Aerodynamic Flashcards
- What 3 types of instrument in an aircraft?
➢ Pressure instrument, which use variation of atmospheric pressure
➢ Gyroscope using the properties of gyroscope
➢ Compass system sense the earth’s magnetic field
- What is Basic T?
➢ Airspeed Indicator (ASI)
➢ Artificial Horizon Indicator (AHI)
➢ Direction Indicator / Directional Gyro (DI)
➢ Altimeter (ALT)
- What are pressure flight instruments
➢ Altimeter, Vertical Speed Indicator, Airspeed Indicator are pressure flight instruments
- How does ASI/ VSI/ ALT works in principle?
ASI
➢ Total pressure can be measured by the pitot tube
➢ The static pressure can be measured by the static port
➢ Dynamic pressure can be calculated by the difference of total pressure and static pressure
➢ Dynamic pressure represents the airspeed in knots per hour
➢ There is a flexible diaphragm separate the total pressure and the static pressure
➢ The movement of the diaphragm drive the pointer to move via mechanical lever
➢ If I am requested to draw the ASI
➢ Must indicate 5 speed: VSO (Stall Speed at max weight, landing gear down, flap down, power off), VS1( Stall Speed at max weight, landing gear up, flap up, power off), VFE, VNO (Maximum Structure Cruising Speed), VNE
Altimeter
➢ The ambient pressure is directly related to the altitude of the aircraft
➢ The higher the altitude, the lower the pressure
➢ As the aircraft climb, the static pressure in the instrument decreases, this make the enclosed capsule to expand and drive the pointers, via mechanical linkage
Vertical Airspeed Indicator
➢ VSI measures the rate of change of static pressure and present in rate of climb or rate of descend
➢ When the aircraft is descending, the aircraft move to higher pressure
➢ The new and higher pressure at the lower level is fed directly from the static vent into a flexible capsule.
➢ The same pressure is also fed into the casing that surround this capsule, but via a smaller hole
➢ Therefore, the flexible capsule expand to drive the pointer to move via mechanical linkage
- What impacts on ASI/ VSI/ ALT if static port is blocked?
➢ ASI: When aircraft remain in the same flight level, the ASI is showing the right airspeed
➢ When aircraft is climbing => The IAS is under-read
➢ When aircraft is descending => The IAS is over-read
➢ ALT: The altimeter will show the altitude where the static port is blocked, the reading in altimeter will not change
➢ VSI: The VSI can read zero rate of climb and rate of descend
- For ASI, if the ram air input and the drain hole is blocked, what will be the reading of ASI?
➢ The ASI would act as uncelebrated altimeter
➢ Since the total pressure unchanged and the static pressure is changing
- For ASI, if the pitot tube and the drain hole are blocked, what will be the reading of ASI?
➢ The total pressure in pitot tube is constant
➢ When the aircraft is climbing, the airspeed indicator increases
➢ When the aircraft is descending, the airspeed indicator decrease
➢ It is like uncelebrated altimeter
- Tell me the error of ASI
➢ Instrument Error, friction exists in the moving part of the ASI, no more than one to two knots
➢ Density Error: the ASI is calibrated to read correctly in ISA condition
When the density is lower, the ASI underread
When the density is higher, the ASI overread
➢ Block pitot and static system
- Tell me the error of Altimeter
➢ Instrument Error, friction exits in the moving part of the Altimeter
➢ Temperature, keeping the same altimeter reading, flying to cold region, the aircraft actually fly lower than indicated altimeter
➢ Block static system
- What is position pressure error?
➢ Variation of static pressure near the source is called the position pressure error
- Tell me what is the temperature error?
➢ In real life, assume we can always adjust the QNH
➢ If the temperature is lower than ISA, the altimeter will over read
➢ If the temperature is higher than ISA, the altimeter will under read
- What if we cannot adjust the QNH?
➢ The altimeter reading will not change
➢ But the airplane is flying in a lower true altitude
- What if pitot is blocked?
➢ ASI: If the pitot tube is blocked and the drain hole open
➢ The pitot pressure is equal to ambient pressure
➢ The indicated airspeed drop to zero
➢ If the pitot and the drain hole is blocked
➢ The pitot pressure measure if unchanged
➢ It changes according to the static pressure when the aircraft change its altitude
➢ VSI and ALT is unaffected, since they used the static port to measure the performance
- How can we prevent icing of pitot-tube?
➢ Switch on the pitot heater to melt the ice
- How many pitot tubes does a commercial jet usually has?
➢ There is 3 pitot tubes for B777 and A330
➢ Two is used for two ASI in two pilots seat respectively
➢ One is for emergency used
