1
Q
Pressure equation
A
Force / area
2
Q
What is absolute pressure?
A
Pressure measured relative to a perfect vacuum
3
Q
What is differential pressure? Give an example of a type of differential pressure.
A
Pressure measured relative to another pressure source.
Eg. Gauge pressure is differential pressure between the measured source and ambient.
4
Q
ISA sea level pressure in hPa, mb, bar, inHg, psi.
A
1013.25, 1013.25, 1.01325, 29.92, 14.7
5
Q
What is static air pressure and how is it measured?
A
Pressure of air when stationary. Measured by a partially evacuated aneroid capsule.
6
Q
What is dynamic air pressure and what are two equations for it?
A
Pressure of air, entirely attributable to its movement.
1/2 * rho * TAS^2
Total pressure = dynamic + static pressure
7
Q
What is the pitot tube? Where does it point? What features does it require (x2)?
A
Open tube
Points into airflow
Electrical anti-icing and water drain
8
Q
What are static ports and where does they point and where are they situated? Requirements for valid readings (x2)? Which manoeuvre error is reduced by having PAIRS of ports? What is the alternate static source?
A
Pair of ports at right angles to airflow, usually on opposite sides of the fuselage.
Air must not be accelerating or turning over the port.
Manoeuvre error reduced: yaw in particular
Alternate static source is an alternative to having PAIRS of static sources in light aircraft. Causes instruments to overhead because cabin pressure is lower than ambient outside.
9
Q
Can a combined pitot/static probe use on light aircraft? Downside?
A
May be used; less accurate
10
Q
4 errors associated with pitot/static systems? How can you correct 2 of them?
A
Instrument error
Manoeuvre error: too many variables to calculate
Position error: corrected for manually by a computer
Static system error: reduced by converting air data to digital data at or near the static port, or by reducing the length of pipe runs between static port and instrument.
11
Q
To which 3 things do pitot/static system outputs go? (Large ac)
A
Flight instruments, pressurisation systems, flight control systems.
12
Q
How do CAT aircraft improve system redundancy with pitot/static systems?
A
Multiple systems and data interchangeability
13
Q
Why is icing a risk to pitot/static systems and how is this risk reduced?
A
Prevents systems working properly
Heating is essential
14
Q
What are alternate static sources used for and what it’s important to remember about them?
A
Used in the event of static port ice build up
Cabin pressure substituted for static pressure. Slightly lower than static pressure so instruments over read.
15
Q
What is a property of CAT aircraft’s pressure sensors? How do they output data? Which 4 systems need this data?
A
Solid-state pressure sensors.
Digital output via a data bus
Data available to all systems needing it: ADC, FADEC, flight control synthetic feel system, aircraft pressurisation systems.
16
Q
What does ADM stand for?
A
Air data module
17
Q
What does ADC stand for?
A
Air data computer
18
Q
2 units used for altimeters?
A
Ft and metres
19
Q
What is height and when is it indicated on the altimeter?
A
Vertical distance of aircraft from a point on the ground. Indicated when altimeter sub-scale is set to QFE.
20
Q
What is altitude and when is it indicated on the altimeter?
A
Vertical distance of aircraft above mean sea level. Altimeter set to QNH.
21
Q
What is indicated altitude and what causes i. Small (x3) and ii. Large (x2) errors in it?
A
The altitude shown on the altimeter
Large errors from temperature and pressure error
Small errors from instrumentation error, position error, static system error
22
Q
What is true altitude? (What 2 things is it corrected for?)
A
Indicated altitude corrected for barometric and temperature error
Barometric error: caused by altimeter reference pressure being different to local sea level pressure.
23
Q
What is pressure altitude and how are pressure altitudes described?
A
Altitude shown on the altimeter when 1013.25hPa is set.
Described as flight levels, where the flight level is the pressure altitude minus the last two digits.
24
Q
What is density altitude and how is it calculated?
A
The ISA altitude equivalent to actual pressure altitude in ambient conditions
DA = PA + (ISA dev. x 120)
25
What is QFE?
Pressure measured at ground level at an airfield. Altimeter reads approximately 0 at touch down.
26
What is QNH?
Pressure measured at ground level at an airfield, adjusted for sea level using known ISA conditions. Altimeter reads airfield elevation on touchdown.
27
What is SPS?
Standard pressure setting 1013.25hPa. Altimeter reads pressure altitude.
28
Operating principle for altimeters generally? 5 points.
Partially evacuated dry aneroid capsule contained in sealed casing connected to static pressure port
Stack of capsules used to increase range of movement
Spring limits collapse of capsules under casing (static) pressure
As aircraft climbs case pressure reduces, capsule expands
Suitable system of levers and gears move instrument pointer to indicated altitude
29
How many capsules does a simple altimeter have? How many pointer hands? How good is its accuracy and range? Does it have a subscale? What does this mean? What is simple altimeter insufficient for (x2)?
One capsule
One pointer hand
Limited accuracy and range
No subscale, so can only be set to 0 before flight (QFE)
Not sufficient for training or commercial
30
6 points sensitive altimeter. How is some (not all) friction reduced? Can it be used in controlled airspace? What about high levels of airspace?
