

Answer 33

1. Volts are abbreviated as V and is measured in volts. 2. Current is abbreviated as I (capital I) and measured in amps. 3. Resistance is abbreviated as R and is measured in ohms Here's how they work together - Amps x ohms = volts

Answer 34

A starter motor - it's not a generator. It draws a lot more power / amps during start than when it's just running after that. Note that starter circuits do not have either a fuse or circuit breaker.

Answer 35

Sometimes smaller jet aircraft have starter generators instead of separate starters and generators and all the extra weight. Starters and generators have a lot of common parts anyway. Part of the time it acts like a starter. The rest of the time it acts like a generator. As the speed increases, the starter and ignition circuits are automatically disengaged and the generator circuits are enabled.

Answer 36

After you press the start button and watch the rpm's come up to about 10 percent, you bring the throttles out of idle cutoff. That turns on the ignition and introduces fuel. The starter motor and ignition will automatically turn themselves off themselves during the sequence. When the engine starts to run on its own, the starter-motor will pull less current. It won't have enough current to keep the starter solenoid closed. The solenoid is spring loaded, so it will pop open. That will shut off your starter motor.

Answer 37

Magnetos create their own sparks for the spark plugs and allow the engine to keep running if the electrical system of the aircraft fails. A magneto is a combination of a generator and a transformer / coil that increases the voltage. A generator is a magnet run near a coil of heavy copper wire to create a current in the wire. When the points open, the field collapses and abruptly shuts off the current in the primary, which induces the current in the secondary. Any time you have a change in current in the primary coil, that creates a current in the secondary coil. The amount of voltage generated in the secondary coil is determined by the number of windings and by the rate of the magnetic field of the primary. So the more windings and the faster the rate of collapse, the higher the voltage in the secondary coil. The condenser is two metal plates with an insulator in between them. It keeps the spark from jumping / arching the gap whenever the points open. If that happened, the field would not collapse. So the condenser prevents that and quickens the collapse of the field by stopping the arching so the current no longer flows. If you have duel magnetos, they share the rotating magnet.

Answer 38

Poles are the number of legs a circuit uses. For example, a regular 120 volt outlet is single phase, so it uses a 1-pole breaker. That means that it connects to just a single leg of the power supply. In the US, typically any 240 volt appliance is supplied by a 2-pole breaker, which gives you 240 volts, single phase (electric ovens, electric dryers, etc.). Four poles means the generator has four magnetic poles. Magnetic poles always come is sets of two, so two will be north and two will be south.

Answer 39

Three. The magnetic circuit is when the poles line up with the shoes. The primary and secondary circuits both go through the coil.

Answer 40

Volts of Alternating Current. It's just AC power.

Answer 41

The windings around three-phase generators are arranged in such a manner that each phase is 120 degrees out of phase with the other. The outputs of an AC generator are connected in what is called a star method. The three phases are joined to form a neutral point that is grounded.

Answer 42

The main difference between a DC generator and an AC generator in an aircraft is that in a DC generator, the armature of the generator turns. In an AC generator, the field or the magnet turns around a stationary armature.

Answer 43

It automatically retards the spark and spins the magneto fast. In order to generate a lot of electrical current, the magneto must be turning fast. However, during start, it won't be. Also, when an engine is starting, you need to retard the spark. The impulse coupler does both things. There are flyweights in the impulse coupling. When the magneto is turning slowly, they stay retracted and do not sling out. The flyweights also delay turning the magneto even though the engine is turning. The magneto has a spring tension that builds up. Once the tension gets to a certain amount, the flyweights are released, and the magneto all of a sudden spins rapidly. That makes the magneto spin faster and retards the spark. The impulse coupler only affects the magneto during the start.

Answer 44

Insulating. A dialectic material is an insulating material. The distributer - that distributes the spark - is made of a durable dialectic material. The distributer has to withstand high temperatures and stresses. Since the distributer has to distribute a spark to all the cylinders, it turns at the same speed as the crankshaft.

Answer 45

To protect circuits from damage if there is a fault and too much current flows through it. When a wire carries current, it gets hot, and the more current it carries, the hotter it gets. If it's a thin wire with a large current, it will get so hot that it glows like an electric radiator. Larger current still will cause a wire to melt - or fuse - and it will break. Fuses and circuit breakers are marked with a rating of how much current they can carry without blowing. Although fuses can take a higher current for a short time, they will blow if they have that current continuously.

Answer 46

A rectangle with a line through it.

Answer 47

Cartridge fuses and Cartridge fuses use tin copper wire that is enclosed in a casing with the ends sealed with brass caps. They are used with currents of less than 100 amps. Their advantages are that they are cheap to make and easy to change. Their disadvantages are that the climate may affect their ratings and the voltage could be enough to cause arching across the gap after the fuse has blown. The high rupturing / HRC fuse doesn't have those disadvantages and can be used up to several hundred amps. These are made of several strands of silver passing through ducts in an earthenware / hardened clay casing. Quarts power is packed around the strands. When too much current flows, the wire and quarts powder around it melt. It's a good insulator, so no arching across the gap can occur.

Answer 48

If it's less, the fuse will blow. If it's more, the fuse won't blow when it should because its rating hasn't been exceeded, and that is dangerous. The wiring could over heat and easily cause a fire. Many electrical fires are caused by using a fuse rated too high for the circuit wiring.

Answer 49

They are a good indicator of overall engine health.

