Definition
In a turbofan engine, the ratio of the air pressure leaving the fan to the air pressure entering the fan. It is a measure of how much the fan compresses the air it accelerates rearward to produce thrust.
Plain English
A number that shows how much the big fan at the front of a jet engine squeezes the air as it pushes it through. The higher the number, the more the fan is compressing the air.
Context Anchor
Seen in turbofan engine performance, engine design, and maintenance discussions.
Why Pilots Care
It indicates how effectively the fan contributes to engine thrust and fuel efficiency.
Analogy
It is like comparing water pressure before and after a pump. The ratio tells how much the pump increased the pressure.
Grounding Statement
Picture air entering the front fan of a turbofan engine and leaving it more tightly squeezed; fan pressure ratio measures that increase.
Intuition Check
Do not read this as the fan’s pressure by itself. It is a comparison: pressure after the fan divided by pressure before the fan.
Example Sentence 1
High-bypass turbofans typically have a low fan pressure ratio, which helps reduce noise and fuel burn.
Example Sentence 2
A higher fan pressure ratio improves thrust output at low speeds.