Stack of aneroid capsules to increase accuracy and operating range
Multiple pointer hands allow more accurate indication
Potential to be mis-read because of multiple hands
When equipped with altitude reporting is the minimum required in controlled airspace
Jewelled bearings and vibration or knocking system reduce friction and sticking to improve accuracy
Remaining friction in linkage system results in still not being suitable for some airspace
31
Servo altimeter. 5 points. Can it be used in airspace (what kind)? What feature does it always have?
What current? Lag?
Stack of aneroid capsules moving only the I part of an E/I transducer
Almost 0 friction means almost no lag
E bar feeds AC to a servo motor which moves it to realign with the I bar. At same time drives pointer hands and numerical display
Minimum standard altimeter for RVSM airspace
Always has an altitude reporting facility
32
What four types of display can altimeters be?
Pointer (simple altimeter)
Multi pointer (sensitive altimeter, servo)
Pointer and drum numerical scale (servo altimeter)
Vertical straight scale (electronic flight instruments altitude tape)
33
What is barometric error, what is it caused by and how is it corrected? (+ true alt. Equation)
Caused by altimeter reference pressure nit being the same as local sea level pressure
Corrected: true alt. = indicated alt. + (actual hPa - set hPa) x 30
34
How do you calculate temperature error?
4 x (indicated altitude/1000) x ISA deviation
35
What is altimeter lag error? 2 ways of reducing, 2 ways of removing.
Friction in the mechanism connecting the aneroid capsules to the pointer hands means that indicated altitude lags behind actual altitude when climbing or descending.
Reduce: using jewelled bearings for the mechanism
Reduce: use a vibration/knocking device to prevent static friction
Remove: E/I bar and servo motor system
Remove: use of MEMS sensors feeding air data computers.
36
What does MEMS stand for?
Micro electro-mechanical systems
37
What causes position error in pitot/static systems? Where is it mostly a problem and why? What can be used to adjust?
Airflow disturbances around the static port
Mostly problem on small aircraft with no large areas of fuselage with stable airflow for siting static ports
Correction table may be required to adjust for gear and flap changes
38
What is a static system blockage? What do complete / partial blockages cause in an altimeter?
Obstructions (plugs, tape, insects, nests) blocking static system causing altimeter errors.
Complete blockage causes altimeter to lock up
Partial causes very large lag: underreads in a climbs, over read in a descent (bad)
39
What happens to altimeter reading with static system leak in i. Pressurised aircraft ii. Unpressurised sircraft.
i. Air leaks from cabin into static system, increasing casing pressure, causing under reading.
ii. Air leaks from static system to cabin, which is slightly below ambient pressure due to Venturi effect, causing altimeter to over read.
40
Why is GPS altitude useful? X2
For checking altimeters which are disagreeing, to determine which one is correct and which is faulty.
Can be used as a backup system in some aircraft, in which labels and alerts remind crew that it is inaccurate.
41
Why is GPS altitude inaccurate? X3
Limits of satellite coverage
Lateral (not vertical) navigation prioritised
Earth model inaccuracies
42
Basic of converting from pressure altitude to true altitude.
P-I-T. Pressure - Indicated - True.
Pressure corrections converts from pressure to indicated altitude.
Temperature corrections converts from indicated to true altitude.
43
True altitude equation in terms of temperature error correction.
True altitude = indicated altitude +/- TEC
TEC = 4 x (height above pressure datum / 1000) x ISA deviation
44
Units used for VSIs? Conversion between them?
Feet per minute
Metres per second
1m/s ~ 200fpm
45
3 operating principles of VSIs?
Capsule connected to static press.
Metering unit feeds static press. into case with controlled lag.
Difference in pressure between capsule (static) and case (static with delay) causes capsule to expand or contract, moving pointer on face of instrument.
46
In order to function, what must the VSI establish? What’s the magnitude of this thing?
Pressure difference
1-2 secs
47
What combinations of data may be used in an inertial VSI?
Either blended air and inertial data or just inertial data
48
4 principles of IVSI operation?
Mass located in a cylinder which is open at each and and connected either side of a restrictor in the static line to the IVSI capsule. Acts as a piston.
Mass held centrally in cylinder by springs.
When aircraft changes pitch rate, inertia moves piston in cylinder, casing pressure rise or fall in capsule, giving instant indication of climb or descent.
As rate of climb stabilises, piston returns to middle of cylinder. IVSI now operates as per normal VSI.
49
4 VSI errors (+1 for just VSI)
Position
Manoeuvre
Instrument
Static system
Lag (VSI only)
50
What happens to a VSI reading if there is a static system blockage?
Capsule and case pressure equalise, so reading moves to 0
51
What happens with a static system leak in VSI reading?
Unpressurised: little effect
Pressurised: erroneous indications depending on relationship between actual rate of climb/descent and cabin rate of climb/descent.
52
2 sources of error for IVSI specifically.
Instantaneous vertical speed indicator
Turbulence: movement of mass causes false reading.
Manoeuvre: movement of mass under g causes false readings.
53
3 types of VSI display?
