FAA Powerplant Written Practice Test

According to the defined equation, how is Indicated HP represented?

1. Indicated HP = PLANK/30,000

2. Indicated HP = PLANK/33,000

3. Indicated HP = PLANK/40,000

4. Indicated HP = PLANK/50,000

The correct answer is: Indicated HP = PLANK/33,000

Indicated horsepower (HP) is a measure of the power produced by an engine before any losses due to friction or other factors. The formula for calculating indicated horsepower uses the pressure of the gas in the cylinders (often represented as "PLANK") and divides it by a specific constant that represents the number of foot-pounds of work per minute for one horsepower. In the case of indicated horsepower, 33,000 foot-pounds per minute is the standard conversion factor used in the U.S. This value comes from the definition of horsepower as the ability to do 33,000 foot-pounds of work per minute. Thus, by dividing PLANK (which stands for pressure, length, area, and the number of strokes per minute) by 33,000, you derive the indicated horsepower for the engine. Using this equation allows for a straightforward understanding of how many horsepower the engine is generating based on its internal pressures and strokes without accounting for any inefficiencies in the power transmission. This is why the correct representation for Indicated HP is indeed PLANK divided by 33,000.