Definition
A gas-turbine engine in which one compressor and one turbine are mounted on a single shaft and rotate together as one unit at the same speed. All compressor stages turn at one rpm, driven by all turbine stages on the same shaft.
Plain English
A jet or turbine engine built around just one rotating shaft. The compressor at the front and the turbine at the back are joined by that one shaft, so they always spin together at the same speed.
Context Anchor
Seen in turbine-engine theory, engine descriptions, and aviation maintenance discussions about engine construction and operation.
Derivation
‘Spool’ here refers to the rotating assembly of a compressor and turbine joined by a shaft — named for its spool-like shape. ‘Single-spool’ simply means there is only one such rotating assembly in the engine.
Why Pilots Care
Single-spool engines are simpler in design and common in smaller turbine aircraft, influencing throttle response and maintenance procedures.
Analogy
Think of one handle turning one connected set of parts. In a single-spool engine, the main rotating engine parts are tied together on one shaft rather than split into separate rotating groups.
Intuition Check
“Spool” does not mean a loose reel of thread inside the engine. Here it means a connected rotating shaft-and-rotor group.
Example Sentence 1
The early turbojets were single-spool gas-turbine engines, with one shaft connecting the compressor and turbine.
Example Sentence 2
Training materials compare the single-spool gas-turbine engine to multi-spool designs to show differences in rotational speeds.