Logarithmic dial display: more accurate at smaller rates of climb/descent
Linear dial display
Logarithmic electronic display on PFD
54
Three possible units for airspeed?
Nautical miles per hour (knots)
Kilometres per hour
Statue miles per hour (mph)
55
4 operating principles of ASI?
Metal capsule connected to pitot pressure
Instrument case connected to static pressure
Difference between pitot and static pressure (dynamic pressure) determines the extent to which the capsule expands
Linkage of arms and gears connects capsule to pointer hand against scale calibrated to IAS
56
3 indication types IAS
Pointer hand (traditional instrument)
Vertical straight scale (EFIS speed tape)
Numerical (some HUDs)
57
5 types of errors affecting ASI and magnitudes? IPS CD
Static system error: small
Instrument error: small
Position error: varying magnitude depending on aircraft configuration. On some small aircraft adjustments must be made to IAS.
Compressibility error: negligible below 300kts, can cause significant underreading at higher speeds. Use navigation computer to correct for this. ADCs automatically correct.
Density error: air density decreases rapidly as altitude increases, causing significant discrepancies between IAS and TAS at altitude.
58
What may be used to account for position error on an ASI in a small aircraft?
ASI correction table
59
What effect does pitot system leak have on ASI?
Underread because some total pressure is lost
60
Static leak effect on ASI i. Pressurised ii. Unpressurised
i. Underread as cabin pressure higher than static pressure
ii. Slight overread from slightly lower cabin pressure to static
61
Effects of blockage in i. Static and ii. Pitot systems during descent
i. Overread
ii. Underread
62
Effects of i. Static and ii. Pitot blockage during climb?
i. Underreading
ii. Overreading
63
What do the following mean on the ASI?
White arc
Green arc
Yellow arc
Red line
Barber’s pole
Blue line
Flap operating speed range
Normal operating speed range
Caution speed range
Never exceed speed (VNE)
Maximum operating speed (VMO) or Mach number (MMO)
Multi-engine piston light aircraft best rate of climb speed with one engine
64
What is unreliable airspeed? Through 5 methods (problems) can it be recognised?
Discrepancy between two or more ASIs, leading to uncertainty over which is correct and which is defective.
Indicated airspeed differences between ASIs
Unexpected aircraft behaviour (eg control response not as expected)
Unexpected buffet (caused by high or low airspeed)
Aircraft warning systems
Aircraft’s attitude not as expected for phase of flight
65
Three methods of judging approximate speed?
Wind noise around cockpit: possible indicator of gross airspeed deviations.
GPS speed only useful if wind is known (noted or on OFP)
Pitch and power settings (accurate and reliable)
66
What is LSS and what does it depend on?
Local speed of sound is the speed at which sound propagates through the air in current conditions.
Depends only one on ambient temperature.
67
LSS equation (measured in knots)
39 * sqrt(absolute temp)
Absolute temp - kelvin
68
What is Mach number and its equation?
Dimensionless unit representing ratio between TAS and LSS
TAS/LSS
69
How can M be measured?
Ratio of pitot to static pressure
70
Three principles of operation for machmeter.
Pitot pressure moves a ratio arm, which pushes against a ranging arm fixed at one end to a shaft.
The shaft is connected to the instrument pointer to read Mach.
The ratio arm is moved up and down by the ranging arm by the expansion and compression of altitude capsule. For any given deflection of the ratio arm, needle deflection increases with increasing altitude.
71
What is compressibility error proportional to and what effect does it therefore have on Mach number reading?
Proportional to dynamic pressure / static pressure
This is what the machmeter is reading, so no effect.
72
4 ways of displaying Mach number?
A pointer against a scale (machmeter)
A numerical drum indication in an analogue ASI dial
A component of a vertical scale speed tape of electronic instruments PFD
A digital indication on HUDS
73
From where are digital Mach number displays’ reading derived?
Calculations performed by air data computer
74
Where are conventional (mechanical) Machmeters now used?
Obsolete
75
Effect of static and pitot blockage on machmeter in DESCENT?
Static: overread
Pitot: underreads
76
Static leaks for pressurised and Unpressurised cabins (machmeter)
Pitot leaks effect?
Static pressurised: underreads
Static Unpressurised: slightly overreads
Pitot: underreads
77
Relationship between CAS, TAS, M at constant EAS with altitude change?
All others increase in climb; decrease in descent
78
Relationship between EAS, TAS, M with constant CAS with altitude change?
EAS decreases in climb, others increase
Reverse is true
79
How to remember how the different airspeeds change with altitude?
80
How does the TAS/M relationship change when in i. warmer air and ii. colder air, for same M?
What happens to the other airspeeds?
i. TAS increases; EAS and CAS stay the same
ii. TAS decreases; EAS and CAS stay the same
81
What are VMO and MMO?
Maximum operating speed
Maximum operating Mach number
82
How are VMO and MMO displayed on instrumentation? Which is the more restricting at which altitudes?
Both indicated by the same visual method (“bricks” of a speed tape), indicator displays the more restrictive of the two.
VMO usually dominant at lower altitudes; MMO at higher.
83
What risk does climbing at a constant IAS pose?
Exceeding MMO
84
What risk does descending at a constant M pose?
