spool up

1. To wind up onto a spool.

2. To increase in rotational speed, producing an increase in thrust.

   The large rotational inertia of the heavy compressor and turbine rotors makes the engine slow to spool up from idle.

3. (figuratively)To be brought into full operation; to reach full potential or capacity.

   Near-synonym: spin up

irregular

• spool upTo wind up onto a spool.
• spool outTo appear in succession, as if from a film spool.
• spool downTo decrease in rotational speed, producing a decrease in thrust.