Cockpit Flashcards
Evolution of cockpits
- With the introduction of early flight instruments, the pilots were able to determine their position along the desired route and assess the situation of the aircraft more efficiently and accurately.
- However, more instruments can lead to a higher complexity and may require more people to monitor them.
- Additional instruments were replaced with digital systems to reduce the workload and number of persons in the cockpit: Starting with two pilots, a flight engineer, a navigator and a radio operator, some crew members were replaced with automated systems, leading to the modern 2 pilot cockpit.
- With the introduction of digital displays and digital instruments, information could be displayed on different pages, prioritizing messages and warnings.
- The development to these new systems, however, lead to new problems with the design of the user interface and the usability of the overall system
Change of the tasks performed by pilots:
Transition from flying the aircraft to supervising aircraft systems
Flight envelope, flight envelope boundaries: Which ones exist?
Ma-h diagram -Stall limit n = 1 -Thrust limit T = D -Buffeting -Dynamic pressure limit -Temperature limit (MIL) V-n Diagram -Structural failure area -Structural damage area -stall speed 1g/ -1g(inverted)
Constrains issued by air traffic control that have to be adhered to:
Altitude, heading, course, vertical speed, navigation along pre-defined routes
which additional information can be taken into account:
- Weather: Wind, turbulences
- Traffic situation
- Altitude prediction
which parameters can be optimized
fuel consumption, time, noise and costs
Difference between classical flight instruments and state-of-the-art integrated systems
classical layout: 1 Sensor -> 1 instrument
state of the art integrated systems: sensors -> flight computer -> instruments
Layou tof the flight instruments
which parameter are shown
basic T; airspeed, altitude, artifical horizon, kompass/ils
Air data system: available sensors. What is directly measured?
Instruments using static and total air pressure:
Altimeter (ALT), Vertical speed indicator (VSI), Airspeed Indicator (ASI), Machmeter
Gyroscopic instruments:
Compass, Turn indicator / turn coordinator, Attitude Indicator, Directional Gyro, Slaved Compass
Radio instruments:
Radio altimeter
Modern digital instruments:
Primary Flight Display (PFD), Navigation Display (ND)
Categories of instruments
Instruments using static and total air pressure:
Altimeter (ALT), Vertical speed indicator (VSI), Airspeed Indicator (ASI), Machmeter
Gyroscopic instruments:
Compass, Turn indicator / turn coordinator, Attitude Indicator, Directional Gyro, Slaved Compass
Radio instruments:
Radio altimeter
Modern digital instruments:
Primary Flight Display (PFD), Navigation Display (ND)
Principle of temperature measurement, definition of SAT and TAT
Static air temperature (SAT or 𝑻𝒔):
The temperature of the undisturbed air through which the aircraft is about to fly (very hard to measure);
Total air temperature (TAT or 𝑻𝒕):
The maximum air temperature which can be attained by 100% conversion of the kinetic energy of the flight (impossible to measure, because the complete energy conversion is not possible);
Air data system: available sensors.What is directly measured?
- Pitot tube
- Static pressure sensor
- Angle of sideslip sensor
- Angle of attack sensor
- Total air temperature (TAT) sensor
- Static air temperature (SAT) sensor
Sources of error in the temperature measurement
•THERMAL CONDUCTION
A condition error may occur when the fuselage of the aircraft is at a different temperature than the sensor. This usually occurs on the ground during taxi conditions on hot summer days or in the winter.
•THERMAL RADIATION
When the total temperature being measured is relatively high, heat is radiated from the sensing element, resulting in a reduced indication of temperature.
•TIME CONSTANT
An instantaneous response by a sensor to a temperature change is impossible due to the heat capacity of the sensor parts and surrounding structure. This results in an indicated temperature/time transient. The time constant is a performance parameter typically used to describe this temperature/time transient.
•AIRFLOW DIRECTION
When the airstream approaches the inlet of a total air temperature sensor from a direction other than directly forward, errors may be introduced.
•SELF-HEATING
Total air temperature sensors which use resistance elements require that a small electrical current pass through the sensing element. This current causes a self-heating effect (I2R -Joule heating) which results in a small increase in the measured temperature.
