Avionics (PRELIMS)

ELECTRICITY

Is the flow of electrons

Current

~Movement or flow of an electrical charge

~Is directly proportional to voltage and inversely proportional to resistance.

Voltage

Electromotive force behind current flow

Resistance

Tendency of a conductor to oppose electrical current

Frequency

Number of cycles per second

Alternating Current (AC)

Reserves Direction at regular intervals

Direct Current (DC)

Flows continuously in one direction

Electromotive Force (EMF)

Force that cause flow of Electrons

Potential Difference

Also known as electromotive force

Statistic Electricity

~Produced by friction which physically “strips” electron from one material

~Electrical Potential builds up on surface and discharges

Piezoelectricity

~Some crystalline material such as quartz develop electrical potentials between Facets as they are physically deformed

~Crystals will vibrate at a certain frequency when excited by electrical energy

Thermocouple

~ Dissimilar metals (chromel/ alumel or iron/constantan) Joined at 2 places (Junction)

~ When temperature difference exists between junctions, current flow.

Solar Cell

~ Photo Emissive materials absorb light energy (photons) and discharge electrons

~ typical materials used in Selenium

~ 10% Efficiency Considered high

Battery

~ Converts chemical energy into electrical energy

~ Voltage produced depends on type of anode/cathode and electrolyte

~Are a collection of one or more cells whose chemical reactions create a flow of electrons in a circuit.

Generator

~Conductor is moved through lies of magnetic flux , flow of electrons is induced

~Process is called Electromagnetic Induction.

~Voltage produced depends on how many times lines of flux are “cut”

~ Converts mechanical energy into electrical energy by electromagnetic induction.

~Output is controlled by voltage regulator.

~Alternators

Magnetism

~Cause by the motion of electric charges

~Most common means of generating and using electricity involves _____.

~Current flowing in conductor produces magnetic fields

Conductivity 

~Is the measure of the ease at which an electric charger or heat can pass through a material 

~Depends on ability of material to exchange electrons

~Number of valence electron, the more _____ the material.

Circuit

conductors connected to provide electrical path

Open circuit

~Is one where the continuity has been broken by an interruption in the path for current to flow.

Closed circuit

~Is one that is complete, with good continuity throughout.

Capacitor

~Ability to store an electric charge is measured in Farads

~Store electrical energy in electrostatic fields that exist between 2 conductors separated by an insulator or dielectric.

Inductance

~Is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor.

Step Up

~Increases AC voltage

Step Down

~Reduces AC voltage

Resistance

~Is opposition to current

Resistors

~Are used to control amount of current flow, it converts current to heat.

Power (P)

~Rate of doing work per unit of time, measured in watts

Series Circuit

~Circuit that has only one path for current flow

~Same current flows through each section

~Total resistance is equal to sum of individual resistances.

~Total voltage is equal to sum of individual voltage drops.

~Voltage drop across a resistance is proportional to ohmic value of resistors.

~Total power is equal to sum of power consumptions of individual resistances.

Parallel Circuit

~Circuit that has more than one current path connected to a common voltage source

~Same voltage exists across each branch of circuit and is equal to source voltage

~Total current of circuit equals the sum of currents in each branch.

~Total resistance of circuit is equal to reciprocal of the sum of the reciprocals of individual resistances.

~Total power consumed is equal to sum of power consumption of individual resistances.

Combination Circuit

~Circuit that has both types of current pathways. Also called compound circuit.

Series connected cells

~Increase voltage with no increase in current.

~Higher Voltage 

Parallel connected cells

~Increase current with no increase in voltage.

~Higher Current

Series – Parallel Cells

~Increases both voltage and current

~Higher Voltage and higher current

Primary cells

~Are the ones that cannot be charged

Secondary cells

~Are the ones that are rechargeable.

NICADS

~Have high discharge rate and voltage remains constant to discharge.

Lead-Acid

~Type more economical, no danger of thermal runaway.

Switch

Is an electrical component which can make or break electrical circuit automatically or manually.

Fuse

~Protects circuit from overloads.

~Melts when amperage exceeded.

Circuit breakers

Same function as fuse but resettable.

Alternating Current (AC)

~AC voltage varies and changes direction

~AC voltage can be stepped up or down to meet load

~AC voltage is easier to transmit

Direct Current (DC)

~Constant and one directional.

~Must be same as load.

Electric motors

~Converts electricity into mechanical energy, providing a power source for machinery.

Ammeters

~Measures current (amps) and is either connected in series or induction type.

Voltmeters

~Measures voltage

Multimeter

~Used to measure current, voltage or resistance.

Frequency meters

~An instrument for measuring the frequency of an alternating current; the scale is usually graduated in hertz, kilohertz, and megahertz.

Bonding

~Is the act of mechanically connecting two or more conductive materials together to establish a conductive path between them, it serves as a protection from electric shock.

Open circuit

~Has complete break in conducting pathway.

Short circuit

~Is accidental path of low resistance which passes abnormally high current

Electrical power

~Is used for the control, operation and indication of the various airplane systems on the ground and in flight.

~Is supplied from isolated generators located on each engine and APU. The three AC generators have the same ratings.

