Avionics Flashcards
What is an Ion?
- A positive or negative charged atom
- Unequal number of electrons and protons
Why are atoms electrically neutral?
Equal number of electrons and protons
Explain the term electric current. When does it occur? Name the unit of measurement.
- Charge/time = current
- Ampere
Explain the term electric voltage. Name the unit of measurement
- Potential difference
- Volt
What is electric power? Name the unit of measurement
- Voltage*current = power
- Watt
What is electric work? Name the unit of measurement
- Power*time = work
- Watt hour
What is an insulator or electric nonconductor? Give two examples
- No free electrons = no current possible
- Rubber, air
What is the special characteristic of an electric semiconductor? Give an example of device which use semiconductors.
- The resistance can alter
- Resistance can decrease with rising temperature
- Diodes
- Transistors
Example of material: silicon
What is an electric conductor? Give two examples
- Material with free electrons in outer shell
- Copper, aluminium
Describe the single-pole conductor configuration. What are the advantages of this configuration for aircraft design?
- Positive power supply via cable
- Negative via fuselage
- Less weight and negative power supply via cable
Every conductor has an ohmic resistance. It depends on:
Conductor length
Material
Temperature
Cross section
What is a galvanic element?
Two different metals (base or noble) with different electric potential in an electrolyte connected by a conductor.
Name two types of galvanic elements
Noble, base
E.g. Zinc and copper
Two identical batteries are connected in parallel. What happens?
The total voltage equals the voltage of one battery
What are the tasks of a rechargeable battery in an aircraft?
- Supply electrical system with power, without generators running (before startup, failure of generators)
- Supply starter with power during startup
What may happen to a battery, if the charging current is too high?
- Battery warms up = kaBOOOM
- Electrolyte escapes
Define the term “capacity of batteries” and state the unit of measurement used?
- How long a battery can supply power with a given voltage and current.
- Ampere hour Ah
How long can a battery supply a system with a load of 30A, if the capacity is 40Ah?
40/30 * 60 = 80min = 1h 20min
What is the nominal voltage of a battery commonly used in a helicopter?
24V (the generator = 28V)
Two identical batteries are connected in series. What happens?
The total voltage is twice of the battery voltage
Describe the working principle of a simple DC generator and name its main components.
A conductor loop is rotating in a magnetic field perpendicular to the magnetic flux lines- A voltage is induced and picked up by a commutator.
Commutator, loops, electromagnet (+exciting current)/permanent magnet
What is the purpose of a DC generator in an aircraft electrical system?
Supply electrical system with power and charges the battery during flight
Name three different types of DC generator excitation and their subgroups, if there are some.
- Self excited (shunt; series; compound)
- Direct excited
- Separately excited
Name three different types for the design of voltage regulators
- Vibrating
- Carbon pile
- Trasistorized
State two functions of a circuit breaker
- Decouple electrical subsystem in case of failure (overload, short circuit)
- Manual decouple of electrical subsystem.
Circuit breakers…
Are switches, which are combined with a bimetal and/or solenoid (I think this is the correct answer. But not sure)
Why are two main generator connected in a parallel circuit in an aircraft?
- If one fail, the other can take over.
- One generator for start up and power supply, one for power supply only
What are the tasks of an external power unit?
- Supply electrical system with power on ground for maintenance
- Supply electrical power for startup
What is the advantage of splitting the load into different busses (DC power distribution)?
- In case of failure of the generators, necessary electrical subsystems can be supplied with power and non necessary parts can be shut down
- Failure in one bus doesn’t harm the whole electrical distribution
Which devices are used for monitoring the electrical system of the aircraft? State which parameters are used to monitor an electrical system.
- Voltmeter: 24V/28V indicates if the generators are active
- Amperemeter: Indicates the total load of the electrical system
What is the purpose of an inverter in an electrical system powered by DC generators?
Invert DC voltage to AC voltage
Name two types of inverters
- Rotating inverter
- Static inverter
What are the nominal voltage and frequencies of an AC system used in helicopters?
- 115V 400Hz
- 26V 400Hz
Which different color marking are painted on instruments? What is their meaning?(4)
- Green: Normal operating range, proper operation is assured
- Yellow: Caution range, unsafe operating conditions, time limited, monitored constantly
- Red: Warning range, danger, outside permissible limits, requires immediate corrective action, attempt not to poop in pants
- White: slippage marking, joint between instrument case and cover glass
What is static pressure, dynamic pressure and total pressure?
- Static pressure: pressure from all sides
- Dynamic pressure: generated by speed
- Total pressure: Both pressures added
Name three pressure units
- hPa
- Bar
- mmHg
Which pressure is measured by the Pitot-tube?
Total pressure
Why is a heater for the Pitot-tube necessary?
Icing in clouds or moist cold air. To burn away insects and other solids.
