Instruments Flashcards
What does a moving red and white pointer on an ASI indicate?
Maximum speed in VMO operations versus altitude
What does an aircraft’s outside temperature probe measure?
Total air temperature - kinetic heating effects = static temperature
At temperatures greater than ISA aircraft separation will be _______ than indicated.
greater
At sea level in standard atmosphere, how do calibrated airspeed and true airspeed compare?
CAS = TAS
At a constant CAS in level flight, what would a fall in ambient temperature result in?
Lower TAS
(due to increase in air density)
How is barometric error corrected for on a simple altimeter?
Adjusting the subscale
How does a VSI work?
The capsule is fed with static pressure
The case is filled with static pressure via a metering unit so it changes pressure at a slowe rate
The differential indicates the rate of pressure change and thus the vertical speed
How will an airspeed indicator behave with a pitot blockage but an open static port?
Like an altimeter
If temperature > ISA then TAS ___ IAS
>
In a large aircraft, static pressure is ______ and _______. Pitot is supplied individually to ______, _______ and _______.
Balanced and duplicated.
Captain, first officer and standby instruments.
In a servo assisted altimeter, what information is sent to the transponder?
Flight level
In a non-pressurised aircraft, what is the ultimate emergency measure to be used if static ports are blocked/damaged?
Breaking the rate of climb indicator’s glass window
In a non-pressurised aircraft, what would a leak in the pitot line to the airspeed indicator do?
Cause it to under-read
(pitot pressure would be reduced)
Name the four pressure instruments.
Altimeter
Vertical speed indicator
Airspeed indicator
Machmeter
On a light piston twin VSI what does the blue line indicate?
Velocity for best rate of climb with a single engine operating.
VYSE
Name the three types of altimeter from least to most accurate.
Simple
Sensitive
Servo-Assisted
On an ASI what does the green arc indicate?
Normal operating speeds
Stall speed (maximum all up mass clean) to normal maximum operating speed
VS1 to VNO
On an ASI what does the white arc indicate?
Flap operating range
Stall speed (max all up mass in landing configuration) to the maximum speed for flaps extended.
VS0 to VFE
On an ASI what does the yellow arc indicate?
Maximum normal operating speed to the speed never to be exceeded.
VNO to VNE
The speed of Mach 1 decreases with _______ _________.
decreasing temperature
Total air temperature = ________ + ________
Static air temperature + dynamic heating
Total pressure = ______ + _______
dynamic pressure + static pressure
What are the advantages and disadvantages of Instantaneous vertical speed indicators?
Instantaneous reaction due to accelerometer unit.
Innaccurate when entering/leaving a turn (reacts to the aircraft’s changing inertia even though it is in a different plane)
What does a machmeter consist of?
What is the sequence to show a reading?
An airspeed indicator and altimeter interacting in the same case.
Ratio arm, Ranging arm, Indicator
What does a pitot tube measure?
Total pressure
What does a VSI measure?
The rate of change of static pressure
What does an airspeed indicator assume air density to be?
1223gm/m3
What errors do machmeters suffer from?
Instrument error and pressure error.
So small they’re negligable
What errors is the VSI subject to?
Manoeuvre, particularly on take off, go around and in turbulence.
What information do the electrical signals from angle of attack transmitters convey?
The angular position of a wind vane
A differential pressure in a probe, depending on the variation of angle of attack
What does CAS become when corrected for compressibility error but not density error.
EAS
equivalent air speed
What is CAS?
Callibrated airspeed
IAS adjusted to counteract configuration error (Instrument and position/pressure error)
What is dynamic pressure?
The kinetic energy of the air changed to pressure energy.
What is instrument error?
Inaccuracies due to construction, friction and play in the moving parts.
What is position error?
Also called pressure error
Errors in the static pressure reading
What is RAS?
Rectified airspeed
Indicated airspeed manually corrected for instrument and position error
What is static pressure?
Atmospheric pressure.
What is the formula for calculating a good approximation of total air temperature?
TAT = SAT + (TAS/100)2
Where temperatures are in °C and true air speed is in mph
What is the formula for calculating density altitude?
Density altitude = pressure altitude + (120 x ISA deviation)
What is the formula for calculating Mach number?
M = TAS/LSS
What is the formula for calculating the local speed of sound?
