When calculating propeller efficiency, what can the result never exceed?

When calculating propeller efficiency, the result is a measure of how effectively the propeller converts input power (typically from the engine) into useful thrust. This efficiency is expressed as a ratio, specifically the ratio of the useful power output (thrust power) to the power input.

Because both power output and input are measured in the same units (typically, watts or horsepower), the efficiency is a dimensionless quantity ranging from 0 to 1. A value of 1 indicates 100% efficiency, meaning all the engine power is converted into thrust without any losses due to drag or other factors such as slipstream effects or mechanical inefficiencies.

It is important to note that while theoretical efficiencies may suggest higher numbers in some contexts (due to simplifications or ideal conditions), actual propeller efficiency cannot exceed 1 in practical scenarios. This is grounded in the fundamental principles of thermodynamics and fluid dynamics, which dictate that energy cannot be created, and thus a system can't output more energy in thrust than it inputs from the engine.