•DEICING HEAT ERROR
For total temperature sensors with deicing heaters, application of the deicing heat can cause 𝑇𝑚to increase at low airspeeds. Basically, this effect is a conduction error, internal to the sensor, caused by the close proximity of heated portions of the sensor housing to the sensing element.
•AERODYNAMIC DRAG
Although the drag is not involved with the accuracy of total air temperature sensors, it can be important in trade-offs with other performance parameters. For example, deiced total air temperature sensors usually exhibit a higher drag than non-deiced sensors. The drag is influenced by the shape and size of the sensor and varies with the aircraft speed and altitude
Principles of altitude measurement
- The altimeter is a sealed pressure container, consisting of pressure capsules and a mechanical system. To display the altitude, the container is connected to the static pressure.
- Difference between static air pressure in the container and pressure in the capsules causes an expansion or contraction of the capsules.
- The lever and a (in the image simplified) mechanical system translates the movement into a rotation of the different pointers
formel Geopotential height
𝐻𝐺=𝑟𝐸⋅ℎ/𝑟𝐸+ℎ
Definition of QNH, QFE and QNE, explain by using drawings
QNH
•Air pressure with reference to the mean sea level (MSL) altitude
•Air pressure is a local setting, calculated for each station
•This setting is used for terminal flight phases and also for flights at low altitude(VFR Flights)
QFE
•Local air pressure at the station (usually the airport)
•Height above ground level (AGL)•Reference is the local station.
QNE
•Standard air pressure for navigation: “Flight Level”
•1013.25 hPareference pressure•In cruise almost all airplanes use this setting, to avoid changing the reference pressure (flights over oceans)
•Vertical separation is maintained if all aircraft use the same setting
Explain, Change of pressure altitude depending on temperature and pressure
Flying between different pressure zones, without correction of QNH:
•With the altitude depending on the local air pressure, a flight over a different pressured area changes the true altitude above ground
•When flying to a low pressure area, the true altitude is smaller than the shown altitude on the altimeter
Flying on same altitude with changes in ISA
•Altimeter is calibrated to standard ISA temperature
•With ISA deviations, the altimeter shows incorrect altitudes despite the correct QNH setting
•These changes in the temperature have to be taken into consideration especially in winter. With temperatures at a lower level than the ISA assumptions, it appears that obstacles and mountains are higher compared to summer time.
Varying the temperature 𝑇𝐴 on the surface (𝐻𝑀𝑆𝐿=0) from the standard ISA model leads to a change in the indicated altitude. The decrease of static pressure over altitude is getting bigger the cooler 𝑇𝑀𝑆𝐿becomes.
This gradient is the reason why with cooler temperatures the indicated altitude on the altimeter is bigger than the true altitude over ground
Principles of the vertical speed indicator
2 basic principles:
•Using the capillary action OR
•Using a second pressure container
Both principles measure the difference between the current static pressure and the static pressure a short period of time earlier. This difference in pressure Δpcauses the pointer to move.
How it works:
•Change in altitude causes a change in pressure p; In this example a decent is in progress so Δp> 0, for climb Δp< 0
•Due to the capillary effect, the rates of change are delayed, so the system is out of balance.
•The difference causes a force on the pressure capsule / flap which then displays a change in vertical speed on the instrument.
•Over time, the pressure difference Δpgets smaller if the plane stops changing altitude.
•The decrease in pressure difference causes the indicator to show a smaller rate of climb.
Principles of the speed indicator
- Static and total pressure from the pitot-tube, or 2 different pressure measurement probes
- Pressure capsules expand and contract depending on the total pressure.
- The mathematical equations are embedded in the mechanical system that drives the pointer
speed indicator arcs
White arc (from 𝑉𝑆𝑂to𝑉𝐹𝐸): Operation speeds with flaps extended Green arc (from 𝑉𝑆1to𝑉𝑁𝑂): Operation speed with flaps and gear retracted Yellow arc (from 𝑉𝑁𝑂to𝑉𝑁𝐸): Caution area: only in smooth air and without abrupt control inputs
Definition of the Indicated Airspeed (IAS)
Indicated Airspeed (IAS):
▪Speed actually measured with the pitot tubes
▪Used for flight operations (stall speed, maximum speed)
Calibrated Airspeed (CAS): ▪CAS corrects instrumentation errors of IAS due to wrong positioning of the static port. ▪Relationship between IAS and CAS is calculated by the manufacturer, typically shown in a look-up table
Equivalent Airspeed (EAS): ▪Compressibility is taken into account with increasing Mach ▪When flying with constant dynamic pressure EAS does not change with altitude ▪Used in research and engineering (flight envelopes)
True Airspeed (TAS):
▪Correction of density decrease with increasing altitude
▪EAS with additional compensations of density reduction due to altitude
▪Used for performance calculations (curve radius)
Conversion from CAS to EAS toTASto GS: Which effects are considered in each step?Which of them (CAS/EAS/TAS) typically has the largest value?
