Definition
An instrument used to measure the power output of an engine by applying a controlled load to the engine's output shaft and measuring the resulting torque and rotational speed. From those two values, brake horsepower can be calculated.
Plain English
A test device that measures how much power an engine actually produces. The engine drives the device, the device pushes back with a known load, and the resulting numbers show how strong the engine really is.
Context Anchor
Seen in aircraft engine maintenance, overhaul, and test-stand work when confirming engine performance.
Derivation
From the Greek 'dynamis' meaning power or force, and 'metron' meaning measure. So literally, a power-measurer — which is exactly what it does.
Why Pilots Care
Dynamometer testing is how an overhauled or newly built engine is verified to produce its rated power before it is released for service. If the engine cannot make rated power on the dyno, it will not make it in the airplane.
Intuition Check
A dynamometer does not make the engine stronger. It measures the power the engine is already producing under a controlled test load.
Example Sentence 1
After overhaul, the engine was mounted on a dynamometer to confirm it produced its rated horsepower before installation.
Example Sentence 2
After the overhaul, the rebuilt engine was run on the dynamometer before reinstallation.