What best defines a turboshaft engine?

• A. A turbine engine that integrates a turbocharger.
• B. A gas turbine engine that delivers power through a shaft to operate something other than a propeller.
• C. An engine that uses exhaust to generate electricity only.
• D. A turbojet version designed for vertical takeoff.

Answer: (C)

A turboshaft engine is a gas turbine whose main purpose is to produce shaft power to drive a mechanical load, such as the rotor of a helicopter, rather than to produce thrust from exhaust. The turbine powers a shaft that goes to a gearbox and then to the load, with only the remaining energy in the exhaust not used for propulsion. This is why the defining feature is shaft output driving a load, not generating electricity or directly expelling thrust.

The other ideas don’t fit as well. A turbocharger is a device used with some piston engines to force more air into the cylinder, not a defining aspect of a turboshaft. An engine that generates electricity from exhaust describes a turbine-generator setup, which is different from a turboshaft whose purpose is mechanical shaft power. A turbojet version intended for vertical takeoff describes a jet propulsion arrangement, not a shaft-driven load.