IAS->Error of device correction->CAS->Compressibilitycorrection->EAS->Density correction (due to altitude)->TAS
For low altitudes and speed (V<200kts, h<10000ft): CAS = EAS =/(ungleich) TAS
Computation of the Mach number depending on static pressure and total pressure (formula has to be memorized)
Starting with Bernoulli’s equation :
𝑝𝑡/𝑝0=(1+((𝜅−1)/2)+𝑀𝑎^2)^(𝜅/(𝜅−1))
The Mach number is: umgestellt
Gyroscopic instruments: Which instruments can be found inside the cockpit?
Attitude indicator (AI) Horizontal situationIndicator (HSI) Turn coordinator (TC)
Gyroscopic drift: Causes and description
External moments influence the alignment of the gyroscope
Drift proportional to the acceleration
•It is desired for a gyroscope that the center of gravity of the rotor and the center of suspension of the rotor coincide. However, this is not always the case.
•If an acceleration is applied to the gyroscope, the force in the center of suspension and the acceleration due to gravity in the center of gravity can lead to a misleading momentum.
•This effect is proportional to the acceleration that acts on the gyroscope.
Drift proportional to the square of the acceleration
•Even in a gyroscope with coincided center of gravity and center of suspension, an acceleration can cause a misleading momentum.
•An acceleration causes an inertial force which results in an elastic deformation of the system, which causes the points to shift.
•Due to the shift, the center of gravity and center of suspension do not coincide, which causes another momentum.
Dynamic drift
•An ideal gyroscope requires massless gimbals without any inertial moments. However, the real gimbal of any system has an inertial moment which is not aligned with the rotation axis, the system will be influenced with an additional misleading momentum.
•Dynamic drift causes a conical rotation of the rotation vector around the intended axis.
•This movement can be caused by a non homogeneous mass distribution of the rotating body.
…und noch mehr
Compass error during acceleration and turn
Turn errors
Positive acceleration when flying in north/south direction in a right turn
Positive acceleration when flying in eastern/western direction in a right turn
In order to compensate these errors, a simple principle can be followed to anticipate necessary corrections.
Example:
Turning on heading 330°
-Turn from West exit at 310°
-Turn from East exit at 350°Turning on heading 120°
-Turn from West exit at 110°
-Turn from East exit at 130°
Radio altimeter: Both methods of measurement:
Time measurement and phase shift:
- Zeit die das Signal braucht um reflektiert zu werden (Flugzeug-Boden-Flugzeug)
- A triangular dither waveform is modulated with a change in the frequency of 0,1 GHz. Instead of pulses, one continuous signal is generated and transmitted. The difference in modulation on the received signal is used to calculate the runtime.
The increase in frequency also leads to an improvement in accuracy
Engine instruments: Which values are typically shown?
Piston Engine:
•Engine rotational speeds (N)
•Temperatures
–Exhaust gas temperature (EGT)
–Cylinder head temperature (CHT)
•Manifold pressure•Oil pressure
•Oil temperature
•Fuel flow indication
Jet Engine:
•Engine rotational speeds (N1 and/or N2, N3 if applicable)
•Engine Pressure Ratio (EPR)
•Temperatures
–Exhaust Gas Temperature (EGT)
–Turbine Inlet Temperature (TIT)
•Oil pressure and temperature
•Fuel flow indicationPrinciples of the weather radar
The transmitter of the weather radar is placed under the nose cone (radome) of the fuselage. It sends out electro–magnetic waves and a part of this energy is scattered back by precipitation in the atmosphere. In order to provide the pilot with the best possible information the system calculates the intensity of the system based on the percentage of received energy. Inflight, the most dangerous kind of cloud is the cumulonimbus(CB) due to turbulences and heavy precipitation.