Exceeding VMO
85
What is a climb/descent profile and why are they used?
Switching from airspeed to Mach number in a climb, or Mach number to airspeed in a descent at the point which the values cross over, to prevent exceeding VMO or MMO.
86
What happens with IAS/M close to the aircraft’s ceiling?
Climbing at constant M reduces IAS. Close to ceiling, there may be little margin to stall speed.
87
What is temperature?
A measure of concentration of thermal energy in an object.
88
Freezing point of water in ISA conditions, boiling point of water in ISA conditions, 1°C, conversion to C. FAHRENHEIT.
32°F
212°F
1°C/K = 1.8°F
°C to °F = x 1.8 then add 32
°F to °C = -32 then / 1.8
89
What is OAT and where is it measured? (Simple)
Outside air temperature, measured at a point not in direct sunlight
90
What is SAT?
Static air temperature, inferred temperature outside an aircraft for air that is not affected by movement.
91
What is TAT?
Total air temperature. Sensed temperature outside an aircraft which is affected by adiabatic heating as the air, relative to the aircraft, is slowed to 0.
92
What is RAM rise the difference between and what is it caused by?
The difference between TAT and SAT caused by adiabatic heating
93
Equation for SAT in terms of TAT and ram rise? Equation for ram rise?
SAT = TAT - Ram Rise
Ram Rise = (TAS/100)^2
94
Which temperature is used to derive TAS? What’s piece of equipment it therefore useful to and on what aircraft is it displayed?
TAT, useful for ADC, displayed on CAT aircraft
95
What kind of dial does a direct-reading temperature probe have? What is it connected to and what does this pass through?
What 3 errors can be significant here and why?
Simple dial
Connected to a probe passing through the skin of the aircraft near the windshield
Position error due to airflow disturbances at the front of the aircraft, and sunlight affecting the sensed temperature
Also instrument error due to basic construction
96
How do systems and displays receive SAT measurement (what other component calculates this and what other temperature is involved in this)?
Where is the indirect probe placed and why? What does the probe have to protect against the boundary layer and why?
How is the sensor protected from sunlight?
Electrical TAT measurement giving accurate data to ADC, which calculates SAT and sends TAT and SAT to systems and displays.
Placement of probe on fuselage where airflow is stable. Probe has a strut to position it out of the boundary layer.
Sensor is inside probe body to protect it from sunlight.
97
How is sensor icing protected against? What would this cause without special design measurements? What are these designs reliant on, and what 2 things does this require?
Electrical heating.
Sensor would heat up, making measurement inaccurate.
Heat shield and airflow are between the probe body. This relies on airflow, which requires the aircraft to be in motion or an aspirated probe (eg. By using air from APU)
98
How does a vane sensor (AoA) function? Where is it pivoted? How is AoA inferred?
Like a wind vane. Pivoted well forward of its centre of press.
Vane angle measures to infer AoA.
99
How does a null-seeking AoA rotor work?
Pressure in two ports compared.
Pressure difference commands servo-motor to realign rotor until port pressures are equal.
100
How are AoA sensors protected from icing conditions?
Electrical heaters
101
2 types of AoA display?
Gauge showing proportion of maximum AoA (or a number)
Light display showing green, yellow, red according to margin to stall
102
What are 3 systems using AoA data?
ADC
Stall warning systems
Flight envelope protection systems
103
What 5 things can incorrect AoA data cause?
Degradation of flight control systems
Malfunction of stall protection systems
Reversion to degraded control modes or laws
Incorrect or unnecessary function of flight envelope protection systems
Loss of situational awareness
104
How can incorrect AoA data be identified? (Awareness of 3 things)
Awareness of pitch, power, airspeed
105
What is an ADC? What does it sense, perform, and output?
Air data computer. (Usually) a digital computer which senses raw data and makes mathematical calculations to output to instrument displays and aircraft systems.
106
Role of ADMs? Where are they in relation to sensors?
How is this data passed to ADC? What happens in ADC?
Analogue data converted to digital data in air data modules. ADMs close to sensors.
Data passed by data bus to ADC, where processors perform calculations using stored aircraft data and algorithms.
107
6 possible input data for ADCs? SPAT WC
Static pressure
Pitot pressure
TAT
AoA
Weight on wheels
Config (flaps/gear)
108
Which 3 errors can ADCs eliminate and how (2 methods)? (Data and input)…
Position, pitot and static.
Using stored calibration data, along with aircraft configuration input.
109
7 typical ADC outputs? I AM SAVP
IAS and TAS
SAT/TAT/OAT
M
AoA
Altitude
Vertical speed
Position of MMO/VMO pointer
110
How do ADCs provide an accurate TAS reading?
Compressibility and density errors calculated
111
What does ADC failure lead to and how is this mitigated (x2)?
Loss of data to all instruments supplied
Multiple ADCs for redundancy
Switching data sources used by various displays
112
9 systems that might use ADC outputs?
P TAFFS OGE
Primary flight instruments
Transponder
Autopilot and FD
FMS
Flight data recorder
Stall warning systems
Overspeed systems
GPWS
Engine management system / FADEC
113
What is the name given to Earth’s magnetic field? From where does it emerge and re-enter the Earth? How far do these magnetic poles move per year?