Answer 50

Spark plug fouling is the inability of a spark plug to produce a spark inside the combustion chamber. It will ground without jumping through the electrode. The plugs are essentially shorted out. This occurs because of damage or dirt on the electrode in the spark plug. You might see carbon, fuel or oil on the plug, creating trouble with performance, fuel economy and starting the engine. A little dust or sand can also cause fowling.

Answer 51

The metal tips on spark plugs. The spark plug's job is to ignite fuel within the engine cylinder, by sending a high voltage spark across the gap between its core and ground electrodes. The gap distance between these sides is critical. Too narrow, and the spark will discharge before it has built up to the correct voltage. Too far apart, and the voltage will have to exceed the desired amount to overcome resistance and jump the gap. In turn, the buildup of this excess voltage can damage the aircraft's ignition system.

Answer 52

The plane has been flown with the mixture too rich.

Answer 53

A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.

Answer 54

When the electrodes have been worn to about 1/2 of their original dimensions.

Answer 55

1. More complete and quick burning of the fuel 2. Backup magneto system 3. Increases the power output

Answer 56

1. The more turns, the stronger the field. 2. The greater the current flowing, the stronger the field produced. 3. Adding an iron core to the coil concentrates the lines of force.

Answer 57

Electromagnets An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. They usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic / highly magnetic material such as iron; the magnetic core concentrates the magnetic flux / strength of a magnetic field over a given area and makes a more powerful magnet. The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field. Electromagnets are widely used as components of other electrical devices, such as motors, generators, electromechanical solenoids, relays, loudspeakers, MRI machines, etc.

Answer 58

Electromotive force / EMF. It is measured in volts. Whenever you find two bodies in a different state of charge and connect them, there will be an EMF driving a current between them. It isn't necessary for one to be negative and the other positive. If one is negative and the other is still more negative, meaning it has accumulated more free electrons, and you connect them, there will be a driving force from the more negative body to the less negative body.

Answer 59

A substance with easily detached electrons, which allow current to pass easily. They have low resistance. Good conductors are silver, aluminum, and copper along with carbon and water.

Answer 60

A poor conductor that has high resistance - things like glass, paper, plastic, rubber, and wax.

Answer 61

1. Length - The longer the conductor, the higher the resistance. So a greater EMF would be required to drive the current through it. 2. The cross sectional area - The larger cross section, the lower the resistance. 3. Temperature - The hotter the material of the conductor, the higher the resistance.

Answer 62

It prevents the current from leaking away. The longer the wire, the easier it will be for the current to leak away from the insulation. The thicker the insulation, the harder it will be for the current to leak away.

Answer 63

If a dart is moving away from you, you'll see an X. If a dart is moving towards you, you'll see a point. So that's how current is written. Current that's moving away from you is shown with an X, and current that's moving towards you is written with a dot.

Answer 64

An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. A coil of wire will be wrapped around the magnet. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a highly magnetic - known as ferromagnetic - material such as iron. The magnetic core concentrates the strength of the magnetic field, known as magnetic flux, and makes a more powerful magnet.

Answer 65

High tension and low tension. High Tension... - Deliver more than 8,000 volts per spark - Used on most large commercial aircraft. - The service life can be as long as 3,500 engine hours - Larger and heavier then low-tension ignition systems. Thus, some engine manufacturers prefer lighter and smaller low-tension ignition systems. Low-Tension - Deliver less than 8,000 volts to the engine's combustor. - Igniter plug life is normally less than 500 hours.

Answer 66

The exciter uses power from an electrical bus or engine-mounted generator to convert relatively low voltage to more useable, high-voltage energy pulses that fire an igniter plug and in turn ignite the fuel/air mixture. In order to deliver a high-energy discharge given the relatively low input power, a capacitor is charged up, and then all of the energy stored in the capacitor is released at once.

Answer 67

The armature is the winding - or set of windings - of an electric machine which carries alternating current. The armature can be on either the rotor / rotating part or the stator / stationary part.

Answer 68

A magneto is an electrical generator that uses permanent magnets to produce alternating current. It is categorized as a form of alternator, although it is usually considered distinct from most other alternators, which use electromagnets (also known as field coils) instead of permanent magnets. The magneto is a self-contained generator of high voltage that provides ignition to an engine through spark plugs. A magnet—hence magneto—spins close to a coil of wire. As the magnet spins (or the magnet rotor is turned), it generates a strong magnetic force that is “held back” by a primary coil. The moment the contact points open, a rapid magnetic flow generates a high voltage in the secondary coil, which ignites the spark plug, thus firing the engine. The two magnetos on most GA aircraft—the left and the right—each fire one of two spark plugs on each cylinder. There are two magnetos so that if one fails the engine will continue to run.

Answer 69

It's a safety measure and can also be used as a return path. Say the insulation around a wire in a case broke down. If the live wire touched the case, and you also touched it, you could get a severe or even fatal shock. But if you had grounded the case, even if the insulation had broken down, the case would stay at ground potential of 0 volts, and you wouldn't be shocked. Normally, the ground wire doesn't carry any current. It's just there to create an easy path for the leaky current if the installation breaks down. A large current that does leak through it would likely blow a fuse. That would cut off the supply and open the circuit.

Answer 70

Weak batteries can lead to a hot start because they fail to “spin up” engine compressors enough, so battery condition must be checked before each attempt. It takes a lot of electrical power to start a turbine engine. For only one-half second or so, an average electrical turbine engine start requires almost 2,000 amps! Therefore, a battery start requires a very healthy battery.

Electrical Systems Flashcards

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