Definition
A small metering tube inside the propeller dome of a constant-speed turboprop propeller that meters oil pressure to control blade angle when the propeller is operating in the beta range (ground operations below the flight idle blade angle, including reverse). It mechanically follows the position of the power lever and feeds back blade angle to keep the blades at the angle the pilot has selected.
Plain English
A sliding tube inside a turboprop's propeller hub that lets the pilot directly set the blade angle for ground handling and reverse thrust, instead of letting the governor decide.
Context Anchor
Seen in turboprop propeller systems, especially in maintenance descriptions of beta control, ground idle, and reverse thrust operation.
Derivation
The word 'beta' is the second letter of the Greek alphabet and is used in propeller systems to label the second mode of operation. 'Alpha' range is normal in-flight governing; 'beta' range is direct blade-angle control on the ground. The tube takes its name from the range it serves.
Why Pilots Care
It prevents engine or propeller damage by confirming the correct blade angle before reverse thrust is applied.
Grounding Statement
The beta tube is a feedback part: it helps the propeller control system match actual blade position to the position being commanded.
Intuition Check
Beta does not mean a test version of something here. In this context, beta refers to the propeller blade-angle control range used mainly for ground operation and reverse thrust.
Example Sentence 1
During the post-flight inspection, the mechanic checked the beta tube for proper rigging after the crew reported sluggish reverse thrust.
Example Sentence 2
Maintenance checked the beta tube after the propeller failed to enter reverse during rollout.