Terrestrial magnetic field
Emerges from magnetic South Pole and re-enters at magnetic North Pole.
Several miles per year.
114
What is dip angle?
Angle between total field and local horizon.
Total field is the combination of horizontal and vertical components of each magnetic field line.
115
Which components of Earth’s magnetic field are strong/weak when dip is large/low?
Large dip: vertical component’s strong; weak horizontal component.
Low dip: vertical component’s weak; strong horizontal component.
116
What is magnetic direction measured relative to?
The local magnetic field horizontal direction (magnetic north)
117
What is the magnetic north symbol shape?
Half diamond or single-sided arrowhead
118
What is magnetic variation, and which direction is positive/negative?
Difference in direction from magnetic north and true north
East (positive)
West (negative)
119
Phrase to remember variation when calculating magnetic / true headings? What is an alternative equation that can be used instead of this?
Variation east, magnetic least.
Variation west, magnetic best.
True direction = magnetic direction + magnetic variation
120
What do direct-reading compasses provide? How are they powered?
Provide a back-up means of finding the aircraft’s heading.
They require no electrical power.
121
What role does pendulous suspension play in the direct-reading compass?
Keeps the magnet assembly more horizontal than the Earth’s field but residual dip is still present.
122
What are compass errors caused by? What happens whenever dip is present?
Residual dip.
Any acceleration causes the assembly to rotate.
123
Acceleration errors aide-memoir?
NANDS
Northern hemisphere: accelerating north, decelerating south.
124
Turning error aide-memoire?
NUNOS
Northern hemisphere: undershoot north; overshoot south
125
Rate 1 turn?
3°/second
126
When does the compass freeze?
During some pitch manoeuvres: when the card touches the casing around 18°
127
2 serviceability checks before the flight to check compass?
Check for physical damage and fluid leaks
Compare indicated heading with known direction such as another compass or runway direction
128
Compass error when in northern hemisphere, accelerating east?
Indicates an apparent turn towards north (to the left)
129
Compass error when in northern hemisphere, accelerating west?
Indicates an apparent turn towards north (to the right)
130
Compass error when in northern hemisphere, decelerating east?
Indicates an apparent turn towards south (to the right)
131
Compass error when in northern hemisphere, decelerating west?
Indicates an apparent turn towards south (to the left)
132
Why does compass deviation exist?
The compass doesn’t always sense magnetic north accurately.
133
What 2 symbols could compass north be depicted as?
A line with a C
A teardrop arrowhead
134
What is compass deviation?
Angle between compass north and magnetic north, expressed as east (positive) or west (negative)
135
Equation for magnetic heading, including compass heading and magnetic deviation?
Magnetic heading = compass heading + magnetic deviation
136
Phrase to remember compass deviation?
Deviation east, compass least.
Deviation west, compass best.
137
What is compass deviation caused by and what 2 things does vary with?
Deviation caused by interaction of aircraft’s magnetic field and earth’s magnetic field.
Varies with location and aircraft heading.
138
What 3 types of components cause aircraft magnetism? What 2 factors affect their magnetism?
Soft iron components: temporary magnetism depending on attitude and location
Hard iron components: permanently magnetised components
Electromagnetic components: magnetised when current flows
Attitude and direction
139
When is electromagnetism from onboard electrical items present?
When power is applied
140
What 3 things does the strength of the electromagnetic field from onboard electrical items vary because of?
Number of coils
Strength of current
Material of core
141
What 3 elements make up compass calibration?
Compass swing to determine initial deviations
Compass compensation to reduce deviations as much as possible
Compass calibration to determine residual deviations
142
What does a compass deviation card allow, and where is it placed? Through which 3 ways may it be annotated?
Allows for correction of deviation
Annotated E/W, +/-, “for ‘x’, steer ‘y’”.
143
Phrase to incorporate equations for compass deviation and variations?
C D M V T
Cadbury’s dairy milk very tasty
(Compass deviation magnetic variation true)
Compass + deviation = magnetic = variation + true
144
How are compass deviations minimised?
Swinging the compass
145
At what stage of the calibration process is the deviation card produced?
Swinging
146
What is a gyroscope and how does it maintain rigidity? What is a gyro’s orientation in inertial space used for?
Spinning mass which maintains rigidity in space because of its inertia
Its orientation in inertial space is used as a reference datum for instruments
147
With what 3 properties does gyroscopic rigidity increase with?
Higher gyro RPM
Greater gyro mass
Mass located at a greater distance from the gyro’s spin axis
148
On what is a gyroscope mounted in and why?
Gimbals to let it maintain all or some of its orientation in inertial space as the aircraft pitches, yaws, or rolls around it.
149
How many gimbals do displacement gyros have? How many degrees of freedom and axes of freedom?
How do they provide a datum for measuring the aircraft’s orientation?
Give 2 examples of instruments that use them and how each is tied.
2, 2, 3
They retain orientation in inertial space
DI - horizontally-tied gyro
AI - vertically (Earth) - tied gyro
150
Why aren’t untied space gyros useful for aircraft navigation around the Earth?
