Definition
A jet engine exhaust nozzle operating in a condition where the gas flow at the narrowest point (the throat) has reached the local speed of sound and cannot accelerate further at that point, regardless of any further increase in upstream pressure. Once choked, the mass flow through the nozzle is fixed by the throat conditions, and any additional thrust gain comes from pressure differences downstream rather than from faster flow at the throat.
Plain English
An engine exhaust opening where the gases are moving so fast they have hit the speed of sound at the narrow part. At that point, you cannot push more flow through that opening just by adding more pressure behind it.
Context Anchor
Seen in jet engine and high-performance airplane discussions, especially when describing exhaust flow, thrust, and fixed exhaust nozzle design.
Derivation
‘Static’ here refers to a fixed-geometry nozzle (one whose shape does not change). ‘Choked’ comes from the everyday sense of being blocked or restricted — the flow has reached its physical speed limit at the throat and cannot be ‘pushed’ any faster.
Why Pilots Care
When a nozzle is choked, the engine no longer responds to throttle input the way a pilot might expect at lower power. Mass flow is capped, so further thrust changes come from pressure and temperature effects rather than from more air moving through. Understanding this helps explain thrust behavior at high power and high altitude.
Grounding Statement
Imagine a garden hose where the water at the nozzle tip has reached its top speed — squeezing the tap harder does not make it shoot out faster at that point; it just builds pressure behind the restriction.
Intuition Check
Do not read static as static electricity, and do not read choked as clogged or blocked. Here, static means fixed in size, and choked means the gas flow has reached its maximum through that fixed opening.
Example Sentence 1
At high thrust settings, the engine's exhaust reaches a static choked nozzle condition, meaning the flow at the throat is sonic.
Example Sentence 2
Performance charts assume a static choked nozzle when calculating initial takeoff thrust for this powerplant.