LSS = 38.94 </sub>/T
Where T is in Kelvin
What is the formula for calculating static air temperature when the true airspeed is given in mach?
SAT = TAT/(1 + 0.2K x M2)
Where temperature is in Kelvin and K is the recovery factor of the temperature probe.
What is the formula for dynamic pressure?
½pV2
What is the formula to calculate TAS from dynamic pressure?
v2 = (2 x dynamic pressure) / p
So if p > ISA, TAS
if p IAS
What is the formula to convert °C to farenheit?
°F = (1.8 x ºC) +32
When descending through an isothermal layer at constant CAS, what will happen to the TAS?
Decrease
(as descend air density increase so at constant CAS, TAS will decrease because the density correction will be wrong)
When does an ASI display true airspeed?
When p is the ISA value (1225gm/m3)
What is the formula regarding Mach number, static temperature and total temperature?
Ts = Tt / (1 + 0.2M2)
When studying the relationship between Mach, TAS, EAS and CAS what order should you draw the lines on a graph?
E C T M
When TAS > 300kts there is ________ error
compressibility
______ and _____ are configuration errors and are _______.
_______ error is _______.
Instrument and position
predictable (can be adjusted for)
Manoeuvre
unpredictable (can’t be adjusted for)
______ determines aircraft behaviour. ____ is needed for navigation.
IAS/CAS
TAS
If flying in an atmospher where all layers below the aircraft are warm, how will the altimeter read?
Lower than the real altitude
(high temperature means high pressure aloft)
What is hysteresis error caused by?
The elasticity of the capsule changing with temperature
Depends on; length of time at altitude; rate of temperature change (rate of climb/descent)
What is the error in altimeter readings caused by the variation of the static pressure near the source known as?
Position error or pressure error
What is a vibrating device put in an altimeter for?
To reduce the effect of friction in the linkages
What is the main factor which makes a servo-assisted altimeter more accurate than a simple altimeter?
An induction pick-off device
(the E and I bar)
In an altimeter what pressure is:
a) in the aneroid capsule?
b) in the casing?
a) vacuum
b) static
In the event of the accidentl closing of an aircraft’s left static pressure port (rain. birds etc) how does the altimeter read when:
a) sideslipping to the left?
b) in symmetric flight?
a) over-reads
b) correct
(sideslip in opposite direction to yaw
in this case open port on the right where pressure decreases as the aircraft is yawing right)
What is density altitude?
The altitude of standard atmosphere at which the density is equal to the actual density of the atmosphere.
If the static port of an altimeter becomes blocked during descent, how will the altimeter read?
Continue to read the altitude at which the blockage occurred
(blockage causes pressure in case to become fixed so altitude indication won’t change)
Which errors are machmeter readings subject to?
Position (pressure) error amd instrument error only.
What is the velocity of sound at sea level in standard atmosphere?
661KT
LSS = 38.94 x </sub>/(15 + 273)
What is the speed of sound dependent on?
Temperature
What is mach number the ratio of?
TAS to the sonic velocityat the altitude considered
What is a VMO-MMO warning device connected to?
A barometric aneroid capsule subjected to static pressure and an airspeed sensor subjected to dynamic pressure
What ratio is a Mach indicator based on?
(Pt - Ps) to Ps
(pitot static - static) / static
On descent from a high level what limits the maximum descent speed?
Initially MMO, then VMO below a certain flight level
When climbing at constant Mach number in ISA conditions, what will the Calibrated Airspeed do?
Decrease
(ECTM graph)
How is lag decreased on a VSI?
By including an accelerometer sensor
(responds to G force in climb/descent so instantly reacts when entering the climb/descent manoeuvre)
What advantages are there for using an air data computer to indicate altitude?
Position/pressure error correction
Hysterisis error correction
Remote data transmission capability
What are the inputs to the Air Data computer?
(3 primary, to others)
Primary: true air temperature, static pressure, pitot pressure
Angle of attack
Electrical input
What kind of speed is VMO expressed in?
(ECTM)
Calibrated Air Speed
What is VS0?
The level flight stalling speed in the landing configuration.
What is VS1?
The level flight stalling speed for the specified configuration
What are the two key properties of gyroscopes?
rigidity
procession
What is gyroscope rigidity and what can increase it?
