11.5.1 Instruments- Pitot Static Flashcards
What are the five types of aircraft instrumentation?
Pressure
Gyroscopic
Compasses
Mechanical
Electronic
What covers the certification for aircraft instruments?
CS25.1303
What are the four categories of aircraft instrument?
Flight
Engine
Navigation
Other
What are the primary flight instruments?
Attitude
Altitude
Airspeed
Direction of flight
Navigational instruments gauge factors such as?
Path of flight
Ground prox warning
Weather avoidance
What is the basic T?
The standard layout of instruments
What instruments are part of the basic T?
Airspeed Indicator (ASI)
Attitude Directional (ADI)
Altimeter
Horizontal Situation (HSI)
What does the Airspeed Indicator display?
Shows a speed which is a reference for all aerodynamic parameters
What is the attitude directional indicator?
Shows the roll and pitch attitude of the aircraft in relation to the horizon.
What does the horizontal situation indicator?
Shows the direction of the aircraft’s longitudinal axis in relation to the magnetic north.
When was the basic T first used?
Early 1950’s
What may you find adjacent to the basic T?
Turn coordinator and vertical speed indicator.
What are the three basic ways of measuring pressure?
Absolute
Gauge
Differential
How does absolute pressure measure?
Compares atmospheric pressure against zero
What can atmospheric pressure be measured in?
InHg (inches of mercury)
hPa
PSI
What is the most commonly used type of pressure gauge?
Gauge
What is gauge pressure?
The contained pressure vs atmospheric e.g. tyre pressure
What instruments use a bellow or diaphragm?
Altimeter
VSI
Machmeter
Cabin pressure
Manifold pressure
What types of pressure sensing elements are there?
Bourdon
Aneroid
Pressure Transducer
How does the bourdon tube work?
A copper, bronze or brass tube rolled into an elliptical cross section that distorts when the pressure increases.
What is a direct reading pressure gauge?
Similar to a bourdon used in general aviation aircraft.
What is a pressure transducer also called?
Pressure transmitter.
What is a pressure transducer?
A sensor that converts pressure into an analogue electrical signal.
What is the advantage of pressure transducers compared to the other systems?
The pressure can be measured at source and not brought all the way to the flight deck.
What does LVDT stand for?
Linear Variable Differential Transformer
What is Wheatstone bridge system?
Used to measure strain in a pressure system.
What are the two types of strain gauges?
Foil strain
Silicon based
What are pitot-statics used for?
Airspeed, Altitude and rate of climb.
What is the pitot tube named after?
Henri Pitot a french scientist.
What does the static system give information too?
Altimeter, ASI and vertical speed indicator.
Where are static ports located?
Where there is smooth airflow.
What is SSE?
Static source error.
What does SSE depend on?
Fuselage shape and the airspeed.
What do modern computers do with SSE?
Automatically calculate a correction factor to compensate for SSE.
When an aircraft has higher static pressure on one side of the fuselage than the other for example during side slip what device helps equalise the pressure?
Cross-porting tube.
What do pitots have to avoid ice build up?
Heaters
What is the diameter of the pipeline related too?
The distance between the pressure source and the instruments to eliminate pressure drop and time lag factors.
What are drain taps designed to do?
To have enough capacity to hold the max water that could enter a system between servicing.
What safety improvement does the static system have?
Alternate system.
If a pitot becomes blocked, the dynamic pressure will become trapped, what will happen at altitudes above where the pitot tube became blocked?
ASI displays a higher than actual airspeed that increases steadily in line with altitude.
When carrying out a leak test on the static system what should the climb rate not exceed?
4000ft per minute
What is QNH?
Atmospheric pressure at sea level
What is QFE?
Atmospheric pressure the airfield level.
What is QNE?
Pressure level of 1013 hPA
What are Q codes?
They provide a succinct and accurate way to communicate.
What does QNH stand for?
Question nil height
What does QFE stand for?
Question field elevation
What does QNE stand for?
Question nil elevation.
When is QNH used?
Below the transition altitude.
What is flying above the transition altitude referred too as?
Airways flying
Western countries use feet to measure altitude, what countries use meters?
