Instruments Flashcards
Gyros
What is Rigidity and what does it vary based upon?
Resistance to movement
Varies based upon:
- Mass
- Distribution of the mass
- Spin Speed
What is precession?
A force on a Gyro acts at 90 degrees to the applied force
Varies inversely with Rigidity
Varies directly with Applied Force
Main parts of a Gyro?
Spindle
Gimbals - Inner - X Axis
Outer - Y Axis
Case ( gimbal 3 )
Gyros - What are the two types of Wander and what do they mean?
(Topple and …..)
Drift - Only affects a horizontal mounted Gyro. The spindle moves up in the horizontal access
Topple - The Y Axis
Gyro: What is Real and Apparent Wander?
Real - The Gyro actually moves through Drift or Topple
Apparent - The earth moves, therefore the Gyro appears to have moved.
Gyros: Two methods to drive the spindle?
And advantages and disadvantages of both
Air - vacum pump sucks air out. Tubes let air in. Tubes are point at the Spindle.
Cons:
- Spin speed affected by Air Density
- Spin speed affected at low RPM
- Dust can get in a clog bearers, resulting in Wander
Electrical.
Pros:
- Spin is constant.
- Unit can be sealed from dust
Con:
Need electrical supply
How does the Artifical Horizon work?
Gyro - mounted horizontally.
Case is in the inner gimbal.
Horizon bar attached to outer Gimbal
Turn indicator attached to outer Gimbal.
How does an Artifical Horizon self correct?
Spindle rotates Anti-clockwise.
Looking from the top there are 4 vents
These have gravity covers on them.
If the spindling is toppling left:
- ForwardVent - closes
- Aft Vent opens - opens
- Force is applied to the right
Correcting the topple.
What is Topple in Artifical Horizon?
The Horizon bar has a limit, from the guide pin.
If the pitch is exceed, this will move the spindle causing ‘topple’
It will self correct in level flight.
Usual limits are :
Pitch +/- 60 degrees
Bank 110 degrees
Old models allow for the case to the ‘cage locked’
When a Gyro is said to be a Vertical Gyro or Horizontal Gyro - what does this mean?
This is the AXIS it spins around.
How does the Directional Indicator work?
How is topple Managed?
How is drift managed?
A Gyro spinning around the Horizontal plane - therefore earth Tied to a point in space.
As the Gyro topples, the air jet will put pressure on one side leveling it out.
Drift is managed manually.
With a Directional Indicator - what are the 3 causes of Drift?
Real - due to imperfections in construction
Apprent - due to the rotation of the earth.
Transport - a subset of apparent, if the gyro travels over Lat lines.
What is the Latitude nut in a Directional Indicator Gyro?
False precession, to offset earth rotation ( apparent wander)
If set exactly, the gyro will prescess against the earth rotation.
This is set by a technician.
The ‘left over drift’ is said to be Residual earth rate drift.
How does the Turn Indicator work?
A gyro in with a Horizontal axis , spinning up and away.
As there is yaw, the force pushes the bottom due to precession, rotating the Gyro.
Note: SINGLE AXIS OF FREEDOM.
The axis is spring loaded, which means increased force is required. Therefore it’s possible to measure.
Turn indicator - Diagram
Difference between turn indicator and Turn Co-orderinator
Turn co-orderinator shows limited information about the roll of the aircraft, as it is canted.
It gives rate of bank and rate of turn.
Turn indicator does not give Rate of Bank.
Instruments - what is a bi-metalic strip
Used to adjust gauges based on temp.
Two pieces of metals are pressed together, that expand different lengths at a given temp.
Resulting in the strip bending.
How does an Air Temp Gauge work?
Probe outside.
Helix of bimetalic
As the temp changes, the helix will rotate.
Main types of measuring devices for measuring pressure for instruments?
Aneroid Box - partial vacuum box with a flexible lid.
Membrane box - opening in one end, and expands and collapses.
Spring Tube ( AKA Bouren Tube ) - semi circular. Closed at one end. Radius changes
How is Oil Pressure measured?
Fairly high pressure.
Either Bourden tube or electrical
How is fuel pressure measured?
Low pressure. Uses bellows.
How and where is manifold Pressure measured?
Uses a bellows capsule as well.
After the throttle butterfly, in the intake manifold.
How is suction measured?
Inline between the intake and the instrument.
Difference between Hobbs time and Tach time?
Hobbs measures engine start to shut off
Tach is relative to the RPM of the engine ( high RPM = tach rolling faster )
With Mechincal Fuel measurements - how is it done? What are the 4 types of error?
Float inside the tank
Errors are:
Position errors - plane pitching
Friction errors - gears between gauge and float. Means over read when float is going down and under read when float is going up.
Temp Error - fuel expands with heat.
Instrument error - if the tank gets deformed in shape.
How does electical fuel measuring work?
Capicator.
Two probes are in the tank.
Conntected to a AC power source.
The impedance measures fuel to air in the tank.
