Pitot Static Flashcards
Pitot static instruments
Airspeed Indicator
Altimeter
Vertical Speed Indicator
Altimeter
- Simply a barometer that measures static pressure of the air around the aircraft.
- Uses only the static pressure
Altimeter operation
- Aneroid wafer
- Stack of hollow, elastic metal wafers
- Expand and contract as pressure changes
Pressure window
Kollsman window
•Small adjustable subscale that allows the current altimeter setting to be set in
•Important to reset with current altimeter reading
•Above 18,000’ always set at 29.92
Pressure error
- Caused by not setting the current altimeter setting
* High to Low-Look out below, low to high plenty of sky
Altimeter density error
- Caused by change in temperatures, not all altimeters account for a change it temperature
- Temperature lapse rate slower in hot air, faster in cold air (standard lapse rate -2 degrees per 1,000 ft)
- Hot to cold = low, cold to hot = high
Airspeed indicator
- Displays the speed of the aircraft through the air
- Only instrument that uses both types of pressure
- Measures the difference between the two pressures
Airspeed indicator operation
- Instrument is contained within a sealed case
- Inside of the case is vented to the static port
- Pressure sensitive diaphragm
- Ram pressure line is connected directly to one side of the diaphragm
- Diaphragm expands and contracts in proportion to the difference between the two pressures
Position error
Occurs when the static port senses an erroneous static pressure
•Mainly caused by slipstream
Airspeed density error
Occurs when there is a change in the altitude or temperature that the instrument does not take into account.
Compressibility error
Caused by high speed packing of air into the pitot tube.
Vertical speed indicator
- Provides reference to rate of change
- Shows both rate and trend
- Uses only static pressure
VSI Operations
- Expandable Capsule (Diaphragm)
- Directly connected to static port
- Connected through mechanical linkage
- Calibrated Leak: Instrument Case’s connection to the static port- Allows capsule to change pressure more gradually
- Pressure inside of diapragm changes the same as the outside air
- Pressure in instrument case changes slower because of calibrated leak.
Blocked pitot
Airspeed- 0
Altimeter- works
VSI- works
Blocked pitot and drain hole, static open
Airspeed- high during climb, low during descent
Altimeter- works
VSI- works