Russia and china
Because of the pressure lapse rate (non-linear pressure changes) what type of gauge allow linear expansion?
Aneroids due to their corrugated design.
What is a rad alt?
Radio altimeter
Some aircraft use altimeters with additional bellows and electrical connectors what are they called?
Encoding altimeters.
What do the three pointers on an altimeter show?
Long- 1000ft
Short- 10,000ft
Triangle mark- One turn per 100,000ft
How does a rad alt work out the altitude?
Half the time it takes x speed of the pulse (speed of light)
At 18,000 feet what percentage is the pressure of that at sea level?
50%
At 36,000 feet what percentage is the pressure of that at sea level?
25%
At 54,000 feet what percentage is the pressure of that at sea level?
12.5%
What does an evacuated capsule do?
Expands as static pressure decreases with an increase in altitude.
At sea level what is the change in static pressure with altitude?
1mb = 30ft
At 20,999ft what is the change in static pressure with altitude?
1mb = 50ft
When the temp exceeds the standard ICAO limits how many feet are added per degree Celsius exceeded?
118.8ft
What is hysteris?
The lag in mechanical altimeters due to the friction in the bearings and linkages.
What conditions trigger the fail safe in an altimeter?
AC failure
Servo motor fail
Amplifier fail
Circuit fail
What is the VSI also known as sometimes?
ROC, Rate of Climb
In a VSI what two parts give compensation?
Orifice and Capillary type
Ceramic type
What material must be used for orifice type?
Rigid and non rusting.
What is the flow through a orifice?
Turbulent
What happens if you combine orifice and capillary types?
Calibration of the airflow.
What is the wall thickness of the capsule inside a vsi?
0.076mm
Which type of VSI display is more accurate a lower rates of descent?
Logarithmic.
Where is VSI located on an EFIS basic T?
Right hand side
How is an IVSI (Instantaneous VSI) ran?
If an aircraft has an inertial reference system.
What does an IVSI use to eliminate lag?
Accelerometer unit.
In an IVSI what is the vertical accelerometer unit called?
Dashpot
During a climb what does the IVSI dashpot do?
Fall
On modern aircrft where is the VSI displayed?
The PFD
What is the CADC?
Central Air Data Computer
What are the two types of pressure sensor?
Absolute- Static
Differential- Pitot
What are the three common pressure sensor designs?
Piezoresistive
Bonded Strain
Capacitive
What is the Piezoresistive connected too?
Wheatstone bridge.
What is the Piezoresistive effect?
A change in electrical resistance of a semi-conductor when mechanical strain is applied.
How does the Piezoresistive element work?
Applied pressure bends the diaphragm which results in a bridge imbalance causing a few millivolts to be unbalanced.
What is the bonded strain gauge based on?
Piezoresistive elements however they are used for larger strain measurements.
What makes bonded strain gauge preferable?
It is cheaper than Piezoresistive.
What is a capacitive sensor?
Very accurate low pressure sensing device.
What is a nautical mile equal too?
6080ft (1.15 miles)
How are ASI’s modified to expand the scale at low speeds and compress at high speeds?
Banana slots and ranging springs.
What principle are ASI’s based around?
Bernoulli’s
On an ASI what do the red radial lines indicate?
Max and min limits of airspeed.
On an ASI what does the yellow arc indicate?
Precautionary ranges, operation is only permitted in smooth air and with caution.
On an ASI what does the green arc indicate?
Normal operating range.
On an ASI what does the white arc indicate?
Ranges in which the flaps can be lowered
What is Vso?
The stall speed in landing config
What is Vs1?
The stall speed in clean config.
What is Vfe?
The max speed with flaps down
What is Vno?
Max airspeed for cruise
What is Mmo?
Limit designed to prevent aircraft from shockwave damage
What is Vmo?
Structural limit of dynamic pressure.
What is IAS?
Indicated airspeed, read directly from the ASI.
What is TAS?
True airspeed or Knots True airspeed, speed of the aircraft relative to the air mass through which it is flying.
What is density error?
Where the ASI is calibrated to give IAS the same as TAS at sea level but less as it climbs.
What is position error?
The difference between the calibrated airspeed and the IAS, due to the recorded static being unequal to the ambient pressure.
