11.5.1 - Instruments Flashcards
What instruments need pitot and static pressure and which need static pressure only?
Altimeter - static pressure only
Vertical Speed Indicator (VSI) - Static pressure only
Airspeed Indicator - Pitot and Static pressure
Mach Indicator - Pitot and Static pressure
Where are pitot probes and static ports located?
Pitot probes are located outside the aircraft pointing directly into the relative airflow. (RAM air pressure to measure airspeed indicator)
Static ports are located on either side of the fuselage or vertical fin or even small holes in the pitot-static head.
(Still or static air to measure VSI, altimeter & airspeed indicator)
What type of device measures pressure on an Air-Data computer?
Air Data Module convert pitot or static pressure into digital output signals.
What metal is used on a T.A.T?
(T.A.T = Total Air Temperature probe)
The temperature dependant resistor (thermistor) is made of platinum
What pressure source does an altimeter use?
Static port pressure source
Explain QNH
QNH is when an altimeter is set to measure altitude above the existing mean sea level pressure level of that region.
(Also known as indicated altitude)
Explain QFE
QFE shows the local baro-pressure of the airfield.
An aircraft on the ground at this airfield will have an altimeter reading of 0.
Explain QNE
STD (Standard) or QNE is an altimeter set to measure altitude above a standard reference in order to maintain clearance.
Standard reference = 1013.25 HPa or 29.92 inches of mercury
Explain Altitude, height & elevation
Altitude is the vertical distance between sea level and the aircraft. Barometer set to QNH
Height is the vertical distance between aircraft and the terrain. Barometer is set to QFE
Elevation is the vertical distance from sea level to the airport or terrain.
Explain the major difference between an altimeter and a Vertical Speed Indicator.
The Vertical Speed Indicator has as it’s operating mechanism a bellows, or pressure capsule, similar to that of an altimeter
Except that rather being evacuated and sealed, it is vented to the inside of the instrument case through a diffuser which is an accurately calibrated leak.
What parameter does a Vertical Speed Indicator use?
Static Port Pressure
What parameters does an Air Speed Indicator use?
An airspeed indicator is a differential pressure gauge that measures the difference between the pitot and the static pressure.
What are I.A.S, T.A.S and G.S?
I.A.S = Indicated AirSpeed and is the uncorrected reading of an airspeed indicator
T.A.S = True AirSpeed and is the Calibrated Airspeed (CAS) with a correction applied to temperature and altitude
G.S = Ground Speed represents the actual speed of the aircraft over the ground. It is true airspeed adjusted for wind. A headwind decreases groundspeed while a tailwind increases it.
Explain TAT and SAT.
TAT = Total Air Temperature and is the temperature of the compressed air against the flying aircraft. Higher speeds will cause TAT to be higher. Used for power setting of engine.
SAT = Static Air Temperature and is the temperature of the undisturbed air around the aircraft. The Air Data computer reads the TAT and uses MACH number to equate SAT.
As altitude increases and I.A.S stays the same, what is happening to T.A.S?
T.A.S (True Airspeed) increases
i.e at 10,000 ft I.A.S = 400 kts, T.A.S = 450 kts
What is the purpose of a barber pole?
Aircraft whose maximum speed is limited by structural
considerations have their never-exceed speed marked by a fixed red line on the dial of the airspeed indicator.
But if the maximum speed is limited by
the critical Mach number, the fixed red line is replaced by a red pointer (Barber pole) that is driven as a function of altitude.
What parameters are needed to calculate Mach?
Mach number = Speed of aircraft / Speed of sound
Speed of sound is dependant on temperature which changes with altitude. As altitude increases, temperature decreases and speed of sound also decreases
(Speed of sound is speed at which small pressure disturbances move through the air, easier when air it hot)
Mach meter is connected to the pitot probe and static port.
List the devices used to detect a stall
Electrically operated vane on leading edge of wing (stall indicator only)
Slotted probe sticking out side of fuselage (angle of attack indicator)
vane that senses angle between longitudinal axis and airflow (angle of attack indicator)
What is a vertical gyro used to indicate?
Roll and pitch signals
-Artificial horizon
autopilot
flight director
Weather Radar Antenna Stabilisation
What is the purpose of a Directional Gyroscope?
A directional gyroscope along with a magnet compass indicate heading.
In large commercial transport category aircraft what is an auxiliary pitot/static system used for?
The auxillary pitot-static system is used for the autopilot, yaw dampers, overspeed warning system, flight recorder, two flight directors and the reference for cabin differential pressure.
What instruments use air from the static probes?
The altimeter, airspeed indicator and vertical speed indicator
What is the function of the Air Data Modules(ADM’s)?
The function of the ADM is to convert pitot or static pressure into digital output signals.
What altimeter altitude setting is used by aircraft at their cruising height?
Pressure altitude or Flight level is used (STD or QNE). It is an altimeter altitude setting above a standard pressure level which may be above or below mean sea level, usually 29.92 inches of mercury or 1013.2 mB or HPa
Explain the difference between altitude and height.
Altitude is the vertical distance between an aircraft and sea level (QNH)
Height is the vertical distance between an aircraft and the terrain (QFE)
What changes happen to true airspeed with increasing altitude?
Under non-standard sea level atmospheric conditions, A correction for the temperature and altitude is applied to the calibrated airspeed (CAS) which is normally done by a computer.
What is the ‘Barber pole’ in an airspeed warning indicator?
If an aircraft’s maximum speed is limited by it’s critical Mach number, as Mach number varies with increasing altitude, a red pointer or ‘Barber pole’ is driven as a function of altitude and indicates the maximum speed.
What are the inputs to a Central Air Data Computer and what does it output to?
The Central Air Data Computer (CADC) inputs include pitot and static pressures, baro setting, angle of attack and total air temperature.
The outputs of the CADC include autopilot, instruments, displays and navigation systems.
Name a problem encountered by laser gyros and how is it prevented?
Laser lock-in which is where the two light beams get coupled together at low rotation rates.
This is prevented by a dither motor which helps prevent the loss of information at these low rates by vibrating the gyro assembly.
What does an Inertial Navigation System(INS) measure and what information does it need to work?
The Inertial Navigation System (INS) measures the reaction forces of the various accelerations.
The information it needs to work are the initial starting location of the aircraft in terms of latitude and longitude which are inputted into the computer.
A pneumatic altimeter contains:
They have an electronic device in them that sends a digital code to the radar beacon transponder.
The barosetting is QNH. After landing the altimeter shows the:
The elevation
(altitude of airport above mean sea level)
During cruise flight the altimeter setting is:
QNE or STD (Flight level)
Which is the vertical distance between the aircraft and some set reference point that may be below or above mean sea level (29,92 inches of mercury or 1013.25 HPa)
The pneumatic vertical speed indicator needs the ______ pressure.
Static pressure
What changes happen to true airspeed with increasing altitude?
It increases
