Definition
In a reciprocating engine, the portion of crankshaft rotation during which more than one cylinder is delivering power to the crankshaft at the same time. Engines with more cylinders have greater power overlap, which produces smoother running because the power pulses blend together rather than arriving as separate, distinct pushes.
Plain English
It's the moment when two cylinders are both pushing on the crankshaft together. The more cylinders an engine has, the more often this happens, and the smoother the engine feels.
Context Anchor
Seen in twin-engine helicopter performance planning, especially when considering what happens if one engine quits during takeoff, climb, hover, or landing.
Derivation
Overlap comes from the everyday idea of one thing partly covering another. Here, the usable power range of one engine partly covers the power normally shared with the other engine.
Why Pilots Care
Power overlap contributes to smoother torque delivery and reduced vibration, which improves reliability and passenger comfort.
Intuition Check
Power overlap does not mean the engines physically overlap or that extra power is always being used. It means one engine has enough available power to cover part of the load normally carried by the other engine.
Example Sentence 1
The six-cylinder engine ran smoothly because its power overlap kept the crankshaft under constant driving force.
Example Sentence 2
Mechanics check firing order to confirm proper power overlap on the rebuilt radial engine.