What type of engine powers the APU in the C-5?

The correct answer is that the APU in the C-5 is powered by a gas turbine engine. This type of engine is specifically designed to run efficiently at a constant speed, which is ideal for producing electrical power and pneumatic energy for starting the main engines and supporting other aircraft systems.

Gas turbine engines are compact and lightweight, making them suitable for use in aircraft environments where space and weight are critical factors. They provide the necessary thrust and power without the mechanical complexity and size of piston engines, which are more commonly found in ground vehicles.

Using a gas turbine engine in the APU allows for rapid start-up and provides high reliability and performance, which is essential for military and cargo operations that the C-5 performs. This capability ensures that the APU can deliver the performance needed to support the functions of the aircraft, particularly during preparation for flight and when the main engines are not running.