Has complete freedom to retain orientation
151
How many gimbals, degrees of freedom, axes of freedom do rate gyros have? What’s an instrument that uses one?
1, 1, 2
Turn coordinator
152
2 COMPONENTS of gyro wander?
Topple
Drift
153
What are topple and drift?
Topple: motion in the vertical plane (toppling off the true vertical)
Drift: motion in the horizontal plane (drifting off a set heading)
154
What is apparent wander caused by?
Change of orientation of observer relative to the gyro.
155
Explain 2 types of apparent wander.
Transport wander: wander caused by moving a gyro across the Earth
Earth rotation: caused by Earth moving a gyro resting on its surface
156
What is real wander (gyro)? 2 types (and their names)?
Actual change of orientation of a gyro
Random wander caused by mechanical imperfections or gimbal geometry
Latitude compensation intentionally caused drift or topple to maintain a gyro’s orientation with respect to Earth
157
What is gyroscopic precession?
Where any applied force tending to reorientate a gyro’s spin axis is precessed through 90° in the direction of spin
158
Where does an applied force act in gyroscopic precession?
As if it has been applied 90° from the point of application
159
How is the gyro’s rate of precession related to its rigidity?
Inversely
160
2 methods of driving mechanical gyros?
Air using vacuum pump
Electrically using electric motor
161
What use does a horizontally-tied gyro provide?
Reference datum for heading
162
How is the display card of the DI driven to show heading?
Heading ring attached to the outer gimbal drives display card.
163
What 2 things does a HSI add to a DI?
Radio magnetic indicator needles and (sometimes) ILS deviator bars
164
3 reasons why directional gyros drift over time?
Earth rotation: type of apparent drift
Aircraft manoeuvres: causing the gyro to move out of alignment as it tries to erect relative to the aircraft
Transport error: type of apparent drift.
165
What is apparent drift proportional to? (From equation for apparent drift)
Sine of latitude
166
What drift is produced during transport drift relative to ER i. Moving east ii. Moving west
Same
Opposite
167
What does i. pushing in the knob, and ii. then turning the knob, do on the DI re-align system?
i. Cages the gyro
ii. Reorients the caged gyro at the desired datum
168
In which direction of travel is total directional drift greatest?
West
169
What 5 components are remote reading compasses comprised of? GFHTP
Gyro: kept aligned with Earth’s magnetic field
Flux valve: senses direction of Earth’s magnetic field
Hooke’s joint: allows flux valve to hang vertically, but not rotate in the horizontal
Transducer: stator and detection coil
Precession amplifier: converts transducer’s AC to amplified DC
170
What is the flux valve in the RRC immersed in and why?
Fluid, to dampen any swinging
171
How many detector legs are in the RRC? What do they pick up, and where are they fed to (how are these arranged)?
3
Pick up 3 field component currents which are fed to similarly arranged stator coils
172
What does the stator recreate in an RRC? Around what?
The relative orientation of Earth’s field around the drive shaft from the gyro
173
How is the gyro in an RRC kept aligned?
A null-seeking detector coil on the drive shaft creates an electrical signal which drives a procession motor to keep gyro aligned
174
Where are flux valves usually mounted? Why?
In wingtips or tail plane, as far as possible from interference from the aircraft’s magnetic field
175
When the gyro is aligned, what does the RRC’s compass card indicate? How are the detector coil and precession motor linked in this case?
Correct magnetic heading
Detector coil produces no electrical signal to the precession motor
176
Which 2 systems are used in conjunction to slew the gyro onto the correct magnetic heading in an RRC?
Precession motor and slave switch
An indicator shows the signal being sent to the precession motor, which should oscillate slightly every few seconds
Used in conjunction with a slaving switch to rapidly slew the gyro onto the magnetic heading
177
3 RRC annunciation unit components?
Compass card
Set-heading knob
Course select knob (sometimes)
178
What 3 things does a HSI combine?
RRC, CDI, (sometimes) ILS glideslope deviation bars
179
How can the RRC be reverted to a simple directional gyro? (Isolate the…)
A slave/free (or compass/DG) switch isolates the flux detector system to revert the RRC to a simple directional gyro
180
How can slaving be disabled during manoeuvres?
Cut-out switches
181
2 disadvantages of RRC vs. DI and DRC?
Heavier, more complicated and takes more space.
Requires electrical power.
182
5 advantages of DDC vs. DI and DRC? DTASH
Deviation similar but no deviation card needed as slaving circuit is calibrated to account for this
Turning and acceleration errors much smaller
Attitude errors very small (no jamming)
Stable and accurate indication
Heading info. available for other aircraft systems (eg. AFCS and RMI)
183
What does the AI DISPLAY and how? What kind of “tied” is the gyro?
Aircraft attitude relative to the Earth, via an attitude card attached to the outer gimbal of an Earth-tied gyro.
184
How does an AI display roll?
Aircraft rolls around gyro. Aircraft is attached to the case.
185
How does an AI display pitch?
Guide pin attached to the inner gimbal moves display card up and down and amplifies movement.
186
Colour of typical AI display card? How frequent are pitch indication lines? With what is roll depicted?
