A jet engine is often built with multiple independent rotating sections to improve efficiency at different speeds. Each of these sections is called a spool. The high-pressure spool connects the high-pressure turbine directly to the high-pressure compressor via a hollow shaft. A low-pressure spool runs through the centre of that hollow shaft, connecting the low-pressure turbine to the fan and low-pressure compressor.
We need to check the bearing clearances on the high-pressure spool before we button up the core.
Engines are typically classified by their number of spools. A twin-spool design is standard for commercial turbofans, while some high-bypass engines use a three-spool architecture to optimize the speeds of the fan, low-pressure, and high-pressure sections.
Related terms
Core lock
The mechanical seizure of a jet engine caused by unequal cooling of its internal components.
Blisk
A single engine component consisting of a rotor disk and blades machined from one solid piece of metal.
Gas generator
A gas generator burns propellant to create high-pressure gas that drives turbines or pumps.