Definition
A specially shaped tube that narrows in the middle and widens again at each end. As air flows through the narrow section (the throat), its speed increases and its pressure drops. In aircraft, a venturi tube mounted on the outside of the fuselage uses this pressure drop to drive air-powered gyroscopic instruments such as the attitude indicator and heading indicator on aircraft not equipped with an engine-driven vacuum pump.
Plain English
A tube with a pinched middle. When air flows through it, the air speeds up where the tube narrows, and the pressure inside drops. That drop in pressure can be used to power some flight instruments.
Context Anchor
Pilots may encounter venturi tubes in discussions of older vacuum-driven flight instruments, carburetors, and airflow-measuring systems.
Derivation
Named after Giovanni Battista Venturi, an 18th-century Italian physicist who studied how fluids behave when forced through a constriction. Knowing the name comes from the man, not from a Latin or Greek root, prevents the reader from guessing at a hidden meaning.
Why Pilots Care
The pressure drop allows precise fuel metering in carburetors and can generate vacuum to drive gyroscopic instruments.
Analogy
Think of putting your thumb partway over the end of a garden hose. The water speeds up as it squeezes through the smaller opening. A venturi tube does the same thing with air, and the speeded-up air leaves behind a drop in pressure that can be put to work.
Grounding Statement
Picture air entering a tube, squeezing through a narrow middle, and coming out faster, with lower pressure at the narrow point.
Intuition Check
A venturi tube is not just any tube. The important feature is the narrowed throat, because that shape is what makes the pressure drop.
Example Sentence 1
The trainer was equipped with a venturi tube on the side of the fuselage to drive the attitude and heading indicators.
Example Sentence 2
A venturi tube installed on the fuselage generates the vacuum required to spin the gyros in the attitude indicator.