Describe the design and operating principle of the barometric altimeter (important components, sensed pressure)
Android vafer with fixed pressure.
Housing is connected to the static ports
The Vafer is connected to a pointer via mechanical linkage.
You set the chosen QNH in the kollsman window.
Some barometric altimeters are equipped with an altimeter encoder. What is the task of the altimeter encoder?
Supply digital system with digital altitude information = transponder
What is the task of an electrical vibrator located in an altimeter with encoder?
To reduce friction in bearings = easier movement of mechanical links = higher accuracy
What happens if the power supply of the altimeter fails?
- No encoding = transponder can’t send altitude information
- No vibration = less accuracy
What is the ration between the units “feet” and meter”?
1 : 0,3048
What is the difference between CALIBRATED ALTITUDE and INDICATED ALTITUDE?
Calibrated altitude is the indicated altitude corrected by the instrument and installation errors.
Name both values needed to calculate the TRUE ALTITUDE from the CALIBRATED ALTITUDE
- Outside air temperature
- Pressure altitude
How can you measure the OAT and the PA in the aircraft?
- OAT : ambient air thermometer
- Pressure altitude : set kolsmann windows 1013,25 = indicated altitude
Explain why the TRUE ALTITUDE differs from the CALIBRATED ALTITUDE
Instruments are calibrated for ISA standard atmosphere. 15 degrees C; 1013,25 hPa. Real weather differs. So in short; because of shitty german weather.
What is QNH?
Pressure on airfield reduced by ISA standard atmosphere to MSL
What is QFE?
Pressure on airfield (field elevation)
What is QNE?
Equals pressure altitude (PA) = 1013,25hPa
What happens to the altitude indications if the static ports are blocked?
Freezes
Describe the design and operating principle of the differential capsule vertical speed indicator. Which pressure is required for the indication?
Diaphragm connected to the static port.
Casing with a calibrated leak.
Mechanical linkage and a pointer
Lag between pressure change in diaphragm and casing
Can be minimized with an accelerometer
Name the unit for vertical speed in aviation.
Feet/minute
Describe the design and operating principle of the airspeed indicator (important components, used pressure)?
Diaphragm connected to the pitot tube measuring total pressure.
Casing connected to the static port measuring static pressure
Name the unit for horizontal speed in aviation
Knots
State the relationship between the horizontal speed in aviation and km/h
1 knot = 1,852 km/h
What is CALIBRATED AIRSPEED?
Indicated airspeed corrected by instrument and installation errors
What is TRUE AIRSPEED
Calibrated airspeed corrected by OAT and PA. The actual speed you are moving through the air.
What is the meaning of VNE
Velocity never exceed
Name three reasons for incorrect indications of the airspeed indicator
- Rotor downwash if speed less than 25 KIAS
- Clocking of static ports or pitot tubes
Complete the table. What is shown by the indicators?
Look at the giant table in your papers
Name the inputs needed by the AIR DATA COMPUTER and the outputs which are calculated by the ADC?
Inputs: Static pressure Total pressure QNH (OAT)
Outputs: Calibrated altitude IAS, CAS, (TAS) (OAT) Values for the autopilot
Describe the design and operating principle of the radar altimeter
- The transmitter sends a radar signal via an antenna in a cone to the ground. The signal is reflected by the ground and received via an antenna and guided to a receiver. The receiver measures the time and converts the fastest signal to distance via the value for speed of light. This is the indicated distance.
When is the red warning flag in the radar altimeter displayed?
- Radar receiver receives no signal
- Turned off
- Failure (no power supply, …)
What is the gyroscopic property of a semi rigidly mounted gyro? How many degrees of freedom does it have?
Under influence of a force the turning axis can be changed. 2 degrees of freedom.
Gyroscopic precession
What is the gyroscopic property of a universally mounted gyro? How many degrees of freedom does it have?
Axis is stable in space. 3 degrees of freedom.
Rigidity in space
Name 3 gyroscopic instruments operated by fully gimbaled gyros
- Artificial horizon
- Vertical gyro
- Directional gyro
What is the attitude of the spin axis and the degree of freedom of a Gyromagnetic compass? Artificial horizon? Turn indicator? Vertical gyro?
Gyromagnetic compass; Horizontal plane/ 3
Artificial horizon; Vertical /3
Turn indicator; Lateral /2
Vertical gyro; Vertical /3
What is measured and indicated by the artificial horizon?
Pitch and bank
Explain what can be set using the cage knob located at the housing of the artificial horizon
The spinning axis can be set up in vertical direction
What could be the reasons for using the pitch offset knob at the artificial horizon?
- Forward or aft loading
- For comfort under long cruising flights/making life easier during instrument flying
What is the difference between the vertical gyro and the artificial horizon?
Vertical gyro digitalizes its data for electrical systems and can be mounted somewhere else
What is a standard rate turn?
