In a propeller-driven plane, what is one of the secondary functions of the engine?

In a propeller-driven aircraft, one of the engine's secondary functions is to create electrical power. This capability is essential for the operation of various onboard systems, such as navigation instruments, communication equipment, and lighting. While the primary purpose of the engine in such aircraft is to provide thrust through the propeller, the need for electrical power ensures that the aircraft can maintain operational functionality and safety during flight.

This electrical generation is typically accomplished through an alternator or generator attached to the engine, which converts mechanical energy into electrical energy as the engine runs. Hence, while providing thrust is crucial for flight, the ability to create electrical power supports other necessary systems within the aircraft, making it a vital secondary function.