Definition
An engine oil tank with an internal compartment, called a hopper, that holds a smaller portion of the total oil supply. Oil returning from the engine is routed first into the hopper, where it circulates back to the engine before mixing with the rest of the oil in the main tank. This design allows a smaller volume of oil to warm up quickly to operating temperature, with the remaining oil acting as a reserve.
Plain English
An oil tank with a small inner section that lets a portion of the oil heat up fast, while the rest of the oil sits in the main tank waiting its turn.
Context Anchor
Seen in aircraft engine lubrication system descriptions, especially when learning how external oil tanks manage oil temperature and supply.
Derivation
The word hopper comes from the funnel-shaped containers used in mills and grain storage, which feed material from a larger holding area into a smaller working area. The oil tank uses the same idea: a small inner compartment is fed from, and feeds back to, a larger surrounding tank.
Why Pilots Care
Ensures reliable oil circulation and reduces engine wear during cold-weather starts.
Analogy
Think of it like a small cup inside a larger bucket. The engine drinks from the small cup first, and the returning warm oil refills that cup before the rest overflows into the larger space.
Intuition Check
Do not read “hopper” as just the outside tank or the filler opening. Here it means the smaller inner section of the oil tank that receives return oil first and feeds the engine outlet.
Example Sentence 1
The radial engine's hopper-type oil tank allowed the pilot to begin taxi sooner on cold mornings because only the oil in the hopper had to reach operating temperature first.
Example Sentence 2
Mechanics prefer a hopper-type oil tank on radial engines because it speeds oil warm-up and protects bearings on startup.