3 degrees / sec
= 2min for 360 degrees
What is shown by the ball of the slip indicator?
The ball shows if you are flying coordinated (the needle shows angular speed)
Slip or skid
On which pedal should be stepped when the ball is on the left hand side?
Left pedal (step on the ball!)
Describe the operating principle of a laser gyro (rough description)
Light is emitted and separated in both ways of the circuit and the intensity is the value for the rate turn. (His. Exact. Words.)
What are the advantages of a laser gyro compared to a mechanical gyro?
No moving parts
How can torque be measured by the use of inductive sensors?
A reference shaft with a drive shaft within. If there is a difference in turning of the shafts it results in a twisting. A sensor measures the frequency of the changed impulses which vary with the twisting. Maybe make a drawing.
Name two other (other than inductive sensors) possible ways of measuring torque in a helicopter
- Hydraulic sensors
- Piezzoelectric pressure sensors
Explain the operating principle of a mast moment measuring system
Strain gauges are placed on the inside of the mast. When the mast bends, the gauges are stretched or compressed, and the resistance in the gauges changes. This data is digitalized and indicated. The transmission is done via induction to avoid direct connection.
What kinds of rpm’s are measured in a helicopter? What is the reason for this?
- Rotor RPM; Rotor monitoring, autorotation
- N1 RPM = Engine compressor RPM = Gas producer
- N2 RPM = Engine turbine RPM
Explain the design and operating principle of a three phase RPM indicator(tachogenerator)
Alternator(tachogenerator) connected via electric lines to syncro motor, eddy current bell, spring, pointer with scale.
What is the difference between a three phase RPM indicator and a short distance RPM indicator?
Short distance: no electric lines
Explain the design and operating principle of a RPM indicator working with an inductive sensor
Phonic wheel connected to solenoid, signal pulses, frequency indication for RPM
(Like a speed sensor on a bike)
What kinds of pressures are measured in an aircraft besides air pressure?
- Oil: Transmission, engine
- Fuel: pumps
Hydraulic
Name two mechanical and two electrical pressure sensors (without air data sensors)
Mechanical:
- Bourdon tube
- Mechanical linked resistor
Electrical:
- Strain gauges
- Piezzo electric
Explain the operating principle of a piezzo-electric pressure sensor
- Pressure acts on crystal = deformation = electrons are shifted within the crystal
- Voltage can be measured on the surface of each side of the crystal
- With constant pressure and thereby constant deformation there is no voltage
Why could it be necessary to measure vibrations in some aircrafts?
To detect engine damage before failure
An A/C DC system with 28 VDC has one consumer load. A second one shall be connected in series. What does that mean for the total ohmic resistance and the total electric current flowing?
The total resistance increases
The total electric current flowing decreases
What causes static charge of an A/C in flight?
Friction with the air/wind
Name three negative effects of static charge of an A/C
Hoist operations
Air refueling
Landing
Calculate Rtot, U, P and W for 10 hours
________[R1=4 ohm]________
| | |
( V ) = ( A )
| | |-[R2=3 ohm]-| |
————— |-|
|-[R3= 6 ohm]-|
I=24 A
Rtot=
1/(R1+2)=1/3 +1/6 = 2/6 + 1/6 = 3/6
R1+R2= 6/3=2
Rtot =2+4=6 ohm
U=RI=624=144 volt
P=U*I=144v *24A= 3456 W =3,456 kW
W=ptime=3,456 kW10 hours=34,56 kWh
How does “voltage control” act on the generator in order to keep the output voltage constant
U= BIV*N
V and I is constant
N is changed by the RPM
B (intensity of the magnet) is therefore changed when PRM changes
When does reverse current flow from battery to generator occur?
When battery power is higher than generator power due to an electrical failure
Explain why reverse current flow from the battery to the generator must be prevented
The battery might be drained
Name two devices for preventing reverse current flow
Relay and diode
What are the tasks of a starter /generator in an A/C
Starter: started the engine
Generator:generates power to the electrical system
Define the term variation
Different between magnetic and true north
Define inclination
Angle between flux lines and the surface of the earth
What is an isoclinic line
Lines with the same inclination
What are the two main components of a gyro magnetic system
Directional gyro and magnetic flux valve
What is the purpose of a magnetic flux valve
To detect the flux lines and to make the directional gyro More precise
Explain the operating principle of the temperature sensors! Name the temperature range (low, med, high) and give an example!
Thermocouples:
Thermistors:
Bimetals:
Thermocouples:
Difference in potential
High temp
Engine/turbine
Thermistors:
Change in resistance due to temperature changes
Medium temp
Oil
Bimetals:
2 different metals together. 1 expands more than the other and will therefore bend.
Low temperature
OAT
Name the two types of fuel quantity gauges
Floater (possibly with side glass)
Capacitive fuel sensor
