Aerospace Engineering Practice Exam

The defining feature of a turbofan is the large ducted fan that sits in front of the compressor, driving a substantial amount of air around the engine core. That bypass air flows through a separate path, not through the hot core, which adds thrust with a lower exhaust velocity and improves overall propulsive efficiency and noise characteristics. This combination—a core plus a separate, bypass air stream from a ducted fan—is what clearly distinguishes turbofans from pure turbojets, which have no large bypass fan or ducted bypass path and rely entirely on the high-velocity exhaust from the core for thrust. The other statements don’t capture this fundamental difference: lacking a compressor would describe a non-turbojet air-breathing device, no fan or ducted flow describes a pure turbojet, and relying only on afterburner propulsion is not the defining feature of a turbofan.