This is measuring Weight.
Pros:
- Temp does not matter - as temp goes up, Volume goes up Specific gravity goes down - so measure is the same.
- For position errors, it is accurate to within 5% upto 15% of pitch
- Can be used for irregular tank sizes
Two ways of measuring RPM
Mechnical - rotating cable (Centrifual Cable)
Mechnical / electrical (Drag Cup)
- AC generator on engine
- turns motor
- Motor turn magnets inside a cup. Creating Torque
- Gearing reduces torque to guage.
What does the Pitot Tube measure?
Both static and dynamic pressure.
How does the airspeed indicator work?
Using a capsule that is exposed to Static Pressure.
Because Pitot = Dynamic + Static - using static means you only get dynamic
What are the 4 errors for Airspeed indicators?
- Compressibility - Over 300 kts and/or high altitude. The air is compressed.
- Density - less dense = lower reading
- Instrument - imprecisions on manufacturing
- Position Error - disturbed airflow over Static and Pitot
The IAS is calibrated for ISA at sea level.
How and why does density affect the airspeed indicator
High altitude means less air which means less pressure and a lower reading.
However - this is useful, because it measures ‘what the plane feels’.
It is not useful for navigation - we need the TAS.
What is the impact of position errors for Airspeed Indicator
Error range
The airspeed indicator has a +/- 2 knts variation, depending on speed and other factors.
Manuerviours usually has a low impact.
How are errors and corrections applied from ASIR -> IAS ->CAS -> EAS -> TAS?
ASIR + Instrument correction ( flight manual ) = IAS
IAS + Position Correction ( flight Manual ) = CAS
CAS+Compressibility Error = EAS ( only used for design )
EAS + Density Error = TAS ( use EB 6 )
IPCD
What happens to IAS if there is leak in the Static source
Two impacts
If cockpit is unpressurised, it will over read.
If cockpit is pressurised, it will under read
What will a blockage in the Pitot Tube do?
Depends on where.
If it is ahead of the drain, the airspeed will fall to zero.
If it is behind the drain, air is trapped and it will get stuck.
What happens to airpseed if the static tube gets blocked?
No affect at same altitude.
On Desent - overread
On ascent - under read
This is bad… because coming into land it will over read.
Other indications is a stuck altitmeter.
For the Altimeter what is Hytersis Error?
The capsule does not match the atmospheric curve exactly.
Therefore it will over read on ascent and under read on descent
For the Altimeter - what is lag?
The capulse and gearing does not respond immediately. This is different from Hytersis error.
The lag is worse at high rates of altitude change
How does Barometric error affect Altimeter
(incorrect QNH setting)
High to low, lookout below.
The plane will follow the pressure line ( as the pilot is keeping the same indicated altitude )
How does a VSI work?
Instant pressure change to the capsule.
Lag pressure change to the case
VSI errors are?
4 of them
Instrument error
Static Source (Position) Error
Lag Error
Manuover Error
How does a Instaneous VSI (IVSI) work? ( and differ from VSI )
Contains accelerometers vacuum air pumps which reduces the lag, ideally to zero.
The Dashbot pistion is affected by G forces - so it pushes air into our pulls air out of the diaphram ( aneroid ).
How is the compass constructed to deal with dip?
It is suspended, and place in fluid. The magnet and the card are floating.
When accelerating east or west in the southern hemisphere - what will the compass show ( and why )?
SAND
South Accelerate
North Declerate
This occurs because the magnitic dip means that the CG is slightly north when the compass is in the southern hemisphere
How many transmitters does a GPS satelite have?
Two
L1 - Civilan ( C/A ) and Precision ( P)
L2 - Precision
For GPS - what is Uplink and what is it used for?
The Master station transmits corrections to the satilete ( time and location )
These are calculated from the earth bound stations.
How many satelites in the GPS constellation
4 per orbit
6 orbits
which is 24 satelites.
3 are backups - this ensures at least 4 any where on the planet at any time.
What is in the Nav Signal from a GPS satelite?
Clock and Propergation Errors
Empheriss ( location of this satelite )
Special Messages
Satelites Emphersis ( location of all satelites )
What is the accuracy of GPS ( with and without Selective availabiltiy )
If SA is OFF - 30m.
With SA.
100M with 95% prob
200M with 99% prob
How does a reciever deal with satelites that are low on the horizon?
If they are low, the path propegation estimation will be less accurate, due to the volume of atmosphere.
Therefore - that satelite is discarded.
What transponder information does TCAS require?
Mode S - Sierra. It needs position and altitude to be able to provide RAs ( resolution advisories )
What is a Traffic Advisory (TA) vs Resolution Advisory (RA)
Traffic Advisory is at 30 seconds or more. Trigger pilots to look for other aircraft
Resolution Advisory will tell the pilot to climb or descend - and is triggered at 20 - 30 seconds of potential collision. ATC is notified as well.
For an RA the pilot:
MUST perform the action
Inform ATC
