Although turbojet and turbofan jet engines are similar, the things that set them apart make them very different. Here's what you need to know.

Between Mach 2 and Mach 3, the turbojet transitions to a ramjet engine, which powers the plane at hypersonic speed. “That's actually pretty tricky and pretty difficult,” Case said.

The first type jet engine was a turbojet that went into production in 1939, finding a home on the German Me 262, making it the first fighter jet to fly during WWII.

Using an off-the-shelf J85 turbojet engine as the foundation for Chimera contributed to the comparatively low price tag. About 15% of the engine is 3D printed, also helping to keep costs down.

Pratt & whitney developed the 4,500-kilogram (10,000-pound) thrust JT3 turbojet engine in 1950. It powered such military aircraft as the Boeing B-52, Convair F-102, Douglas A3D, Lockheed U-2, ...