Brown (Earth)
Blue (sky)
Lines every 10° and smaller marks every 5°
Sky pointer or ground pointer (marks on casing at 10°, 20°, 30°, maybe 45° and 60°
187
What extra indications do attitude and direction indicators (ADIs) have (4 inc. 2 on some models)?
Flight director guidance (crossed bars or ‘V’ symbol)
ILS localiser and glidepath deviation indication
Rising runway symbol (some models)
Relative speed indications (some models)
188
How many degrees of freedom does an AI gyro have?
2
189
What gives rise to pneumatic gyro errors? Which way are they assumed to rotate when viewed from above?
What errors occur in pneumatic gyros during i. Acceleration and ii. Deceleration?
Pendulosity
Anti-clockwise
i. Pitch up and right roll
ii. Pitch down and left roll
190
Why are errors complex in AIs? Angle of Bank (underreads, correct, overreads) and pitch angle (overreads, correct, underreads) error for 90°, 180°, 270°, 360° turn so far?
Turns transfer pitch or bank errors to and from the roll and pitch axes.
191
How do electrically driven gyros’ error compare to pneumatic gyros’ error and why?
Smaller because unit isn’t pendulous
192
When are erection errors possible in gyros? (X2) What errors do accelerations/decelerations cause? What any happen in a very prolonged turn?
Prolonged gentle turns
Accelerations
Acceleration: false indication of pitch up
Deceleration: false indication of pitch down
Prolonged: gyro may re-erect to horizontal giving false bank indication
193
What type of gyro is the turn indicator?
Rate gyro
194
How many gimbals does a turn indicator have? What is/are it/they constrained by? What forces cause the gyro to roll and when? How is direction of turn shown on the instrument?
1, a spring
Yaw forces in a turn
A turn needle linked to the gimbal
195
What index marks does a turn indicator have?
Central index mark indicating non-turning flight
Three index marks each side indicating rate 1, 2, 3 turns
196
How does a turn coordinator compare to a turn indicator in terms of design? What 2 movements is the turn coordinator sensitive to? How is turn immediately indicated? How is direction and rate of sustained turn indicated?
A variant of, with its gimballed gyro inclined at 30°
Roll and yaw
Initially roll in turn causes gyro to roll, indicating turn immediately.
Subsequent yaw forces cause unit to indicate direction and rate of sustained turn.
197
What may the turn coordinator indications be mistaken for? What’s a danger of the turn coordinator? What are skid and slip?
Bank indications
Danger of incorrect spin direction indicated
Skid: too much into-turn rudder
Slip: too little into-turn (or opposite) rudder
198
What does balance indicator show? What is the ball located in? How does it move?
Slip or skid when displaced from centre
Located in liquid-filled, curved tube
Moves under centrifugal force
199
What is the balance/slip indicator used for?
To show the correct amount of rudder required for current bank angle
200
When is residual dip present? What does this mean in relation to the compass’ CG and pivot positions (which is closer to pole)? In which direction does compass’ magnet dip? About what does the compass rotate? Through what does acceleration force act in compass when aircraft is accelerating?
Always
Compass’ CG and pivot positions are in different places (pivot closer to north pole)
Dips towards pole, rotates about pivot
When aircraft accelerating, force acts through pivot
201
Explain NANDS.
Northern hemisphere: if you accelerate in the northern hemisphere, compass will indicate a turn towards north. If you decelerate in the northern hemisphere, compass will indicate turn towards south.
N: northern hemisphere
AN: accelerate = (turn towards) north
DS: decelerate = (turn towards) south
202
Are direct reading compass errors greater i. passing through E/W during a turn, or ii. passing through N/S during a turn, and why? What 2 forces are present on the compass’ magnet during a turn, what does this create and when?
When passing through N/S, because the forces don’t act through the axis of the pivot.
Force 1: acceleration towards centre of turn, acting through pivot.
Force 2: inertial force acting opposite to force 1, but through CG. Couple created if CG and pivot aren’t both aligned with pole in a line.
Remember: pivot always closer to north pole than CG
203
What does the compass read when turning left through north in the northern hemisphere? Explain in terms of the 2 forces acting on the magnet, and the points at which they act.
Compass overreads (indicates a heading further to the right)
Acceleration force acts to inside of turn about the pivot (closer to north pole), inertial force acts to outside of turn about CG (further from north pole)
Anticlockwise couple formed, rotating assembly AC.
204
What does the compass read when turning right through north in the northern hemisphere? Explain in terms of the 2 forces acting on the magnet, and the points at which they act.
Compass underreads
Acceleration force acts to inside of turn about the pivot (closer to north pole), inertial force acts to outside of turn about CG (further from north pole)
Clockwise couple formed, rotating assembly C.
205
What does the compass read when turning left through south in the northern hemisphere? Explain in terms of the 2 forces acting on the magnet, and the points at which they act.
Compass underreads
Acceleration force acts to inside of turn about the pivot (closer to north pole), inertial force acts to outside of turn about CG (further from north pole)
Clockwise couple formed, rotating assembly C.
206
What does the compass read when turning right through south in the northern hemisphere? Explain in terms of the 2 forces acting on the magnet, and the points at which they act.