The ability to maintain a spacial reference
Greater moment of inertia
Faster spin
Describe gyroscope procession.
When a force is applied it will process 90° in the direction of rotation before it acts
What are the two forms of gyroscope wander?
drift
topple
(both relate to earth alignment)
How is apparent gyroscopic drift calculated and where is it at a maximum?
Apparent drift (degrees per hour) = 15 x sin(lat)
How is apparent gyroscopic topple calculated and where is it at a maximum?
Apparent topple (degrees per hour) = 15 x cos(lat)
Transport wander is a type of ________ drift.
It occurs when a compass is alligned with north then moved to a different longitude. Moving east ______, moving west ______ the total apparent drift (in the northern hemisphere).
Apparent
increases
decreases
How many degrees of freedom does a DI have?
2
pitch and roll
On a DI, what do erection and synchronisation refer to?
levelling the gyro
making it read the correct magnetic heading
How is the gyroscope in a DI held erect?
There are buckets cut into the edge of the gyro.
Air nozzles blow air into them to make the gyro turn
If unaligned the force of the air is greater to one side of the bucket
This force precesses and acts at the top of the gyro pushing it back to the erect position
What is the apparent drift due to the earth’s rotation?
15 x sin(lat)
in degrees per hour
What does the latitude nut on a DI do?
induces real wander to counteract the apparent wander due to the earth’s rotation
How do you calculate transport wander?
= convergency
= chlong x sin(mean lat)
What are the 4 constituents of total drift of a DI?
Are they +ve or -ve in the northern hemisphere?
Real wander (either, value is given)
- Earth’s rotation
+ Latitude nut
- Transport wander East (+ if west)
How is the gyro in an artificial horizon kept erect?
4 exhaust hole half covered by pendulous vanes
if unerect then one of the holes will be more open
force of air exiting open hole precesses 90° and re-erects the gyro
Air driven AHs experience turn errors.
facing 90° to initial direction, if you pitch up then the bank _____reads.
facing 180° to initial direction, if you pitch up then bank _____reads.
under
over
What is the name of the system that compensates for turning error in an artificial horizon?
What level of turn and what speed is it usually set to compensate for?
compensation tilt
Rate 1
250KT
What are slip and skid?
Slip is the force towards the centre of the turn
skid is the force away from the turn
On a rate gyro, the spring force produces a secondary precession _____ and in the _____ direction as the yaw.
equal to
same
What will the rate of turn indicator indicate if the air/electrical supply is cut?
zero
(the gyro is not moving)
How many degrees per minute does a rate 1 turn equate to?
180° per minute
How do you calculate the angle of bank of a turn?
AOB = (TAS/10) + 7
How do you calculate the radius of a turn?
radius of turn = TAS/(rate of turn x 60π)
Order the following types of gyroscope from most to least accurate:
Rate integrating
Air driven
Ring laser
Electrically driven
Fibre optic
ring laser
fibre optic
rate integrating
electric
air
What is the error associated with ring laser gyros?
How is it solved?
Frequency lock (when frequencies are to close they ‘lock’ together and give an output of zero)
Dither (rotating it back and forth to prevent the frequencies becoming too close)
Apparent drift is 15° at the _____ and in ________ direction when viewed from above.
poles
a clockwise
Where is the latitude nut located on the DI?
inner gimbal
The axis of the turn indicator gyroscope is parallel to which aircraft axis?
pitch
A turn co-ordinator is sensitive to ____ rate and ____ rate.
roll
yaw
How many degrees of freedom does a rate integrating gyro have?
2
What are the 4 things that cause a DI to read inaccurately?
The earth’s rotation
The aircraft’s motion over the earth
The mechanical defects of the gyro
The gimbal mount of the gyro rings
What causes gimbal error of a DI?
Pitch or roll of the aircraft
(the gyro hits the limitation stops)
In a level turn what does a classic artificial horizon show at 90° to the original heading?
Pitch over reads
bank under reads
In a level turn what does a classic artificial horizon show at 270° to the original heading?
Pitch over reads
bank over reads
At low bank angle, the measurement of rate-of-turn actually consists in measuring the ______.
yaw rate of the aircraft
Which 2 systems use rate integrating gyros?
Inertial attitude unit
inertial navigation system
