FAA Powerplant Written Practice Test

What is the horsepower developed in the cylinders of a reciprocating engine known as?

1. Brake HP

2. Indicated HP

3. Friction HP

4. Net HP

The correct answer is: Indicated HP

The horsepower developed in the cylinders of a reciprocating engine is known as Indicated Horsepower (IHP). This measurement represents the total power generated by the combustion of fuel within the engine’s cylinders before any losses occur due to friction and other inefficiencies in the engine components. Indicated horsepower is derived from the pressure exerted on the pistons as they are pushed down during the power stroke, which is measured using pressure gauges and the engine's stroke length and area. Since IHP reflects the engine's theoretical output based solely on combustion, it does not factor in mechanical losses, making it a key indicator for evaluating an engine's performance under ideal conditions. In contrast to Indicated Horsepower, Brake Horsepower (BHP) accounts for the power available at the engine's output shaft after losses, while Friction Horsepower represents the power lost due to friction in the engine's internal mechanisms. Net Horsepower usually refers to the usable power output after all losses and is more relevant to applications involving power delivery in real-world scenarios.