Compass overread
Acceleration force acts to inside of turn about the pivot (closer to north pole), inertial force acts to outside of turn about CG (further from north pole)
Anticlockwise couple formed, rotating assembly AC.
207
What is compass north?
Direction North Pole of compass points to
208
Why is compass north a thing? Why doesn’t the compass just point to magnetic north?
Aircraft’s own magnetic field and terrestrial magnetic field creates a combined field that deflects compass
209
When does compass north vary from magnetic north?
Whenever aircraft’s field is not aligned with terrestrial’s
210
How do deviation and variation change with aircraft heading
Variation doesn’t; compass deviation does.
211
At what latitudes is compass deviation worse and why?
Higher, because horizontal component of terrestrial magnetic field is less, so aircraft’s field has a greater effect on compass.
212
What is a space gyro in simple terms? How many planes of rotation are there about the space gyro, and therefore how many DOF and gimbals?
A gyro that completely retains its orientation in space, regardless of what the aircraft is doing.
3,2,2
213
How does the number of degrees of freedom compare to the number of gimbals used? How does number of planes of rotation about the gyro compare.
Equal
Number of planes = DOF (or number of gimbals) + 1
214
Applications of 2 gimbal gyros? (Types of instruments)
DI and AI
215
What is gimbal lock and why is it bad?
Where two gimbals become aligned, and rotate in the same plane.
Bad because erroneous readings occur as the movement of the gimbals can’t be distinguished or thus interpreted correctly.
216
Formula for gyro drift?
15sin(latitude)
217
Explain what topple and drift are.
Topple: vertical spin axis goes out of whack
Drift: horizontal spin axis goes out of whack
218
Which orientations of gyro can i. both topple and drift, and ii. only topple.
i. Horizontal
ii. Vertical
219
What does a gyroscope appear to be doing from earth when i. vertical, standing on equator; ii. vertical, at poles; iii. horizontal, at poles; iv. horizontal, at equator; v: a gyro, at 45°N (mid-latitude).
i. Topple
ii. No topple
iii. Drift (15°/hr)
iv. No drift
v. Both topple and drift (10.6°/hr)
220
Equations for drift and topple, and units?
Topple: 15cos(latitude)
Drift: 15sin(latitude)
Degrees / hr
221
Formula for rate of transport wander in degrees per hour?
(East-west ground speed) x tan(latitude) / 60
222
How is the DI’s gyro tied? What does this mean?
Horizontally - spin axis (parallel to aircraft’s longitudinal axis) is always parallel to Earth’s surface.
223
When does transport wander occur and why?
With east-west components because the meridian where the di was aligned has been deviated from.
With just north-south movements (along the meridian which the di was set), the di is still aligned.
224
What is latitude compensation? Equation for ER drift?
Where DI’s are intentionally drifted opposite to ER
Works best at a certain latitude, as ER drift varies with latitude, 15sin(lat)
225
How is a gimbal modified to introduce latitude compensation? How is this done? Role of latitude nut?
Inner gimbal purposely unbalanced
Weight attached each side of gimbal
One is fixed, other is moveable (latitude nut)
LN moved to produce a net torque. This causes drift, after precession.
226
How does the slaving circuit work?
Stator recreates Earth’s magnetic field orientation detected by Flux Valve.
Stator on drive shaft, connecting outer gimbal to compass card.
If output from null-detector coil is sensed, it means displayed heading is not aligned with detector heading.
This causes precession motor to drive gimbal back to north, aligning gyro.
227
How does a rate gyro vary from an earth gyro?
Te defining feature is precession instead of rigidity.
228
How do rate gyros work simply? (Turned at low vs high rate vs no rate)
When turned at a low rate, output axis is slightly deflected
Fast rate, highly deflected.
No rotation, no deflection.
229
How does a TURN INDICATOR work?
Vertical orientation of rotor, horizontal gimbal.
Springs either side of gimbal.
Yaw processes to roll, moving indicator pointer.
230
How does turn COORDINATOR compare to turn INDICATOR?
Gimbal inclined at 30° to the horizontal (pitched up) to make it sensitive to both roll and yaw, not just yaw.
231
Simplified compass diagram?
232
Pressure altitude vs. Density altitude?
Pressure altitude is altitude relative to ISA
Density altitude is pressure altitude corrected for temperature (what aircraft feels like it’s at)
ATPL MOD1
flashcards
Decks in class (19)
# Cards
-
Human Performance LOs354
-
TEM4
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Principles Of Flight LOs (1)500
-
Meteorology LOs (1)497
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Instrumentation - Basic LOs232
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Mass & Balance LOs166
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AGK - Airframes & Systems LOs249
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Instrumentation - Advanced LOs346
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Jack And Dad - Gyros7
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Air Law - LOs471
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Air Law - Regulation (EU) No 965/2012 on Air Operations25
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AGK - Electrics LOs146
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AGK - Engines LOs243
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Principles Of Flight LOs (2)38
-
Meteorolgy LOs (2)17
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Engines Ch. 1-9116
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Engines Ch. 10+126
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Principles of Flight Ch. 26-32173
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Air Law (conventions, EASA Basics)14
