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What are 3 types of instruments?
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What are the 4 colors that are used on engine gauges?
- green
- blue arc
- yellow arc
- red
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What does the Green identify in engine gauge markings?
normal range
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Define what the Blue Arc
Yellow Arc
Red
on a engine instrument gauge
- Blue arc-range of operations under unique circumstances
- Yellow Arc- Precautionary range of time limited operations
- Red- Min or Max allowed (transient limites)
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What is the purpose of the white mark on the glass and case for?
What is it called?
Witness mark-so you know if the glass has shifted
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What are some of the common gauges used on recip engines?
- Carb air temp
- fuel pressure
- fuel flow indicator
- mainfold pressure
- oil temp/pressure
- CHT
- EGT
- TachSuction gauge for vaccume pressure
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Name some common Turbine gauges?
- EGT-ITT, TIT, TOT
- EPR
- RPM %
- Torque
- HP
- oil, fuel pressure
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What does PSIG, PSIA and PSID stand for?
- G-reads in atsmospheric
- A-absolute pressure, gauge pressure + absolute pressure
- D-difference between 2 pressures
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What is a Burdon tube used for?
oil pressure gauge-when the tube is under pressure it wants to straighten out
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Define a Diaphragm type of gauge?
used for fuel pressure, MAP and torque-movement of the diaphram converts in and out motion to mechanical movement
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How do Bellows gauges work?
Spring loaded against pressure
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What type of application would you used a differential pressure gauge?
used on filters
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What type of gauge works on a diaphram and pressure?
Pressure Switch
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What is a D'Arsonval type meter?
Gauge-perminate magnet with spring and neddle attached
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What type of gauge is used in AC circuits
Dynamometer
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Name 5 different methods of measuring temp ?
- Wheatstone bride
- Ratiometer
- Vapour Pressure
- Thermocouple
- bi-sexuals (metallaic)
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What is the basic concept behind measuring voltage with a Wheatstone bridge?
What's the disadvantage?
- Potential difference between A&B
- AC normally doesn't have consistent voltage
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How does a Ratiometer operate?
As variable resistor moves, changes voltage, there is a voltage difference between
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How does Vapor Pressure cause the Bourden tube to expand?
liquid or gas expands bourden tube because of heat
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Explain the therory behind bi-metallic strips?
under temp change brass and steel expand at different rates
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How does current flow in a thermal couple?
current flows at the temp rises
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What is the theory behind thermocouples?
Voltage generated in a thermocouple system is proportional to the temp difference between the 2 ends
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In a thermocouple, what does the green and white colors means?
- green-Alumel (magnetic)
- white-Chromel (non-magnetic)
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Why do some engines have thermocouples in parallel?
- heat is different at diferent spots in engine, take an average
- prevents them from all buring out if one burns out
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How in the FUCK do you check a Thermocouple?
- Heat response test (with a Barfield tester)
- you check for a rise when heat is applied
- also check resistence and insulation test
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What is the effect of shortening a thermocouple harness?
Cannot be shortened or repaired, system operates on very specific total resistence (2 or 8 ohms)
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What is the effect if you have a bad connection on your thermocouple harness?
gauge will read low
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What would you use a EGT compensation Box for?
Trim temp so it reads accuratly
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Name the 5 types of tach's that are used?
- Mechanical
- Magnetic drag cup
- Tach generator
- electric tach
- magnetic pickup
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In a mechanical tach, what two forces are causing the steel cable to move?
flyweights and spring
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How does a magnetic drag cup work?
- Cup spring loaded to zero, magnet spins, pulls cup to give RPM indication
- Cup rotation is proportional and calibrated to engine speed
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What type of electricty does a tach generator produce?
What type of a/c is it used on?
- AC
- large a/c
- similar to Mag drag cup, cable is replaced with AC electrical
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How does a electric tach pick up the engine RPM?
Extra set of points in the magneto, pilse taken off P-lead, counts how many times the mag turns
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What is the purpose of a dual tach?
shows left and right engines or rotor and engine speed
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What does a triple tach read and how is it driven?
reads as a percent, driven by the N2, both engines and rotor RPM have needles
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What is a turbine tach reading?
fan speed, engine speed or N1 N2
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What are the 4 ways to measure torque?
which two are the most common?
- Foot Pounds
- HP
- PSI, % (most common)
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How is the resistence varyied in a Pressure Transducer for DC?
what supplies the pressure to move the potentiometer?
- Uses Potentiometer to vary resistence
- bourden tube, bellows diaphram
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In a linear var differential transformer, how is the probe moved?
uses inductance-probe moved by bourden tube
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Why is a dead weight test done?
check/confirm accuracy of torque
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What are two ways you can adjust a compensating transducer?
What is it compensating for?
- screw
- index dial
- comps for system inaccuracy (adj small amounts)
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Why is calibration needed?
Takes out inaccuracies in system cause not all engines are the same
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What type of gauge would be used on gears to measure torque?
Stress gauge-goes under compression and tension, measures the change in resistence on a bridge circuit
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How does does a shaft using mag pickups measure torque?
shaft within a shaft- measures the twist of the shaft to get torque
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Ina EPR gauge, how is the signal sent to the cockpit?
Differential Pressure Bellows to Auto-sin, moves the needle in the cockpit
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What is the name of the 3 remote position systems? and what type of electricty do they work with?
- Selsyn-DC
- Autosyn-AC
- Magnesyn-AC
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Where does the Magnesyn recieve power from?
permanant magnet and Bus or inverter supply power
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What is the function and location of chip detectors ?
- located in scavenge lines
- can determine excessive engine wear
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How do chip detectors detect chips in the system
debris will bridge chip detector and close circuit
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How do Pulsed Chip detectors work?
discharges capactors to burn off small flakes or chips, if its to big a light will be turned on in the cockpit
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How does a piezoelectric sensor generate electricty?
How is it to be mounted?
- when compressed it generates a electric current
- mount at the centre of rotation
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What causes a indication on a differential pressure switch?
When the pressure difference between P1 and P2 gets to low, sends signal to indicate that the filter has been bypassed
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What is the name of the electrical meter system used to check and calibrate and check the integerity of the ITT systenm?
Barfield
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What is used to allow the removal of a chip detector without oil spilling out?
plunger
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How can a differential pressure switch be used to indicate fuel filter is bypassed?
Difference in pressure, closes switch, turns light on in c/p
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How is fuel flow measured in a piston engine?
turbine engine?
- piston-measures fuel as pressure
- turbine-fuel flow measured by mass-swirl vanes
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Why would you preform a power check? what is the power check based on?
- to determine if the engine can operate to spec
- based on manufactures specs
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What does EICAS stand for?
what are the 4 levels?
- Engine indicator and crew alert system
- Level A-Warning-Red
- Level B-Caution-Amber
- Level C-Advisories-Amber of light blue
- Level D-Memos-White
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What does ECAM stand for?
Electronic Centralized Aircraft Monitor
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If you have a thremocouple harness with 8 probes and one burns out, what would the temp reading in the cockpit read?
It would read slightly less after the probe burned out to an increase in resistence
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What type of fuel flow meter gives the highest accuracy ?
Mass
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What are 3 systems that are used on a turboshaft to measure torque?
- helical gear
- strain gear
- heat
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