Definition
A thrust-augmentation method used on vectored-thrust turbofan engines in which extra fuel is injected and burned in the cold-bypass airflow inside the plenum chamber ahead of the forward (cold) nozzles. The added combustion increases the velocity of the bypass air leaving the front nozzles, producing additional thrust for short takeoff and vertical landing operations.
Plain English
It is an afterburner-style boost, but applied to the cool air going to the front nozzles of a vectored-thrust engine instead of to the hot exhaust. Burning extra fuel in that cool airflow makes it shoot out faster, giving the aircraft more lift and thrust when it needs it.
Context Anchor
Seen in turbine engine and powerplant maintenance discussions about thrust-increase systems and unusual engine fuel-burning arrangements.
Derivation
‘Plenum’ comes from the Latin plenus, meaning ‘full.’ A plenum chamber is a space inside the engine kept ‘full’ of pressurized air — in this case, the cold bypass air being routed to the forward nozzles. ‘Burning’ refers to igniting fuel in that chamber to boost thrust.
Why Pilots Care
PCB is what allows certain vectored-thrust aircraft to generate the extra thrust needed for vertical or short takeoffs and landings. Understanding it helps explain why these engines have additional fuel systems and why their forward nozzles can produce hot exhaust during high-power operations.
Intuition Check
Do not read PCB as ordinary burning in the engine’s main combustion section. In this term, the key point is that extra fuel is burned in a plenum chamber to increase thrust.
Example Sentence 1
Plenum chamber burning gave the engine the additional thrust needed for vertical takeoff with a heavy weapons load.
Example Sentence 2
PCB provides extra thrust for takeoff without requiring a full afterburner installation.