Primary power source

Include main generators, inverters, and transformers.

Secondary power sources

Include electronic power supplies, and emergency/backup power sources such as emergency generators, batteries, and external power supplies.

Electrical power is controlled and monitored prior to distribution as

115 volts AC, and 28 volts DC

Alternating current power

is supplied by two engine driven generators for normal inflight operation.

Generator

Driven by the auxiliary power unit, it can supply all power for ground or flight operation. Power can be supplied on the ground through the external power (AC) receptacle. The DC power is supplied from the battery or conversion from the AC power.

AC generators

~ Supply the aircraft with AC electrical power at constant frequency for the operation of various aircraft systems, instruments, indicators, controls and monitors.

~Produce 115/208V, 3- phase AC power at a constant 400 Hz frequency ± 20 Hz.

Auxiliary Power Unit

Allows an aircraft to operate autonomously without reliance on ground support equipment such as a ground power unit, an external air-conditioning unit or a high pressure air start cart.

Main battery

is installed in the lower forward section to furnish emergency power to certain critical loads when the basic power sources are de-energized.

Generator Control Unit (GCU)

~is provided to regulate and control each of the three generators.

~Limits power input to the generator shaft to 160 horsepower

~Provide protection for abnormal system conditions such as: overvoltage, undervoltage, differential current, overcurrent, over frequency and under frequency

ram air turbine (RAT)

~in the belly fairing will extend automatically in case of loss of AC Bus 1 and 2. Then, the emergency bus supplies the DC essential bus trough AC essential directly TR.

~is a small turbine that is installed in an aircraft and used as an alternate or emergency hydraulic or electrical power source.

Battery

~supplies power to the aircraft only when the generating systems are unable to supply power.

Lead-acid

~Red

~Storage Battery is used as a DC Standby Power for certain essential circuits and for short-period DC loads when no basic power source is available. The battery is located in the E/E compartment.

Nickel-cadmium

Blue

~Storage Battery is used as a DC Standby Power for certain essential circuits and for short-period DC loads when no basic power source is available. The battery is located in the E/E compartment.

Power Distribution

Three phase AC power is distributed to user systems through three main load buses which are monitored for differential current, short circuits and overcurrent.

Battery Charger

~ is provided to charge the battery whenever the aircraft Battery Switch is placed to ON.

~determines the amount and rate of charging necessary from the amount of loads on the battery bus

DC Indications

A DC Ammeter and Voltmeter are provided on the overhead panel.

Radio theory

emphasizes the transmission and detection of communication signals consisting of electromagnetic waves that travel through the air in a straight line or by reflection from the ionosphere or from a communications satellite.

Electromagnetic waves

Are formed when an electric field comes in contact with a magnetic field. They are hence known as ‘electromagnetic’ waves.

Radio wave

~Is from the portion of the electromagnetic spectrum at lower frequencies than microwaves.

~Is transmitted via omni directional, directional or pulse & echo method. From the antenna it moves out along three paths, depending primarily upon its frequency. These paths are surface waves, sky waves, and space waves.

Low Frequency

~ Long Wavelength

~ Low Energy

~ Poor Quality

High Frequency

~ Short Wavelength

~ High Energy

~ Good Quality

Diffraction

Occurs in low frequency radio waves, it is the bending of a radio wave.

Reflection

Occurs in high frequency radio waves, it is the bouncing back of a radio wave.

Refraction

Occurs in high and low frequency radio waves, it is the changing in direction of a radio wave caused by a disturbance. (E.g. Rain)

Attenuation

It is a reduction of signal strength during transmission, it is the loss of energy of a radio wave, friction may cause attenuation.

Omni directional

Radio wave is propagated in all directions.

Directional

Radio wave is propagated in one direction.

Pulse & echo

Bouncing back of radio waves.

Ground waves / Surface waves

~ Follows the curvature of the Earth, this wave is restricted by gravity.

~ VLF, LF, and MF

Sky wave

~ This type of radio wave is stronger than the ground waves and it can overcome gravity, but it cannot penetrate the ionosphere.

~ HF

Space wave

~ This type of radio wave can overcome gravity and can penetrate the ionosphere, its limitation is line of sight.

~ VHF, UHF, SHF, EHF

Radiotelephony

~Phraseology that consists of a set of standardized words and phrases approved for the radiotelephony communications by ICAO in all routine aircraft situations.

Transceivers

Is a self contained transmitter and receive

VHF Communication

~30MHz to 300MHz portion

~This range of frequencies will provide short-range LOS (line of site) communications.

~typically 2 to 20 miles

HF Communication

~3-30 MHz

~used for long range communications

SELCAL

~ Is a signaling method which can alert an individual aircraft that a ground station wishes to communicate with it.

~ alerts the crewmembers by means of a light and a chime whenever a message is to be received on one of the communication systems.

The chime

~ is enclosed within the aural warning unit on the forward right side of the control stand. The SELCAL control panel is installed on the pilots' aft overhead panel.

The service interphone switch

on pilots' overhead panel P5 is used to disconnect these jacks from the system when they are not in use.