Pressure Instruments

Three instruments rely on your two pressure tubes.

The airspeed indicator (ASI), vertical speed indicator (VSI) and altimeter.

The pitot and static tube are located outside of the cockpit, generally very close together out on a wing or on the fuselage away from the thrust of the propeller.

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The static tube has a hole in the side of the tube that is not affected by airspeed. This measures atmospheric pressure.

The pitot tube has a hole directly facing into the oncoming airflow. This measures the dynamic pressure, the same as you would feel pushing your hand back if you held it out the window. Make sure you cover your pitot tube to avoid bugs making a home in them and blocking it.

pitot

Note the big red flag, it is labeled “Remove Before Flight”

The altimeter uses the static pressure to determine altitude. The altimeter simply increases by 30 feet for every 1 hPa decrease. We tell it what the references point for AMSL is on the dial and it calculates our height based on how many hPa we are away from AMSL

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The ASI uses total press which is the sum of pitot and static pressure. This determines our airspeed indicated on the ASI.

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The VSI measures how fast the static pressure is changing, to indicate how fast we are climbing or descending.

vsi