The powerplant converts chemical energy to mechanical energy.

• A. Mechanical energy to chemical energy
• B. Electrical energy to mechanical energy
• C. Chemical energy to mechanical energy
• D. Thermal energy to chemical energy

Answer: (C)

The main idea here is that the engine’s job is to release the chemical energy stored in aviation fuel and turn it into motion that drives the propeller or rotor. In operation, fuel undergoes combustion, producing heat that expands gases and pushes components like pistons or a turbine. That push is converted into rotary mechanical energy, which is what actually produces thrust. So the powerplant is transforming chemical energy into mechanical energy, with heat being the intermediate form produced by combustion. The other options describe energy transformations that don’t match how aircraft engines generate propulsion.