Power Absorption

The amount of engine BHP a prop can absorb and convert to thrust depends on a variety of factors, including the prop’s diameter, number of blades, the blade’s aspect ratio, which all have an affect on the solidity of the prop, while the engine’s BHP and the prop disc area determine the amount of prop disc loading

Activity Factor

Each different type of aircraft can accept a range of engines of varying amounts of horsepower, within certain limits. Likewise, each engine can accept a variety of propellers, also within certain limits. One of these limitations is the propeller’s ability to absorb the power provided by the engine. How much power the prop can absorb is measured by the ‘activity factor’. In the fictitious aircraft example presented here, the maximum thrust horsepower available is 84% of the engine’s BHP; therefore, the activity factor is 0.84. The activity factor is just another way of expressing the prop’s efficiency.