Definition
The drag produced by a turbine engine as it captures and accelerates outside air into its inlet. Because the incoming air must be slowed and turned to enter the engine, its forward momentum acts as a rearward force on the airframe. Ram drag is subtracted from the engine's gross thrust to determine net thrust.
Plain English
It is the resistance an engine creates just by scooping in the air it needs to run. Pulling that air on board takes effort, and that effort shows up as a backward pull on the aircraft.
Context Anchor
Seen in turbine engine thrust and performance discussions, especially when comparing gross thrust with usable thrust in flight.
Derivation
Ram' comes from the idea of forcing or driving something forward, as in a battering ram. Air is being 'rammed' into the engine inlet by the aircraft's forward motion, and the cost of doing that shows up as drag.
Why Pilots Care
Ram drag reduces net thrust at higher speeds and must be accounted for when calculating available engine performance.
Intuition Check
Do not think of ram drag as ordinary outside drag on the airplane’s skin or shape. Here, it means the thrust lost because moving inlet air already has momentum before the engine accelerates it.
Example Sentence 1
At higher airspeeds, ram drag rises, so the engine's net thrust is lower than its gross thrust.
Example Sentence 2
Engine performance charts subtract ram drag from gross thrust to show usable power in flight.