Definition
A piston engine in which all cylinders are arranged in a single straight row along the crankshaft, rather than being opposed, in a V-configuration, or radial.
Plain English
An engine where the cylinders sit in one straight line, one after the other, instead of being spread out in other patterns.
Context Anchor
Seen when comparing aircraft engine types, aircraft descriptions, or basic aircraft systems in ground training.
Derivation
From 'in line,' meaning arranged along a single line. The name simply describes the layout: cylinders sitting in a row along the crankshaft.
Why Pilots Care
Inline engines create a narrow nose profile that reduces drag but can complicate engine cooling in flight.
Intuition Check
Inline does not mean the engine is lined up with the runway or simply mounted straight in the airplane. Here, it means the cylinders are arranged in one straight row.
Example Sentence 1
The trainer's inline engine had four cylinders arranged in a single row along the crankshaft.
Example Sentence 2
Many early trainers used inline engines because they fit easily into the fuselage.