Definition
An engine oil system in which the oil supply is stored in a separate external tank rather than in the engine's crankcase. A scavenge pump removes oil from the bottom of the engine and returns it to the tank, while a pressure pump draws oil from the tank and circulates it through the engine.
Plain English
An engine lubrication setup where the oil lives in its own tank outside the engine, instead of pooling at the bottom of the engine itself. Pumps move the oil between the tank and the engine continuously.
Context Anchor
Seen in aircraft engine oil system descriptions, preflight oil checks, and discussions of how the engine is lubricated.
Derivation
"Dry" because the engine's sump (the bottom collection area) stays dry — oil is pumped out as soon as it drains down, rather than being allowed to collect there. Knowing this makes the name self-explanatory: the sump is kept dry on purpose.
Why Pilots Care
Prevents oil starvation and loss of lubrication during aerobatic or inverted flight and provides steadier oil pressure and cooling.
Analogy
It is like keeping water in a separate jug and pumping it through a small machine, instead of storing the water in the bottom of the machine itself.
Intuition Check
“Dry” does not mean the engine has no oil. It means the engine’s bottom collection area is not the main place where the oil is stored.
Example Sentence 1
Because the aerobatic trainer uses a dry-sump system, the engine continues to receive oil pressure during inverted flight.
Example Sentence 2
Before flight the pilot checks the oil quantity in the external tank of the dry-sump system.